# OK, the PDX 4.100 sucks



## LondonRS4 (Jul 16, 2009)

So I wired everything up this weekend only to find a hiss through the tweeters. I did everything by the book. Power cables from battery + and -, RCA's are triple shielded Monster, speaker wires are shielded twisted pair 18 gauge. Hiss was there even in the accessories position. There was no whine when running.

So I pulled one of the PDX's out of the car. Connected it to a spare 12V battery and drove both a tweeter and a midrange speaker. No RCAs connected, or 50kohm shorting resistor to ground. No hiss on the midrange (which hits it's 3dB point by 5 kHz), but plenty on the tweeter. So then I put the amplifier on my spectrum analyzer and low and behold, there was a significant 48.5 kHz signal, which I would guess is the fundamental switching frequency of the power supply. It's strong enough that you can hear it come through the tweeter I guess.

Same story with the other 4.100.

So I'd say if you want to drive a sub or a midrange, this amp is great. For the highs, think again.

I've got two DLS RA-40s on order.


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## digital (Sep 12, 2008)

LondonRS4 said:


> So then I put the amplifier on my spectrum analyzer and low and behold, there was a significant 48.5 kHz signal, which I would guess is the fundamental switching frequency of the power supply. It's strong enough that you can hear it come through the tweeter I guess.


You can hear 48.5 kHz? Wow!

But seriously, I had PDX 4.150 on tweeters... for 5 minutes only. Lack of details (class D) and some buzzing (PDX).

Now I want to sell my PDXs 

K, enough venting


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## Mooble (Oct 21, 2007)

Nope, I'm sorry. All watts sound the same. You didn't measure that spike and you can't hear it. You are confused and misguided.


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## [email protected] (Jun 12, 2008)

Mooble said:


> Nope, I'm sorry. All watts sound the same. You didn't measure that spike and you can't hear it. You are confused and misguided.


Class D definetly doesnt sound like class A/B, switching is present, if you can hear it or not that is a different story. Those class d amps suck IMO, I think they do sound dull and lifeless, there has been many other people that have said the same thing


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## Mooble (Oct 21, 2007)

BeatsDownLow said:


> Class D definetly doesnt sound like class A/B, switching is present, if you can hear it or not that is a different story. Those class d amps suck IMO, I think they do sound dull and lifeless, there has been many other people that have said the same thing


I was being facetious


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## [email protected] (Jun 12, 2008)

Mooble said:


> I was being facetious


You know I was thinking that at first and was about to delete my reply after finally seeing the smiley on there:laugh:


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## placenta (Feb 2, 2008)

BeatsDownLow said:


> I think they do sound dull and lifeless, there has been many other people that have said the same thing


You're copyright infringing on my PDX review bro.

:laugh:

My ARC Mini's aren't much better from that standpoint, but at least they're even smaller still.. 
I'm picking up my ARC 125.4 today after work.


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## TREETOP (Feb 11, 2009)

The PDXs _are_ LOUD though.


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## capnxtreme (Feb 5, 2008)

1) Turn down the gain on the tweeter channel.
2) You can't hear 48kHz.


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## Wheres The Butta (Jun 6, 2009)

I dunno. I run a pdx 150.4 and it sounds great to me. I haven't compared it to any really high level stuff, but compared to the JL slash series amp I was using before, this sounds perfectly fine and takes up ALOT less space.


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## Lash (Nov 26, 2008)

BeatsDownLow said:


> Class D definetly doesnt sound like class A/B, switching is present, if you can hear it or not that is a different story. Those class d amps suck IMO, I think they do sound dull and lifeless, there has been many other people that have said the same thing


Do you feel the same way about the JL Audio HD amps?


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## capnxtreme (Feb 5, 2008)

Seriously, any amp will make your tweeters hiss if you don't adjust the gains appropriately.


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## FoxPro5 (Feb 14, 2006)

capnxtreme said:


> 2) You can't hear 48kHz.


For real.

Treetop said it best; they're just loud.

And anyone who claims they can hear amp class is not playing with a full deck IMO. Isn't it the attributes of the amp itself that give it "sound": distortion, gain, power, noise, FR? ? ? ? ? ? ? ? ?


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## ItalynStylion (May 3, 2008)

Yeah, sounds like we're talking about a noise floor and not some mystical 48khz noise. Not only would you not be able to hear it, but the tweeters likely roll off WELL before that point anyways.

Here is a question though as I've run into the same problem with my old setup. Captnxtreme said to turn down the gains on the tweeters. I agree that will bring the noise floor down on the tweeters. However, it will obviously bring the tweeters down in their output. What do you do if the tweeters need to be louder to keep up with the midbasses/sub but you want the noise floor lower?


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## placenta (Feb 2, 2008)

ItalynStylion said:


> Here is a question though as I've run into the same problem with my old setup. Captnxtreme said to turn down the gains on the tweeters. I agree that will bring the noise floor down on the tweeters. However, it will obviously bring the tweeters down in their output. What do you do if the tweeters need to be louder to keep up with the midbasses/sub but you want the noise floor lower?


You simply buy a stronger tweeter amp so you can keep the gains at MIN.


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## tspence73 (Oct 14, 2008)

Time to take your favorite 4-channel 100-watt class A/B and the PDX4.100 to Richard Clarke for a test trial.


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## evident (Apr 10, 2009)

my alpine pdx 4.150 kicks butt. i've heard the JL HD series before and yes they are marginally better but if you get a good price on the PDX series(which in alot of cases you can, even authorized) then it rocks


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## LondonRS4 (Jul 16, 2009)

(a) It's there with nothing connected to the amps or (more properly) a 10 kohm or 50 kohm terminator on the RCA inputs.

(b) It's there with the gains turned all the way down. Strike 1 for the snarky people.

(c) It's there with the filters on LP, HP or off. So it's in the output stage, not the input stage. Strike 2 for the snarky people.

(3) My dog might be able to hear 48.5 kHz, but I sure can't. But when you throw that crap at high power into a good tweeter, it comes out as distortion and undertones. Strike 3 for the snarky people.

(d) OR, yes, it may just be the noise floor. However, you cannot hear any hiss driving a midrange or a sub. So the noise floor is frequency dependent and much higher at high frequencies.


I tested these at work on the same rig we use to test our 2000 V, 650 Amp MRI gradient amplifiers (which slew at 20,000V/s btw at 0.001% THD). SAME problem. Incidentally, our gradient amps switch at 100 kHz, and you can hear them hiss into a tweeter as well. It's actually how we tune the PID loop in the regulators. We minimize the hiss.

This is a decent amp for low down. It has lots of power in a small package. Not so much for up high. Crutchfield sent me 2 more today which I just tried at home. SAME problem. All 4 are going back.


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## ItalynStylion (May 3, 2008)

LondonRS4 said:


> This is a decent amp for low down. It has lots of power in a small package. Not so much for up high. Crutchfield sent me 2 more today which I just tried at home. SAME problem. All 4 are going back.


I'm not saying this to be mean but to point out what I feel is obvious. What are the chances of 4 consecutive amps all having the exact same problem? The problem seems to be install dependent. My suggestion would have been to do what you did in A) because I had done that same test with my last install.


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## placenta (Feb 2, 2008)

no one can handle the fact that the PDX amps are getting a bad reputation and will be known as crap soon. too many people here run em.


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## BTA (Nov 5, 2005)

I don't run them anymore, they were okay, but not my cup of tea.

I never had any noise issues though (hiss or otherwise)


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## capnxtreme (Feb 5, 2008)

LondonRS4 said:


> (3) My dog might be able to hear 48.5 kHz, but I sure can't. But when you throw that crap at high power into a good tweeter, it comes out as distortion and undertones. Strike 3 for the snarky people.


Huh? Where do you get this from?



> (d) OR, yes, it may just be the noise floor. However, you cannot hear any hiss driving a midrange or a sub. So the noise floor is frequency dependent and much higher at high frequencies.


Which driver in the system is the most efficient? Do you really expect to hear hiss out of your subwoofer? If you're gonna hear the noise floor, the tweeters are where you will hear it.



> I tested these at work on the same rig we use to test our 2000 V, 650 Amp MRI gradient amplifiers (which slew at 20,000V/s btw at 0.001% THD). SAME problem. Incidentally, our gradient amps switch at 100 kHz, and you can hear them hiss into a tweeter as well. It's actually how we tune the PID loop in the regulators. We minimize the hiss.


Sooooo... it's not just the PDX's?


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## capnxtreme (Feb 5, 2008)

placenta said:


> no one can handle the fact that the PDX amps are getting a bad reputation and will be known as crap soon. too many people here run em.


Are you saying that too many people here run them, and therefore aren't willing to admit that they're crap?

Or are you saying that they're so popular and played out, that it's time for the bandwagon to start calling them crap?


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## ItalynStylion (May 3, 2008)

capnxtreme said:


> Sooooo... it's not just the PDX's?


This is like Blues Clues.


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## Wheres The Butta (Jun 6, 2009)

Who cares what the bandwagon says. If something sounds good, run it. If it sounds bad, don't. 

It's a pretty simple concept - it's called do what you like rather than what people tell you to like


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## ItalynStylion (May 3, 2008)

bd5034 said:


> Who cares what the bandwagon says. If something sounds good, run it. If it sounds bad, don't.
> 
> It's a pretty simple concept - it's called do what you like rather than what people tell you to like


^FTW! I've always been about that.


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## capnxtreme (Feb 5, 2008)

We just figured out Blue's Clues! We just figured out Blue's Clues! We just figured out Blue's Clues, because we're really smart!


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## placenta (Feb 2, 2008)

capnxtreme said:


> Are you saying that too many people here run them, and therefore aren't willing to admit that they're crap?
> 
> Or are you saying that they're so popular and played out, that it's time for the bandwagon to start calling them crap?


#1. Or that they arent nearly all they were thought to be cracked up to be when they first came out. Everyone went gaga. I myself had 2 PDX amps once..


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## Wheres The Butta (Jun 6, 2009)

Not everybody thought they were the greatest thing since sliced bread. Some of us run the PDX amp because it's a small footprint amp that puts out good power at a great price. I don't expect it to make my breakfast for me, just put out good power and not take up much space while doing it.


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## LondonRS4 (Jul 16, 2009)

capnxtreme said:


> Huh? Where do you get this from?


The switching frequency has all kinds of "schmutz". There is something resembling a square wave at 48.5 kHz and at double that. Just because a transistor is being switched at 48.5 kHz doesn't mean that it's output only switches at that frequency. It's fair enough to say that this just becomes part of the noise floor effectively, but that floor drops off as you drop in frequency. See response to next question.




capnxtreme said:


> Which driver in the system is the most efficient? Do you really expect to hear hiss out of your subwoofer? If you're gonna hear the noise floor, the tweeters are where you will hear it.


Actually my midrange driver has a spec'd and measured sensitivity of 92 dB. So does my tweeter. They will both produce exactly the same SPL for a 1 volt sinusoidal drive signal in their respective sweet spots. If the noise floor were flat (like white noise), you'd hear it in both equally well. I only hear it in the tweeters. Therefore (1) the noise is higher at higher frequencies or (2) I've learned to tune out the mid range where my wife's voice is most often found. 



capnxtreme said:


> Sooooo... it's not just the PDX's?


Correct. I have no axe to grind. I'm a newbie at this car audio thing. But I do have 2 Ph.D.s, one in NMR Physics and one in Electrical Engineering both in 1990. So I believe I know how to characterize amplifiers. The MRI gradient amplifier I referred to is made by Siemens and it costs about 400 grand for 3 channels. It too has breakthrough into the output from the switching supply. No shame in that. 

I had hoped the PDXs would work for me. They seemed good on paper. They didn't. On to the next thing. Just wanted to document it for others.


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## LondonRS4 (Jul 16, 2009)

capnxtreme said:


> 1) Turn down the gain on the tweeter channel.
> 2) You can't hear 48kHz.


(1) READ my post. Gain was ALL THE WAY DOWN.
(2) Take a 48kHz square wave and run it into a high efficiency tweeter. You will hear hiss. However, see my post about switching power supplies and transistor outputs.


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## capnxtreme (Feb 5, 2008)

LondonRS4 said:


> (1) READ my post. Gain was ALL THE WAY DOWN.


Sorry, next time I'll time travel to gather details from your future posts.

I still don't understand your point. If a $400k amp makes tweeters hiss, why are you disappointed that a $300 one does too?


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## quality_sound (Dec 25, 2005)

placenta said:


> You're copyright infringing on my PDX review bro.
> 
> :laugh:
> 
> ...


From what standpoint? I like my Minis better than my XXKs. Not quite as ballsy (it was a MASSIVE step down in power) but sonically they're easily better than the XXK. I think the full size FDs and SEs are better though.


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## LondonRS4 (Jul 16, 2009)

ItalynStylion said:


> I'm not saying this to be mean but to point out what I feel is obvious. What are the chances of 4 consecutive amps all having the exact same problem? The problem seems to be install dependent. My suggestion would have been to do what you did in A) because I had done that same test with my last install.


Here's my test install. 12V lead acid battery. 4 gauge wire from positive terminal to PDX. 4 gauge wire from PDX to negative terminal. 22 gauge from positive terminal to remote on. 18 gauge speaker wire from any of the 4 speaker outputs to a speaker. Battery wires 3 feet and run to the right of the amp. Speaker wires 4 feet and run to the left of the amp.

Doesn't get any simpler.


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## quality_sound (Dec 25, 2005)

ItalynStylion said:


> I'm not saying this to be mean but to point out what I feel is obvious. What are the chances of 4 consecutive amps all having the exact same problem? The problem seems to be install dependent. My suggestion would have been to do what you did in A) because I had done that same test with my last install.



Because it couldn't _possibly_ be a faulty amp design cuz Alpine _aways_ puts out first rate gear. *cough*BlackBird*cough*


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## danssoslow (Nov 28, 2006)

Someone will have to elaborate on this. I remember a while back my brother talking to me about sampling rates and Nyquist and sympathetic noise; lost me pretty quick. What I recall from all of it is that above or below 44.5kHz that the distortion from the fundamental can reach the hearing threshold, blah blah some **** like that. Could this, in any way, be what the op is hearing?

Does any of this make sense?


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## 14642 (May 19, 2008)

We've done some pretty extensive testing of the PDX amps and didn't uncover any huge spikes, but testing of Class D amplifiers is usually done with the AP and a filter specifically designed for switching amps to eliminate that kind of inaudible stuff from the measurment. that's industry standard, BTW. The 48k spike, if there is one, won't be reproduced by many tweeters and won't be heard by many (if any) humans. 

The noise floor of the amplifier does rise a bit at high frequencies and in our measurements tested a little below the spec of 80dB @ 1 watt between 6k and 20k. I suspect that's what you may be hearing, especially if the tweeter has an irregular frequency response. 

BTW, white noise would sound much brighter (more high frequency), since it's equal energy at every frequency rather than equal over every octave, but a sine at 10V at two frequencies within the passbands of the drivers would be the same output if they had the same voltage sensitivity and FLAT FREQUENCY RESPONSE. The sensitivity spec is usually calculated rather than measured.


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## LondonRS4 (Jul 16, 2009)

The important thing in a PWM Class-D amplifier is the PSRR or power supply rejection ratio. In other words the rejection of noise from the PWM power supply. Here's the measurement from the PDX4.100. As you can see, the power supply frequency rejection gets poorer at higher frequencies, just as I suspected. You can see the low pass filter start to kick in just over 20 kHz to get rid of the fundamental at 48.5 kHz. But note the PWM approach still produces a frequency dependent noise floor, and that noise floor is worst at the higher frequencies. _By 50 dB compared to 20 Hz._
But I'm sure you all knew that already.


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## capnxtreme (Feb 5, 2008)

LondonRS4 said:


> But I'm sure you all knew that already.


Huh?

So what you're hearing is the noise floor? Because actually, we did know that.

In all seriousness, we <3 test measurements and data. The only "snarkiness" here seems to be coming from your side of the table.


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## 14642 (May 19, 2008)

London,
That's similar to the shape we measured, but the magnitude is very different. Hmmm...Interesting.


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## LondonRS4 (Jul 16, 2009)

capnxtreme said:


> I still don't understand your point. If a $400k amp makes tweeters hiss, why are you disappointed that a $300 one does too?


I have no real point I guess. I'm just stating my observations. Do with them as you please. 

Amplifiers with PWM supplies, whether they be $400 or $400,000 are going to have some hiss. They are best suited to mids and subs from what I've measured myself. They excel at power efficient delivery at those frequencies. There are some tricks and some cool patents on frequency dependent PWM to alleviate hiss. Or really good stiff power supplies and fancy filters. Obviously I expected magic. Maybe all class-D amps do this to a certain extent. I don't intent to find out. I use Class A and AB at home. I'm going to use it in my car too.


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## FoxPro5 (Feb 14, 2006)

Just a quick question to either Andy or the OP so I understand. Will the noise floor (produced by the switching or otherwise) rise as you turn up the volume of the system overall? Or does it always stay the same.....as it's just kind of there and annoying?


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## capnxtreme (Feb 5, 2008)

LondonRS4 said:


> I have no real point I guess. I'm just stating my observations. Do with them as you please.
> 
> Amplifiers with PWM supplies, whether they be $400 or $400,000 are going to have some hiss. They are best suited to mids and subs from what I've measured myself. They excel at power efficient delivery at those frequencies. There are some tricks and some cool patents on frequency dependent PWM to alleviate hiss. Or really good stiff power supplies and fancy filters. Obviously I expected magic. Maybe all class-D amps do this to a certain extent. I don't intent to find out. I use Class A and AB at home. I'm going to use it in my car too.


OK, thanks for clarifying, and thanks for posting that data. It is interesting.


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## 14642 (May 19, 2008)

The noise present should be about the same regardless of the volume, but at high volume, it doesn't much matter, since the music will be much louder than the noise. Turning up the input sensitivity may raise the level of the noise, though. 

This is precisely why CEA 2006 indicates noise at 1 watt--where the music isn't loud. rating signal to noise at rated power makes it look like big amps are quieter unless you do the math. In reality, they're usually not. 

The problem for the OP is that that shape of the noise makes the problem worse--it's much louder at high frequencies.

I'd relly like to know the test setup that you used to make that measurement.


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## 89grand (Nov 23, 2006)

LondonRS4 said:


> The important thing in a PWM Class-D amplifier is the PSRR or power supply rejection ratio. In other words the rejection of noise from the PWM power supply. Here's the measurement from the PDX4.100. As you can see, the power supply frequency rejection gets poorer at higher frequencies, just as I suspected. You can see the low pass filter start to kick in just over 20 kHz to get rid of the fundamental at 48.5 kHz. But note the PWM approach still produces a frequency dependent noise floor, and that noise floor is worst at the higher frequencies. _By 50 dB compared to 20 Hz._
> But I'm sure you all knew that already.


If that test was accurate, and I'm reading the graph right, the performance of that amp is horrible.


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## LondonRS4 (Jul 16, 2009)

Yes noise is same regardless of volume. So you can drown it out (though I agree with others that the PDX is rough in the high frequencies).

I measured the PSRR very simply. deltaV(power supply)/deltaV(amplifier) as a function of frequency expressed in dB (voltage dB, not power dB) . The two curves are for positive and negative deltas respectively. They are different because of the way the amp produces a negative output from the +12V supply I guess.

Class AB amps also get somewhat worse with frequency, but not like this !


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## 89grand (Nov 23, 2006)

Well luckily I sold off my PDX amps before people started bitching about them.

I never even hooked them so I can't say if they had any noise.


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## MarkZ (Dec 5, 2005)

I don't understand your rationale behind why amps with PWM supplies generate hiss. Most car amps these days rely on switchers. But the switching frequency is >20kHz.

Maybe you just got a bad amp?


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## captainobvious (Mar 11, 2006)

MarkZ said:


> I don't understand your rationale behind why amps with PWM supplies generate hiss. Most car amps these days rely on switchers. But the switching frequency is >20kHz.
> 
> Maybe you just got a bad amp?


Well, he did have 4. And Andy confirmed the high noise floor.


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## Z3Sooner (Aug 2, 2008)

The first amp for my Z3 was a PDX4.100. Obvioulsy I bought it because of size. It had similar noise floor issues and I felt it sounded brittle. I was also somewhat unhappy with the useable power. When I decided to go active I bought an Arc Audio KS300.4 and compared the two. It basically confirmed everything I felt about the PDX. I have since sold the PDX and I won't buy another full range Class D. None of what the OP posted surprises me one bit.

Honestly, I replaced the pdx with a couple blaupunkt VA2100s and they were a FAR better amp.


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## underPSI (Dec 2, 2008)

Interesting there are so many complaints about these amps. I honestly think people induce noise into their heads that really isn't there or isn't audible to the human ear. I couldn't be happier with my two PDX amps and one of them is the 100.4.


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## MarkZ (Dec 5, 2005)

captainobvious said:


> Well, he did have 4. And Andy confirmed the high noise floor.


I think Andy was surprised at how high the noise was in London's post.


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## LondonRS4 (Jul 16, 2009)

underPSI said:


> Interesting there are so many complaints about these amps. I honestly think people induce noise into their heads that really isn't there or isn't audible to the human ear. I couldn't be happier with my two PDX amps and one of them is the 100.4.


I found this forum through Googling "Alpine PDX hiss". Unfortunately, I discovered this forum AFTER I bought and installed my PDX 4.100s. There are an awful lot of hits for those 3 words, far more than anything else I have since researched. So I don't think the power of suggestion put the hiss in my head....nor in my measurements.

This forum is terrific though. Based on some really positive reviews, I'm replacing the PDXs with two DLS RA-40. They are bigger than the PDXs, but I have the room in my trunk quarter panel well. They don't as much power, but the SQ is better, and that's really what I'm after. I hated the Bose system that the RS4 came with.


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## tspence73 (Oct 14, 2008)

LondonRS4 said:


> (1) READ my post. Gain was ALL THE WAY DOWN.
> (2) Take a 48kHz square wave and run it into a high efficiency tweeter. You will hear hiss. However, see my post about switching power supplies and transistor outputs.


There is more hiss picked up by mics from air current in a room than the hiss produced by the amp. That means when you hit 'play' on any music CD or ipod, the hiss on the recording will mask the hiss on the amp. I think this overly critical schpiel is just that. RC challenge or take a hike. You could take home 10k.


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## tyroneshoes (Mar 21, 2006)

I would like to see if there was any testing done on my kenwood x4r or their newer line. They sounded way better to me than the pdx I also found lackluster. I still think they sound great.


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## tspence73 (Oct 14, 2008)

LondonRS4 said:


> I have no real point I guess. I'm just stating my observations. Do with them as you please.
> 
> Amplifiers with PWM supplies, whether they be $400 or $400,000 are going to have some hiss. They are best suited to mids and subs from what I've measured myself. They excel at power efficient delivery at those frequencies. There are some tricks and some cool patents on frequency dependent PWM to alleviate hiss. Or really good stiff power supplies and fancy filters. Obviously I expected magic. Maybe all class-D amps do this to a certain extent. I don't intent to find out. I use Class A and AB at home. I'm going to use it in my car too.


The rational and logic behind using Class-D amps in a car are these:

1. Efficient use of electrical. (A car isn't overflowing with excess amps. Efficiency counts!)

2. Small footprint. (Installs neatly and gives owners FAR more installation options. Generates less heat, therefore doesn't require a big heatsink.)

3. The loud 'din' inside a car easily masks any ultra-low noise produced by switching. (Let's get real here. 80db S/N ratio amps aren't going to sound any more hissy than 90db S/N ratio amps. A car environment certain allows for small/modest compromises. Heck, you're not likely to detect this kind of difference in a home environment and it has a FAR quieter average din.)

If you want a 'no compromises' audiophile setup that goes into extremes where you're worrying about sounds that are inaudible to your ears, then by all means, buy those products and enjoy. I'll pick up products that have far fewer (inaudible) 'bonus' features and stick to great power, a good/low noise floor, fantastic DSP on frequencies I CAN hear and highly modular gear that allows me to customize my install to my aesthetic taste.


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## DynamicAudioLodi (Jul 13, 2009)

PDX don't suck, they always sound great when we use them on Harleys.


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## chad (Jun 30, 2005)

placenta said:


> You simply buy a stronger tweeter amp so you can keep the gains at MIN.


dear god please.........


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## michaelsil1 (May 24, 2007)

chad said:


> dear god please.........


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## Technic (Oct 10, 2008)

I have a PDX 4.150 and a 4.100... _my second_ PDX 4.100. The first one definitely was defective, the hiss and plain noise was terrible. That was returned to the seller and the second/current PDX 4.100 have as much hiss as the OEM system before the upgrade, almost none. 

No noise issues at all with the 4.150.

I have read several threads in different forums about the PDX and hiss and my theory is simpler than they being inherently noisy: either Alpine has a quality control issue or there are too many refurbished PDX being sold as "new".


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## FoxPro5 (Feb 14, 2006)

chad said:


> dear god please.........


Yes, my son. How may I help you? 

I got me a 1.600 that's been great for me. Maybe I'll put'er on my tweets...see if she got that "hisss." Y'all think she'll sound liak a snake, er'waat?


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## GregU (Dec 24, 2008)

I install atleast 5 PDX's a week into customers cars. I'm not gonna knock it, but I'm also not going to compliment it. I can say the 1.'s are fairly strong, but as far as the 4.'s....... nothing special. IMO.


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## Wheres The Butta (Jun 6, 2009)

I love my 4.150, I'll stand by that any day of the week.


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## mikey7182 (Jan 16, 2008)

tspence73 said:


> There is more hiss picked up by mics from air current in a room than the hiss produced by the amp. That means when you hit 'play' on any music CD or ipod, the hiss on the recording will mask the hiss on the amp. I think this overly critical schpiel is just that. RC challenge or take a hike. You could take home 10k.


Is it difficult for you to walk around, being balls deep in RC's ass like that? I would think it'd be tough. If you could drop your RC reference : overall post ratio to at least 1:5, that'd be much appreciated. While you're adjusting ratios, go ahead and drop the number of times you defend equipment you've never owned to 0.


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## Wheres The Butta (Jun 6, 2009)

mikey7182 said:


> Is it difficult for you to walk around, being balls deep in RC's ass like that? I would think it'd be tough. If you could drop your RC reference : overall post ratio to at least 1:5, that'd be much appreciated. While you're adjusting ratios, go ahead and drop the number of times you defend equipment you've never owned to 0.



wow this really did turn into a flame war.

somebody lock this thread please and put us all out of our misery?


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## duckymcse (Mar 15, 2009)

I second that. Pair that with my Eclipse CD7200 mkII and DLS Nobelium 6.2 produce some stunning detail dynamics sound. I don't know why people say the Alpine PDX is harsh and lifeless. Mine sound so warm and smooth as butter. Alpine PDX is an awesome amps if it is working properly, I guess.



bd5034 said:


> I love my 4.150, I'll stand by that any day of the week.


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## mikey7182 (Jan 16, 2008)

bd5034 said:


> wow this really did turn into a flame war.
> 
> somebody lock this thread please and put us all out of our misery?


It's so bad, you're using a phrase that is commonly associated with death? 

Tspence showers just about every thread he dumps in with this BS about Class FD amps (namely the PDX) and Richard Clark's 10k challenge. What he continues to miss, although people are generously pointing it out to him, is that there are parameters set up in that test to eliminate amps that may "sound" different, i.e. excessive noise floors, etc. Would the PDX even qualify for his test? Who knows. To have never owned the amp, and spout off the RC challenge in a thread where someone with a double PhD and Andy have both acknowledged test results indicating an excessive noise floor, is ridiculous.


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## circa40 (Jan 20, 2008)

How about buying an AB amp for the tweeters and using the PDX (bridged) for MR/MB duties since they seem to sound fine with mid/lower frequencies?


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## 89grand (Nov 23, 2006)

I'm glad bd5034 likes the 4.150 because I sold it to him, but tspence needs to shut the **** up until he uses one.


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## pjhabit (Aug 12, 2008)

I experienced the same dull sound & high noise floor w/ my PDX5...was glad to see it go.


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## Mooble (Oct 21, 2007)

mikey7182 said:


> Tspence showers just about every thread he dumps in with this BS about Class FD amps (namely the PDX) and Richard Clark's 10k challenge. What he continues to miss, although people are generously pointing it out to him, is that there are parameters set up in that test to eliminate amps that may "sound" different, i.e. excessive noise floors, etc. Would the PDX even qualify for his test? Who knows. To have never owned the amp, and spout off the RC challenge in a thread where someone with a double PhD and Andy have both acknowledged test results indicating an excessive noise floor, is ridiculous.


Oh god, thank you for pointing this out before I have to rip him a new one. I'm sick and tired of debunking RC's challenge to the logically challenged. Obviously the PDX would instantly be disqualified by RC if it has an audible noise floor, saving him $10k.

For the last time tspence, WE KNOW WHAT NOISE FLOOR IS!!! If you want to start a nice lil' thread about ambient noise picked up through the mic, feel free, but leave it out of here. We are smart enough to know the difference. Do you know what a digital silence track is? Play one. If you hear hiss, IT AIN'T FROM THE RECORDING!


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## simplyclean (Jan 23, 2009)

underPSI said:


> Interesting there are so many complaints about these amps. I honestly think people induce noise into their heads that really isn't there or isn't audible to the human ear. I couldn't be happier with my two PDX amps and one of them is the 100.4.


On the other hand, just because you can't hear it doesn't mean it doesn't exist. Some people can hear mouse farts, some people can't. If someone has hearing damage or used tweeters that lacked upper end detail because of poor response they probably wouldn't hear it. 

But the OP has provided a graph that proves his claim and many people are backing his statement with their own first hand experiences.

Excellent thread. I almost bought a PDX amp last week and after seeing this and googling "PDX noise" I'm glad I didn't.


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## tspence73 (Oct 14, 2008)

Mooble said:


> Oh god, thank you for pointing this out before I have to rip him a new one. I'm sick and tired of debunking RC's challenge to the logically challenged. Obviously the PDX would instantly be disqualified by RC if it has an audible noise floor, saving him $10k.
> 
> For the last time tspence, WE KNOW WHAT NOISE FLOOR IS!!! If you want to start a nice lil' thread about ambient noise picked up through the mic, feel free, but leave it out of here. We are smart enough to know the difference. Do you know what a digital silence track is? Play one. If you hear hiss, IT AIN'T FROM THE RECORDING!


I own a class-D full-range. With no RCA's plugged in, to hear any hiss, the car must be off and I have to put my ear within inches of the tweeter to detect it (and that's with a sensitivity set for a 2V headunit). If the Class-D Alpine amp is anything like it, then methinks people are exaggerating about this so-called "noise-issue". And it's hard to believe that after all this time of the Alpine/Kenwood/Eclipse Class-D ICE amps being on the market that this hasn't been talked about by tons of people. From what I can tell, these amps have all performed well.


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## 14642 (May 19, 2008)

London has provided measurements and feedback based on his REAL EXPERIENCES with four of the amps. I can't imagiine that there's any firm footing from which to argue with him, especially not if the arguement is pure speculation. 

Is it possible that in his system he hears the noise and in another system it might not be audible? Sure.


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## Deton Nation (Jul 3, 2009)

tyroneshoes said:


> I would like to see if there was any testing done on my kenwood x4r or their newer line. They sounded way better to me than the pdx I also found lackluster. I still think they sound great.


I have the new one and it doesnt make a peep. And its very musical, detailed.. and even top to bottom.. not that that matters since you will adjust the eq anyway. The Kenwoods are very good considering price, and doesnt exhibit Class D weirdness. Though it sounds to me like there is some issue (not functioning correctly) with the Alpines.


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## michaelsil1 (May 24, 2007)

tspence73 said:


> I own a class-D full-range. With no RCA's plugged in, to hear any hiss, the car must be off and I have to put my ear within inches of the tweeter to detect it (and that's with a sensitivity set for a 2V headunit). If the Class-D Alpine amp is anything like it, then methinks people are exaggerating about this so-called "noise-issue". And it's hard to believe that after all this time of the Alpine/Kenwood/Eclipse Class-D ICE amps being on the market that this hasn't been talked about by tons of people. * From what I can tell, these amps have all performed well.*


Just because they perform well doesn't mean that they sound good. The whole point of this Amp is a small foot print and lots of power; that makes some people very happy. I'm glad you like yours, but I'm not a fan and you're not going to convince me otherwise.

BTW

I owned a PDX and now I don't.


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## tspence73 (Oct 14, 2008)

Andy Wehmeyer said:


> London has provided measurements and feedback based on his REAL EXPERIENCES with four of the amps. I can't imagiine that there's any firm footing from which to argue with him, especially not if the arguement is pure speculation.
> 
> Is it possible that in his system he hears the noise and in another system it might not be audible? Sure.


I have not disputed his graph or data. I'm thinking that under the conditions of a vehicle install, this noise is very likely inaudible. It's surprising that no reviewers in the past have posted any such noise graph regarding this amp. Something like a 50db S/N at frequencies over 10KHz? Just seems unlikely that an amp manufacturer would allow that much noise at an audible frequency. If that graph is correct, the noise levels above 10KHz are similar to what you'll hear with Dolby B Noise Reduction on cassette tape. That's hard to miss. Any reviewer worth a crap would spot noise that loud. It's hard to believe the noise is really as loud as the graph indicates. If true, that would be audible, even in a car.


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## underPSI (Dec 2, 2008)

> On the other hand, just because you can't hear it doesn't mean it doesn't exist. Some people can hear mouse farts, some people can't. If someone has hearing damage or used tweeters that lacked upper end detail because of poor response they probably wouldn't hear it.


That's true. But I also hear how people can "hear" a difference between 12 awg speaker wire vs. 16 awg. Seeing something on a meter is different than actually being able to hear it.


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## placenta (Feb 2, 2008)

LondonRS4 said:


> Yes noise is same regardless of volume. So you can drown it out (though I agree with others that the PDX is rough in the high frequencies).
> 
> I measured the PSRR very simply. deltaV(power supply)/deltaV(amplifier) as a function of frequency expressed in dB (voltage dB, not power dB) . The two curves are for positive and negative deltas respectively. They are different because of the way the amp produces a negative output from the +12V supply I guess.
> 
> Class AB amps also get somewhat worse with frequency, but not like this !


i cant even wrap my head around how technical you guys are. good reading!


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## placenta (Feb 2, 2008)

simplyclean said:


> Some people can hear mouse farts, some people can't.


About a year ago, I posted that I can hear ants if i put my ear up next to them. I have more sensitive ears than most. I couldnt care less if everyone thinks I'm high.


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## ErinH (Feb 14, 2007)

OP, thank you for actually posting some authentic technical results rather than just your opinion which is too easily swatted away by naysayers.  I wonder if you have means to test another Class D amp for me if I were to send it to you?... 





FoxPro5 said:


> Just a quick question to either Andy or the OP so I understand. Will the noise floor (produced by the switching or otherwise) rise as you turn up the volume of the system overall? Or does it always stay the same.....as it's just kind of there and annoying?





Andy Wehmeyer said:


> The noise present should be about the same regardless of the volume, but at high volume, it doesn't much matter, since the music will be much louder than the noise. Turning up the input sensitivity may raise the level of the noise, though.


IME, this is true. All 3 of my PDX’s gave me noise floor issues was always constant. Turn up the volume to drown it out, but you ask folks who heard it and I swear it was untolerable.

Regarding gains vs. noise floor:
Turn the gains down = lose dynamics/output/loud (whatever you want to lable it), IMO and IME. I understand the issue and the way to ‘fix’ it, but I just dealt with the compromise until I decided enough was enough and sold them off. It’s very possible the new owner(s) have no issues, but I had some. Might be attributed to how I tuned (raise gains higher, make cuts; don’t lower gains and make raises). I like it loud and the PDX’s just didn’t provide this comfort for me without a very noticeable noise floor. And FWIW, ALL my amps were set to WELL under clipping and verified with an oscope on multiple occasions. 

My tweeters permitted the most ‘hiss’. The mids, not so much. The midbasses did very badly as I had bridged two of the 4.150 channels together to get some more ‘headroom’ out of them, which in essence was doubling the noise floor although the DMM/test tone method showed me I had 80w @ 4ohms. :/


Again, I understand all the arguments. I made a decision based on the fact that these amps just werne’t for me. No idea if it’s strictly a class D design issue. I really don’t care right now. I’ve got 3 more class D amps waiting to go in the car so we’ll see how that goes. I’ll draw my conclusions from my own experience rather than relying on talk from others who have zero experience. 



PS: Guys, ignore t-tard. Seriously. I’m sick of seeing people bashing him. I ignored all his posts… the ones I couldn’t ignore were yours and I’ll tell you why: I see tspence has a post… I don’t read it. I don’t even skim it. I go right on. 
I see where you fellas make a post and I think “cool, more talk”, so I start reading and realize quickly that you’re just going OT arguing with t-tard. So, STOP, please!


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## Oliver (Jun 25, 2007)

Bikin, waiting to hear how the ZEDS do


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## ErinH (Feb 14, 2007)

a$$hole said:


> Bikin, waiting to hear how the ZEDS do


Nah, Jim. Not those. I really wanted to try them but buying sight unseen is just too much of a gamble for me given the price range right now. It sounds silly to some, but I actually do consider amp aesthetics a factor...why, I have no idea. But, they really would’ve fit the bill power-wise; though not sure about footprint as I’d have to look back at the specs. 
I’ll just wait a while and see what folks have to say about them. That’s assuming that I have issues with the new ones I’m using (crossing fingers all is well). 
I’ll definitely stay tuned to hear for input on those Zeds, though.


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## Deton Nation (Jul 3, 2009)

If you hear hiss, its not in the 40K range because you cant hear that high. I can barely hear 16K and 20K is more a feeling than a hearing. Hiss would be in the audible range. I think this may be a Alpine specific occurrence, perhaps a bad board design. I have Nuforce 9SE v2 Class D amps at home and these are some of the best sounding amps I have ever heard (Of course I am an owner.. lol) To me AB amps exhibit graininess on the top end..(not always though) Class D is extremely smooth and revealing of the source and components upstream. But its like politics... you will either like it or not. If you enjoy it, then its a good thing.
Mike
I do like Class AB though. I have a Parasound HCA-1500A amp designed by John Curl and the sound is phenomenal. I bought it used, its from the early 2000s or late 1999s. Something like the first 15 watts is class A. And this thing will heat your entire house!!!!


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## blamus (Mar 9, 2009)

interesting that at least one person mentioned the kenwood x4r. That is what I have now, I do hear light hiss as background noise, but I assumed that it is 1. my non-lossless mp3s, 2. my install issues (RCAs, grounds etc.) before I blame class-D. I have always LOVED class T in my HT setups (sonic T-amps etc) and they are CLEANER than my A/B HT amps. In the HT department I can easily pin point sources of noise/problems, and I KNOW my t-amps are cleaner, i know when i switch back to my other amps I can hear a light hiss. But in car audio, I can only assume. 

Since the car audio market has pretty rejected the T-amp (god knows why), I assume that the modern D-amps designs are already superior, but apparently thats not the case here.

Anyway, I do hear hiss on my class D kenwood X4r, I don't cry about it though, I don't have a choice anyway, its the only small, efficient amp with DSP that does not cost half of my car. I did however consider switching to the very good deal clarion G/H amps on crutchfield, since I am using fullrange + midbass, their built in XO works for my active set-up, and I am thinking I might be able to live with the lack of time delay. But I cannot live without the high efficiency and small footprint. My battery simply won't handle it!


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## Deton Nation (Jul 3, 2009)

I hear tape hiss, but that is because I listen to tape masters of the Grateful Dead and such, that were recorded from the audience. idk... I will double check but Im not hearing it.


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## LondonRS4 (Jul 16, 2009)

underPSI said:


> That's true. But I also hear how people can "hear" a difference between 12 awg speaker wire vs. 16 awg. Seeing something on a meter is different than actually being able to hear it.


Just to confirm. I can't hear a difference between 12 and 16 gauge ! Or monster cable versus lamp cord. Nor can I measure a difference on my Agilent U8903 spectrum analyzer. But I do hear the PDX hiss when the windows are rolled up and the car is running or when the car is off. With the windows down, I hear the glorious sound of the V8 in Audi's RS4, a sound the BBC said must be just like "when God snores". Now that's music 

I suppose I should be surprised by the reaction I got here, but it's really no different in cars, home audio, motorcycles, politics, religion or anything else. At least not one person attacked my choice of DLS RA40 amps to replace the PDXs, so I take some comfort in that !


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## tspence73 (Oct 14, 2008)

I'm more concerned with reality and truth. I'm not saying what you're saying isn't so, but I'm "skeptical" about this claim. The graph you provided was first I've seen like this. I would like another party with the gear to provide a test like this to confirm. I'm reading some people denying that there is audible hiss and it''s rather hard for me to believe that there is audible hiss since I haven't even heard a $30 pyle amp from back in the 90's give out audible hiss @ 50db S/N ratio. That would be downright outrageous. It would be like buying chocolate cherrios but the chocolate is poop.


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## mikey7182 (Jan 16, 2008)

bikinpunk said:


> PS: Guys, ignore t-tard. Seriously. I’m sick of seeing people bashing him. I ignored all his posts… the ones I couldn’t ignore were yours and I’ll tell you why: I see tspence has a post… I don’t read it. I don’t even skim it. I go right on.
> I see where you fellas make a post and I think “cool, more talk”, so I start reading and realize quickly that you’re just going OT arguing with t-tard. So, STOP, please!


My bad. 

I'd like to ship the OP a class FD amp as well (Premier PRS-D2100T) and have him test it in his install if he doesn't mind. It would be nice to have something similar to Klippel-like results for amps.


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## LondonRS4 (Jul 16, 2009)

I'd love to do this and it's a great idea. But I do have a day job, and my wife already complains I spend too much time with my car and my motorcycle ! More to the point, I have to open the amplifiers to measure things like PSRR, although the usual noise measurements can be done without that. What we really need in this world is a noise spec normalized to some kind of standard speaker efficiency. That is, with a NF of XXdB can you hear any hiss or hum in (say) a 1 kHz band at a certain frequency with a certain speaker efficiency.

Then you'd know whether a certain amp, paired with your speaker was likely to give audible hiss. I do agree with tspence73 that even the crappiest amps generally aren't too bad for hiss, so my hunch is that the PDX series of amps is just plain finicky. The circuit board is so densely populated that crosstalk or power supply noise could easily make its way into the output stage.


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## vageta (Oct 11, 2006)

I have a Kenwood KAC-X4R and I used to think I could hear "hiss" that was from the background noise. Then I put my tweeters on an old school Denon DCA-400, turned the gains all the way down AND my tweeters are attenuated 4 notches down on my head unit. And guess what? It's still there. I'm starting to realize that alot of the hiss I hear is music dependant. I love older music and I find that even the best of the old recordings just have a higher noise floor from the get go and you simply can't get rid of it. It seems the noise floor is a constant so on recordings with lower volumes it is far more noticeable due to having to turn it up louder.

Also so we're all on the same page, when do you consider what you hear is truly the noise floor of the system itself versus the recording? If I pause my stereo while listening to CD or MP3 and crank the volume all the way up I hear nothing. Nada. But when I play a track and it's at the beginning or end before any musical information is present I do hear a hiss. Would one say that I have non audible noise floor? Or do modern head units mute the speakers during a pause so that you can't actually hear the noise floor?

Valid question and I want everyone to be on the same page here since some may have a different idea of what is is they're truly hearing.


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## mikey7182 (Jan 16, 2008)

LondonRS4 said:


> I'd love to do this and it's a great idea. But I do have a day job, and my wife already complains I spend too much time with my car and my motorcycle ! More to the point, I have to open the amplifiers to measure things like PSRR, although the usual noise measurements can be done without that. What we really need in this world is a noise spec normalized to some kind of standard speaker efficiency. That is, with a NF of XXdB can you hear any hiss or hum in (say) a 1 kHz band at a certain frequency with a certain speaker efficiency.
> 
> Then you'd know whether a certain amp, paired with your speaker was likely to give audible hiss. I do agree with tspence73 that even the crappiest amps generally aren't too bad for hiss, so my hunch is that the PDX series of amps is just plain finicky. The circuit board is so densely populated that crosstalk or power supply noise could easily make its way into the output stage.


Well I have no doubt it would be returned in the condition it was sent, so you'd be welcome to crack it open. If you end up feeling like you have the time to test a few sometime, feel free to shoot me a PM. It'll be on the shelf for awhile.


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## bassfromspace (Jun 28, 2016)

If you have doubts about the amplification abillities of class D amps, take a seat in Mark Eldridge's NASCAR.


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## simplyclean (Jan 23, 2009)

underPSI said:


> That's true. But I also hear how people can "hear" a difference between 12 awg speaker wire vs. 16 awg. Seeing something on a meter is different than actually being able to hear it.


I definitely agree that psychoacoustics comes into play and seeing something on paper will definitely influence what people think they hear. But when many people are hearing the SAME thing, I don't think it's just one's imagination. For the record, I've never used a PDX amp, don't know anyone who is running one or ever heard on in real life in a car. 

To me, this thread is proof in the pudding that it's a noiser than "average" amp and has the potential to make music less enjoyable and cause headaches, especially in the case of oem integration which is what I was planning to use it for. New cars have enough **** going on nowadays that you really don't know what's coming out of the oem head, even it's just level/high level output.



placenta said:


> About a year ago, I posted that I can hear ants if i put my ear up next to them. I have more sensitive ears than most. I couldnt care less if everyone thinks I'm high.


So were you high? If you smoked a spliff, would you hear ant farts? 



bassfromspace said:


> If you have doubts about the amplification abillities of class D amps, take a seat in Mark Eldridge's NASCAR.


I don't think anyone is doubting the amplification abilities of class D amps. Who is Mark Eldridge, what's this nascar and is he running PDX amps?


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## vjgli (Nov 4, 2007)

Mooble said:


> Nope, I'm sorry. All watts sound the same.


???:behead:


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## placenta (Feb 2, 2008)

simplyclean said:


> So were you high? If you smoked a spliff, would you hear ant farts?


No, this was in my later years. The ants vocal range is sort of like crinkling plastic paper, but at a super high frequency. Just barely audible to me. Everyone thinks I'm joking too.. There are such things as oddities...


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## Wheres The Butta (Jun 6, 2009)

What I don't understand is this - even if there is a higher noise floor, isn't it still inaudible? The signal to noise ratio should still be plenty high enough that the noise would be masked by the heat/air conditioning in the car even on the very lowest setting (assuming you listen with your windows up) or by the slightest breeze or ambient noise with the windows down. It should masked even by your own breathing. 

The only way this noise would actually be audible is if you are intently listening for it to the exclusion of other sounds.


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## Wheres The Butta (Jun 6, 2009)

placenta said:


> No, this was in my later years. The ants vocal range is sort of like crinkling plastic paper, but at a super high frequency. Just barely audible to me. Everyone thinks I'm joking too.. There are such things as oddities...


I have crappy hearing and even I can hear that if I put my ear close enough to them, so you're definately not crazy. 

It's not ants talking, but their limbs moving and creaking. It's perfectly normal. They're arthropods and they clickclack at a very high frequency as the move. Listen to a crab move and you will hear the same exact noise except at a lower frquency and higher db level.


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## Mooble (Oct 21, 2007)

vageta said:


> I have a Kenwood KAC-X4R and I used to think I could hear "hiss" that was from the background noise. Then I put my tweeters on an old school Denon DCA-400, turned the gains all the way down AND my tweeters are attenuated 4 notches down on my head unit. And guess what? It's still there. I'm starting to realize that alot of the hiss I hear is music dependant. I love older music and I find that even the best of the old recordings just have a higher noise floor from the get go and you simply can't get rid of it. It seems the noise floor is a constant so on recordings with lower volumes it is far more noticeable due to having to turn it up louder.
> 
> Also so we're all on the same page, when do you consider what you hear is truly the noise floor of the system itself versus the recording? If I pause my stereo while listening to CD or MP3 and crank the volume all the way up I hear nothing. Nada. But when I play a track and it's at the beginning or end before any musical information is present I do hear a hiss. Would one say that I have non audible noise floor? Or do modern head units mute the speakers during a pause so that you can't actually hear the noise floor?
> 
> Valid question and I want everyone to be on the same page here since some may have a different idea of what is is they're truly hearing.


This is not terribly hard to diagnose. Does the hiss get louder when you turn up the volume? Bam! It's in the music. Does it stay constant regardless of volume and actually get drowned out when you turn the music up? Bam! Noise floor from some component, be it amp, line driver, HU, etc. Problem solved.

Play a digital silence track, otherwise noise gates may mask a noisy amp or HU. If you hear ANYTHING, it's from a noisy component-NOT MUSIC. (Ok, you will always pick up some cosmic background radiation sounds but this is well below the threshold of human hearing).


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## geom_tol (Jul 9, 2007)

LondonRS4 said:


> The important thing in a PWM Class-D amplifier is the PSRR or power supply rejection ratio. In other words the rejection of noise from the PWM power supply. Here's the measurement from the PDX4.100. As you can see, the power supply frequency rejection gets poorer at higher frequencies, just as I suspected. You can see the low pass filter start to kick in just over 20 kHz to get rid of the fundamental at 48.5 kHz. But note the PWM approach still produces a frequency dependent noise floor, and that noise floor is worst at the higher frequencies. _By 50 dB compared to 20 Hz._
> But I'm sure you all knew that already.


What signal did you put on the input of the amp for these measurements and what generated it? And how did you load the powersupply/output?
Just curious.


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## Deton Nation (Jul 3, 2009)

placenta said:


> No, this was in my later years. The ants vocal range is sort of like crinkling plastic paper, but at a super high frequency. Just barely audible to me. Everyone thinks I'm joking too.. There are such things as oddities...


lol...


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## Wheres The Butta (Jun 6, 2009)

FYI, that's not ants "vocal range" you're hearing. I said it before but I don't think anyone read it. 

It's the sound of their appendages moving and clicking. It's similar to the sounds a crab makes, since all arthropods exhibit some audible "click clack" - it's simply in a different range, and not anywhere near as loud as a larger arthropod.

It's not impossible to hear if you put your ear close enough. It does, however, require the listener to have excellent focus and the ability to listen to one noise to the exclusion of all others.


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## chad (Jun 30, 2005)

I swear there are certain species of small ants I can smell, smells like Murphy's Oil Soap to me.


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## placenta (Feb 2, 2008)

bd5034 said:


> FYI, that's not ants "vocal range" you're hearing. I said it before but I don't think anyone read it.
> 
> It's the sound of their appendages moving and clicking. It's similar to the sounds a crab makes, since all arthropods exhibit some audible "click clack" - it's simply in a different range, and not anywhere near as loud as a larger arthropod.
> 
> It's not impossible to hear if you put your ear close enough. It does, however, require the listener to have excellent focus and the ability to listen to one noise to the exclusion of all others.


That explains what I was hearing then. Makes perfect sense. And this was indoors in a quiet house with a line of 1000 ants.


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## Wheres The Butta (Jun 6, 2009)

placenta said:


> That explains what I was hearing then. Makes perfect sense. And this was indoors in a quiet house with a line of 1000 ants.


Must have been pretty cool to hear. There are lots of interesting things in the natural world that sound very interesting. Lots of nice smells and sights too 

I must admit my senses are dulled and jaded from loud listening levels and chain smoking and alcoholic drinking for years. It takes alot to really stimulate my senses.


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## tspence73 (Oct 14, 2008)

chad said:


> I swear there are certain species of small ants I can smell, smells like Murphy's Oil Soap to me.


Wow. Maybe you can. Aren't ants supposed to emit scents to communicate? Perhaps your nose could be picking up some of their language?


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## Wheres The Butta (Jun 6, 2009)

tspence73 said:


> Wow. Maybe you can. Aren't ants supposed to emit scents to communicate? Perhaps your nose could be picking up some of their language?


I wonder if that's how my dog communicates, because he smells AWFUL 

maybe this whole time he's been telling me something!?!


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## chad (Jun 30, 2005)

tellin you he needs a bath


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## quality_sound (Dec 25, 2005)

I can tell it's going to rain by the smell...


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## Wheres The Butta (Jun 6, 2009)

new signature for me. <3


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## finfinder (Apr 15, 2006)

This is getting too weird ... we've gone from amps to ants


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## chad (Jun 30, 2005)

quality_sound said:


> I can tell it's going to rain by the smell...


I'll be damned, I can hear if it's about to storm!


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## quality_sound (Dec 25, 2005)

Seriously. It gets kinda musty smelling. It's hard to describe but it ALWAYS happens. Weird.


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## Wheres The Butta (Jun 6, 2009)

quality_sound said:


> Seriously. It gets kinda musty smelling. It's hard to describe but it ALWAYS happens. Weird.


Once again, not weird. You're just sensing the increased moisture content in the air. 

Most of the things that we think are weird are entirely explainable with a little research and perhaps some creative thinking.

I say most because there are definately things out there that are truly weird.


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## trebor (Jun 30, 2008)

If I concentrate really hard on this thread I swear I can smell a hint of sarcasm at times.


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## quality_sound (Dec 25, 2005)

Not with me, I'm dead serious.


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## chad (Jun 30, 2005)

If you stand too close to me during a storm you may know it's storming by the smell of burning hair and skin.... with my tendency to get struck by the finger of mother nature


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## chad (Jun 30, 2005)

quality_sound said:


> Seriously. It gets kinda musty smelling. It's hard to describe but it ALWAYS happens. Weird.


That's... the smell of rain, it happens all the time. a good storm will promote an ozone smell for miles in front of the storm even when it's sunny where you are at.


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## Oliver (Jun 25, 2007)

bd5034 said:


> I wonder if that's how my dog communicates, because he smells AWFUL
> 
> maybe this whole time he's been telling me something!?!





chad said:


> tellin you he needs a bath


My aunts dog marked my oldest sister while she slept , his name was Saber , about 135 Lb black lab. 

He pissed on her :laugh: shoulder and head . . . she was 11 yrs old .


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## quality_sound (Dec 25, 2005)

Is that what it is? I always wondered.


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## chad (Jun 30, 2005)

a$$hole said:


> My aunts dog marked my oldest sister while she slept , his name was Saber , about 135 Lb black lab.
> 
> He pissed on her :laugh: shoulder and head . . . she was 11 yrs old .


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## BTA (Nov 5, 2005)

So the consensus is that PDX amps tend to have a noise floor that sounds and smells like ants farting?

am i close??


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## michaelsil1 (May 24, 2007)

BTA said:


> So the consensus is that PDX amps tend to have a noise floor that sounds and smells like ants farting?
> 
> am i close??


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## lbc240 (Mar 1, 2008)

Yes I have personally heard this problem on the pdx-4.100


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## LondonRS4 (Jul 16, 2009)

geom_tol said:


> What signal did you put on the input of the amp for these measurements and what generated it? And how did you load the powersupply/output?
> Just curious.


I measure with both an open circuit and a 10k ohm terminator to ground on the input RCAs. No real difference. Not surprising, this is a multistage amp and the noise is really a characteristic of the output stage. I loaded them with 4 Polk DB1001 tweeters or 4 of the Polk 5.25" mids. No difference. Again not surprising, both loads are very closely matched. The actual PSRR measurement was done using a variant of the Texas Instruments Application Report SLEA049 dated June 2005.


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## Thoraudio (Aug 9, 2005)

I'm pretty sure Richard Clark will pay you $10,000 if you can tell the difference between a line of carpenter ants and a line of fire ants....

if they're all walking in the same direction that is.


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## Mooble (Oct 21, 2007)

Thoraudio said:


> I'm pretty sure Richard Clark will pay you $10,000 if you can tell the difference between a line of carpenter ants and a line of fire ants....
> 
> if they're all walking in the same direction that is.


Not exactly. 

First: you will need to paint the fire ants black.

Second: you must cut off the legs of the carpenter ants so they are the same length as the fire ants.

Third: you must test them in an environment that will not showcase any of their natural differences. You CANNOT test them in wood for instance, otherwise the carpenter ant would have an advantage.

Fouth: you must disqualify any ants which emit a characteristic noise.

If you do all these things RC might pay you $10k if you can hear a difference between them (if he's in a good mood).


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## kurtlou (Jul 8, 2009)

thanks for sharing


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## Wheres The Butta (Jun 6, 2009)

lol. keep coming kurtlou


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## Deton Nation (Jul 3, 2009)

Hahaha!!!
Goodstuff!


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## Mahna Mahna (Mar 2, 2008)

If the PDX is no good...what amp is? DLS, ARC KS????


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## Ziggy (Nov 29, 2007)

I got bit by some fire ants this past weekend... Bit or stung?... I think they do both... 
They bite you to hold on... and then they sting you!


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## placenta (Feb 2, 2008)

Mahna Mahna said:


> If the PDX is no good...what amp is? DLS, ARC KS????


both of those are generally better than a PDX.


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## Wheres The Butta (Jun 6, 2009)

placenta said:


> both of those are generally better than a PDX.


well, they're also different.... the PDX is a class D

there aren't too many class D full range to compare to...

There are tons of class A/B that are great though.


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## LondonRS4 (Jul 16, 2009)

I'm the OP. I replaced the 2 PDX's with 2 DLS RA-40s. Bigger amps (twice the size of course), but no discernable hiss at max gain. Nice sound too. Warm like an old Tandberg receiver...Scandinavian sound I guess.


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## michaelsil1 (May 24, 2007)

LondonRS4 said:


> I'm the OP. I replaced the 2 PDX's with 2 DLS RA-40s. Bigger amps (twice the size of course), but no discernable hiss at max gain. Nice sound too. Warm like an old Tandberg receiver...Scandinavian sound I guess.


Are you saying your new Amp has a Nordic accent?


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## LondonRS4 (Jul 16, 2009)

michaelsil1 said:


> Are you saying your new Amp has a Nordic accent?


Yaa, yoouu betchya....

just remembering how my Minnesota born and raised wife hated the movie Fargo. She claimed "her" people didn't really talk like that...so wrong she was. :laugh:


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