# High pitch noise from Alpine PDX amp... help.



## Wheelhaus (Jan 4, 2008)

So in anticipation of new-car delivery, I hooked my new system up the bench to get familiar with it. I'm running everything from a 25a 12v power supply (13.xx volts) and volume levels are staying pretty low, nothing is even getting warm (besides the amps, but they are also getting warm at 0 volume, from what I've read, this is normal for the PDX amps). My only intention with this setup is to get to know the head unit adjustments and amps before everything is installed. Anyways...

Here's the scenario...

I was originally getting the turn-on pop before I realized I missed hooking up the remote wires to the head unit remote wire (Alpine CDA-9887). Now it powers up smoothly with no pop, but the PDX 4.100 amp emits a very high pitch noise that wasn't there before. When I originally hooked everything up the sound was clean and clear, no faint 16-20khz tone. Now suddenly this terribly annoying noise is there.


Every time the H/U remote power turns the amps on, the noise is definitely there.
Applying 12v directly to the amp's remote lead and the high pitch tone seems to vary in intensity, but its still there.
It happens only with the 4.100 amp (not the 1.600).
The noise is there when the amp is on and speakers connected.
Disconnecting RCA cables or turning off the head unit does nothing.
Since its indoors running from a regulated 12v power supply, it cannot be alternator noise or chassis grounding problems. 
The noise was NOT there before.
The noise does not audibly change with volume levels. 

The strangest part is this... When I disconnect the amp's remote wire *by itself*, the H/U shuts off and powers back up. (This happens whether I'm using the H/U remote or straight 12v remote wire).


Could something be damaged in the amp? Its brand new and only hooked up this once. Besides the remote wire, everything else was checked three times before powering up. Again, it was all working perfectly until I rewired the remote, and now no matter what I do, i can't get rid of this high pitch tone.


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## Wheelhaus (Jan 4, 2008)

I also noticed I'm getting audible hissing from the amp. When the speakers are powered by the H/U they are clean and quiet. When they are powered by the amp, they hiss and have the high pitch noise.


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## Wheelhaus (Jan 4, 2008)

According to this thread, the amp has been completely isolated on the bench from any possible sources of noise. It still has noticeable hiss, high pitch "teakettle" noise, and a very very faint, strange fast clicking sound, all audible through the speakers. 

Ugh. Hopefully www.onlinecarstereo.com will be able to swap it out, its only a few days old.


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## CBRworm (Sep 1, 2006)

I noticed a similar thing with my 4.150 The whine would kind of spool up after being connected to power - regardless of whether it was connected to a battery or a power supply. The noise was faint, but bothersome to me.

I think it is noise from the amps power supply.


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## Wheelhaus (Jan 4, 2008)

You're probably right. I definitely don't think its normal because it didn't do it for the first 3-4 hours I was listening to it. Then after I started experimenting with turning the system on/off and the hookup issue I had with the remote wire, causing the excessive popping, thats when it started.


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## mobeious (Jan 26, 2007)

iv had this problem with my arc kar amps sounds like the sound is coming directly from the amps not from the speakers in the car its sounds around 10k+ barley hear it but u can hear it


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## 89grand (Nov 23, 2006)

I had that in one of my JBL amps too, it was coming from the amp. They were in the trunk and you couldn't hear it in the car, but if you opened up the trunk, you could barely hear it.

I never bothered to trouble shoot it because it never really caused a problem.


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## Wheelhaus (Jan 4, 2008)

This is 100% audible from the speakers... If you pick up one of the mid-woofers or tweeters and put it to your ear, there's no question. The H/U and amp are set for active, and it affects all channels. The only thing audible from the inside of the amp is a strange clicking sound, which is sometimes also audible from the speakers.

The speakers also have noticable hiss that wasn't there before, they sound like background noise from a silent recording turned up to mid to mid-loud volume (but volume and gain adjustments do nothing to change it). 

I have a feeling the power supply (or some random circuit) is a lemon and its affecting the speaker outputs. It the amp circuits were making a faint buzzing or humming but the sound though the speakers was crystal clear- I'd have no qualms. 

The hissing combined with the high-pitch tone is subtle, but its enough to drive you mad.


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## Wheelhaus (Jan 4, 2008)

well I got the replacement, looks to be a brand new unit.

This one does not have the same high pitched whine, so that's good.

Now Ch2 (front right tweeter) has a hiss. This hiss is very audible, even when the head unit is muted. If I swap another speaker to ch2 (such as the left front tweeter), the noise is audible on the new speaker. The other channels are silent. The noise on ch2 is audible with the RCA's unplugged and the car turned off.

The problem has been isolated to the amp (yet again). Do I have ANOTHER bum PDX?   

I'm going to try a straight 12v remote, if that doesn't fix it I'll put it on the bench to see if I can recreate it.

edit-
It was actually audible on all channels, for some reason ch2 was more noticeable.


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## xDeLiRiOuSx (Apr 26, 2005)

Hrm, I have a PDX 4.100. Channels 1 and 2, are connected to tweeters (Seas Silk Neo) and they have that high pitch noise too. I'm thinking that I might have some grounding issue with the back of the tweeters in contact with metal from the door. But After reading your thread, I am starting to worry that the noise is due to a bad amp =/

I'll have to do more investigation and get back to you on this (i'm going to first try to isolate the tweeter from the chassy ground, then I'm going to try to switch midrange channels with tweeter channels).

--David


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## Wheelhaus (Jan 4, 2008)

Mine is wired the same, Ch 1 and 2 are L/R tweeters, 3 and 4 are L/R mids. 

This hissing is definitely not congruent with the high pitch whine I had with the first one.

After further investigation I found out that a couple speakers were in the wrong terminals, I guess that was somehow causing the hiss. Each door's pair of speaker wires are loomed together for about 12 feet, maybe having the channels crossed at the amp was generating interference that resulted in audible noise. (Maybe something to do with Alpine's correction circuit?)

After quadruple checking the hookups, the strange hiss appears to have been eliminated. Its now at an expected level (very very faint white noise like a recording from a silent room), which is only audible if the car is absolutely silent and not running. 

Oddly enough a new strange noise is now very intermittent, audible maybe once every 15-60 seconds. It sounds similar to what you hear when changing tracks on a cheap CD player (or a poor quality portable CD player with high quality headphones). Its a weird static/squeaking noise that only lasts about 1 second then its gone. This happens even when the head unit is muted and no CD present. Oh well.


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## Wheelhaus (Jan 4, 2008)

xDeLiRiOuSx said:


> Hrm, I have a PDX 4.100. Channels 1 and 2, are connected to tweeters (Seas Silk Neo) and they have that high pitch noise too. I'm thinking that I might have some grounding issue with the back of the tweeters in contact with metal from the door. But After reading your thread, I am starting to worry that the noise is due to a bad amp =/
> 
> I'll have to do more investigation and get back to you on this (i'm going to first try to isolate the tweeter from the chassy ground, then I'm going to try to switch midrange channels with tweeter channels).
> 
> --David


If your problem is similar to what I had with the first amp, it's a very high pitch tone 16-18khz. Check this link, for a nice online hearing test. Click in the 16khz column, this is what I was hearing and it nearly drove me insane. It may have been 18khz. 

My amp ended up being replaced under warranty by Online Car Stereo (it was a week old).


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