# Preamp outs - 2v vs 4v



## Juice75 (Sep 18, 2010)

Hey Guys,

For head unit preamp outs, is there a big difference between 2v and 4v? Aside from the obvious, of course. Wondering if it's worth passing on a head unit that has 2v, just because of that fact.

It's feeding an Alpine PDX-5.


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## fonque (May 30, 2008)

I dont know a whole lot about this topic, but I do know the more preamp voltage, the less gain you need to reach the desired output. As far as I know it is just simple multiplication. This has, in my personal experience, allowed me to reduce my noise floor on a crappy amp. 

to sum up what I have noticed:
low volume + high amp gain = hiss
high volume + low amp gain = quiet

but you can take that with a grain of salt because I am by no means an expert on the topic.


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## sqshoestring (Jun 19, 2007)

I ran 2v for many years with no problems, I don't think you need it for a typical system unless you have noise problems or something, and a few amps do not like to gain very high you might have them all the way up. If you use old amps you notice they have more gain. I would use a good 2v HU anytime.


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## Cruzer (Jul 16, 2010)

2v is fine, but for example in my truck my head unit is 2 volts. my sub amp must have been designed around 4volts, because i have the gain maxed out, and have to have head unit volume about 20 of 36 before i get any bass.

i dont have hiss, or noise, because im not clipping anything.

my speakers amp is designed around 2volt input(its older), and i can barely have the gains up and it gets plenty loud.


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## kyheng (Jan 31, 2007)

Well, 2V is a must, >4V is bonus. As long as wirings are done right at the first place, proper speakers/amps selections, the HU's pre-out voltage doesn't matter much.

But then have to know this also, HU with 2V usually are "lower end" or "entry level" with lesser functions. HU with 4V usually bundled with more functions, can play active.


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## Cruzer (Jul 16, 2010)

kyheng said:


> But then have to know this also, HU with 2V usually are "lower end" or "entry level" with lesser functions. HU with 4V usually bundled with more functions, can play active.


this is true


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## Niebur3 (Jul 11, 2008)

Just keep in mind those are peak numbers (kind of like max power on an amp). Neither will be doing that continuously. You are probably looking at maybe 3/4 of a volt difference between the two. Buy which ever has the better features (that you will actually use) for the money and if you need, get a line driver that will actually deliver good voltage.


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## t3sn4f2 (Jan 3, 2007)

Niebur3 said:


> Just keep in mind those are peak numbers (kind of like max power on an amp). Neither will be doing that continuously. You are probably looking at maybe 3/4 of a volt difference between the two. Buy which ever has the better features (that you will actually use) for the money and if you need, get a line driver that will actually deliver good voltage.


Nope, that is a RMS continuous AC voltage. Look at Erin's head unit measurements and see how they hit that mark with a 0dB tone and the head unit set to max. Even a little more then rated on some.


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## Niebur3 (Jul 11, 2008)

t3sn4f2 said:


> Nope, that is a RMS continuous AC voltage. Look at Erin's head unit measurements and see how they hit that mark with a 0dB tone and the head unit set to max. Even a little more then rated on some.


You said it, "with the head unit set to max". Who rides around with their head unit set to max? Also, I guarantee many HU clip even before max.


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## kyheng (Jan 31, 2007)

But my Pioneer never clips, most of the time.


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## Niebur3 (Jul 11, 2008)

kyheng said:


> But my Pioneer never clips, most of the time.


Never clips, most of the time? That is like say probably maybe :laugh:

Which Pioneer do you have? If you have the P9 or similar, then probably not, but I don't think that is what the OP is looking to buy.


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## kyheng (Jan 31, 2007)

Emm..... From my old school 2300(alomst 10 years old), 7700, 9600 to my current P9. Amp clips I do believe, but HU I doubt....


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## Niebur3 (Jul 11, 2008)

They do clip...that is why most tell you not to go above 75% on the dial.


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## ErinH (Feb 14, 2007)

Niebur3 said:


> You said it, "with the head unit set to max". Who rides around with their head unit set to max? Also, I guarantee many HU clip even before max.


I don't get your point here, though. If the headunit doesn't clip at maximum volume, then it won't clip on a lower volume (of the same source material). 
Maybe I'm misunderstanding what you're trying to say. 

all the headunits I've personally tested do not clip (alpine 9815, w505, w200... pioneer p9, 800prs/880prs, z110bt).
that was with a 560ohm load on them (well, most of them) per Chad's suggestion, playing 0dB, 1khz tones, measuring the outputs with a scope.

the "75%" thing is moreso for the listener to have headroom on 'quiet' tracks; not because the headunits clip at "75% max volume". 

*if anyone wants to send me their headunit, I'll be happy to throw it on the bench and test it for you and send it back. I'll even measure the FR on the outputs. (at your shipping expense)*


As far as 2v vs. 4v, it's simple: the reason one is 'better' than the other is SNR related. The higher the preout voltage, the less the amp's gain pot has to be turned up to make the same volume/power/whatever compared to that of the 2v. If you don't have SNR issues in your system, then you're fine. 
This is essentially the same reason that higher power amplifiers are used... lower point on the gain pot = less SNR introduction. 
Seems most of my testing has shown me that noise in systems is majorly because of the amplifier's own SNR, rather than it amplifying SNR from upstream source.
If Chad begs to differ, I'm all ears, though.

Edit: Fonque nailed it.


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## Niebur3 (Jul 11, 2008)

bikinpunk said:


> I don't get your point here, though. If the headunit doesn't clip at maximum volume, then it won't clip on a lower volume (of the same source material).
> Maybe I'm misunderstanding what you're trying to say.
> 
> all the headunits I've personally tested do not clip (alpine 9815, w505, w200... pioneer p9, 800prs/880prs, z110bt).
> ...


I understand the benefit of SNR, I just always read (never tested personally) that HU do not put out what they are rated volt wise and they clip as they reach full volume. What I have read must be confusing the internal amp with the RCA voltage out...lots of **** out there and learn something new everyday. What is funny is that a well know amp company (will remain nameless) is one of the companies that insist this . Maybe there is an agenda there.


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## ErinH (Feb 14, 2007)

Cruzer said:


> i dont have hiss, or noise, because im not clipping anything.



You can easily have hiss/noise while not hitting clipping. The two, IME and testing, are not related. 
Perfect example: high efficiency drivers. If you set the gains to clipping point with a 4 ohm load, you'll hear the hiss much more easily with a set of 97dB efficiency drivers than you will with 89dB efficiency drivers, and the 'power' is still the same because the load and voltage out are the same.


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## ErinH (Feb 14, 2007)

Niebur3 said:


> I understand the benefit of SNR, I just always read (never tested personally) that HU do not put out what they are rated volt wise and they clip as they reach full volume. What I have read must be confusing the internal amp with the RCA voltage out...lots of **** out there and learn something new everyday. What is funny is that a well know amp company (will remain nameless) is one of the companies that insist this . Maybe there is an agenda there.


I used to think the same because audio companies seemingly say that. I agree.

But, once I started doing my own testing, I realized it was not the case. Most headunits I've tested easily make rated power while being under the clipping point. The pioneer headunits and the alpine heads I've tested don't come near clipping. Heck, I can't _make_ them clip. That's with a load on them (560ohm... which is ~ the pre-in impedance of amps/DSPs). 

The 75% thing, as I said above, is mainly just so the user has more 'headroom' on the volume knob to turn the music up louder for quiet cds (ie: Dire Straits' _Brothers in Arms_ ). There may be cases where this is the rule of thumb to keep from clipping, but I've personally not found that to hold any truth. Maybe if it's a crappy headunit.


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## Niebur3 (Jul 11, 2008)

bikinpunk said:


> I used to think the same because audio companies seemingly say that. I agree.
> 
> But, once I started doing my own testing, I realized it was not the case. Most headunits I've tested easily make rated power while being under the clipping point. The pioneer headunits and the alpine heads I've tested don't come near clipping. Heck, I can't _make_ them clip. That's with a load on them (560ohm... which is ~ the pre-in impedance of amps/DSPs).
> 
> The 75% thing, as I said above, is mainly just so the user has more 'headroom' on the volume knob to turn the music up louder for quiet cds (ie: Dire Straits' _Brothers in Arms_ ).


Thanks for setting me straight! Have you testing the output voltage of DSP's? I was told they can never be more than 2 volts because of the power supply and that fact that the architecture is based of a home design and that limits the output voltage. Is this true?


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## ErinH (Feb 14, 2007)

I have, but I honestly don't recall. I didn't take pictures.
It's easy as pie to do, though, if all you want to see is the voltage. Just grab a 1khz, 0dB track (since it seems most companies rate their outputs at this frequency/level), unplug all RCAs to keep from accidentally blowing a tweeter or pico fuse , grab a multimeter, attach probes to shield/pin of a single attached RCA, turn headunit up to max and see what your DSP's voltage out is. Make sure to note if the DSP's channel has attenuation from your tuning. 

It won't tell you if it's true unclipped voltage, but it'll at least let you know if it's above 2v. 
I'll bet that you won't hit clipping, though. As I said, most modern stuff doesn't seem to have this problem at all. At least not the stuff I've tested.


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## Cruzer (Jul 16, 2010)

bikinpunk said:


> You can easily have hiss/noise while not hitting clipping. The two, IME and testing, are not related.
> Perfect example: high efficiency drivers. If you set the gains to clipping point with a 4 ohm load, you'll hear the hiss much more easily with a set of 97dB efficiency drivers than you will with 89dB efficiency drivers, and the 'power' is still the same because the load and voltage out are the same.


u can say whatever u want, but if i dont hear it its irrelevant, and thats all that matters, is the sound.


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## t3sn4f2 (Jan 3, 2007)

Cruzer said:


> u can say whatever u want, but if i dont hear it its irrelevant, and thats all that matters, is the sound.


He's trying to tell you that the reason you don't have hiss or noise has NOTHING to do with whether something is clipping or not.


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## ErinH (Feb 14, 2007)

Cruzer said:


> u can say whatever u want, but if i dont hear it its irrelevant, and thats all that matters, is the sound.


what? I didn't say anything abut what you hear. 
You made a statement: that if an amp clips, it hisses. That's not true.

the end, you're right, as long as it sounds good and you don't have hissing, then it's a non issue. But, you said the two are related. The fact is: _They are not_. 
That's all there is to it. Nothing to argue.


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## t3sn4f2 (Jan 3, 2007)

Niebur3 said:


> Thanks for setting me straight! Have you testing the output voltage of DSP's? I was told they can never be more than 2 volts because of the power supply and that fact that the architecture is based of a home design and that limits the output voltage. Is this true?


"DSP" like a processor? Nope thats not true either, the MS-8 and the bit one put out more then 2 volts RMS. Also the reason the home _sources_ put out ~2 volts clean at most is so that they can be integrated and align properly with the next device from any maker (ie so they dont clip an input, which nothing can be done about since sources have fixed outputs and can not be padded down). However, on quality home preamps and processors, you see outputs ratings well over 2 volts RMS since THAT is where you need to have extra available gain for low recordings. That's why you see a (-xdB) - (+ydB) volume scale. 0dB is no gain added on top of the amount coming in to the inputs (limited to the max that input is rated for). Then anything +dB over 0dB is added gain (ie line driving IOW). Take a look at the specs for the Lexicon processor I linked below.

Lexicon - Product Details


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## Niebur3 (Jul 11, 2008)

t3sn4f2 said:


> "DSP" like a processor? Nope thats not true either, the MS-8 and the bit one put out more then 2 volts RMS. Also the reason the home _sources_ put out ~2 volts clean at most is so that they can be integrated and align properly with the next device from any maker (ie so they dont clip an input, which nothing can be done about since sources have fixed outputs and can not be padded down). However, on quality home preamps and processors, you see outputs ratings well over 2 volts RMS since THAT is where you need to have extra available gain for low recordings. That's why you see a (-xdB) - (+ydB) volume scale. 0dB is no gain added on top of the amount coming in to the inputs (limited to the max that input is rated for). Then anything +dB over 0dB is added gain (ie line driving IOW). Take a look at the specs for the Lexicon processor I linked below.
> 
> Lexicon - Product Details


That is kind what I was thinking. Hmmmmmm, always an agenda. Thanks for the info and verifying what I thought!


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## Cruzer (Jul 16, 2010)

bikinpunk said:


> You made a statement: that if an amp clips, it hisses. That's not true.


i didnt say anything about hissing.

i said i can hear my subs clip/distort, whatever u wanna call it, never said anything about an amp other than my amp comes with a bass knob which has a clipping light.


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## ErinH (Feb 14, 2007)

Cruzer said:


> i didnt say anything about hissing.
> 
> i said i can hear my subs clip/distort, whatever u wanna call it, never said anything about an amp other than my amp comes with a bass knob which has a clipping light.





Cruzer said:


> i dont have hiss, or noise, because im not clipping anything.


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## ChristianM (Jun 15, 2009)

wow im really confused now:S i can say that according to my bitone and its input settings, i can see where my deck (Clarion NZ500, 2V preout) clips, usally around 80% of max volume, some songs i can go 100% volume and it wont clip, all depends on the songs quality aswell, i generally follow the 75% of max volume idea for tuning and rarely ever cross it:S just my observations lol


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## t3sn4f2 (Jan 3, 2007)

ChristianM said:


> wow im really confused now:S i can say that according to my bitone and its input settings,* i can see where my deck (Clarion NZ500, 2V preout) clips*, usally around 80% of max volume, some songs i can go 100% volume and it wont clip, all depends on the songs quality aswell, i generally follow the 75% of max volume idea for tuning and rarely ever cross it:S just my observations lol


The bit one is only telling you where _your deck _clips _its_ input stage.


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## ErinH (Feb 14, 2007)

^ yep.


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## n2caraudio (Sep 22, 2010)

bikinpunk said:


>


me too. I thought you were quite clear and concise.


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## n2caraudio (Sep 22, 2010)

cajunner said:


> If I saw someone do that while I was in their car, I'd be flabbergasted.


Flabbergasted FTW


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## Cruzer (Jul 16, 2010)

bikinpunk said:


>





fonque said:


> low volume + high amp gain = hiss
> high volume + low amp gain = quiet


which is why i said i dont have hiss. maybe im wrong, and thats fine because i dont hear it, so its not a problem.

however u said this:



bikinpunk said:


> You made a statement: that if an amp clips, it hisses. That's not true.


u cant quote those exact words in my posts. maybe u inferred thats what i meant, but its not


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## ErinH (Feb 14, 2007)

Cruzer said:


> which is why i said i dont have hiss. maybe im wrong, and thats fine because i dont hear it, so its not a problem.
> 
> however u said this:
> 
> ...


You gave a conditional statement. You said you don't have hiss _because_ you weren't clipping anything. That's where you lost me. 



Cruzer said:


> i dont have hiss, or noise, because im not clipping anything.


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## Cruzer (Jul 16, 2010)

ya i said it that way because to my knowledge no speaker, head unit, sub, or amp is being pushed to affect its performance or sound to cause said hiss or noise. so whatever causes noise or hiss is beyond what i know and im not going to pretend i know.

im sure im wrong, but like i said i dont hear it so it really is pointless to even bring it up or discuss it.


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## fonque (May 30, 2008)

So to sum up what I have read in this thread so far....
4V output will need less gain than 2V output = potentially lower noise floor
Some digital sound processors cannot handle a true 4v output into their input

Is there anything else to consider?


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## Cruzer (Jul 16, 2010)

How does an amp or other device handle a hu signal that is say 6 or 8 volts but is designed for 2 or 4?

Will it be just like it was a 2 or 4volt signal?


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## t3sn4f2 (Jan 3, 2007)

Cruzer said:


> How does an amp or other device handle a hu signal that is say 6 or 8 volts but is designed for 2 or 4?
> 
> Will it be just like it was a 2 or 4volt signal?


It handles it the same way as a weaker voltage. All the amp is doing it using an in line variable resistor (ie a pot) in order to _pad down_ that strong voltage coming in (same as a resistor does to a tweeter in order to lower its output, just on a lower scale). If you want to set it up so that there is no clipping on the inputs of the amp, then you need to make sure that that pot (ie the amps gain range) can pad down the amount of voltage that is coming in. If the _input sensitivity _of the amp is rated from 4-.4 volts and you have an 8 volt head unit. Then you can only pad down to meet a 4 volt input. Anything more when sent from a combination of music/EQ/tone/volume setting will clip the amps input stage.


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## SpeedEuphoria (Sep 15, 2010)

So installing my old Eclipse 55040 8v to my old Memphis CA 150 2v-.2v on the gain.

What issues am I going to have?

I think the only issue would be if I were trying to match output since I cannot turn it down any lower.


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## t3sn4f2 (Jan 3, 2007)

SpeedEuphoria said:


> So installing my old Eclipse 55040 8v to my old Memphis CA 150 2v-.2v on the gain.
> 
> What issues am I going to have?
> 
> I think the only issue would be if I were trying to match output since I cannot turn it down any lower.


The only issue would be the you would not be able to turn your volume knob as high as someone that had a lower voltage head unit. Think of it like a home setup. Do you have a receiver or preamp? How often do you turn it past half way?


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