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Here's one that always amuses me.

Higher pre-out voltages DO NOT make your system louder. They DO NOT make your amplifier work less. The benefit of a higher pre-out voltage is that any distortion signals that may be transferred into your RCAs will be a lower % of your original signal, and that if you are running a large number of amps(ie more than 1 off each pre-out) you will have a higher voltage signal at each amp.

Here's why, your amplifier can only output up to a certain voltage before it clips. That's a more or less "set in stone" thing based on the amplifier itself. For the sake of argument, we'll say its 20V. The gain on your amplifier is used to match the amplifier's output voltage to its maximum by compensating for your different input voltages. Thus say we have a input voltage of 2V, you could set it to 10, or if you had a 5V pre-out, you would set it to 4. IF you had a 2V pre-out, then upgraded to a 5V pre-out without adjusting your gains you would be trying to make your amplifier run up to 50V, which is MEGA clipping.

It will not make your amp "work less" or run cooler. You amp is only capable of a certain voltage. If you want to make your amp work less, turn down your volume. A higher pre-out voltage will actually make your amp work harder and run hotter, as it will reach its maximum output voltage faster.

Also, your gain knob is NOT a volume knob!
 

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you realize that clipping the amp is the best way to run the signal..as the transistors are fully open and operating at as close to 100% efficient as possible..
 

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True. Although it may seem louder if you don't set your gains right, but that's only because you start clipping.

However, there is one way that higher pre-out voltages can make your system louder. If you do something like have a stereo with 0.5 volt signal output, then you run RCA splitters and split the signal to 50 different amps, the gain knob at max won't reach RMS power. But that's not a common problem for people to have :)

There is a single big advantage to high volt outputs. Noise rejection. I know lots of people have problems with noise in their setups, especially if the RCAs get close to power wire. For laughs, I wrapped my RCAs around my power wire, and get no noise. 8 v pre-amp outputs really help with that, the lower your gains are, the less noise you get in the RCA cables :)
 

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here is a good example of high output voltage... ok lets say we are in a machine shop... and you are the manager trying to get the attention of one of the workers... so you are up on the mezzanian and you yell as loud as you can to get his attention.. thats a low ac output deck, but take the same time and add a megaphone to his voice and now he can hear you.. has the noise in the system changed no, but the output has masked the noise of the system... so high output dosent lessen the noise, its still there, it just goes higher than it is..
 

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this is the premis of class d amps as they are running at almost full power and are very efficient.. make sense?
Well actually class D amps are less efficient when stressed. Said to be closer in efficiency to a class A/B @ full power.

Kelvin
 

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this is the premis of class d amps as they are running at almost full power and are very efficient.. make sense?
Actually you have it backwards. At lower volume levels class d amplifiers are more efficient than their class ab counterparts due to the nature of their switching power supplies.

At max volume, the most inefficient component will be the subwoofer since it will take all that power and convert most of it to heat.:p
 

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The majority of the original post is correct with the exception that high pre-out voltage reduces distortion.

The purpose of high pre-out is to reduce noise. The signal traveling to the amplifier can pick up all kinds of stray signals. Also the amp's front end gain is high so it can introduce more hiss, etc. By increasing the output voltage from the signal source, we can reduce the amp gain and thus reduce noise.

They use this concept on satellite receivers by putting the LNA at the antenna before the cable.
 

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Also, your gain knob is NOT a volume knob!
Well, if you are going to be technical, you should say "your gain know is NOT [MEANT TO BE USED AS] a volume knob!"

It's a potentiometer that, although serving a different purpose, is designed like and works the same as those same mystical little knobs we see labeled "volume"
 

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As a couple of people have stated above, all higher voltage pre-outs will do is lower certain types of noise... but that's only if you have noise to begin with... if you have no noise, it will do absolutely zero for you.
 

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Well, if you are going to be technical, you should say "your gain know is NOT [MEANT TO BE USED AS] a volume knob!"

It's a potentiometer that, although serving a different purpose, is designed like and works the same as those same mystical little knobs we see labeled "volume"
I think this is another possible myth. "your gain knob is NOT a volume knob!"
But this myth serves as a good purpose because it makes it easier for the installer to deterr customers who don't know what is going on from touching the settings.
 

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I think this is another possible myth. "your gain knob is NOT a volume knob!"
But this myth serves as a good purpose because it makes it easier for the installer to deterr customers who don't know what is going on from touching the settings.
I find that sometimes, a lot of customer will change all the setting regardless of what I tell them. I tried to explain to them that is a sort of multiplier of the level of sound coming from the headunit. That explanation seems the satisfy most but, I'm sure it's not the most correct answer.
 

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So... (noob question time) ...if you have a balanced differential signal going from HU to an amp that accepts this noise-rejecting signal, there won't be any benefit from increasing the voltage with a line-driver? I can just add in a little more input gain until I reach the edge of clipping, right?
 

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"gain knob is NOT a volume knob"

Damn, I know this is not a thread dedicated to that, but I am having some issues with the gain on my new amp.
 

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So... (noob question time) ...if you have a balanced differential signal going from HU to an amp that accepts this noise-rejecting signal, there won't be any benefit from increasing the voltage with a line-driver? I can just add in a little more input gain until I reach the edge of clipping, right?
Probably not...I'm pretty sure your balanced signal has enough juice to drive the amp to it's max. The point of this thread is about noise and you have balanced so you're good.

Yes just add gain.
 

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So... (noob question time) ...if you have a balanced differential signal going from HU to an amp that accepts this noise-rejecting signal, there won't be any benefit from increasing the voltage with a line-driver? I can just add in a little more input gain until I reach the edge of clipping, right?

A balanced differential input will reject noise incurred prior to the input stage. You would still have whatever level of noise the various circuits in the amp themselves produce; so, if you have a really low input signal then boosting it would help you keep more of the music well above the amp's noise floor.
Typically, though, unless your amp has a really low S/N and your input voltage is really low, I wouldn't worry about it.
 

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However, there is one way that higher pre-out voltages can make your system louder. If you do something like have a stereo with 0.5 volt signal output, then you run RCA splitters and split the signal to 50 different amps, the gain knob at max won't reach RMS power. But that's not a common problem for people to have :)
It's also not really true.

Using splitters sends the same voltage to each output with an ideal source with zero output impedance. If you are using so many splitters that the combined load is getting close to, or lower than, the source's output impedance, you're in trouble regardless of the source output voltage.

Nor is it true that higher output voltages are intended to reduce the % distortion. That will remain the same - or even get worse - when the internal signals are amplified for output. The only argument for running higher voltages across your interconnects is to improve signal to noise ratio - the noise from external EMI is constant for a given installation, and independent of source voltage.

This doesn't really have any significant effect either. The whole output voltage phenomenon is a marketing scam designed to ensnare the ignorant. Just avoid running interconnects at unnecessarily low voltages (low output on HU, high gain on amps, for example) and you shouldn't have noise problems.

The proper way to solve this problem, if it existed in a car environment, is with a balanced line.

Studio equipment runs millivolts of microphone signal over enormous lengths of electrically noisy environment by doing it properly - with a balanced line connection. This runs two signal lines per channel, one an inverted form of the other. Here's how it works.

Conductor 1 carries a signal x
Conductor 2 carries its inverse -x

Along the line, interference y affects both lines equally:

Cond 1 becomes x+y
Cond 2 becomes -x+y

At the "far" end, the receiving equipment subtracts Cond 2 from Cond 1 to get the signal:

output = (x+y)-(-x+y) = 2x

Boom. No interference. That's the real way to do it.
 
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