DIYMobileAudio.com Car Stereo Forum banner

Preamp advantage?

1 reading
12K views 10 replies 6 participants last post by  gstokes  
#1 ·
I've been using a JVC KD-A535 head unit for a couple years. The HU claims to have "2.5V x 3 Pre-Outs/Sub W. Out." I'm not sure if this means that its a total of 7.5V preamp or if its 3 RCA outs at a total of 2.5V.

I have had a Clarion EQS746 graphic equalizer/crossover that claims a "6-Channel/7-Volt RCA Line-Level Output."

Is there any advantage in terms of power (and therefor better sound quality at higher volume) with adding the in-line Clarion pre-amp?

Even if the head unit was putting out 7.5V (doubtful), would adding the Clarion add 7V or limit it to 7V?

How much impact does preamp power have in the end result?
 
#3 ·
If the Clarion is in the dash with the HU, you would run the 2.5V preouts into the EQ and it would provide up to 7V output to your amp. Higher voltage is desirable for s/n ratio, but most amps can only handle up to 5V anyway.
 
#4 ·
So, if each line out of the HU is 2.5V, that means its 7.5V in total. Running it through the Clarion would SUBTRACT .5V and make it worse instead of better?

I was originally under the impression that the HU could only handle 2.5V total, as its normal for car audio companies to try to stretch the truth in their claims.
 
#11 ·
Forget the 7.5 number, you have three preouts and each one is 2.5 volts so the only number you need to concern yourself with is 2.5, run the preouts to the amplifier and set your gains.
 
#5 ·
Higher power outputs in the preamp stages don't affect the total power your amp can put out. A higher voltage level in the preamp side (between your HU and EQ, and the EQ to amps) increases the signal/noise ratio, and really benefits if you are running long RCA lengths to your amplifier.

Also, the output levels of your HU do not affect the output levels of your EQ (and so forth down the signal chain). The HU presents 2.5V (per channel - don't combine) to each input of the EQ. The EQ will present 7V to your amplifiers.

As stated earlier - you adjust the gains of your EQ and amplifiers to match the input stages. If your EQ expects a 2.5V signal, not much adjust is required. If it's expecting a 1V signal, you raise the gains on the EQ to compensate. Similar with the amp (though I expect, as others do in this forum - you will need to turn down the gains of the amp to help it deal with a high voltage output). Hope this helps.
 
#6 ·
So what I'm understanding is that the only benefit of preamp power is really just to improve S/N ratio.

I talked to someone who works at a car audio shop and when I asked him if it was worth putting in he said good systems usually have around 10V preamp and led me to believe the preamp was like a "multiplier" for the total end result power... Maybe he thought I would pay him to install it so he just made that up :\
 
#7 ·
He is incorrect (or clueless). Most head units have between 2 and 4 volts output from the preouts. And as already stated, that has nothing to do with how much power the amp puts out.

Higher voltage means your amp gains get set lower and theoretically should reduce the noise in the output. That's all.
 
#8 ·
Yes, if you have a 200 watt amp, it's still a 200 watt amp. The difference is how much gain you have to use to get 200 watts from it. Use a lower voltage input and you'll need more gain to get there, which could potentially raise the noise level. Use a higher voltage input (as long as the amp can take it) and you will need less gain, and potentially lower the noise level. Some amps are noisier than others when you start turning up the gain, so noise floor isn't necessarily a problem.
 
#9 ·
Thanks for all the great info guys!

I think I'll just sell the preamp EQ, as I'm pretty satisfied with the sound as is. Although I'm suspecting that with the extra preamp voltage, it might be possible to lower the gains on the amp, and therefor be able to reach higher volumes before getting distortion--am I correct in that thinking? And if so, how much of a difference would it make?

My question is basically answered, I'm just speculating now. Thanks again.
 
#10 ·
Thanks for all the great info guys!

I think I'll just sell the preamp EQ, as I'm pretty satisfied with the sound as is. Although I'm suspecting that with the extra preamp voltage, it might be possible to lower the gains on the amp, and therefor be able to reach higher volumes before getting distortion--am I correct in that thinking? And if so, how much of a difference would it make?

My question is basically answered, I'm just speculating now. Thanks again.
Nope, a higher input voltage to the amp will just let you use less of the amps internal preamp gain to get the wattage out of the amp. That only gets you a lower overall noise level, * assuming the amps preamp is of lesser quality than the EQ preamp's own output, plus the signal runs induced noise.

When it comes to distortion (ie over driving the amps output in this case), the source of that voltage amount is irrelevant.