find preamp voltage with multimeter.

After searching and reading through about 100 posts on here I still couldn't find the proper way to find the preamp voltage. I ended up calling a relative and he told me.

It is as simple as taking one of the rca's going to the amp from the head unit and touching one multimeter lead to the inner tip and the other lead to the outer part. Be sure to have the multimeter in AC mode.

On a side note when I changed my volume the output voltage also changed correspondingly. Keep that in mind when testing it.

Just posting this so anyone else looking for the info will see it.

Forgot to add that I used a 60hz test tone for this.

I've tested for AC voltage at the amp's speaker outputs this way.  Gain all the way to minimum, head unit at full, test tone playing on CD, speakers disconnected.  This gives you the voltage that the amplifier is starting with.

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I've read that method many times on here and that is what I initially tried, but it doesn't give the actual preamp voltage.

Using that method I was getting different numbers on different amps. One was reading 8v and the other was reading 6v with both at minimum gain when my actual preamp voltage is ~2v.

I've seen most decks use a bout a 2v pre amp.  Cheapers ones may be a little less.  And then the higher models just go up from there...Mine was listed in the manual under technical specifications.

I did the same thing for matching them. Multimeter to the speaker outputs and set from there.

"Using that method I was getting different numbers on different amps. One was reading 8v and the other was reading 6v with both at minimum gain when my actual preamp voltage is ~2v."

That method is used for gain matching. That 6 and 8v you were reading were most likely the gain off of the amp.

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The One&Only!

A note of caution: it is pretty easy to short out your preamp using meter leads on RCA connectors, especially with the "fat" probe tips on some lead sets.  All you have to do is let the probe touching the inner conductor lean over and touch the outer ring and poof, you can blow the output stage on some preamps.  If you want to directly measure pre-out voltage level a better way is to build a mating RCA connector with wires that can be split, stripped and used as your meter connection point.  And use gripper probes on your meter so you don't have to hold them by hand.

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I'm still foggy about this, so would someone set me straight?  Voltage is not summed, or is it?  When reading the RCA,  if the left channel reads 4 volts and the right channel reads 4 volts, it's still just 4 volts total?  Which means reading either channel on the RCA will give you the deck output?  And a valuable tip there, DYohn.  I'm glad to know that now.

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Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Stevdart you are correct, preamp output voltage is per channel.  I don't understand some of the earlier comments made by others....

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