2. amps-preamps
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Preamp gain vs. poweramp sensitivity

Hello,

Just purchased an Art Audio Carissa which has input sens. of 600mV (very high). At first, I was thinking that I would want a high-gain pre because the Carissa puts out only 16W/ch and could benefit from some preamp gain.

However, I believe upon considering the sensitivity that a high-gain pre is NOT desired because:

1) I would need to open the VC only a bit before the Carissa was driven to full power.

2) For the above reason, the high-gain is wasted anyway because the pre wouldn't be able to put out what it's capable of without overdriving the Carissa.

Do I have this straight? The relation of gain to voltage is not clear to me. The preamp is specified as outputting 2V yet, with a standard 2V source, that is actually unity gain! So what exactly does "20db of gain" in a preamp mean?

Thanks for clarification on this question.

Paul
paulfolbrecht
paulfolbrecht OP
603 posts
 
Herman,

Thanks so much for that great explanation! Exactly what I was looking for.

I have to ask you now - would you suggest a passive linestage with this setup? My source's output imp. is 300ohm and the amp's is a very high 180K - this seems like a good case for a passive pre to me. Agree?

In other words, I am now concluding that ANY active pre, much less a high-gain one, makes little sense here. Impedance matching would be the only possible reason for an active preamp and that would not be an issue at all, certainly not with a passive pre with a typical 10K output impedance.

What do you think?

Thanks again.

Paul
newbee
4,767 posts
 
Paul, FWIW, I don't believe your amp will see the output impedence of your source. It will see the output impedence of your (passive) line stage. Does the 'passive' line stage you are considering have a constant output impedence, or does the output impedence change with the position of the volume control. Some do, some don't and it can make a difference (but with and input impedence of 180K it might not). It could also affect you choice of IC's and the lengths you could use (short is always good with passives).

Lastly, I observed a lot of folks going to passives with a lot of initial satisfaction over what appears to be a gain in detail, clarity, etc, but concurrently I've seen quite a few change back (including me) feeling that they lost some dynamics with the passive. Try before you buy if you can.
paulfolbrecht OP
603 posts
 
Most passives do vary OI, you're right, with 10K being the top end. Into 180K, I think that'd still be fine.

I have tried a PLS on my system with the previous amps, which have only half the input impedance, and are less sensitive, and it seemed very good to me, including the dynamics.

Active preamps just seem like so much overkill when you've got a strong source and good impedance on both ends.
herman
2,253 posts
 
I agree with the responses about the passive. While your setup is certainly a great textbook match for a passive, some will still prefer an active stage. The good news is you can get a used passive and sell it at no loss if you don't like it. Personally, I've always like one with the right setup. There is usually a Placette or 2 for sale here and they retain their value very well. Give it a try.
unsound
7,329 posts
 
May I borrow this thread? Perhaps Herman can clear my head. I have a stereo amp that is rated at 250 watts per channel in to 8 Ohms with 26.6 db of gain. What is the amps sensitivty?
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