Decrease power amp’s gain to increase resolution of preamp

agencal said:

Hi
I heard from PS Audio videos that at low volumes pre amps loose some resolution. When you increase volume they open up. I am living in an apartment and mostly listen in low volume levels. I hava a CH L1 pre and M1.1 power set up. The power amp allows to reduce gain uo to -12db. If i do that now i can increase the volume of pre amp all the way up. Am i increasing resolution in low listening levels by this or improve distortion?

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Where is your preamp volume set for a normal listening level? If that point is not too close to the minimum or maximum you probably have the amp gain well matched to the preamp. I would imagine since both preamp and amp are from the same manufacturer, the default gain settings are chosen for a good match.

If you find your preamp is always set to low volume (like maybe 25% or less of max) for normal listening, you could try decreasing the amp gain so that you could set the preamp volume closer to the middle of its range. And you could keep going, decreasing the amp gain and turning the preamp up a bit more if you think that sounds better. I seriously doubt that you would hear any difference from just having the preamp be about mid-range for normal listening levels though. Both your preamp and amp have very low noise and distortion specs.

In my opinion if your volume can go max your amp gain is too low. I also thought the less your amp has to work the lower the distortion. Although we are probably talking low levels of distortion. I do think if your preamp is going well over half way up on volume some distortion is being introduced.

I currently use -10db attenuators in line between my Pre and amps for this purpose. I am on systems hold currently as I am moving at the end of the year. If I retain the current pre and amps for the new setup, I will send in my pre for adjustment. They can change out some resistors for a -6db decreased gain.

And of course some power amplifiers come with gain adjustment provisions.

Fed_B said:

Where is your preamp volume set for a normal listening level? If that point is not too close to the minimum or maximum you probably have the amp gain well matched to the preamp. I would imagine since both preamp and amp are from the same manufacturer, the default gain settings are chosen for a good match.

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The amp's ideal gain is where a very loud sound is heard when the preamp volume setting is at about 80% towards maximum. A low level volume should mean the volume setting at about 25% maximum.

However the reason for the need to adjust gain from the default setting is not so much to do with matching the preamp and amp, but to allow for different speaker sensitivities. The default gain will have been set by the amp manufacturer on its output power rating of course) but also anticipating speakers of average sensitivity. If you have particularly sensitive speakers (as I do), you either use a very low output amp, or a beefier one with the gain set low. With my old SETs (6 -18 watts), I needed as much gain as they could offer, but I'm now using amps of 100+ watts and the default gain is too high to keep preamp settings within this (admittedly arbitrary) 25-80% range.

The other big advantage in reducing power amp gain - I'd suggest the most important one for sound quality - is to keep he low-level signal between preamp and power amp as high as you can in order to minimise noise. As you reduce this low-level signal the noise in your system up to this point becomes more pronounced.

Each component, amp and preamp, has a specific noise floor. Most consumer gear has too much gain, so that the volume control is say, at 12 o’clock for full output. By reducing the power amp gain you do two things:
1) you reduce the output noise of the power amplifier, which may increase resolution, especially with very sensitive loudspeakers.
2) you increase the gain of the preamplifier, which may improve its signal to noise ratio and so increase resolution.

I say may in both those statements because the design of these components can vary dramatically and generalized theories have to be tested in your system to see if they apply.

So if your power amp has adjustable gain give it a try. It’s a free tweak, and if it works for you, that’s awesome.

Way too much preamp gain has been a problem for quite a while. Some preamps have adjustable gain switches on the back so you can turn the gain down a bit. That is one reason why I love my Ayon pre so much, you can match it to the amp and speaker sensitivities.