2. amps-preamps
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Educate me about gain and amp/preamp matching

I’ve been doing a bit of research on specifics on my second system. It comprises of a Quad ESL 2805 at 86db / 8ohm nominal driven by a Viva Linea preamp, which seems to have high gain (+12db I believe) at 150 ohm output impedance and an Atma-Sphere S-30 OTL amp at 30w/ch. The acoustically-treated room it’s setup up in is quite small - 9x20 to be exact, with the Quads about 5ft from the wall, and me only sitting about 5-6ft from the Quads, so pretty near field. Quads are ideal in this room since their dispersion is linear and minimizes room reflection. Even without the preamp gain added, an SPL calculator shows I can get up to 101db at listening position. 

Because of the size of the room and listening distance, everything sounds superb, but in many of the threads I read, people always state, including Ralph Karsten of Atma-Sphere, that the Quads need more than 50w of power to perform their best.


Does the fact that I am pairing the Atma-Sphere with a higher gain preamp help this situation? I’m not hearing any clipping or noise due to driving a stronger signal into the amp. And even if the signal coming into the amp has more gain to begin with, at I still limited to small headroom due to the 30w the amp puts out?


Happy to provide any specific information needed to answer this. Thanks for helping me understand the science behind it because aurally it sounds great.


blisshifi

Showing 2 responses by blisshifi

blisshifi's avatar
blisshifi OP
1,230 posts
 
Thanks all, especially @cleeds for such a succinct response. I’m actually surprised that the input gain of a preamp doesn’t really effect the output signal gain of the amp. I thought it would be additive or multiplicative (if that’s a word). Can someone explain why that is? Is it that the output signal gain is usually the same (3-6db depending on unbalanced / balanced) regardless of preamp?

@almarg - thanks for the compliments on the equipment. I got lucky over time, I guess. And I don’t ever need to turn up the volume past 11 on the loudest passages given I’m only 6’ from listening position and the speakers are about 6’ apart center to center. 
And @atmasphere - thanks for the clarification on the efficiency - not sure if you’ll be around tmw but am planning to drop by to drop the S-30 and MA-1 around 10:30. Prepping all the gear now. 
blisshifi's avatar
blisshifi OP
1,230 posts
 
These are all incredible responses, thank you. I think I misinterpreted Cleeds’ answer  because you explained how I actually believed it - the amp always puts out the same amount of power, and the preamp’s power can add gain (if it is active). Together, they are additive, and the preamp’s volume control attenuates the whole.

i’m guessing the idea of headroom then is similar to a well-exposed photograph in that it has the most amount of dynamic range and is uncompressed. Having a preamp that has a lot of gain may also add noise, depending on quality, and sending that to the amp could amplify and raise the noise, making sound have a lower range. Per @millercarbon’s post, it might be that the noise balances between the amp and preamp are what can make a preamp truly successful, as the right match may result in the right blend of 2nd order harmonics, adding body and texture without losing overall range. 
The amp also has to be able feed the speakers with the power it needs to be able to handle generally what is hungry (usually the bass) and still have enough power left over to handle the rest of the frequency range, otherwise it will clip. 

I did this type of exercise last night with a different amp, just to test, which is why I decided to post this thread. The amp in question was a 2W/channel Korneff 45 clone. Of course, I knew pretty well it wouldn’t be able to drive the Quads, but I wanted to experiment even at very low levels. Oddly, combined with the Viva Linea preamp I would have been able to get the SPL I wanted, but the sound started to clip even before the volume was at 12 o’clock. I took it off right away. 

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