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.


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cleeds
5,957 posts
 
thiefoflight

... 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?
Yes. Once an amplifier has been fed an input of sufficient gain to drive it to maximum output, increasing input gain will not increase the amplifier's output power.
almarg's avatar
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almarg
9,670 posts
 
+1 Cleeds.

Also, keep in mind that the difference between 30 watts and 50 watts is only about 2 db, in terms of voltage, power, and (everything else being equal) in terms of the resulting SPL.

Differences in preamp gain will just affect the settings of the volume control that are used (everything else being equal). And as long as you don’t ever find yourself wanting to turn the control higher than max, or having to operate it near the bottom of its range, such differences are not usually an issue.

Nice equipment, btw! Regards,

-- Al
millercarbon's avatar
millercarbon
12,531 posts
 
everything sounds superb, ...
but  ...
the Quads need more than 50w of power to perform their best.


Clearly not.
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atmasphere
11,834 posts
 
Because the Quads are a panel rather than a point source, they are actually more efficient than the specs indicate on account of how that efficiency is measured (at one meter). This is because at one meter a lot of the radiated sound simply isn't picked up by the microphone.

Its likely that the real efficiency is a few dB higher. If you are able to get satisfying levels without clipping the amp then I would say you have no worries.
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