Quietest amp.

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What amplifier is absolutely the quietest of them all? Which amp has the highest s/n ratio?
If I remember correctly Susan Parkers "Zeus" amplifier has a s/n of 130db
can this be beaten?
Which power supply, input stage, and output stage lends itself to low noise ability?
No idea AndrewT

I only ask as I am in the middle of a Line Array project that will be very efficient which will exacerbate any amp noise present. (NAD 2100 at the moment but not for too long I hope)

Lineup; are you using very efficient speakers for this test? Is it totally quiet at full power?
If so, could you share your new design; it must be the quietest.
Jerry, this is more a problem with construction, than design. In theory, a power amp can have the input noise of a very high quality phono stage, which when REFERRED to its rated power output, can give a HUGE S/N. However, it is not really that important, unless you are using HORN loudspeakers, which amplify noise of the power amp, because they may be as much as 20dB more efficient than planar drivers or most direct radiators.
The KEY is the S/N of the preamp, because it has an extra 10-20 dB of gain in front of the power amp. This is where things fall apart, because of the VOLUME CONTROL which adds up to 1/4 the effective loading resistance of the volume control, 50K/4 is typical, that usually limits the S/N.
Hi john curl,
I don't use a pre amp; I just have a cd player feeding my amp directly and therefore rely on the cd players volume control which will I know, not be ideal.
Which form of volume control will introduce the least amount of noise?
Do amp's gradually generate more noise with time due to component degradation?

Leon08; such as Toshiba ?
Every amp that I have ever owned has put out some sort of noise; mainly low level hiss which with a lot of material cannot be heard. However it is an issue with acoustic music like certain minimalist jazz recordings.
Any form of noise detracts from the listening experience with this sort of music. I recently bought a Behringer 32 band eq (1024) to mess around with and that does add quite alot of noise (hiss) You get what you pay for I guess.

So is there a general rule, principle, or best practice that one should follow in order to have a totally silent background coming from your speakers?
This is a case where I wouldn't care about s/n ratio or anything else other than the actual output noise voltage with the input terminated with whatever impedance will be driving it. Why? Because that's what the amplifier will contribute at zero signal level, and that's what you'll hear with your ear next to the tweeter. With a decent design you'll hear near nothing. In general, noise will go up with gain, so lower gain amps will tend to be quieter. It also seems to be easier to design a low or moderately powerful amp with low noise, than a voice coil welder, but it's not a hard rule. Usually, the better the input stage, the lower the output noise. Hint- very low THD numbers require very low noise levels, so that would be a good indicator. A properly designed and built D. Self "blameless" amp should be very quiet.
Referring to an earlier post: I have just been looking at Susan Parkers Audiophonics website and found that her Zeus amp has a s/n ratio of 150db and not 130 db as stated (sorry Susan)
These are amplifiers I would love to hear; actually "not hear" would be more accurate! problem is they would be pretty expensive to put together as the transformers from Sowter come at a price.

Is the fact that Susan is female (one of the very few that I know of on this forum) prevent her amps from being considered more highly by all us blokes, or am I missing something? I have yet to see a more convincing display of an amp with the ideal in mind of a wire with gain.

The Zeus amps strike me as an incredibly ingeneous design with much to be admired. If I had the money I would certainly love to build a pair.
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The quietest amp for audio use has really no meaning because it depends on so many factors. It might be better to start with what is the s/n ratio that you want at your listening position and work backwards to determine what amp s/n will be suitable for you.

Like you say so many dB/spl ( say 40 dB spl ) is what you want at your listening position.
That should sound like very low noise to your ears . Take into consideration your distance from the speakers and also the speakers efficiency ( say 10db loss from speaker to you and 86dB/watt speaker efficiency ) , the electrical noise should be 86-10-40 = 36 db below 1 watt at the power amp output. Easily attainable.

So the listening room behaviour, speaker efficiency, power amp noise contribution AND preamp and signal source contribution all matter. Also note that the noise 'spectrum' makes a difference too. So just a s/n ratio sometimes might not appear to be as quiet as it should.
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