Wossat noise?

thrudge

thrudge

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Hi all,

I could do with a bit of amp/speaker advice, please.

I've got an Art Audio Quintet (EL34-based) integrated and super sensitive speakers - Klipsch La Scalas, 104dB. With no music playing, hiss through the speakers is almost non-existent. It's there, but you have to listen quite closely.

Plug in my mates KT88-based integrated and it's like amplified surf - unbearable. Another mates valve pre/solid state power beast (Musical Fidelity P270) is hissy. Not unbearable, but you wouldn't really want to live with it.

I've also heard unliveable hiss (at least with my oddball speakers) from an otherwise excellent Rogue Audio valve pre/power.

So, my question is - why? Are these varying noise levels down to transformer size? - the transformers on the Art Audio really are whoppers. Or is it transformer quality? Or something to do with my Border Patrol power supply cleaning up the mains? Or something else?
 
Gain mostly, and it depends where in the circuit the gain is applied.

A lot of integrated valve amps are in fact power amps with a passive volume pot on the input acting as the pre amp. If the gain in the power amp is kept moderately low (as it can if you are driving Klipsch at 104dBw!) then audible noise should be low.

However, ramp up the power amp gain, or start making the pre amp part more elaborate with additional gain stages and buffers and you can have problems. These things usually pass without issue into the typical 85-88dBw loudspeakers but one you start hitting the mid 90s+ it can be a problem.

Noise can also come from poor or inappropriate circuit design such as too much series resistance between gain stages, leading to what's known as Johnson Noise.

Noise of this type - mostly loud hiss - isn't usually a function of the power supply. Bad PSU design usually results in audible hum.
 

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