Bias settings mono amplifiers.

VSAT88

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#1
Asking here I got several sets of mono amps, B&K M 200's and Adcom GFA-565's. I have done nothing to the B&K's besides re cap the input boards. the 565's I have put in new Hoppes input boards (https://hoppesbrain.com/product/ebfa-565/). My question is this. On mono amps like these does the bias setting of each amp need to be spot on the same as the other amp? If the settings were a bit different (one amp running a bit warmer than the other) would that change sound quality for the worse?
 

J!m

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#2
I doubt mine are exactly the same and they sound wonderful.

I don’t think it matters much. As long as it’s in spec.
 

VSAT88

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Yeah Jim but yours are Counterpoint how are these mid tier amps ever going to compare to that. lol. No really, that is what I was thinking all along. As long as both are in spec there cant be much of an issue because how could anyone ever get two amplifiers exactly the same mono or not.
 

J!m

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#4
You probably could get them the same but the question is: would it be audible?

And counterpoint is mid tier. Built to a price point which is why Alta Vista audio came along. No expense spared and amps by the same designer were 10X the cost of counterpoint.
 

VSAT88

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You probably could get them the same but the question is: would it be audible?

And counterpoint is mid tier. Built to a price point which is why Alta Vista audio came along. No expense spared and amps by the same designer were 10X the cost of counterpoint.
Yeah, same question but would it be audible? Here at my house never. Because I could never afford Alta Vista. Not at 10X the selling price!
 

J!m

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#7
Before counterpoint went under I had a long email conversation with Mike Elliott the designer and he always lamented being held back by the bean counters.

Front panel is not engraved (it’s screen printed) to cut cost.

A big plus for counterpoint is they had a sister company that manufactured transformers. So arguably the most important bit of a high power amp was well up to the task.

And they did have one preamp that was high end. I think it was the SA5 “isolinear” preamp. Trading around 5g these days if you find one.
 

8991XJ

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#8
Bias simply keeps the transistors awake after amplifying the top or bottom of the signal as it switches to the other transistors. NPN vs PNP amp modules are used in some amps but most just have these in pairs on the same heatsink.

This keeping them awake avoids the miniscule delay of turn-on when the signal shows up again...crossover notch distortion. The amount of bias varies from damn near none to full on (Class A amps).

We don't hear notch distortion when gear is set to spec but there can be some additional leeway in the adjustment to move the amp more toward Class A with a slightly higher bias but this leads to higher operating temperatures and amps are designed for proper operation with specified bias.

So anything within spec should not be audible and shouldn't make the amp run too hot at idle.
 
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