biasing opamps in class a

[carlosfm]

Originally posted by NealG


Carlos, forgive me but I think you meant to say:

"You can't use an op-amp with single voltage rail in the same way as you would use one with +/- rails."

Of course!
Is it so hard to understand?
What a relief.
Thanks, man.

[GregGC]

Originally posted by peranders

This thread is really flipped out. How did bridge connection come in to this?

Anyway, matjans, check
Meta42 and PPA and myQRV-04

You must first consider that many opamps, especially those for audio have very special bias networks for class A or AB and some of them is impossible to do with discrete parts. I suspect that some opamps really can be helped with this external class A circuit and some or not. The question is which one? LM324 can REALLY be helped! A good example of what this current generator does!

My personal experience is that the differnence is hardly worth the efforts. My ears can't detect any difference at all with AD8610 and OPA627 but this isn't the same thing as this is the truth for everybody.

If you just want to test, use a plain resistor to V- or a JFET + resistor (current generator).

My experience shows that biasing it with a resistor can make the opamp sound worse (depending on the opamp). I experienced it when playing with the output stage of a CD player. It compressed the sound, took away all the liveliness and free flow from it.

[matjans]

hi guys,

i tested an opa2132 with bias currents from 0.4 to 8mA and to tell you the truth i don't think i can really hear any difference. As it's a battery powered headphone amplifier i'll just leave it in class ab. disdtortion is very low with this chip (0.00008 or something) anyways,

It might be my somewhat cheap sennheiser hd477's.

I hooked it up to my gainclone and guess what, it sounded pretty good (although gain was far too high), a lot more control in lower freq's. Soundstaging is also better.

So, my next project is an opamp based pre for my gainclone. Maybe i'll give class a biasing another shot there (although the opa627's have an even lower distortion figure).

Viva the opamp! (don't shoot me for saying this!)

[carlosfm]

Originally posted by matjans

I hooked it up to my gainclone and guess what, it sounded pretty good (although gain was far too high), a lot more control in lower freq's. Soundstaging is also better.

So, my next project is an opamp based pre for my gainclone. Maybe i'll give class a biasing another shot there (although the opa627's have an even lower distortion figure).

I'm tired of saying this everywhere, but here it goes again:

The best sound I have is from my (buffered, now LM3886+OPA627) IGC power-amp working with my OPA627+BUF634 stand-alone pre.
I made several other GCs (IGC, NIGC, different chips, etc.), integrated, and none gets to this outrageous performance.

Originally posted by matjans

Viva the opamp! (don't shoot me for saying this!)

And this proves that a high-end op-amp can sometimes be good for the sound.
This defeats the ultra-minimalism theory.

Sometimes I listening to some well-recorded music.