The sound of two transistors switching

[joensd]

Mike, if you´re interested in further tweaks for biasing opamps in class a, I recall having read numerous threads at .Headwize about biasing opamps into class a at and different sorts of current sources.
The resistors in general was not recommended

[millwood]

from the point of view of an ac signal, ground, positive rail and negative rail are exactly the same. so tying a resistor to the negative rail does not achieve a whole lot of anything.

the same is true with a current source: to an ac signal, it is simply an infinetely large resistor / load.

what they (the resistor or the current source) do is to help the lower output transistor but add to the work of the upper output transistor.

[mikelm]

Originally posted by mlloyd1
I'm a little surprise you would sense such a big change - doesn't this device idle at about 10mA per op amp before this change?

Maybe I'm thinking about another part?

Ah well, if you like it, so be it :-)

mlloyd1

Mm... got me thinking.

current is about 7mA according to the data sheet

I think it may be the RF noise and the low impedence filter that is drawing highish currents. There is no filter before the chip

I'll think on it some more and in the mean time enjoy the results...

[5th element]

this all maybe the case, that it isnt what he thinks it is (if ive got the jist right)

But surely all that matters is that it sounds much better to the person who listens to the device in question.

[Christer]

Originally posted by millwood


a current source wouldn't do a whole lot of anything for you.

Hm, interesting then that Walt Jung recommends biasing op amps
into class a using a CCS, but what does he know?

[mikelm]

Thanks Christer - I was hoping someone would say something decisive.

Millwood - I don't fully understand this idea, perhaps we should both do some research, simulation or thinking or some of each.

I do know, like 5th emement says, that I have just tried it and the audible effect was not small, so for sure something is going on.

Mike

[Tube_Dude]

Originally posted by millwood
from the point of view of an ac signal, ground, positive rail and negative rail are exactly the same. so tying a resistor to the negative rail does not achieve a whole lot of anything.

the same is true with a current source: to an ac signal, it is simply an infinetely large resistor / load.

what they (the resistor or the current source) do is to help the lower output transistor but add to the work of the upper output transistor.

What the resistor do, is to force one of the output transistors to supply more DC current...so it become more heavily biased...and work in a more rich classe A/B.


But there are some drawbacks in it...mere suplly noise at the output of the op amp...and a small increase in distortion as the load is smaller.

Nothing is perfect!

[mikelm]

In my cct the supply is very quiet, C L C L C L C regulation !!!

I am more worried about the RF noise at the o/p polluting the rails.
I was thinking about using a separate supply for each resistor...

A CCS would help with the noise is it were fast enough.

This chip can drive video signal into 75ohms so driving into 2kohms should be OK.

mike

[Nelson Pass]

The first mention I encountered of biasing an op amp
with a resistor or ccs to the negative (or positive) rail was
from Barry Thornton, circa 1973.

[mlloyd1]

There's a name from the past. Wasn't he associated with SAE? Wonder what he's doing now ...

mlloyd1

Originally posted by Nelson Pass
... from Barry Thornton, circa 1973.