op amp class a bias

[godfrey]

I mean, simple Ohms law :
The voltage difference between Pin 5 and Pin 6 should be measured.
The current in that resistor is then Vdiff / R.
The resistor value is R = Vdiff / I desired.

Well, it's one diode drop, so probably about 600mV, give or take. I don't have one to measure.

It looks like you could just short pins 5 and 6. Then the idling current is set by the two internal resistors in the protection circuit, and it should operate in class A right up to the current limit.

 

[owdeo]

So trust your ears and try both configurations and report back with which you feel is the best audibly. That way you are not taking anything on trust but determining the result yourself.

I suppose I could try swapping LM49710s for the 5534s in my preamp and seeing what difference there is with and without biasing to +ve rail. Trying a CCS to the -ve rail is going to be too messy on that board and unfortunately I have very little time for my hobby at the moment. Although I'm more than happy to trust my ears so far, I am an EE and would prefer to be starting from a position where I know I'm likely to be improving the measured performance rather than vice versa. Hence my question. Should it turn out that way, I'm not really keen on the idea of a mod that seems like it improves the sound if it involves increasing distortion...

 

[Joachim Gerhard]

What is that compensation scheme ?
I suppose a lead-lag on the negative input and a cap over the feedback resistor.
What is so clever about that especially when you use high value resistors in a shunt feedback arrangement ?
That cries for oszillation.
KSTR; you are very cryptic.

 

[Joachim Gerhard]

Here we go.....

 

[Joachim Gerhard]

It´s a bit more complex, i agree.
I have to study that in detail.

 

[Mooly]

I'm not really keen on the idea of a mod that seems like it improves the sound if it involves increasing distortion...

But therein lies the problem 🙂 Do you see.

 

[owdeo]

Point taken!

 

[Joachim Gerhard]

More second, less third , even if THD is higher ?
I would try that option.

 

[KSTR]

It´s a bit more complex, i agree.
I have to study that in detail.

Normally a 5534 is compensated with a single cap. Next "level" is two-pole comp (seen at other places in SG505 circuit), but here its something I haven't seen anywhere else so far and don't quite understand it yet.
And the JFET error signal booster is also nice but might introduce supply ripple/noise (the SG505's output is quite polluted with mains components by today's precision oscillator standards -- note to self : need replace all supply-related 'lytics).

 

[linuxguru]

*Bump* - Here's a link to the schematic of the LF02 module, which uses a SOIC8 dual opamp and a Class-A buffer for each channel, integrated on a single DIP8 compatible module. The opamp may be optionally biased to Class-A with a single current-setting pull-down resistor. The latest prototype uses all-Japanese BJTs, Dale MFRs, film/foil capacitor bypass and a Class-A biased LM6172 - and it's subjectively the best opamp I've heard in a MiniRef nested gainclone.

http://www.diyaudio.com/forums/anal...screte-hybrid-opamp-module-6.html#post4420882