Discrete Opamp Open Design
 

This is to follow the idea to design a discrete opamp by joint effort, without hi-jacking John Curl's Blowtorch II thread.

The origin of the discussion can be found here :
http://www.diyaudio.com/forums/analo...ml#post3136059


Patrick

Would be grateful if the moderator can copy the following posts from the blowtorch II thread also to here:

post #26829, ..831~..883, ..837~..842.


Thanks in advance,
Patrick

goals/target applications?

a good MC phono pre /= decent condensor mic capsule buffer

improving SOTA requires knowing what it is, where the theoretical limits are

SG-Acoustics · Samuel Groner · Discrete OpAmps

look for the op amp distortion measurements paper - shows some commerical discrete op amps and lots of monolithic with a good set of objective measurements

What performance do you require?

Input impedance, supply voltage, PSRR, CMRR, gain, current drive? Output stage class? Short circuit withstand?

edit:

cross post jcx

Here is a discrete op Amp. Seven SMT packages that are readily available.
not SOA but works via solder simulation.

What is the end goal? Got to define that first.
It seemed, from JC's thead, it was to be a better Jensen 990 using similar or OpAmp topology?

This is a huge subject with many commercial designs already out there.

see JC thread -- goal: 627 performance in discrete design.

IMO cant require IC for dc servo in low gain apps and no large bulky coupling caps required to use this 627 goal equivalent.

OK, to get that here, from your post:

1) 8 transistors or less
2) drives 30 ohms with -105dB harmonics from 20Hz->20kHz
3) S/N -110dB (input shorted, 1Vrms output, unweighted)
4) no DC servo
5) DC offset on output less than 2mV under normal time/temp range
6) all of above with gain = 10 or less

Seems impossible to me but hey go for it. I got nothing.

Afaik, the 990 used this for the front end:

http://www.ti.com/lit/ds/symlink/lm394.pdf

_-_-bear

Also, why is this going to be anything worthwhile (wrt the above specs for example) since there are a slew of ultra super low distortion monolithic IC opamps now available??