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EUVL 22nd August 2012 06:22 PM

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

EUVL 22nd August 2012 06:30 PM

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

jcx 22nd August 2012 06:33 PM

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

counter culture 22nd August 2012 06:36 PM

What performance do you require?

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

edit:

cross post jcx

wayne 22nd August 2012 06:48 PM

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

RNMarsh 22nd August 2012 06:50 PM

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?

dirkwright 22nd August 2012 07:12 PM

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

RNMarsh 22nd August 2012 07:20 PM

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.

dirkwright 22nd August 2012 07:58 PM

Quote:

Originally Posted by RNMarsh (Post 3136205)
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.

bear 22nd August 2012 08:20 PM

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??


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