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/anal...rch-preamplifier-part-ii-537.html#post3136059
Patrick
The origin of the discussion can be found here :
http://www.diyaudio.com/forums/anal...rch-preamplifier-part-ii-537.html#post3136059
Patrick
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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
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
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
Input impedance, supply voltage, PSRR, CMRR, gain, current drive? Output stage class? Short circuit withstand?
edit:
cross post jcx
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?
It seemed, from JC's thead, it was to be a better Jensen 990 using similar or OpAmp topology?
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.
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.
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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??
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??
Gentlemen,
You have a once-in-a-lifetime chance to learn from professionals like Mr. Wurcer, Mr. Marsh, Mr. Curl, maybe even Mr. Jung, .....
on how to design opamps for audio without worrying about cost of production and what not.
Why would one want to miss it ?
Anyway, if it is not your cup of tea, I am sure there are other more entertaining threads on the forum.
Why not just let those interested have some fun ?
Cheers,
Patrick
You have a once-in-a-lifetime chance to learn from professionals like Mr. Wurcer, Mr. Marsh, Mr. Curl, maybe even Mr. Jung, .....
on how to design opamps for audio without worrying about cost of production and what not.
Why would one want to miss it ?
Anyway, if it is not your cup of tea, I am sure there are other more entertaining threads on the forum.
Why not just let those interested have some fun ?
Cheers,
Patrick
Why not ?
My JFET DIP8 discrete opamp use 7. And it is 3 stage.
So we can do better.
http://www.diyaudio.com/forums/pass-labs/120445-pass-discrete-opamp-dip-8-package.html
No challenge, no fun.
Patrick
My JFET DIP8 discrete opamp use 7. And it is 3 stage.
So we can do better.
http://www.diyaudio.com/forums/pass-labs/120445-pass-discrete-opamp-dip-8-package.html
No challenge, no fun.
Patrick
challenge is determining technical specs for "good audiophile performance"
transistor count games aren't about meeting performance goals
even when counting stages you get waffling from Curl, Hansen about cascodes, cascaded followers
transistor count games aren't about meeting performance goals
even when counting stages you get waffling from Curl, Hansen about cascodes, cascaded followers
I was not going to say anything, but why would you want to MAKE something that you could get from an electronics 'junkyard'? '-)
Possibly, a well designed discrete amplification unit will sound better than any existing opamp.
However, in such a case the challenge should aim at an amplification unit.
Even when talking about opamp per se, possibly a well designed discrete one will sound better than any currently existing commercial one.
In such a case, a superb sound quality should be listed along other requirements.
Well, I am not qualified to do this engineering design work, but Mr. Marsh seems to have an idea about what he is looking at/for, so perhaps he will take the lead and present a proposed topology...?
And, what about things like error correction circuitry and feed forward, etc...? Just rambling in public. Don't worry, maybe I am not talking to myself, I have a bluetooth and am on the phone in reality...
_-_-bear
PS. don't forget the commercial opamps from Burson?
And, what about things like error correction circuitry and feed forward, etc...? Just rambling in public. Don't worry, maybe I am not talking to myself, I have a bluetooth and am on the phone in reality...
_-_-bear
PS. don't forget the commercial opamps from Burson?
It must be competitive with what is out there already.
It is less of a challenge to do better with more.
[ I could allow cascoding to be considered as a single transistor if it cant be done otherwise. Current sources, diodes might not be counted]
BUT - Scott wanted to do a discrete version for audio of the 627 opamp and that is fine with me. I dont want to start doing something Scott did not say he wanted to do.
A discrete opamp circuit of 627 opamp would be nice for others to compare with the integrated version.
-RNM
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Absolutely correct. Without "Opamp topology" limitations it is easier to achieve better sound reproduction. When you listen you don't care about such things inside like CMRR or open loop gain on 1 Hz frequency. But if it has to be opamp by conditions, I would take one lowest noise double opamp chip, one powerful opamp, and using nested feedbacks construct from them an opamp with wide bandwidth and flat frequency response way beyond audio band, low noise, inourmously high CMRR, and great load driving capabilities. And it will still be discrete, using discrete chips and resistors. Try to beat it using transistors and resistors only.
Jan, where is my magazine copy? I won already. 😀
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