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General Discussions => Drawing Board => Topic started by: analag on March 25, 2020, 04:51:40 PM

Title: Discrete OPAMP
Post by: analag on March 25, 2020, 04:51:40 PM
(https://i.postimg.cc/hGyCwxMR/oP-Amp.png) I am about to mock this one up and finetune it, Stay tuned, but in the meantime I welcome the wise men to step forward and advise me!
Title: Re: Discrete OPAMP
Post by: john12ax7 on March 25, 2020, 07:30:17 PM
Disregard
Title: Re: Discrete OPAMP
Post by: analag on March 25, 2020, 08:12:50 PM
It's a current feedback opamp which is saidto be much better sounding than the voltage feed back type, I have built the 990 style many times, so this is a welcomed change
Title: Re: Discrete OPAMP
Post by: JohnRoberts on March 25, 2020, 09:08:45 PM
I think I've seen something similar to this inside an exotic IC, back when they used to publish schematics for the innards.

JR
Title: Re: Discrete OPAMP
Post by: john12ax7 on March 25, 2020, 09:28:54 PM
My bad,  been a while since I've used a current feedback opamp.  The feedback resistor usually needs to be optimized for these. What is the application? They wouldn't work for some audio applications,  but a good choice for high speed gain blocks.
Title: Re: Discrete OPAMP
Post by: analag on March 25, 2020, 11:59:30 PM
I want to try it in a microphone preamp. R4 have a hugh control over the offset so optimization, some compensation will be needed.
Title: Re: Discrete OPAMP
Post by: gyraf on March 26, 2020, 04:17:06 AM
Why not just build it IRL and check out how it behaves, then take it from there?

It's probably much easier to help you tweak it if we know what it lacks in the chosen application: imo, sim-games can tell you go/nogo, but not anything about the subjective perceived qualities.

And if it's not the subjective perceived qualities you're after, I think it will be VERY hard to beat the run-of-the-mill integrated micpre chips from that and ssm.

/Jakob E.
Title: Re: Discrete OPAMP
Post by: analag on March 26, 2020, 10:08:08 AM
I fully intend to build it. Just last week I completed an M1 type mic where I simulated and built an 990 type opamp that to my ears sounded better than a clone of the original design. 
Title: Re: Discrete OPAMP
Post by: gyraf on March 26, 2020, 11:20:54 AM
 :) Now we're talking..! Please report back on your findings!

/Jakob E.
Title: Re: Discrete OPAMP
Post by: boji on March 26, 2020, 12:31:25 PM
Gents, might you recommend a book to learn more about audio opa design? 

Perhaps Self's Audio power amp designer's handbook?
https://www.amazon.com/Audio-Power-Amplifier-Design-Handbook/dp/0240521625 (https://www.amazon.com/Audio-Power-Amplifier-Design-Handbook/dp/0240521625)

Thanks
Title: Re: Discrete OPAMP
Post by: abbey road d enfer on March 26, 2020, 12:42:30 PM
It's a current feedback opamp which is saidto be much better sounding than the voltage feed back type
Indeed, with an open-loop BW of about 70kHz and open-loop THD of about 0.3%, you may expect very good performance at the indicated 20dB gain. certainly devoid of TIM.
Fine for line-level operation, e.g. as a line driver, but what about two of the most common uses for DOA's: mic pre and summing amp?
I'm not sure those BC550/560 running at 2mA are optimum for the task.
Title: Re: Discrete OPAMP
Post by: analag on March 29, 2020, 10:14:51 AM
(https://i.postimg.cc/DysbkVQw/20200329-083516.jpg)
It works and it sounds every bit as good as it's said to,  but it needs to fine tuned .