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Old 12th May 2011, 10:58 AM   #21
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"IC op-amps have a nasty gritty distortion that once you have heard and identified you don't want to go back to. The buggers can even be heard in the audio path when used for DC servos. I found a way around that too but that information is for sale only."
Seriously ?
I have never heard a IC Op-Amp giving out any sort of nasty gritty distortion . Maybe that's because i have been developing high-end products , but no , i use common parts like NE5532 and TL072 , TL081 , LM4558 .
They do not give nasty distortion if you design them not to hang on the supply ,
that is a bad thing and usually misdesigned .
Discrete op amps can be a bad thing when speed and efficiency is required badly , because the more capacitance is present in the leads are present , the worser the ability to speed .
Well all of us here know it . Depending on the parts used , JFET input opamps sound good .
But , discrete op amps can be really expensive quick compared to IC , even though they only have so few parts because IC's are just cheap to get around with .
Have any tried to design a OPA2604-like Discrete Op Amp ? Care to give on the figures , cost , BOM ?
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Old 12th May 2011, 12:19 PM   #22
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Originally Posted by CraigBuckingham View Post
Designed a couple of discrete op-amps. Stopped using op-amps after that for serious audio reproduction. It is pretty easy to beat the best op-amps, even with all their tweaks, with a discrete op-amp. But hey why stay with closed loop when you have the option of open loop with a discrete design. Can't do that with an op-amp.

Then there is the question of thermionic vacuum tubes. Those things have no equal in the discrete world let alone IC op-amp world when applied in the right manner and in the right places. But the problem is dwindling supply of those parts unfortunately.

IC op-amps have a nasty gritty distortion that once you have heard and identified you don't want to go back to. The buggers can even be heard in the audio path when used for DC servos. I found a way around that too but that information is for sale only.

One of the other guys I did research with would probably give it away for free if you asked the right way. But hey some people prefer their egos boosted for their hard work and research rather than their back pockets.

Anyway, that's my findings.

Agree 100%.
There are only a few things that sounds worse than opamp @unity gain.
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Old 12th May 2011, 01:36 PM   #23
Bonsai is offline Bonsai  Taiwan
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ho hum.

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Old 12th May 2011, 02:07 PM   #24
SY is offline SY  United States
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Originally Posted by Bonsai View Post

Some specialst applications will demand a discrete approach - e.g. MC head amp or a dynamic mic pre-amp (but THAT corp have that covered with an IC as well now), and it could be argued (though its really open to debate) they may offer some performance benefits on MM inputs.
Is there actually any difference between the THAT1510/1512 and the SSM2019?
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Old 13th May 2011, 03:40 AM   #25
Bonsai is offline Bonsai  Taiwan
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I don't know SY - I am doing some work with the THAT mic pre right now, but I have not looked closely at the SSM2019. The THAT part is around 1nV/root Hz.
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Old 13th May 2011, 04:23 AM   #26
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Originally Posted by CraigBuckingham View Post
...

There is something else you can do that I never see mentioned on this forum, or anywhere else for that matter, that makes a significant inprovement. Maybe more than the O/P biasing. It has to do with common mode distortion - and I am not going to say anything more than that..
then I suppose you really don't want anyone looking at my High loop Gain Composite Op Amp Circuits

or to look up Jung's substrate bootstrap, or Dimitiri's
Supply Bootstrapping Reduces Distortion In Op-Amp Circuits | New operational amplifiers optimized for high-performance audio and ultrasound applications combine extremely low total harmonic distortion plus noise (THD+N), -130 dB, with large output vo
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Old 13th May 2011, 05:51 AM   #27
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Not addressed in your circuit.
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Old 13th May 2011, 06:18 AM   #28
Bonsai is offline Bonsai  Taiwan
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"IC op-amps have a nasty gritty distortion that once you have heard and identified you don't want to go back to. The buggers can even be heard in the audio path when used for DC servos. I found a way around that too but that information is for sale only."


I can absolutely agree that this may be a problem on an opamp audio circuit IF you do just one of the things below

1. run a non-unity gain stable opamp at unity gain
2. run a decompensated opamp without a comp cap, or too small a comp cap for the gain setting
3. fail to fit an isolation resistor in series with the output when driving a real world load - like a cable for example, or a capacitive load
4. fail to ensure that the junction of the feedback network is located physically very close to the op-amp feedback input pin (usually the inverting input)
5. fail to locate the input filter as physically close as possible to the op-amp input (usually the non-inverting input)
6. fail to decouple the supply rails adequately
7. you use an opamp not characterized for wide band audio usage that has an inadequate slew rate
8. etc

I've done all of these things, and yes, if just one of them occurs, the sound can be truly awful. OTOH, if you follow the engineering rules and guidelines associated with high performance opamps, you will get great performance and great sound.

That said, probably 99% of the CD and SACD players on the planet use opamps of some description in their signal chains (whether stand alone or integrated into the converter) . . . but I seriously doubt that 99% of them sound crap. Keep in mind that almost all music is mixed on desks using op-amps, passed through filters and what have you. Douglas Self mentions '100's' in a typical signal chain. Again, if opamps were as bad as some claim, there would be no good music available. Just about everything would sound bleached, gritty and truly terrible. But that's not the case, is it?

As for affecting the sound when used in servo applications, well, that's nonsense. Read Robert Cordell's book for a bit of enlightenment on that subject.

I don't suspect I will be able to convince opamp detractors that they are by and large wonderful devices for audio, but that's ok. Am I against discrete designs? No, they are great, but so are opamps.
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Last edited by Bonsai; 13th May 2011 at 06:21 AM.
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Old 13th May 2011, 09:08 AM   #29
Bonsai is offline Bonsai  Taiwan
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Here's another one:-

Fit the comp cap across the wrong pins - some op-amps are pins 1-8 and others 8-5.
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Old 13th May 2011, 09:57 AM   #30
fotios is offline fotios  Greece
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I do insist. In one thing that i have seen with my eyes in oscilloscope. I don't know exactly the reason, but discrete are perfect in low-mid frequencies. Inject a 50Hz square wave in input and you will see exactly the same square in the output. I don't know if there is any IC that could obtain this.
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