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#3,141
AD797

And in the meantime I'm listening to / having my adventures with the AD797..
And will continue with others.
I hope I can make it clear that my intention is to stir up the waters, with the statement that on the contrary to the long time belief with respect to this amplifier, the LM318 chip is not the only possible one for use.
Though I must underline again: simple chip rolling is off limits, too.
Chip rolling with technical approach, stability tests and confirmation, maybe yes.
So I intend to give a hand in this procedure, provide more or less proven configurations that can be tried by adventurous minds later on.
Then democratic procedures, hopefully, will find a 'common denominator' or will find out that certain chips are fitting better one's particular taste..

Back to my adventures with the AD797: It happened again. I started out with a capacitor from a yesterday's BOM in the position for C9: Nichicon FG.
This chip, being a bipolar one, basically needs some offset control.
My first impression after assembly was: wov, the chip is oscillating, notwithstanding the scope and spectrum measurements (and simulatons) ascertaining it to the contrary..
It just sounded so heavily different than usual. than it got better / or got used to it, fact is that a heavy sweet seductive sirupy sound +big boomy bass settled in, in a quite fascinating way.. For a time I was listening quite amused, new sounds flying in my home..

Then it come to mind to search for the reason, and for this I had just repeated my previous experience: did not exchange, just excluded fom the config the feedback capacitor, C9, replaced by a wire.
Yes, it can be done, in some circumstances, there is a correct technical explanation why. For me, the experimenter, not in general!

All the strange effects had gone, like blown away by this one move. What remains is a truely correct, wide space, great depth, tonally very correct, very fine, great resolution of massed strings, with controlled bass.
Almost as good as the OPA827 in the other amplifier..
Or the ADA4627 in that again other amplifier..

Ciao! George
 
#3,142
Joseph K said:
I hope I can make it clear that my intention is to stir up the waters, with the statement that on the contrary to the long time belief with respect to this amplifier, the LM318 chip is not the only possible one for use.
Click to expand...

Absolutely, keep going! 🙂

It's an interesting experimentation field.

Joseph K said:
It just sounded so heavily different than usual. than it got better / or got used to it, fact is that a heavy sweet seductive sirupy sound +big boomy bass settled in, in a quite fascinating way.. For a time I was listening quite amused, new sounds flying in my home..

Then it come to mind to search for the reason, and for this I had just repeated my previous experience: did not exchange, just excluded fom the config the feedback capacitor, C9, replaced by a wire.
(...)
All the strange effects had gone, like blown away by this one move. What remains is a truely correct, wide space, great depth, tonally very correct, very fine, great resolution of massed strings, with controlled bass.
Click to expand...

Interesting, my experience with AD797 fits better with your initial impression.

It often sounds different than most other opamps.

Joseph K said:
Almost as good as the OPA827 in the other amplifier..
Or the ADA4627 in that again other amplifier..
Click to expand...

Pretty weird... they all sound so different from each other...
 
#3,143
Dario,

"Pretty weird... they all sound so different from each other..."

My little contribution, based on my listening experience, would be like :

OPA827 -- is Caravaggio
ADA4627 -- Botticelli

And I would not like to decide..

Ciao, George

and maybe, maybe the AD797 is closer to the OPA827 shade, too
 

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#3,147
One point that interests me about this experiment. And it wouldn't necessarily show in Dario's DAC experiment. The main point for me may be the elimination of C9 and it's effect on sound. Even if an alternate opamp had the same characteristics as the 318, the ability to remove C9 (more possible on JFET opamps) could be worthwhile beyond differences in the opamps themselves.

Jac
 
#3,152
Joseph K said:
Caro Giovanni,

in short, the reason, the method, all explained in here:

http://www.diyaudio.com/forums/chip...on-build-thread-tutorial-308.html#post5074936

Principally means, that with a lot of caution, but in case a of fet-input opamp one can remove C9, that is, short-circuit it with a piece of wire.

Ciao, George
Click to expand...
Unfortunately dear George I have been out of this thread for a long time.
Your post reported has clarified everything.
And I'm taking the pleasure of experiencing this wonderful amplifier again.
 
#3,155
Instead of OPA1642 you can try OPA140. The specs look almost identical but input offset voltage is much lower and open loop output impedance is a bit higher. I use OPA2140 (dual) in my OPA1622 based head amp after recommendation from agdr and it works great.
 
#3,156
Joseph K said:
in short, the reason, the method, all explained in here:

http://www.diyaudio.com/forums/chip...on-build-thread-tutorial-308.html#post5074936
Click to expand...

A bit of additional information. C9, combined with R10 form a high pass filter on the feedback leg to ground of the opamp. What this does is decrease the gain of the opamp at low frequency. That way, the imbalances George mentions won't be amplified as much.

When you short circuit C9, the gain due to feedback remains constant with frequency.

Jac
 
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