AD811 as I/V stage for current DACs (and test some other opamps including Burson Audio opamps as I/V)

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#362
Vunce said:
@grunf,
Slightly off topic, but AD811 related.
Did you ever experiment with W. Jungs line amp/preamp AD744/AD811 circuit?
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Another article from W Jung in AD AN-232 aplication note.
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#363
michaelbehrendt said:
@grunf ,my idea for I/V converter with 2x PCM1704 per channel, I/V with 2xAD811, then low pass filter with OPA1633 and symmetrical output, then symmetrical to single ended with OPA1611, what do you think?, all resistors visual PNM or Yageo NT, all caps COG (NPO), regards Michael.View attachment 1426571
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Hi , @michaelbehrendt
Thanks for your interest for the AD811 I/V, I would throw out the OPA1633 and go for a simpler solution like in this Circuit design document for the PCM1794 but configured with unity gain after the AD811.
If I were doing something like you, I would put a Broskie Cathode Follower with ECC88 behind the AD811 and not even think about op amps🙂.
I must point out one error on the AD811, you must connect the 1.47K/1nF feedback before the 1K resistor .
Igor
 

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#366
Yes, but in combination with the AD811, every other op amp in my opinion degrades the sound of the AD811 itself, so the less of it behind the AD811 the better.
The AD811 is quite capable of dealing with even the most stubborn SS amplifier.
 
#373
The names of what, good OP?
It depends of where to use it and the specific schematics.
OPA1655/1656, 1611/1612, 2156, 2140, OPA837, AD8397 (AD45048), ADA4898, 4899...
In case of FDA - OPA1632/1663, LME49724, THS4551...
A lot, and of course - I can't remember everything right away.

Alex.
 
#375
altor said:
Maybe. I finished with 811 (and all other CFA) many years ago.
It's like the 627 - very good OP, but there are lot of better (or no worse, at least) ones and much cheaper.

Alex.
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I don't like op amps in the signal path, I like to avoid them at all costs but when I have to then I test at least 5 different ones in that position so the AD811 is on my list again, otherwise I used it a long time ago in my first DAC with TDA1541 when I was still young and green.
As for the new BB op amps I'm not satisfied, everyone is talking about them but in the applications where I've used them the cheap ADA4610 beats them well. OPA828 is something else and it can go hand in hand with the ADA4625 that I use in my regulators.
By the way I compared both with AD811 and in my system as an I/V stage they sound worse (they are also the only op amps in my system).
It's all relative and depends on ourselves, the application where they are used and many other factors, nor op amps can be changed like shoes but professionally speaking CFA op amps (as well as discrete current conveyor) are the best for I/V because of their uniform frequency characteristics.
 
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#378
So anyone about my idea to use a discrete current mirror JFet input helped by an opa (it is not in the signal path) to reduce the impedancce input and shot noise to the lowest levels, before the AD811 and its noisy input stage (relative to much modern quieter ones) ?
 
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