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Old 12th December 2012, 05:42 AM   #21
EUVL is offline EUVL  Europe
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Not in the CEN IV circuit.

The added bonus is that Zin of the IV now equals Zout of the opamp.
And since the open loop gain is >120dB, and open loop output impedance is <1k,
you can argue that the OPA1641 Zout in follower mode would be <0.001 ohm.

And no, I don't have measurements to prove.
But yes, we have a PCB and will try it out some time.




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Old 12th December 2012, 06:33 AM   #22
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like I said, I like it, I like it a lot and the fact it come in duals and quads is pretty sweet too. its just a bit lacking in the current department. i'll be trying it too, since I have some spare 1641.

such a whacky looking schematic =)
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Old 12th December 2012, 09:22 PM   #23
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Quote:
Originally Posted by jcx View Post

below is a simmed comparison of the PCM1704 datasheet I/V on the left and the noise gain compensated ADA4637 with higher feedback C
jcx , to compensate the ada4637 that is compensate to gain >5 , I think that is need a 10 ohms resistence in serie with c1 ,or at high frequencies c1 will bring gain below 5 . Or am I missing something ?

R3 and C3 forms a snubber, and snubbers are very good in limiting (dV/dt).

I think adding r3 and c3 is a good idea and can be use with compensated to unity gain opamp.
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Last edited by smms73; 12th December 2012 at 09:31 PM.
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Old 12th December 2012, 09:27 PM   #24
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Quote:
Originally Posted by Shinja View Post
smms
these documents are informative.
Thanks for the literature, Shinja. It comes very handy.
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Old 12th December 2012, 09:59 PM   #25
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I use the OPA1641 in one of my phono amps in the second stage. I biased it into class A and added a buffer. That way it worked so well that a discrete design was not better.
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Old 12th December 2012, 10:04 PM   #26
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Quote:
Originally Posted by Joachim Gerhard View Post
I use the OPA1641 in one of my phono amps in the second stage. I biased it into class A and added a buffer. That way it worked so well that a discrete design was not better.
Really interesting, did you ever tried OPA827?
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Old 12th December 2012, 10:14 PM   #27
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Yes, i prefer the OPA1641 but the OPA827 is very good too. I also preferred the ADA4627 slightly over the OPA827. That is not based on measurements but only on listening.
The differences for me where slight though except for one woman in my listening panel that found the differences pronounced and send me a long list of surveys.
It is a bit like wine tasting. The longer and more eager you listen the more differences you find. I would say in a blind ABX test the differences will be swapped. I value topology higher in importance then swapping opamps anyway. In I/U converters we must be really sure that the opamps do not slew and snubbering and integrating is the right way to go i think. I just got back a digital preamp i friend of mine builds since many years and it sounded much better then before. I asked him what he did and he answered that he uses a bigger integrating cap now. The sound was much more analog like. Richer and more fluid without any loss of detail. I think he uses the LME49990.
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Old 12th December 2012, 10:17 PM   #28
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Here are test circuits for settling time and slew rate.
Attached Images
File Type: png test circuits.png (52.0 KB, 333 views)
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Old 12th December 2012, 10:23 PM   #29
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Quote:
Originally Posted by Joachim Gerhard View Post
Yes, i prefer the OPA1641 but the OPA827 is very good too. I also preferred the ADA4627 slightly over the OPA827. That is not based on measurements but only on listening.
Thanks Joachim

In my listening tests I preferred the OPA828, richer and fuller sounding in tested configuration (an old Sony CDP-797).

The OPA1641 was really interesting but as already posted seemed a bit current challenged (power consumption figures are suspect in this regard, IMHO) , you tested it with the buffer and class A biasing?
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Old 12th December 2012, 10:25 PM   #30
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Yes.
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