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Old 9th January 2013, 07:45 AM   #81
Mooly is offline Mooly  United Kingdom
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I've always liked the OPA2604 too but sometimes its very difficult judging differences. I find you have to listen for a long time to get a true opinion.

Why do opamps colour the sound... well I guess when you think in terms of the discrete circuit each opamp represents and how different they all are then its no real surprise sonic differences exist, even though the specs suggest they should be very similar.
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Old 13th January 2013, 07:48 AM   #82
Mooly is offline Mooly  United Kingdom
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New thread on the AD844 I/V

Using the AD844 as an I/V

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Old 16th January 2013, 01:12 PM   #83
Shinja is offline Shinja  Japan
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how about TPA6120, which is known as hifi headphone amp IC.
it has high slew rate why it is CFB opamp.

it can be a competitor of AD812 or LM49713 etc..
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Old 16th January 2013, 02:05 PM   #84
qusp is offline qusp  Australia
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originally it was an ADSL driver I think, great care in layout needs taking, not the most DIY friendly package but can be managed. sounds quite well if handled properly, kinda needs output damping R or L, which complicated it a touch for lowZ headphone drive but not an issue here
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Old 23rd January 2013, 05:29 PM   #85
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Well, due to my own stupidity, I blew up two LM6181's yesterday. Sigh. I should have read this app note before playing with a current feedback amplifier:
http://cds.linear.com/docs/Design%20Note/dn46fa.pdf

The filter caps in the feedback loop of my IV converter made the LM6181's oscillate and get so hot that I burned my finger on them. I'm sure they are dead now.

It's not easy as far as I can see to limit the bandwidth of a current feedback amplifier. Some kind of prefilter is needed according to the app note. So, using current feedback amplifiers for limited bandwidth audio DAC's appears to be a difficult thing to do.
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Old 23rd January 2013, 05:48 PM   #86
jcx is online now jcx  United States
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if your I/V R is larger than the min stable feedback R then you can add a series RC in parallel to give a shelving low pass - its a start

"noise gain" series RC to gnd at the input lets you use a smaller feedback
R, lowering, pushing out the "shelf"

in fact a quick sim showed a low enough Z "noise gain" input network stabilizes a LT1227 with pure feedback C - but that is in sim - depends on op amp output Z modeling which is often poor at CFA in/stability frequency
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Old 23rd January 2013, 06:09 PM   #87
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The only filter that appears to work is a big capacitor from the minus input to ground.
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Old 23rd January 2013, 06:44 PM   #88
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Of course, this is a bad design. The S/N is really bad. I don't have a solution.
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