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Old 30th December 2003, 05:14 PM   #1
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Default opa602

has anyone heard of that IC?

I have it, and I think it sounds wonderful as a preamp.
Itīs current output is a relatively weak -20mA-, but there is certain ĻsomethingĻ in the way it delivers music... very smooth.

I wish to read about your opinions, and how you compare it with opa 604, opa134 and opa627.

And yes, Iīm a BB fan...
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Old 30th December 2003, 06:39 PM   #2
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Default OPA602

I have used them for years in measuring instruments and also tried them for audio. They are very good opamps (quite fast and able to drive capacitive load), the only problem is phase inversion after clipping in non-inverting mode.

Regarding your question, i would prefer (best to worst) OPA627, OPA134, OPA602, OPA604.
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Old 30th December 2003, 07:21 PM   #3
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Thank you very much for your reply, Pavel.
I have tried it alone -noninverting configuration, gain +6, ps:+/-15volts-, and liked it a lot.
Now Iīm trying it in something very similar to your audio buffer, but without r12 and without the 200 pF cap.
I have noticed a slight hardening of the sound in such configuration. I donīt know, maybe the BUF634 could be responsible...
When I leave the BUF in normal mode, the sound gets warmer and fuller, more in the line of the sound of the chip alone. But when I connect the BUF in wide bandwidth mode the sound gets harder.
I have noticed that trend with other opas too, in the same configuration. Have you any idea about that paradoxical behaviour of the composite amp, sounding mellower in normal mode?
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Old 31st December 2003, 09:57 AM   #4
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Hello Federico,

your question is not easy to reply. Firstly I would like to ask you if the R12 was connected at the end of output cable. It should not be connected directly behind R10. R12 is the cable terminating resistor. When used in the beginning of the cable then its function is incorrect.

Now about influence of R12 properly connected (at the end of the cable). Compared to typical low power voltage transfer (R12 not used) the bass is more tough, not so "full" and "lazy", but better "readable" and more natural. The mids and treble loose grain. The "cable sound" is highly supressed. The sound seems to be less loud (compared to same voltage level without R12), but more dynamic and lively. All of the phenomena described can be heard on good quality audio chain. The kind of sound with R12 properly connected would be highly appreciated when listenning to the classical music. It is all about HF interference, signal power and about cable phenomena, they have not been satisfactorily explained yet.

Once more I would like to emphasize the correct R12 position - it is at the end of the buffer output cable, not at the buffer output.

Pavel
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Old 31st December 2003, 02:07 PM   #5
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Pavel:

Iīll try R12 as you suggested -at the end of the cable, not at the end of the buffer output- and then Iīll let you know about the results.
In my last visit to your site I have noticed that the ubication of R12 was changed to that way.

Thank you for your help, and happy new year.
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Old 31st December 2003, 02:22 PM   #6
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Could one of you fine persons point us lesser ones to the schematic under discussion?
(and I did search for "audio buffer" AND'ed with PMA but that is wwwaaaayyyyyy to many posts!)

thanks
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Old 31st December 2003, 03:19 PM   #7
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[URL=http://www.pha.inecnet.cz/macura/audiopage.html]

There you can see the schematics of the composite amp, and the cable scheme with the proper termination.

Regards
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Old 31st December 2003, 05:34 PM   #8
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Thanks !
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