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Re: Rotel RA1060 - upgrade OpAmp

Posted by mb on March 7, 2003 at 18:06:59:
Thanks for your comments, which I broadly agree with.
In the case of the Rotel, I did not suggest any upgrade of the main power caps because my RA 971 has rather nice BHC Aerovox caps, specifically made for Rotel. I feel they are a strength of the Rotel range, so I'm not tempted to try to "upgrade" in this area :).
I'm familiar enough with the circuit to be confident that removing the input DC block caps from the OPA2604 is ok, because they have a pair of output DC block caps. The caps are BG, but polar (ideally non-polar), so they're still a bit of a limitation.
Changing the feedback caps to Caddocks or Dales are a good idea. If you look carefully at the values chosen by Rotel for the RA 971, the gain is higher than neccessary (amp plays too loud at 11 o'clock), so there's an opporunity to fine tune. Also the values chosen are not optimal for minimization of distortion and DC offset. I might look at this upgrade sometime in the future.
A very worthwhile upgrade is to replace rectifier diodes with soft recovery diodes (of correct rating, of course). This is a simple, well-tested upgrade, and imho certainly improves the subjective quality of bass.