I have a Rotel RC-980bx preamp and am attempting to upgrade the 2 AD711JN opamps, all the caps seem to be Black Gate Rubycons, so will leave those as they are. I plan on installing 8 pin sockets to be able to replace the opamps for listening comparison.
The ic501 and ic502 are the AD711JN. What opamps would be a drop in replacement.
Any help would be appreciated.
Thomas
The ic501 and ic502 are the AD711JN. What opamps would be a drop in replacement.
Any help would be appreciated.
Thomas
Hmmmmmm Well There is a long list, and this part of the forum has it's .
But another part of the forum has its !
https://www.diyaudio.com/forums/chip-amps/
!
Hi Thomas i have had a few of those excellent rotel preamps and OPA604 was an improvement. I liked OPA627 even better. There can be said much about opamps but the AD711 is not neutral sounding and the suggested opamps are better in that aspect.
However there is more that can easily be done to the RC-980BX to make it shine. The gain is set way too high and I changed the feedback network resistors to achive a lower gain (I think I set it to a gain of 3.75x by changing R505/R506 to 1 kOhm). If you use the suggested JFET input opamps there is virtually no input offset so you can remove the input caps C501/C502 and put a wire bridge there. Output caps were replaced by the Wima MKS2-XL series caps. I think the value was 10 µF but please check. If the power amp has an input cap you can also remove the output caps and make it DC coupled. The best results are when making it DC coupled but please don't bridge the output caps if your power amp is also fully DC coupled. If not any error in the chain will result in the sweet smell of burned woofers.
* If you like the current gain you could also use OPA637. I think I even have those still in stock.
Edit: just checked the service manual and it are indeed 10 µF output caps. The Wima MKS2-XL 10 µF 50V fits exactly. The weakest parts are the opamps used in the phono amplifier (TL071 which is unsuitable for quality audio). If you don't use phono just leave them where they are.
However there is more that can easily be done to the RC-980BX to make it shine. The gain is set way too high and I changed the feedback network resistors to achive a lower gain (I think I set it to a gain of 3.75x by changing R505/R506 to 1 kOhm). If you use the suggested JFET input opamps there is virtually no input offset so you can remove the input caps C501/C502 and put a wire bridge there. Output caps were replaced by the Wima MKS2-XL series caps. I think the value was 10 µF but please check. If the power amp has an input cap you can also remove the output caps and make it DC coupled. The best results are when making it DC coupled but please don't bridge the output caps if your power amp is also fully DC coupled. If not any error in the chain will result in the sweet smell of burned woofers.
* If you like the current gain you could also use OPA637. I think I even have those still in stock.
Edit: just checked the service manual and it are indeed 10 µF output caps. The Wima MKS2-XL 10 µF 50V fits exactly. The weakest parts are the opamps used in the phono amplifier (TL071 which is unsuitable for quality audio). If you don't use phono just leave them where they are.
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magnificent deadpan
I haven't laughed so unexpectedly delightfully all week, thanks!!
cheers,
Mirlo
I haven't laughed so unexpectedly delightfully all week, thanks!!
cheers,
Mirlo
I think a listening test is called for. Is there a single amp version of lm324?
No, an LM324 won’t work - not pin compatible. Could use an LM709 though, except you’d probably have to add a compensation network.
Those worked great for me in a power converter control circuit running on +/-2.5VDC.
Real cheap too.
Gain should be exactly the same when nothing else has changed. If you have changed the feedback network then the gain has changed yes. Then gain would have changed with AD711 too.
Destroyed the opamps ? Are you sure you can do things like this? Why take the risk and damage stuff? I have owned at least 3 of these and they are really able to shine, when you are not able to work on them better leave it to qualified people.
Destroyed the opamps ? Are you sure you can do things like this? Why take the risk and damage stuff? I have owned at least 3 of these and they are really able to shine, when you are not able to work on them better leave it to qualified people.
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