Hi ! sorry to jump in with a weird question. I have seen a lot of small Rotel integrated amps on the 2nd hand market recently. They seem built quite well. Now i see a 931 on sale very cheap. Looking at its service manual https://www.vintageshifi.com/repertoire-pdf/pdf/telecharge.php?pdf=Rotel-RA-931-Service-Manual.pdf i see a line preamp stage with voltage gain of 19 times followed by a power stage with voltage gain of 18 times. Is all this gain really needed considering the use of a digital source ? Why not use just a buffer for the preamp stage or even by-pass it entirely and rely only on the gain of the power stage ? In the old times i destroyed one ra-930ax in the stupid attempt of reducing its power stage voltage gain. Most of Rotel cheap integrateds adopt this high gain design. With the exception of the 935bx that is more a volume pot followed by the power amp stage. I have noticed that many high quality british integrateds use this scheme. What is your opinion ? do you see any opportunity of improvement maybe ? Thanks a lot. Kind regards, gino
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It uses a passive tone control so expect a gain to offset the passive network loss.
The schematic shows polarized electrolytic capacitors on locations where a bi-polar electrolytic capacitor should have been used. Replace them and calculate the HPF corner frequency, <= 1Hz is my preference to reduce low frequency phase shift.
Add a speaker protection system since it doesn't have one.
The schematic shows polarized electrolytic capacitors on locations where a bi-polar electrolytic capacitor should have been used. Replace them and calculate the HPF corner frequency, <= 1Hz is my preference to reduce low frequency phase shift.
Add a speaker protection system since it doesn't have one.
Hi ! thank you very much for the valuable advice. Actually i do not use the tone controls and i guess that even with the direct button engaged the gain is still all there. Do you think that the amp would work fine even with the preamp op-amp completely by-passed ? i think many british amps used with passive preamp before a power amp stage arrangement and usually with great resulting sound.
What about replacing the existing with higher grade ones maybe with a little film cap in parallel ? i read that at least one very high quality mic preamp uses parallels of high grade NP electrolytics with small film caps.
This is very difficult for me. I do not know even where to start.+
Thanks a lot again, gino
If i am not wrong the Rotel power amps have often been better judged than the preamps on sound quality, with the notable exception of the rc990bx and rc995bx ? and the michi line preamps of course.
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