rotel rcd-971 opamp substitution

karloss · 14th June 2011, 08:48 PM

Recently I changed opamps in my rotel rcd-971 player (opa2604 to lm6172) and was quite happy with the sound, but as I bought ap tempo 3i, there is some kind of overbalance of high tones when listening loudly. I put opa2604 back and everything was flat again, but also very boring and spaceless. I did some searching and tried lm4562, at first without bypass and then bypassed with 1.5uF 25V tantalum capacitors similar as on the site Rotel RCD-971 , but accented highs remains. What can cause this problem?

Mooly · 15th June 2011, 04:54 PM

Without actually hearing the Rotel its hard to say.

With any opamp swaps using highish speed devices a scope check for stability is essential imo.

SoNic_real_one · 15th June 2011, 05:03 PM

When I installed my LM4562 I found out that the sound improved, especially in the high-end of audio band. It wasn't a strong change thou... definetevly not something that I would complain.
Now, I don't know what are you hearing and why. Maybe you are loading the LM4562 output more than it can handle - I didn't understand what are you using at line out...

karloss · 15th June 2011, 07:40 PM

the player is connected through rotel rc-995 to pass aleph 3. I think players output is always at its maximum, attenuated or amplified with preamp. maybe some kind of synergy with the rest of audio chain, noone ever complained about it. going to try burson discrete dual opamp, it should be direct replacement to opa 2604.

goody75 · 16th June 2011, 12:35 PM

I recently modded my Rotel RCD-971 and put in some LME49720's, which I think are the same thing as the LM4562.

Have you given the opamp time to burn in? I will say that the first 12 hrs or so with the new opamps, it did actually hurt my ears to listen to the 971 - because of the high frequency. Just make sure you play it on repeat for a day or two before passing judgement.

After it settled in, I have no problems with high frequencies and I even removed the low pass caps at the RCA jacks.

karloss · 16th June 2011, 01:30 PM

no burn-in, probably that is the problem. But those LM6172 though 100MHz did it even after six months. Did you bypass pin 4 and 8 or it is now good as it is? And low pass caps are those red ones right next to each rca output? Should I just remove them or shortcut that connection? Thank you very much

goody75 · 16th June 2011, 04:01 PM

Bypass for pins 4 & 8:
I don't have a schematic in front of me right now but from what I remember I think there are already 4 blackgates that decouple/bypass the opamp power supplies @ pins 4 & 8. I left those alone and paralleled each with a 0.22 uF Wima MKP4 on the bottom of the PCB. It's not as close to the pin or as clever as the method in the link from your first post but it's pretty much the same thing.

low pass caps:
Yes they are the small, red, ceramic caps and yes there is one right next to each rca output. They form a low pass filter so they allow "low" frequencies through and filter "high" frequencies to ground. If you are having a problem with accentuated high frequencies then you definitely should NOT remove them.

I removed mine based on a controversial recommendation from Lukas Fikus (tda1541 / tube fanatic). It's supposed to give you a more open & airy sound. It definitely helped with my Nakamichi CDP-2A but I did not notice any difference with the Rotel RCD-971. Once again, if you are already getting accentuated high's, removing these caps will only accentuate them even more and I think it's possible their removal can cause damage to your tweeters. At some point, if you do want to experiment with the low pass caps, it's probably a safer bet for you tweeters to calculate a value that will have a corner frequency of 25-30KHZ rather than the 20KHz that most CDP's have. You can easily find a formula online if you need one - maybe even an online calculator.

Warning: I'm a bit of a newbie so I some of my interpretations may be wrong.

karloss · 16th June 2011, 05:14 PM

surely just remove, shorting will mute signal

was just curious, because I already heard about it but didn´t know what it is about. Maybe after installing burson opamps I will find it useful. thank you

SoNic_real_one · 16th June 2011, 10:39 PM

Burson OpAmps are a waste of money...

karloss · 17th June 2011, 05:09 AM

Quote:

Originally Posted by SoNic_real_one

Burson OpAmps are a waste of money...

maybe they are, did not try them yet. Are you basing this statement on your own evaluation or some reviews out there?

14th June 2011, 08:48 PM	#1
karloss diyAudio Member Join Date: Dec 2010	rotel rcd-971 opamp substitution Recently I changed opamps in my rotel rcd-971 player (opa2604 to lm6172) and was quite happy with the sound, but as I bought ap tempo 3i, there is some kind of overbalance of high tones when listening loudly. I put opa2604 back and everything was flat again, but also very boring and spaceless. I did some searching and tried lm4562, at first without bypass and then bypassed with 1.5uF 25V tantalum capacitors similar as on the site Rotel RCD-971 , but accented highs remains. What can cause this problem?

15th June 2011, 04:54 PM	#2
Mooly diyAudio Member Join Date: Sep 2007	Without actually hearing the Rotel its hard to say. With any opamp swaps using highish speed devices a scope check for stability is essential imo. __________________ ------------------------------------------------------- *A simulation free zone.* *Design it, build it, test it.*

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15th June 2011, 05:03 PM	#3
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	When I installed my LM4562 I found out that the sound improved, especially in the high-end of audio band. It wasn't a strong change thou... definetevly not something that I would complain. Now, I don't know what are you hearing and why. Maybe you are loading the LM4562 output more than it can handle - I didn't understand what are you using at line out...

15th June 2011, 07:40 PM	#4
karloss diyAudio Member Join Date: Dec 2010	the player is connected through rotel rc-995 to pass aleph 3. I think players output is always at its maximum, attenuated or amplified with preamp. maybe some kind of synergy with the rest of audio chain, noone ever complained about it. going to try burson discrete dual opamp, it should be direct replacement to opa 2604.

16th June 2011, 12:35 PM	#5
goody75 diyAudio Member Join Date: Apr 2010 Location: Motown (area)	I recently modded my Rotel RCD-971 and put in some LME49720's, which I think are the same thing as the LM4562. Have you given the opamp time to burn in? I will say that the first 12 hrs or so with the new opamps, it did actually hurt my ears to listen to the 971 - because of the high frequency. Just make sure you play it on repeat for a day or two before passing judgement. After it settled in, I have no problems with high frequencies and I even removed the low pass caps at the RCA jacks.

16th June 2011, 01:30 PM	#6
karloss diyAudio Member Join Date: Dec 2010	no burn-in, probably that is the problem. But those LM6172 though 100MHz did it even after six months. Did you bypass pin 4 and 8 or it is now good as it is? And low pass caps are those red ones right next to each rca output? Should I just remove them or shortcut that connection? Thank you very much

16th June 2011, 04:01 PM	#7
goody75 diyAudio Member Join Date: Apr 2010 Location: Motown (area)	Bypass for pins 4 & 8: I don't have a schematic in front of me right now but from what I remember I think there are already 4 blackgates that decouple/bypass the opamp power supplies @ pins 4 & 8. I left those alone and paralleled each with a 0.22 uF Wima MKP4 on the bottom of the PCB. It's not as close to the pin or as clever as the method in the link from your first post but it's pretty much the same thing. low pass caps: Yes they are the small, red, ceramic caps and yes there is one right next to each rca output. They form a low pass filter so they allow "low" frequencies through and filter "high" frequencies to ground. If you are having a problem with accentuated high frequencies then you definitely should NOT remove them. I removed mine based on a controversial recommendation from Lukas Fikus (tda1541 / tube fanatic). It's supposed to give you a more open & airy sound. It definitely helped with my Nakamichi CDP-2A but I did not notice any difference with the Rotel RCD-971. Once again, if you are already getting accentuated high's, removing these caps will only accentuate them even more and I think it's possible their removal can cause damage to your tweeters. At some point, if you do want to experiment with the low pass caps, it's probably a safer bet for you tweeters to calculate a value that will have a corner frequency of 25-30KHZ rather than the 20KHz that most CDP's have. You can easily find a formula online if you need one - maybe even an online calculator. Warning: I'm a bit of a newbie so I some of my interpretations may be wrong.

16th June 2011, 05:14 PM	#8
karloss diyAudio Member Join Date: Dec 2010	surely just remove, shorting will mute signal was just curious, because I already heard about it but didn´t know what it is about. Maybe after installing burson opamps I will find it useful. thank you

16th June 2011, 10:39 PM	#9
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	Burson OpAmps are a waste of money...

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