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?
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...
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...
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.
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.
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.
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
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.
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.
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 youmaybe they are, did not try them yet. Are you basing this statement on your own evaluation or some reviews out there?
Yup. C717 & C718. They are located smack dab between the opamps and the output jacks.
You should also probably listen to SoNic_real_one. Bypassing the existing cap will get you 80% of the way there, it's cheaper than buying a 1 or 2.2 uF film or pio cap and one more thing.... I didn't mention it in my previous thread but if you replace the electrolytic with a large film AND a bypass cap, you might not be able to get the lid back on. The Audiocap Theta & FT-3 that I mentioned in my previous post sound awesome but I can't get the darned lid back on the player - mostly because the FT-3 is about as big as a beer can!
I modified RCD-971 years ago. It has very good power supply and S/PDIF coax out. I used AD8066, LC clock II with dedicated power supply, re-wired analog stage, replaced 4003 diodes with fast switching soft recovery types….. but unfortunately was not experienced in CFB implementation as I/V…. very, very bad…. I posted the photos on these forums; try the search for “RCD-971” and “Extreme_Boky”
I’ll give you a hint on how to modify I/V stage properly:
The output stage in its unmodified / original condition is an ideal contender for dual CFB OP in DIL package - the AD812: remove the link between pin 6 and 7 and insert a resistor of around 1k to 3k to prevent oscillations. Done! Use surface mount resistor (without leads) and solder it straight between IC pins (if possible). If not, keep the distance between the resistor and IC pins short. You will hear amazing improvement not only sound wise, but the CFB OP will drive double-the -current at the RCA’s as well (!) Later, play with RC filter at DAC Iout (remove it, and deal with hf rubbish at the IC-end) AND decouple the Vcc/Vee pins with smd capacitors / SILMIC II’s combination.
I wish I could go back to I/V mods I did before… and do them again… this time properly. AD8066 was good choice as well…. bit fussy on power supply rails.
I believe in single high quality coupling capacitor with no paralleled smaller-value capacitors... anyway, I don’t think you’ll need one.
LM6172 is my favourite VFB (as is AD8066 and AD826). The reason you heard what you heard is because the resistors R707 and R708 (I/V Rf resistors) do not have Cf…. the importance of this capacitor grows as you use faster VFB IC’s….. BUT they are not needed if you use CFB IC’s – hence the reason for my statement at the beginning of my second paragraph (above).
Boky
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