Rotel RCD971: Which Opamps in I/V Converter & Output Stages? - diyAudio
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Old 26th July 2006, 12:02 AM   #1
dtm1962 is offline dtm1962  Canada
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Default Rotel RCD971: Which Opamps in I/V Converter & Output Stages?

I am preparing to receive my 971 in about a week and I want to upgrade the I/V converter & output stages of the Analog Outputs.

So I want to order some better Opamps and have them arrive at same time as Player

Does anyone know what in this player?

Any help would be appreciated!

Anyone hve a schematic or even drawing of the Analog Stage?

Any help would be appreciated!

Dan
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Old 27th July 2006, 06:50 AM   #2
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Take a look at this page:

http://web.aanet.com.au/tobes/rcd971mod.htm
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Old 27th July 2006, 07:32 AM   #3
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I tried several opamps in my RCD971 alongside LM6172 and AD825:

- AD826 - good, clear sound, but somewhat lackiing sparkle
- AD823, excellent choice, the only limitation suggested for this opamp is lowhish output current (15mA), but here is just enough. I did not notice any problem comparing the others.
The sound is very clean and clear, sometime too polite for my taste. Anyway, on the short list of choice.
- AD828. The best of all three, but it is very difficult to implement. Although the LM6172 is very fast and wideband (100MHz) and don't need for extra care of oscillation prevention, the AD828 is musch wider and it is very difficult to make it working properly in in the existing layout
-OP275, OPA2134, OPA2227: more or less the same as original OPA2604, but without so much hiss (yes, AD2604 here is pretty hissy)
- OPA2107, THS4302: too edgy, the sound cam be sometimes harder and leaner than LM6172.
- OPA2132: Good step-up, maybe the best combination of all above mentioned good things. Lot of room, lower noice, good attack, preserved originally intended sound, and very clean. I think somewhere I did read that in this case you can remove the output capacitors (very low DC offset), but not sure here. Bypass the 2132 as suggested elsewhere in this forum (by carlosfm), and enjoy. I think the newer RCD1070 has some "Special Edition" here in Europe using exactelly the same opamps (also in the RA1060 integrated amp), so maybe that's the reason it sounds good in 971 also, since the layouts are almost identical.


Well, that's about opamps.
However, a few minor tweaks will do far more noticable improvements in my opinion:
1. Change the existing rectifiers by some FRED or even better, Schottky diodes, You need 9 pcs (5 for the digital and 4 for the analogue stage). Any 1A/40V+ will work here. This will really lower the noise and the differencies are not just nuances
2. Bypass the big cans for analogue stage (2x4700uF/35V). Tsis is already done in RCD1070 but not in RCD971. Use anything you have, 47-220nF,
3. Change the 100R metal film resistor on the output to some of preffered and better quality, non inductive, low noice...etc.
4. Some suggests to change decopling caps around the opamp (BLack Gate 100uF/25V) with 10u/25V tantal + 100nF fim. I did not tried this.
5. Change the output caps (also Black Gate) to some Elna SIlmic, Nichicon Muse or even Pana FC. The sound is smoother. Panasonic FC is used in RCD1070 through whole layout, so, it can be considered as upgrade, more than step-down than BGs. I think Rotel continued to use FC in all 10xx models.

So, that's it. Hope this helps
Just my 2c
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Old 28th July 2006, 05:46 PM   #4
namcir is offline namcir  Philippines
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hi
have you tried this opamp ths4032?
some say it is better than opa2132 or lm6172 which almost have the same spec if im not mistaken...
so what opamp would you recommend?
ths4302 is different from ths4032
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Old 28th July 2006, 07:21 PM   #5
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Quote:
Originally posted by RICMAN
hi
have you tried this opamp ths4032?
some say it is better than opa2132 or lm6172 which almost have the same spec if im not mistaken...
so what opamp would you recommend?
ths4302 is different from ths4032

Yes, I found it only in SMT version. It is good, extremelly clean and detailed, but somewhat sterile.
In RCD971 as drop-in replacements the best sounding opamps for me were AD825, AD828 and 2132. OP275 is also ok-
I suspect because the first production run was using OP275 before OPA2604, so the circuit was probably optimized for it.
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Old 28th July 2006, 07:24 PM   #6
dtm1962 is offline dtm1962  Canada
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I appreciate everybody's responses for my inquiry!

I have a bunch of OPA2132PA to drop in for a test listen!

I am going to try the LT1469 as well. Has anyone tried this opamp?
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Old 28th July 2006, 07:39 PM   #7
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Moin,

the Rotel RCD 991 has OPA2132 & 132 inside.

Carsten
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Old 28th July 2006, 07:40 PM   #8
namcir is offline namcir  Philippines
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isnt it that the ad828 is used in video application?
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Old 28th July 2006, 09:00 PM   #9
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Quote:
Originally posted by RICMAN
isnt it that the ad828 is used in video application?
Exactly that one. And directly dropped in Rotel RCD971, without additional decoupling, you can hear "birds" - it oscilates without additional care. However, it is very good sounding opamp, smooth, fast and dynamical. AD828 is more than 3 times faster than both LM6172 and THS4032, so this is proof that RCD971 has already very good elaborated layout.
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Old 29th July 2006, 05:31 AM   #10
Ruach is offline Ruach  Singapore
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Hi Dan,

I will send you the pictures over the weekend as the files are big.

There are some very nice mods that you can do to the 971. Putting in a dedicated clock and a transformer for the analog stage will bring the performance of the 971 to another level.

I owned the 991AE and the 971 and both sets sounds similar. As to which is better, it is a matter of preference.
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