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Modification suggestions for Rotel RCD-975
Modification suggestions for Rotel RCD-975
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Old 7th January 2011, 12:02 PM   #1
focal7C is offline focal7C  Australia
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Default Modification suggestions for Rotel RCD-975

Looking for advice and instructions where to start tweaking a Rotel RCD-975?

Not experienced with electronics but can solder and eager to learn in the process. Interested to get your suggestions or experience with this particular player.

Brought back this player into service recently after a speaker building project which revealed that a newer, much more expensive, well regarded CD player did not appear as good...

First explored other threads but could not find specifics for this player.

Then investigated removing attenuation components (free common tweak). Which does not appear to be applicable for this player as it uses a relay with zero effect on the audio
muting transistors / Rotel RCD-975

So which of these these further changes are worth while trying and in what order:

1. Thicker "better" copper insulated power cord. Forget adding new IEC socket just re-solder? Currently no earth wire on lead - a good thing to avoid interference?

2. Changing the two AD711JN OPAMP's (after DAC) is another the easy task. Remove and put in an 8 pin IC socket for easy testing. But what's better/different and compatible with TDA1305T filter-DAC? Only concrete recommendation for this player is to replace with LT1122
Nasotec Home Page
Have not seen these from a supplier in Australia

Other favourites seem to be AD8065 ($13) and LM4562MA ($10). OPA627BP is comparatively at ($65) unless a sure bet. Another one that is readily available is OPA2134PA ($10). Are they all compatible with TDA1305T?
TDA1305T datasheet, Pinout ,application circuits TDA1305T Stereo 1fs Data Input Up-sampling Filter With Bitstream Continuous Dual DAC (BCC-DAC2)

3. Good decoupling and/or regulators for the supply pins of DAC chip. Does this mean feeding individually from a new power source?

4. Replacing the main PSU caps near the transformer. Because they can have degraded, better ones are available or different V/uF values required?

5. A large toroidal transformer and power supply regulators supplying the separate DAC analogue output board or individual components.

6. Bypass low value resistors carrying power supply to chips (1-4 ohms?)

7. Replace the cap(s) carrying HF to the OpAmps with higher uF and quality.

8. Replace rectifiers with fast, soft recovery and bypass with RC snubber (100ohms, 47nF).
Not sure what this achieves or means?

9. Clock upgrade. Read mixed results (minor improvements?) for a lot of effort/expense.

10. Damping and heavy coupling of spinner.

11. Top loader replacement as prevention of spinner vibrations rather than taming them (also added benefit of doing away with CDM-9 transport mechanisms maintenance). Hack of case required.

Irrespectively will dampen feet, case, PCB (with wedged cork), and cap+DAC circuits (with blue tack). There is already a rubber casing around the filter-DAC for that purpose?

Most CAPS on both boards are Black Gate or Nichigon which are supposed to be quite good. So systematically replacing may not offer much improvement.
Attached Images
File Type: jpg Rotel RCD-975 board 2 photo2.jpg (133.1 KB, 487 views)
File Type: jpg Rotel RCD-975 board 1 photo2.jpg (113.1 KB, 479 views)
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Old 8th January 2011, 01:57 PM   #2
focal7C is offline focal7C  Australia
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Default Other possible mods

13. Diconecting the digital output?

14. Unplugging the display as can be done remotely by some new CD players (eg. Audiolab)

15. Replacing opamp IC's with circuit board plug-in constructed from audio graded transistors and resistors (eg. Burson "HD Audio Opamps")
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Old 8th January 2011, 11:13 PM   #3
focal7C is offline focal7C  Australia
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Default Replacing caps in output stage of CDP

17. Replacing the caps in the output stage for better quality Auricap caps (same V/uF values?).

Are these:
- the C356,C357 (see-through type next to output sockets?) CAP POLESTYRENE 160V 1000PF?
- the C354, C355 Black Gate Elec. 16BGF1000 (16V/1000uF)? Which ones are most critical to change in the case of the RCD-975?

See how a little knowledge but a lot of information can be overwhelming to first modification attempts?
Attached Images
File Type: jpg Rotel RCD-975 board 2 photo2.jpg (133.1 KB, 453 views)
File Type: jpg Rotel RCD-975 board 1 photo2.jpg (113.1 KB, 443 views)
File Type: gif Rotel RCD-975 PCB1.GIF (122.6 KB, 448 views)
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Old 22nd January 2011, 03:48 AM   #4
focal7C is offline focal7C  Australia
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Default CDP PSU and Diode component selection

Current plan is to replace:

1. Diodes. Which Schottky diodes shall I use? Can't read what the spec is for the existing ones (Tech Manual part list reads: 9 x DIODE IN4148-86, 9 x DIODE IN4002-TB, 1 x DIODE Zener BZX79-C7V5). I understand that equal or higher values can be used?

2. PSU Caps. Installed are two Black Gate 25V 1700uF. Would the Panasonic FCs or Nichicon Muse KZ of higher 3300uF values be good options?

Manufacturers part numbers and sources in/near Australia would be appreciated?

3. Opamps AD711JN -> OPA604APG4 + cap 0.1uf across supply pins (found them from element14 supplier)
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Old 22nd January 2011, 04:29 AM   #5
SoNic_real_one is offline SoNic_real_one  United States
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Watch out the OpAmps - do not confuse the single with dual ones! AD711 is single, LM4562 and OPA2134 are duals... The singles are LME49710 and OPA134 (I would go for OPA211).

And the caps for decopling should be 2 - each pin to the ground.
I know that it is "easy" to put just one across the supply pins, but it doesn't help, I would say that it makes things worse.
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Old 23rd January 2011, 10:54 AM   #6
focal7C is offline focal7C  Australia
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Thanks for clarifying. Yes, there are currently two AD711JN singles. Maybe the first mod are a cap each across their supply pins...

What are the sound characteristics of the OPA211?

Looks like the the OPA211 is a surface mount opamp and requires a BrownDog adapter or similar? Is the OPA2111KP the DIP equivalent?
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Old 23rd January 2011, 07:00 PM   #7
SoNic_real_one is offline SoNic_real_one  United States
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Yes, the new high quality OpAmps are seldom packaged in DIP. I guess for economical reasons first of all, but also most of the new hi-end audio is done in SMD to minimize the circuit traces lenghts. I don't personally buy it, but... I saw it as argument.
I have the dual LM4562 in a DIP and sounds great.

PS: OPA2111KP is dual in DIP package but has nothing in comun with OP211.

Last edited by SoNic_real_one; 23rd January 2011 at 07:05 PM.
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Old 26th May 2011, 03:17 PM   #8
humanbenIlkley is offline humanbenIlkley  United Kingdom
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My first post
This is what I have done to my recently aquired rcd-975

1. Took out anything that said "Teapo or Jamicon" see too many of these with swollen belly's!!
2. main board p/s mods; c185 & c187 to Panasonic FK 4700uf 25volt, c181 to Panasonic FC 1200uf 16v, c183,188,189 to Panasonic FC 470uf 25v. changed these also c141,142,c148,143,c139&c117 to Panasonic FC 220uf 25v.
3. DAC board mods; changed original op amps AD711GN to AD797ANZ decoupling caps, c348,349,c352,c353 to mmk 0.47uf.
4. DAC p/s mods; d301-d304 change to hfa04tb60 HEXFred diodes, c301-304 ceramic caps are removed, c305-6 to Panasonic FC 2200uf 25v, and diodes D305-306 & D311-312 changed to 11DQ10's.

To my ears it the basic mods above made a night and day difference from stock instantly, will have to report back after a week of burning in!
BTW The op-amps are mounted on turned sockets so I could roll em easier, tried a few; opa604(WEIRD), ad825(MUSHY), opa627(VERY GOOD) but the best so far AD797
and lastly I would have prefered to use Rubycon ZL or ZLH in place of c305-6 Panasonic FC can dry out the sound

Well thats my 10 peneth, Humanben.
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Old 4th January 2012, 10:32 PM   #9
focal7C is offline focal7C  Australia
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Default Caps removal reason

Hi Humanben,

thanks for these instructions it helped me with a plan of attack. Progressing on a similar path and will report back my results.

Can I ask why you removed c301-304 ceramic caps between the diodes and did not replace them with anything?

Cheers, Roger
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Old 9th January 2012, 01:22 AM   #10
focal7C is offline focal7C  Australia
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Phase A of mods:
A1. Main board p/s c185 & c187 to 4 x Panasonic FR 2700uF 25V (2 in parallel for each replacement). The FR claim to have same low FSR as the FM series, but with up to 10000 hours lifetime @ 105C. Bypassed with VISHAY ROEDERSTEIN polypropylene cap 0.1F under board.

A2. DAC p/s mods; d301-d304; d305-306 & d311-312 changed to Schottky 11DQ10 diodes.

A3. DAC p/s mod: c305-6 to Panasonic FM 2200uf 25v up to 7000 hours @ 105C

Impressions after only a few hours running are: sound is more neutral, has an airer (lifted ceiling) feeling to mids, less shrill to high frequencies. Although the latter could be partly due to a 1 ohm resistor on tweeter added recently. Some additional depth to low frequencies although drums were always very "accurately fast". Had perhaps expected deeper bass with slight increase to 2 x 5400uF (combined) paralleled caps on p/s, but probably limited by 7" woofer and characteristics of amp (Cyrus 8vs2). Pleased with improvements so far of an already very good sound.
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