Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

Digital Source Digital Players and Recorders: CD , SACD , Tape, Memory Card, etc.

Sony CDP-950 Mods - NOS mod produces a lot of noise when CD not playing
Sony CDP-950 Mods - NOS mod produces a lot of noise when CD not playing
Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 10th September 2018, 05:58 PM   #1
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
Default Sony CDP-950 Mods - NOS mod produces a lot of noise when CD not playing

Hello All,

I have been working on a SONY CDP-950 (Aug. 1988 with TDA1541A) over the weekend and have hit an issue with spurious sounds when the CD is not playing. The original sound of the 950 was very muffled and veiled. Knowing that the TDA1541A is capable of so much more, as I also have a tweaked (opamps and non-oversampling) Rotel 955AX, I read some earlier posts (eg Mod CDP SONY 950) and broke out the soldering iron.

Step 1 was to remove the 5532 opamps (IC400 and IC500) and the 4 x muting transistors (Q401, Q402, Q501 and Q502).

Click the image to open in full size.

I then dropped in a couple of LM4562 opamps and after a couple of hours of use the sound opened up with a better soundstage and clarity, but still a bit veiled in presentation. The lack of muting transistors caused a thud at power on/off, but that is something I live with on the 955AX and is not a problem for me.

Step 2 was the the non-oversampling mod, described on the lampizator web pages. I did all the work on top of the PCB by snipping jumpers and resistors. The basic mod steps are as below. In the circuit diagram IC521 is the TDA1541 and IC302 is the CXD1125.

Quote:
In Sony CDP-333ESD with one TDA and CXD1125 demodulator and typical digital filter CXD1088
we go like this: the whole job is done on the bottom of the PCB.
  • data goes straight from CCD1125 leg 78 (lift R311) to TDA pin 3 (floated)
  • BCLK goes from pin 76 of the 1125 (trace it to the first breaking point - a jumper or resistor and then float it by lifting that part) to the pin 8 of the 74HC and from there straight to TDA pin 2 (joined with 4 and together - floated)
  • LRCK goes from pin 80 of the 1125 (trace it to the first breaking point - a jumper or resistor and then float it by lifting that part) to the pin 1 of the 74HC and from pin 12 (output of 74HC) to TDA pin 1 floated
Click the image to open in full size.

Now the sound really opened up and sounded way better, but there was a downside. The expected garbage music when skipping tracks was present, but there was also a lot of quite loud electrical noise all the time when the CD was not playing. Really not good at all.

I then put the muting transistors back in, which has cleared up the noise when the CD is not playing, the expected garbage when skipping tracks remains.

I'm wondering what to do next as I prefer the sound without the muting transistors but cannot live with the noise when the CD is not playing. I've double-checked the wiring on the NOS mod and everything seems to be OK, so I am wondering if anyone else has experienced this or has any suggestions.

Thanks for any help
  Reply With Quote
Old 10th September 2018, 06:07 PM   #2
Mooly is offline Mooly  United Kingdom
diyAudio Moderator
 
Mooly's Avatar
 
Join Date: Sep 2007
Sony CDP-950 Mods - NOS mod produces a lot of noise when CD not playing
The muting transistors should be transparent in operation... that's another debate though.

If you are convinced they impair the sound then try using JFET's in place of the transistors. You want something with a low on resistance (low Rds) and you need to confirm the logic levels are suitable to fully pinch off the FET. The muting wont be as deep as the transistors but could be adequate. You could also increase the series resistance through the chain to increase the effectiveness of the FET's
  Reply With Quote
Old 10th September 2018, 07:08 PM   #3
percival007 is offline percival007  England
diyAudio Member
 
Join Date: Sep 2007
I think a lot of Sony's have separate Analogue and Digital Mute Lines.

The Analogue Mute will still be working but the Digital one (if you've bypassed the Digital Filter) won't.
You will need to make the Digital Mute line also activate the Analogue Mute Transistors/Relay. I am just working out how to do this on a Sony CDP-227ES.

P.
  Reply With Quote
Old 10th September 2018, 07:18 PM   #4
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
Quote:
Originally Posted by percival007 View Post
I think a lot of Sony's have separate Analogue and Digital Mute Lines.

The Analogue Mute will still be working but the Digital one (if you've bypassed the Digital Filter) won't.
You will need to make the Digital Mute line also activate the Analogue Mute Transistors/Relay. I am just working out how to do this on a Sony CDP-227ES.

P.
That's jogged something in my brain. I *think* I recall reading something when I was researching which cd players to go for - the Rotel and the Sony models were on the short list. I do recall something about having to tap something in the CXD1088. Now, this could be a figment of my imagination but it does ring a very small bell. Time for some googling.

Edit - I did a quick google on this and couldn't find anything obvious, so it may well be my brain misfiring.

Last edited by ianp; 10th September 2018 at 07:32 PM.
  Reply With Quote
Old 10th September 2018, 09:25 PM   #5
percival007 is offline percival007  England
diyAudio Member
 
Join Date: Sep 2007
The Analogue Mute from the System Control IC301 Drives IC940 then Q521 and then the Mute Transistors themselves.

The Digital Mute comes from the System Control IC301 and feeds the Digtal Filter on Pin 9 but won't have any effect if you've bypassed the Filter.
You should be able to use the DMUTE feed though to also drive the Muting Transistors using another Transistor, it may need inverting but should be possible.

It'll be the DMUTE that mutes during Skip etc.

P.
  Reply With Quote
Old 10th September 2018, 09:51 PM   #6
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
I found the below in the link on the lampizator website I referenced in my original post. This was for a Sony CDP 227ESD. I wonder if we can glean anything from the schematics for that model and how it implements things ?

Quote:
I was getting some noise when the CD player was not playing any CD's but this goes away if you switch the Digital Out at the back of the CD player off.
  Reply With Quote
Old 11th September 2018, 06:38 PM   #7
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
Circuit diagram for the digital out switch on the 227ESD.

Click the image to open in full size.

I also found that this is a problem for others who has NOS'd the CDP-950 - Good Design Bad Design and DIY: Sony CDP950 Tweak Part 3 : NOSed

At this point I think I will look at upgrading some of the caps on the PCB, starting with the decoupling caps on the TDA, to see what changes they can bring.
  Reply With Quote
Old 12th September 2018, 04:55 AM   #8
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
Interestingly, I tried some opamp rolling tonight. I took a well used pair of LM4562 from my bugle2 and they sound a whole lot different than the initial pair of 44562 I had used. Better clarity, less rolled off at the top-end and a lot more punchy and musical.

I wonder if I had a duff pair in the spares box - as I am not sure I believe that opamps need much/any break in time ?

Last edited by ianp; 12th September 2018 at 05:09 AM.
  Reply With Quote
Old 18th September 2018, 05:02 AM   #9
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
The Mouser order of capacitors arrived today. I replaced 4 x duorex caps in the audio output, more as a precaution against leaks than anything else, and not much to report about change in audio.

Not sure if it replacing the decoupling caps on the TDA as the sound is pretty damn good at the moment. Very spacious and some good reach down into the bass levels.

Oh, and the duff pair of LM4562 were cast into the bin. I tried them in the Bugle and they were subpar after more than 48 hours of burn in time. I'm guessing I bought these off ebay in a moment of weakness

Last edited by ianp; 18th September 2018 at 05:22 AM.
  Reply With Quote
Old 19th September 2018, 12:25 AM   #10
ianp is offline ianp  United States
diyAudio Member
 
Join Date: Jan 2008
Yeah, like I wasn't going to replace the decoupling caps .....

All 14 replaced with 4.7uF 63V WIMA MK2 caps, which all fitted neatly together on top of the board. I'll give them some more time to settle in and my ears to get used to them. but initial thoughts are improved bass and highs.
  Reply With Quote

Reply


Sony CDP-950 Mods - NOS mod produces a lot of noise when CD not playingHide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
SONY CDP950 recap mod not playing MaccAu Digital Source 4 9th June 2015 03:27 AM
Nakamichi Dac 101 produces static noise only an2ny888 Car Audio 5 17th February 2014 03:14 PM
SONY CDP-H3700 not(always)playing discs correctly OXAUDIO Digital Source 1 11th May 2013 09:42 PM
Adcom GCD 575 CD on produces static noise apoopoo999 Digital Source 3 22nd May 2010 06:13 PM
Avoid playing Sony/BMG discs on your computer DSP_Geek Everything Else 53 27th December 2005 02:25 AM


New To Site? Need Help?

All times are GMT. The time now is 11:10 AM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 14.29%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2019 DragonByte Technologies Ltd.
Copyright ©1999-2019 diyAudio
Wiki