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Old 20th January 2003, 05:46 PM   #1
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Default Pics of my cdp mods

I finished these mods to my old Yamaha CDX-550 a few months ago, but I haven't had much time to listen to the finished product. I know, it wasn't a great player to begin with, but it was the only one I had laying around to play with, other than my DVD player.

Sorry for the poor quality pics. I really can take good pictures, honestly!

First, the finished cdp and external power supply:

Click the image to open in full size.


Inside the power supply. Most parts are recycled from the junk box, including the chassis itself. The power supply contains + / - 12V supplies for the opamps, + / - 12V pre-regulation for the Kwak clock, and + 12V pre-regulation for some of the logic in the player. All regulators are 317 / 337 types with Kelvin sense points as close to the devices being powered as possible (hence the 25 pin D-sub used to connect the power supply to the player).

Click the image to open in full size.


The inside of the player, showing the 25 pin power connector at the top left, and the Kwak clock in an aluminum box beside it, connected via a small piece of coax to the clock daughterboard, located inside the (original) metal shielding. On top of that shielding is the final + 5V regulation for the clock / DAC logic. To the right are the opamp daughterboards that I built, replacing the original 4570 dual opamps with 2 OPA627s.

Click the image to open in full size.


Here' s a close-up of the opamp daughterboards. The empty sockets are wire-wrap sockets with very long pins, which were used to stand the daughterboard off of the main board. I wasn't content with simply swapping in another dual opamp; I had to go with the best.

Click the image to open in full size.


The inside of the Kwak clock. The clock is on the left, and the final + / - 5V regulation is on the right. I tried to keep the clock layout as tight as possible, and I think it turned out rather well.

Click the image to open in full size.


The limiting factor in the resolution of my system is likely my Yamaha receiver. Hopefully a pair of Aleph X will change that. But it certainly sounds good; the high end in particular seems somehow more defined.

There is only one strange problem... When playing something with near-slience (ie, the very beginning of a quiet classical piece) there is a strange "swishing" noise, that sounds almost like RF interference or something. As soon as a slight audible signal is present (ie, the beginning of the quietest note of the music), the noise disappears. It only seems to be present when the signal level is very near zero.

Any ideas on what this could be, or what is causing it?
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Old 29th January 2003, 06:14 AM   #2
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Nice job!

For the strange noise, the only thing that comes to mind is that maybe you have muting transistors downstream of the op amps that need sorting out?

By coincidence, I came across this post just when I'm planning to mod my Yamaha CDX-410U. This is older stuff, so none of the mods you did translate easily. For instance, there are 8 transformer taps, so it's not just +/-5V & +/- 12V. There's no IC for preamp, it appears made up of transistors. The DAC chip is a B-B PCM56P 16bit, maybe that can be improved?

Any tips on what I should tackle first would be appreciated.
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Old 29th January 2003, 03:58 PM   #3
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Quote:
Originally posted by leadbelly
Nice job!

Thanks!

For the strange noise, the only thing that comes to mind is that maybe you have muting transistors downstream of the op amps that need sorting out?

I left the muting transistors in, for the time being. I don't think they are causing the noise though, since it didn't exist before the mod.

By coincidence, I came across this post just when I'm planning to mod my Yamaha CDX-410U. This is older stuff, so none of the mods you did translate easily. For instance, there are 8 transformer taps, so it's not just +/-5V & +/- 12V. There's no IC for preamp, it appears made up of transistors. The DAC chip is a B-B PCM56P 16bit, maybe that can be improved?

I'm not familiar with this model; it sounds like it is probably better made than mine was. The 8 transformer taps likely provide separate power supplies for the servo section, the logic, and the analogue section, and maybe other things such as the display backlight. What I did was to selectively replace parts of the power supply rather than the whole thing. The original supply still powers the servo system and most of the logic, as well as the backlight. The external supply that I added only powers the opamps, the clock, and some of the DAC/clock logic. This way, any noise produced in the servo section is (hopefully) kept out of the DAC and analogue sections.

It sounds like your player is even more mod-able than mine was; maybe you can replace your DAC as well.
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Old 20th July 2003, 10:15 PM   #4
 is offline  Russian Federation
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Hi.
Does anyone has a copy of the service manual or schematic of the decoder and the DAC module for CDX-550 and the datasheets for YM4317 (DF or decoder????) and for YM7141 (DAC IC) ? If so, would you kind enough to send me a copy?

e-mail me: svinyara(at)mail.ru

Sparhawk

May be you know, where is i2s there?

What for there are established 74HC00 (NoAnd) between the dac outpupts and the op-amps, and the analog signal put on one input of 74HC00, and the system clock signal put on other input?
Is it such artful filter?


Thanx

Best regards.
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sorry my wrong English
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Old 21st July 2003, 12:28 AM   #5
 is offline  Russian Federation
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A similar pic from the dac cover.
Attached Images
File Type: jpg ym550.jpg (44.4 KB, 1149 views)
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Old 31st July 2003, 02:56 PM   #6
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Quote:
Originally posted by
Hi.
Does anyone has a copy of the service manual or schematic of the decoder and the DAC module for CDX-550 and the datasheets for YM4317 (DF or decoder????) and for YM7141 (DAC IC) ? If so, would you kind enough to send me a copy?

e-mail me: svinyara(at)mail.ru

Sparhawk

May be you know, where is i2s there?

What for there are established 74HC00 (NoAnd) between the dac outpupts and the op-amps, and the analog signal put on one input of 74HC00, and the system clock signal put on other input?
Is it such artful filter?


Thanx

Best regards.

I don't have the service manual, but I do have photocopies of some parts of the schematic. I don't have a scanner, but if I get a chance to bring them to work and scan them, I'll send them to you.

I'm not sure if there is an i2s signal, or where it might be.

This player has a "1-bit" delta-sigma type dac, which is the reason for the strange looking dac section. I still don't really understand these, but here is a good introduction:

http://www.ee.washington.edu/consele...bit/primer.htm
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Old 31st July 2003, 04:02 PM   #7
grataku is offline grataku  United States
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"it wasn't a great player to begin with...."

Damn right! I owned that player five years ago, when I got a new sony player it was like lifting an heavy blanket from my speaker. I m talking about a night and day difference that even a deaf person would have heard!

I sold that for 20 bucks to a college student, I should have kept it for experimentation purposes and as a bench music source.


"There is only one strange problem... When playing something with near-slience (ie, the very beginning of a quiet classical piece) there is a strange "swishing" noise, that sounds almost like RF interference or something. As soon as a slight audible signal is present (ie, the beginning of the quietest note of the music), the noise disappears. It only seems to be present when the signal level is very near zero. "

Amazing! That's exactly what I noticed as well! I am not kidding. I never understood it, there was no DIYAUDIO back then.
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Old 31st July 2003, 04:51 PM   #8
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Default Noise near zero

I realized that thing in quite a fiew cd players . Currently in an old Philips CD630 it is the same . I think of it as a poor mechanism-laser-decoding quality and not at receiver/DA stages.
Also a bad power supply for laser can be the cause.I would like to investigate.
BTW , the Sony in my experience never produced that noise.
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Old 31st July 2003, 05:15 PM   #9
A 8 is offline A 8  Sweden
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sounds like a one bit dac with possible clock issues.
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Old 31st July 2003, 05:30 PM   #10
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sparhawk great work on that cd player!!!

the swishing noise is inherent in alot of older cd players because the lasor is trying to track the data on the disk and the 2X oversampling reverted to many problems when there was no data present
I hear the same thing with the older player I have almost like when my cd-rom is looking for data on my computer


DIRT
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