Philips CD650 mods

[SimontY]

Hi all,

Nobody seems to have written an awful lot about this decent old (1986 design) Philips model, so I will.

I bought a CD650 via Ebay for about £10 or so a while back. I can't remember why I bought it but as my main cd player is out of action at the moment I've been listening to it.

It uses the famous TDA1541 DAC and has the immediately familiar character of solid, chunky, warm goodness heard in other TDA1541 designs. The only problem is a lack of detail, a slightly woolly bass and very poor treble.

I popped the lid last night and had a look inside. In particular I noticed:

* TDA1541 PSU lines are decoupled by tiny 47u caps
* Op-amps are NE5532
* Op-amp psu caps are more of the same 47u Nichicon poop
* Signal goes through electrolytics and muting transistors
* The chassis is plastic

I warmed my iron, cleaned off some of the dust and had an initial tinker.

I made the following changes:

* -15V decoupling cap on DAC changed to 2200uF / 25V Panasonic FC
* -5V decoupling cap on DAC changed to 4700uF / 6V Pana FC
* +5V decoupling cap on DAC changed to 220uF / 35V Elna Cerafine
* DC blocking / signal caps cut out and shorted with a solder blob

This has livened the player up a lot. The bass is tighter, the treble less dirty and veiled, imaging is better and the soundstage is more layered. The good qualities of the player don't appear to have been adversely affected.

More to come soon.

Simon

[SimontY]

The to-do list after having a little look at it and chat with others about models using the same or similar chipset:

* replace opamps with DIP sockets (probably to use LM4562 or similar)
* change opamp caps to Rubycon ZA, BG standard or similar
* shield the processor and digital filter chips (maybe others?)
* feed the digital filter/decoder chip with its own regulator
* change PSU diodes to schottky type
* place player on wooden cones and install damping
* install Sercal C1 clock in place of 11.2Mhz crystal
* renew most electrolytics

To take it all the way:

* Sercal S Power regulators everwhere
* consider NOS connection and/or chip stacking?!
* new power supplies with transformers
* S1 or S2 (single or double crown) DAC

I don't think I'll take this one too far as the thing's quite ugly and plastic. A more worthy TDA1541 player is the Marantz CD94 in my opinion. Modified, those are terrific. Not terrible as standard, and not very ugly.

Simon

[philpoole]

Hi Simon,

Welcome to the world of the TDA1541A
The NOS mod will alter the sound, but you might also do well if you keep the SAA7220, improve its power rail decoupling, and reclock the I2S before it enters the DAC. 4xOS is not a bad thing, per se, its just the chip that does it puta lot of jitter in the signal, and noise on the rails.

My 1541 has currently a simple IV (the single opamp IV with just a resistor and capacitor in the feedabck path as in the 1541 datasheet - don't skimp on that feedback cap, some faster opamps oscillate without it) followed by the passive filter Ray used on his CD63. I did try a discrete IV stage, but I'm yet to get it working. As far as I'm aware, the discrete IV for the CD63 won't work as the output of that DAC is voltage not current based.

There's also stuff you can do to alter the voltage levels of the I2S into the 1541, to reduce noise going into it

You'll enjoy the 1541, its a very different DAC to what you're used to. I found it was easy to get a good sound out of it, with relatively little effort.
Improved regulation will help, and many believe increasing the decoupling caps for the most significant bits (can't remember the pins) to about 1 or 2 uF.

Oh, and, I don't think you can easily stack them. They all need their own decoupling capacitors.

AND, might be worth searching for DEM reclocking. I tried it, and didn't have much luck, but some have had great results.

There's quite a few threads about on this (one hilarious one where I fail to understand simple electronics trying to go 4x OS) so have a search.

Send us some photos of what you've done.

Cheers,
Phil

[SimontY]

Thanks Phil,

Did we meet in Chesterfield last July? You've given me plenty to think about, thanks. I don't want to do anything too extravagant just yet, but a few simple mods first and see how it sings.

Some wooden cones arrived in the post from Hong Kong today - lovely! I'll get those put on tonight and I'll rustle up some pics as they're the fun part.

Cheers
Simon

[philpoole]

You did indeed meet me in Chesterfield.
I also did a bit of CD63 modding, until it died and so I moved on to a homebrew TDA1541A DAC.

[SimontY]

Originally posted by philpoole
You did indeed meet me in Chesterfield.
I also did a bit of CD63 modding, until it died and so I moved on to a homebrew TDA1541A DAC.

I thought the name was familiar. I keep killing my CD63.. but a good friend keeps fixing it. The CD650 has opened my eyes to a more appealing sonic character so I want to see how it can be taken further. Detail levels are currently a pathetic joke next to the HEAVILY modified CD63.

Any links to your TDA1541 project? I'd be very interested in reading about it!

Thanks,
Simon

[tubee]

I am busy to mod a CD880. Have been working a lot with CD304MK2, CD660 and CD640. The last two have the same decoderboard as your 650, the 650 has a sort of subpcb for a uController i think.

What i want to say is the CD640/50/60 have a good pcb layout in special the gnd screening is done properly. The CD880 has a more open gnd screen (you can shine a light through the board) i have a lot of interference problems now to solve after a kwak clock install. The 880 has an epoxy board, the 6## series paper-filled, and careful soldering is required

[SimontY]

Thanks for the info Tubee. I have a service manual for the CD660 I think, it appears to look quite similar to my CD650.

Most of what I'm doing won't need a manual too much as it's quite simple work, and I've read that the manual doesn't match up to reality very well!

Simon

[tubee]

Yes the philipses can be allmost all modded with only one 1541 based schematic. Preferably on paper to peek on it through the soldering fumes

[philpoole]

Good point Tubee, they are almost all the same as in the TDA1541A datasheet. Probably worth downloading that. It should be on datasheetarchive.com.