Modding a Marantz CD40

[joydivision]

Hi ppl.

Just got myself a CD40 in great condition (with a nice TDA1541A in it), except for the tray loading gear wheel (like usually...). But cheap replacement part is already on its way (thanks, epos!). Now I'm in the process of modding the CDP. (yes, I do have the schematics)
I want to replace the output stage (so to have a better opamp, not too much passive filtering, and no unnecessary components) and build a better regulated supply board for this.
I also started to "recap" the whole board (at least the 'lytics, as they are 16 years old by now...) and want to add a few decoupling caps or change them.
Of course, it'll get new gold plated RCA outputs aswell as some kind of metal shield around the boards of the output stage and it's PSU so to reduce HF interference from the digital circuits.
And last but not least, I will change it to NOS mode.
For now those are all the mods I plan to do. But I am open to every good suggestion, as long as it seems possible (and worthwhile) for me to realize them. I mean, I don't want to do overkill, you see... and I am no EE... lol

I've already done a little search on this forum and also on others, and found some good ideas, but still decided to open a new thread, because I couldn't find answers for everything. So, for a start, here comes the schematic of my planned output stage and it's PSU. I kept the same design as in the original schematic, simply excluding passive filters and unnecessary stuff (like the deemp. circuit). If you see any mistakes in it (hopefully not :rotfl: ) or anything that could be improved easily, please tell me

About the NOS, I found a little schematic explaining it, what they do is:

they connect WSAB, CLAB and DAAB directly to TDA1541. Now I am wondering if it's better to cut off the leads of the SAA7220, or to cut the traces on the PCB...
They also describe a Mute mod, so that without the muting transistors, one won't run into trouble with clicks and pops:
connect pin 23 (MUSB) of SAA7220 to pin 11 (MUTE) of SAA7210. The thing is, I have SAA7310 in my player... schematic says pin 18 is called MUTE (with trace over the word, as to say it's inverting). I suppose it'll work just like the SAA7210, no? Any experience with that?
Any other change recommended for NOS?
Read somewhere about changing the way the clock signal goes... but for now I don't want to build a new clock for it (would be the best, I suppose, but difficult to do), so I think the best is to leave things like they are, right?

In regards of replacing the 14 decoupling caps of TDA1541, is it worth to increase the size, to, let's say, 220nF?

Also, I was wondering if I should implement a simple RC lowpass filter in the last opamp stage... to filter out any rest of HF noise... keeping in mind that I want to do NOS mod... I know I can't get rid of harmonics (as that's the goal with the Digital Filter...), but that's ok... just thinking I'd like to avoid injecting HF noise to my amp


And finally, to simplify things for everyone, what I'm not going to do (too much hassle for too less a difference, and too much cost in a CDP that's not that good afterall...):

I am not going to replace the power supplies of the whole CD player (although I would do a few tweaks to them, if you have any suggestions. They are nothing fancy, but aren't bad either).
I am not going to make any physical alterations to the player (change the case, make it a top loader, change the transport's mounting, clamping or whatso on), because I think it's quite ok as it is...
And I am not going to do any "crazy" stuff like glueing hundreds of cork or whatever strange materials all over the player, or fitting any real "boutique" componentes, etc, I think you see what I mean .

Thanks in advance.

P.S.: if anyone needs the schematics, f.ex. of the PSU of the player, so to suggest mods, I'll post them here. I also can send the whole PDF per e-mail (it's of CD50, which is almost the same as CD40).

[philpoole]

Hi JoyDivision,

Sounds like a fun project.
When you bypass the SAA7220, you might want to remove it and place a socket in. Then, you can run the I2S from the input pins to the output pins of the socket with wire jumpers. That way, you'll be able to use the SAA7220 again some time.
Looking at the output schematic, there's a great big 100uF electrolytic in the signal path. I think that could come out.


Cheers,
Phil

[joydivision]

That is a good suggestion. Also it would mean, I could install a switch or jumpers, making the modes (NOS and OS) changeable, so I could do direct sound comparisons...

Regarding the cap, I want to have a cap there, because I can't be sure today, where I'll connect my cdplayer to, tomorrow... so no dc-coupling here at home
actually I have been using Panasonic FC caps for that purpose lately, in my amp and also in another project, and they sound really good, nothing to complain about.
I guess the value could be different, though... for now I chose the same like it is in the original circuit, probably meant to be ok for quite every possible strange input impedances of the connected device... but sure 10uF would be enough for standard 10k impedances... probably I'll end up with that value

Also, after talking over this project with some other people and reading a bit more, I decided to put in a simple analog filter in the 2nd opamp stage, and also later, I'll afterall will do a clock mod to it... it just won't be the 1st thing to do for me... I'll go step by step and see how the sound evolves

So, updated schematics to come soon.

P.S: any idea if it's important for the opamps to have +-15V, like they do in the original circuit? I know normally it's not, but here, I mean, regarding the I/V conversion? Or is it irrelevant? Because, as you can see in schematic, it's at +-12.5V so that I can use resistors I already have at home...

[philpoole]

A clock will definitely help.
The opamps should be fine running on +/-12.5v.

[tubenut]

Use soft recovery diodes, especially on the anallogue PSU.
For now just dampen the crystal can with a rubber band or grommet.
AND, big improvement, if you keep the filter (7220) then lift the safety resistor on the supply line to it and feed it with its own regulator taken from the raw digital supply. This makes a big difference. Heatsink the reg, the filter draws quite a bit of current.

[joydivision]

OK, so I've been doing some more progress. Updated the schematic of the output section, and also draw a schematic of what I'm planning to do with the digital section. Any comments/suggestions are highly appreciated.

Additionally to having a new clock (from Elso Kwak), it modifies the circuit so that basically it will be switchable between NOS and OS modes, allowing direct A/B comparison (that's my main aim. I've read a lot from both "sides", saw the measurements, etc, but now I want to hear for myself the difference...).
Also, when in OS mode, the DAC get's a direct clock signal (master clock divided by 2). I alwo implemented the MUTE mod. Main question I still have, is: will it be better to use good quality relays (like in my schematic), or something like 74LS157 (data line switcher)?

tubenut:
thanks for the interesting suggestions. I think, that safety resistor you say, is a ferrite bead, or am I wrong? So, what you say is, disconnect that from the main +5V, and connect it to a new +5V regulated supply, with for example a low noise regulator, well filtered, etc... right? I'll try that.

[joydivision]

digital section

[eta_beta_60]

Someone has the service manual or knows where it is possible to find it?
Thanks.
Bye

[joydivision]

Indicate me your email adress and I'll send you the manual of CD50, which I've been using and which is almost 95% the same like CD40.

Btw, regarding the mods, in the meantime I've almost finished them, and the first results have been very good. I've a problem with NOS mode, though. As soon as I find the fault and get the whole thing finished, I'll post a complete report on here, for those who might be interested.

[sondguy]

Hello, I just bought CD40 & want to do some mods to player! I'm very interested in the non & os mods . I want to compare for myself the difference in sound. I would like to have a copy of schematics for the CD50 please. Can you post some pictures when you have finished the mods & don't forget to report sound improvements. Are you going to come of player thru analog jacks or are you going to install a digtial out jack as well? Ronnie