Marantz CD42 repair and mods

[SimontY]

Hi,

Someone kindly gave me a Marantz CD42, which has a broken drawer gear and a mediocre but not terrible sound quality.

For the fun of it I thought I'd modify and sell it on.

The player uses the SAA7310 decoder, SAA7350 DAC fed from the SM5840 digital filter. I read in another thread that this IC is used to up-sample the signal to 20bits. The disc mechanism is a CDM4.

Output is the typical NE5532 running on +-15V. Most caps are tiny 47uF/25V parts. DC blocking electrolytics and SMT muting transistors are employed.

My aim was to get a very substantial improvement from mainly unremarkable parts.

I've spent the evening with the soldering iron and appear to have achieved that goal.

Simon

[SimontY]

I did the obvious and tackled the cheap decoupling capacitors first:

* PCF3523P (unknown IC) [2673] - 68uF os-con
* MN4264P (RAM chip I think) [2602] - 68uF os-con
* X24C16P (might not be important but why not..) [2612] - 68uF os-con
* SAA7350 (DAC pin 12 / VDDD) [2615] - 68uF os-con
* SAA7350 (DAC pin 18 / VDDAR) [2819] - 100uF Elna Cerafine
* SAA7350 (DAC pin 39 / VDDAL) [2818] - 100uF Elna Cerafine
* SM5840 (digital filter pin 14 / VDD) [2611] - 68uF os-con

I also dealt with the basic 5V feed:

* 10V smoothing cap [2678] - 4700uF / 25V Panasonic FC (was a small 3300uF cap)
* 5V regulator output cap [2680] - 4700uF / 6.3V Panasonic FC (replaced a tiny cap)

And a couple of changes to the output section:

* Op-amps swapped for Burr Brown OPA2132PA [6611] & [6612]
* DC blockers [2665] & [2666] were shorted out with a wire link

Unfortunately one channel gives 125mV (other just 23mV) of DC offset so I may put some caps back in there.

[SimontY]

The sound has opened up quite nicely and now has a fairly sweet midband. Detail has increased and the treble isn't too shabby now. Pretty good sound for an evening's work and parts that I had lying around.

I think I would need to put some of those chips on separate regulators to get much more detail from this machine now, as too many share the same voltage rail. Some cheap 11.2MHz clock option appeals too.

I'm also going to try some different op-amp decoupling caps. Instead of the usual favourites (Black Gate or Rubycon ZA) I'm going to try some cheap 1000uF jobs. The standard caps are 1000uF but TINY!

It's worth noting just how nice this machine is to work on. The bottom panel unscrews and you have near full access to the PCB's underside. No risky PCB removal! Easy to put the player on its side and get at it from top and bottom - ideal!

Also, the player is rather tall and if desired I think there's room for additional transformers on top of the funny plastic cage.

Be aware that you need a small torx driver for the bottom screws.

Simon

[SimontY]

It looks like a replacement for the dodgy cog can be sourced on Ebay, e.g.:

Philips CDM4 CDM-4 cd player tray gear with belt on eBay (end time 22-Oct-09 20:27:11 BST)

I just need to check if that's universal to all CDM4 mechs, as I realise there are various types.

[SimontY]

I ordered that cog from the Ebay seller, and had a little listen after leaving the player on repeat all day whilst I was at work.

The sound is very smooth and enjoyable with a sweet midrange.

I've now put 2 x 7805 on the DAC analogue left and right 5 volt supplies. I used the plastic cross-bracing to screw the regulators in place, as this looks tidy and is secure.

It's too early to say what this modification has done but a quick listen suggests things have opened up a little more.

edit: there's also more impact and the sound is more interesting, very good.

Simon

[SimontY]

My next mod is inspired by this web page:
CD-player mods

That person removed the 39pF ceramics from after the DAC (2622, 2623, 2624 & 2625) and said he got a rather large improvement in SQ.

I will do that one tomorrow I think, it's getting late.

Simon

[UV101]

Ah ha! Here you are!

Yep that cog is a common problem on the CDM 4/19 deck. I got mine from the same place. It certainly fits a Marant CD50 and philips cd850. The chassis are almost identical for 40,42,50,52..... and CD850MkII so you'll be fine!

I didn't do an awfull lot to my player by my standards today but then I didn't know as much!

1st in was a Trichord Clock 4. This made a huge difference. Much more than in any other player where I've upgraded the clock (until I put the C2 in my CD960!). No PSU mods and the clock was just fed from the main +12v reg. A couple of years later, in went AD825 (from memory!) on Brown Dog adapters. This cleaned the sound up again but wasn't a massive change by comparrison. Next came LM4562's and a play with ZA's and SilmicII's on the op amp decoupling. These op amps and caps lifted the player again.

There are a few old photo's on the old pages of my website here. I had planned more but never got round to it.

Then I started on the 63's and put it back as std poss to sell!

I'd def be interested in what you can acheive compared to the other players we have.

[SimontY]

Hi Ian,

It sounds like you covered some of the key basics on your CD850. I read in another thread that a good clock makes a huge difference on these DAC chips. I'm in two minds about whether to install one on this as I'm going to chuck it on Ebay and hope it sells. If buyers can't hear how amazing it is, it won't command decent money, so it might as well be good value with cheap modifications. It's really not bad now actually!

Another thing I've considered is transformer-coupled outputs as the SAA7350 has built-in op-amps so should be happy driving this kind of output, which will do away with the standard external op-amps and filtering. I may try it with some spare 120VAC psu transformers I have lying around.

Simon

[Chivvyp]

Hi,

As a cheaper alternative to a cheap clock.....

I've found good improvements on some players just by disconnecting the clock out feed from the chip to the std crystal and feeding a clean isolated power supply to the crystal instead. I guess by the time the standard 5v feed (or whatever is used) is routed through and out of the chip it's pretty polluted. With a cheap lm317 reg you get quite an improvement for next to nothing.

Regards

Pete

[martin clark]

The SAA7350 is a good dac. To get even more out of it, ensure that the internal voltage reference pins (24, 33) are decoupled well; depending on what marantz have used here, try bumping-up the value to 10-47uF and ensure the cap has good HF properties (no cheapo electrolytics)