Marantz CD40 output coupling question

[Richard]

Hi all,

Can I run this by you in case I'm missing something before I do it.

See pic below, easy to follow,

The CD amp is shown as NE5532 triangle on left but mine is OPA2604 so please work with that if it is an issue. Output comes off pin 1 and onto coupling cap #2700 100uF. There follows shunt resistor #3675 10K to ground.

That's all I'm interested in; that coupling is very low at 0.2Hz and I want to know if there is a reason or if it can be higher.

Two things crossed my mind,

1) it is there to provide a minimum 10K load to the output amp whether or not the player is connected to a following input.

2) they may have used 100uF cap as it is a bipolar electrolytic and a larger value may sound better.

But what also occurs to me is, how stable is the output amp, does it need coupling at that very low frequency or can I get away with a 10uF film cap which would give a coupling to the 10K load at 1.6Hz? Clearly 1.6Hz is usually enough for good audio but am I missing something?

Thanks

[Richard]

Quick update, Dr John was in touch last night and feels 10uF should be fine but there's only one way to find out. I've already got them so will put them in later and let you know. Any info or thoughts still appreciated

Interestingly, the pcb is actually laid out with positions for 2 electros, presumably for using pairs of polarised caps instead of one bipolar.

[colin.hepburn]

Originally Posted by Richard

Interestingly, the pcb is actually laid out with positions for 2 electros, presumably for using pairs of polarised caps instead of one bipolar.

Hi Richard
Yep my Marantz 52 SE has the same circuit with different op-amps and has two Elna Silmiccaps on the output connected back to back one thing i did was to remove the muting transistors
I was going to mod this player up But now it’s starting to skip so unless it something simply I can fix its not worth it shame I have had this 52SE player from new in 1992 I think

[Richard]

Hi Colin, all,

Yes, I've not seen the CD52 circ but I looked at the muting transistors in the CD40 circ shown above and they aren't in the signal path so left them alone. They only come into play to short the signal to ground when muting for track change etc.

All that's in the path is the 100uF coupling cap #2700 and 100R resistors #3677 and #3679. The resistors, I think, will be there to provide a load when the transistors connect signal to ground so I'll leave them and may try upgrading them later.

So, fitted the 10uF polyprops and no problems at all completely stable and plays great. The sound is very much better. Most noticeable is the lack of grain and harshness. In its place is subtle detail making for a very much sweeter and more detailed sound. Every area is better and this really is a very cheap and easy upgrade from the electros.

Fitting them, below, we can see the reason they aren't there as standard; size and cost. The cost to the sound though is great, imagine using bipolar electros on the output of Phono 3 for example. We wouldn't even consider it, so why use them to couple the entire output of an otherwise reasonable CD player

[colin.hepburn]

Great to see you got it sorted Richard

[Richard]

Cheers Colin, I put the standard CD40 "reference" back in the system today and did some AB switching comparisons to confirm, this one is getting somewhere now, very nice indeed

[david]

Hi Richard,
There's bipolar electrolytics and there's bipolar electrolytics, and there's polyprops and polyprops. My DAC gives me a choice of Mundorf polyprops or Black Gate N type bipolars and to my ears, I prefer the Black Gates. Stronger, more musical bass and generally a bit more musical. Both types give a delicious mid band.
David

[Richard]

Good point David. In this case I was trying any reasonable polyprop to see if there was a noticable difference to the Muse electros.

The polyprop doesn't seem particularly brighter. A little more air in a good way not tinkly and there is noticably less splitch and sibilence. It resolves more detail at a micro level rather than just a case of being brighter. You can hear into the recording and the result is sweeter and less fatiguing. By comparison the Muse is grainy and loses detail.

There are plenty of caps out there as you say but these have nailed a good improvement. I wouldn't want less detail or any warmer in this instance but can see it might be useful to have this level of quality with a different balance sometimes.

[Richard]

Re the SMD resistors in that output circ,

there are 2 x 2K4 before the output amp, then a 10K shunt and 2 x 100R after the coupling cap.

Does anyone have any exp of swapping these out? They are 3.2mm and specced as 2% so probably cheapo thick films at the mo. Would it be worth going to metalfilms from them? Bulkfoils are expensive.

[bob orbell]

Richard, your pictures have gone, or is it my computer. BOB