Marantz CD43 / 53 / 63 Service Manual

[Zombie]

I believe it's for the common-mode rejection:
"The following pairs of resistors must be matched to a tolerance of ~0.1%:
RD22-RD24
RD26-RD28
R604-R602
RD21-RD23
RD25-RD27
R603-R601

R602 and R601 can be replaced with trim pots to fine-tune the CMR but this is probably not necessary.
In order to adjust, disconnect RD22 RD24 from the DA
converter.
Apply a sine wave to both resistors and adjust R602 for lowest
output (pin 1). Then do the same for RD21 and RD23 adjusting R601."

It made a big difference in sound and especially depth...

[miguel2]

Hi,

Does the CD48 is equal or not to these units in the service manual?

Miguel

[EC8010]

The common-mode signal being digital switching noise etc. I think I'll probably go with matched 0.1%. Adding a trimpot is fiddly, and I'm not sure how much room there is. We shall see.

Next step is to look up the AD825 and LM6172 data sheets. I'm surprised nobody suggested OPA2134.

[Zombie]

I use the 2134 and 2604 and can't make my mind up. Seems to me that the 134 sounds softer and more detailed (contradiction?)
When I get around to it I'll throw in a 627 (I only use the first opamp) on a veroboard and see what happens, but I guess the 12V supply needs to be a cleaner first...

[EC8010]

Originally posted by miguel2
Is the CD48 equivalent to the units in the service manual?

The service manual doesn't mention CD48, but it might only be tiny differences. It's far more likely to be similar than not, so why not download it and compare? If you can read a circuit diagram and trace circuits, the manual should give you enough clues. All these circuits are likely to be pretty similar since they all perform the same function.

[miguel2]

Thanks EC8010, I´ll try that.

Miguel

[Zombie]

Ergo suggested above to use the alst two FET of the HDAM to improve the output capabilities:

Is there any reason for not cutting the trace AFTER RH17/18? What about the "feedback" to QH01/02 from before RH23/24?

While I am at it:
I have read about the 5V noise in the CD63 and now I wonder if anyone out there has any concrete ideas for a post-regulator (or alternative supply) for the 5 and 12V rails? Veroboard would be convinient as I don't have any good lab facilities.

I have been thinking about using the holes for the remote control rca contact on the back as an input for separate supplies. I believe there are voltage input contacts that have a built-in switch that breaks a circuit when a plug is inserted. In this way the on-board rails are used when no plug is inserted and switched off when an out-board supply is connected. What do you think about that arrangement?

Cheers,
Tom

[EC8010]

LM317 (+ve) and LM337 (-ve) are adjustable regulators that produce less noise than most of the fixed regulators. Do a search, and you will find from the manufacturer's data sheets that they are very easy to use, and Veroboard is fine. You can't regulate a 5V rail from another 5V rail, so what you do is to find the existing regulator, and pick up the voltage going into it, and regulate that for your quiet requirement.

[ALW]

Stuff like this works well in the CD63...

http://www.acoustica.org.uk/t/63/63hacks_vreg.html

Andy.

[EC8010]

Well, blow me down with a feather! It's an LM317. It's a minor point, but when tantalum bead capacitors fail, they fail short-circuit. This can often be a cause of smoke. Modern electrolytics are easily as good as tantalums, and they're cheaper and less risky.