Marantz CD63 & CD67 mods list - Page 1842 - diyAudio
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Old 12th September 2012, 08:49 PM   #18411
mcd99uk is offline mcd99uk  United Kingdom
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Been amassing parts. Now have 5 9v transformer, loads of caps and regulators etc... Surgery will commence soon...

One question, how do you go about putting two regulators on the decoder chip. Is it just a case of making sure that the analog and digital pins get voltages that are closely matched?

Paul
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Old 12th September 2012, 09:22 PM   #18412
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Yes, but they are not too critical at all . Once running say 0.2V difference will be fine.

What is often more sensitive is keeping multiple supply rails to start-up at a similar rate - so use similar caps on each reg.

if you are worried, use a pair of diodes in anti-parallel connected between your two new supplies. These will ensure that neither rail can ever be more than about 0.6v away from the other, but once both regs are running the diodes entirely drop-out of the circuit and have no effect on regulation.

This trick works anywhere else that might be sensitive, esp. for multiple regs on the NPC dac (and some others which can behave oddly if the various rails start-up at different rates, like Crystal Semi CS4390 and later...)

Last edited by martin clark; 12th September 2012 at 09:25 PM.
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Old 13th September 2012, 12:11 PM   #18413
Puffin is online now Puffin  United Kingdom
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Is grounding the crystal a worthwhile tweak to do, or only if you do the other mods suggested by Acoustica?

acoustica.org.uk: modifying the Marantz CD63, part 1
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Old 13th September 2012, 04:15 PM   #18414
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Hi,
What watt Resistors I have to for these positions -> R659/660 and R661/R662?

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Badri
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Old 13th September 2012, 05:04 PM   #18415
RCruz is offline RCruz  Switzerland
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Quote:
Originally Posted by martin clark View Post
Yes, but they are not too critical at all . Once running say 0.2V difference will be fine.

What is often more sensitive is keeping multiple supply rails to start-up at a similar rate - so use similar caps on each reg.

if you are worried, use a pair of diodes in anti-parallel connected between your two new supplies. These will ensure that neither rail can ever be more than about 0.6v away from the other, but once both regs are running the diodes entirely drop-out of the circuit and have no effect on regulation.

This trick works anywhere else that might be sensitive, esp. for multiple regs on the NPC dac (and some others which can behave oddly if the various rails start-up at different rates, like Crystal Semi CS4390 and later...)
Super cool tip... thank you Clark
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Old 13th September 2012, 05:16 PM   #18416
mcd99uk is offline mcd99uk  United Kingdom
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Have to agree, Martin's tip is an elegant solution. The only reservation I have is that it gives a potential path for noise to propogate between the supplies. Or is it a case of using a low end diode, like a 1N400X, which may not be able to pass such noise?
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Old 14th September 2012, 08:20 PM   #18417
RCruz is offline RCruz  Switzerland
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Well I never had any issues with my multireg'd 53 but I believe this is really a good solution if someone gets into this kind of trouble.

Also as we are using the diodes after the regs... noise should be minimal there.

I even use a zener to "level" startup voltages in my shunts and after the voltages rise enough the diode "shuts down" and there is no interference.
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Old 14th September 2012, 08:40 PM   #18418
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Yes, it's only really a fix if you need it. I don't much like the idea of cross-connecting regulated supplies either.

Adding a small resistor in series with such a diode pair would likely do all that is needed; say 2R2 - 4R7. Example using default regs like the LM317 at low output currents (the worst case): since the output impedance is 0.05ohms or less across the audio band, with 4R7 connected to another supply crosstalk is inherently limited to -40dB max, or 1/100th the change on the other supply, because between the dac supply pins is then a C-R-C filter formed by the local decoupling caps. So any effect is likely well into the noise floor of the actual audio output.

Thinking out-loud though, using even more series R improves this, but the limit will be the voltage drop appearing across it if needed to limit that start-up differential voltage. 10 or even 22ohms here is probably workable for typical CMOS dacs though, thanks to the low current demand. I must add I've not tested these values, but it looks right on paper.

(None of this is necessarily relevant to the CD63/67, just a general thought. I never had a problem with separating-out regs to the 63's dac or decoder supplies - at all.)

Last edited by martin clark; 14th September 2012 at 08:48 PM.
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Old 14th September 2012, 08:46 PM   #18419
RCruz is offline RCruz  Switzerland
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I use ten separated TX and eleven different regs on the 53 and never had startup issues also... but it is a very good idea if a problem arises. One couls even add a timer + relay to disconect the diodes after everything settles down
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Old 15th September 2012, 03:41 AM   #18420
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Hi,
I am in the process of modding a fresh cd53. Are all resistors are 1/4watt? May be a noob question but I dont know.

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Badri
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