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CR-800 Ph-oh-no!

cleverdick

cleverdick

Active Member
In my quest to cure a noisy RIAA stage, I did discover a fractured joint at D401 on the so-called EQ Sheet. (PITA to get to, mind!) Now, in this case, somebody before me had fitted a 330R, 5W resistor in the supply line - non-original and not shown on the schematic. Off-load the supply does measure 51V, as it should. (Haven't measured on-load, nor do I know what current the phono stage draws.) Now, assuming a perfect voltage source and a token 0.6V drop across D401, this leaves C421 sitting at a theoretical 50.4V. Given that it's a 50V rated cap, this makes me a little uneasy. I'm tempted to up to 63V - but I'd like to know if anyone else has had problems in this area. No sign of bulging or distress.
 
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Your reasoning makes perfect sense; go with a 63V or 80V rated cap.
Yamaha had to cut a lot of money in making those CR series to maintain profitibility; whilst still providing decent circuitry they did put in a lot of borderline rated components to scrape every cent from the huge part count.
Many CR units from that era suffer from this.
 
I have 51.5V on that 50V cap. I have 24.5V on 25V caps on the same board
I already did recapping :(
Well, those original caps worked for 40 years on their limit voltage. I used Panasonic FM which are GP caps rated 3000-5000 hr. Now all those using audio caps on power supply should think twice.
 
What's an 'audio cap' anyway? o_O

In a power supply, the important parameter is ripple rating (not forgetting working voltage, of course), whereas in a decoupling application it's the impedance (quoted at 100kHz).

My go-to ranges are the Rubycon RX30 and ZL/G/H series respectively, although I have nothing against the other premium brands.

Well anyway, I built a cute little RIAA stage, with the same footprint/fixing as the original, but this time running on +12V. Just grappling with a phono hum problem now, revisiting the grounding topology.

PITA to work on, this thing!
 
All now sorted, and phono stage is as quiet as the grave! :jump:

Yamaha had got it a bit wrong, IMO.

PM me if you want the details.
 
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