Capacitors at 50v vs 25v on replacement in preamp power supply? - Page 2 - diyAudio
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Old 20th July 2013, 02:32 PM   #11
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Quote:
Originally Posted by GoatGuy View Post
Very often, manufacturers choose "by convenience of having fewer parts to stock, with a bit of an over-rating that lets them serve many different purposes interchangeably". Or... "you can buy 100,000 caps at 1000 uF/63V cheaper than 10,000 caps in 5 different values".


GoatGuy

Also think about auto-machining. Far cheaper to have one machine to fit lots of the same cap that lots of different ones.

The simplest way of knowing what voltage to use is to measure the input voltage to the regulators, then allow an extra 10% - just to be on the safe side.
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Old 20th July 2013, 02:55 PM   #12
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Just 10 % ???? What about spikes on the utility power ?

I see I am old fashioned and conservative but then I have to admit my stuff rarely breaks down. Must be a personal thing.
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Old 20th July 2013, 03:17 PM   #13
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Originally Posted by jean-paul View Post
There is something very wrong with that values. I think it is the other way around. You can not have higher voltage after the regs than before them !...

Don't worry about the 1N4003 diodes... While you are at it you can replace them for the better 11DQ10 diodes...

When you get the hang of it you might want to look how well decoupled the rails are locally at the active circuitry. You might win some points there !
You are right, of course. The lower voltages are the later caps in circuit. I was reading the board backwards to the schematic. BTW: the installed electrolytics (c.1992) were all axial and now most of my choices are radial and so 'fit' the space differently, being 'stood up'. So the NKZ-230 are just 4mm too tall. I'll work it out or go with Panny FC or Nichicon FW which can be stood up without hitting the top of the case, even in 2200uF 50v.

For after the regs, I'll use 100uF 50v, which are pretty small, freeing up a bit of space.

I'm with you on the diodes. Have several 11DQ10 Schottky's on my desk for both the preamp and amp.

Yes, once I've gotten the PSU sorted on both the preamp and amp, I'll begin thinking about the main signal circuitry, but that will be a separate project.
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Old 20th July 2013, 03:54 PM   #14
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Originally Posted by jean-paul View Post
Just 10 % ???? What about spikes on the utility power ?

I see I am old fashioned and conservative but then I have to admit my stuff rarely breaks down. Must be a personal thing.

OK I was being conservative. Go for the next highest voltage after adding 10%. In the UK, mains voltage is usually within +/- 10%. Don't forget that the manufacturers also add a tolerance to their products.
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Old 20th July 2013, 03:58 PM   #15
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Originally Posted by brucew268 View Post
You are right, of course. The lower voltages are the later caps in circuit. I was reading the board backwards to the schematic. BTW: the installed electrolytics (c.1992) were all axial and now most of my choices are radial and so 'fit' the space differently, being 'stood up'. So the NKZ-230 are just 4mm too tall. I'll work it out or go with Panny FC or Nichicon FW which can be stood up without hitting the top of the case, even in 2200uF 50v.

For after the regs, I'll use 100uF 50v, which are pretty small, freeing up a bit of space.

I'm with you on the diodes. Have several 11DQ10 Schottky's on my desk for both the preamp and amp.

Yes, once I've gotten the PSU sorted on both the preamp and amp, I'll begin thinking about the main signal circuitry, but that will be a separate project.

If you read the texts of Nelson Pass you will see that Shotkeys are not necessarily the nirvana of diodes in low frequency supplies.
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Old 22nd July 2013, 08:58 AM   #16
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I read the papers of myself and found they are an improvement with this specific diode.

BTW I have a price winning collection of axial high quality (spacelab) caps. If you want some of those please measure the old ones and send me a PM.
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Old 22nd July 2013, 09:56 AM   #17
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Default The old Schottky Snake Oil Rag...

Quote:
Originally Posted by jean-paul View Post
I read the papers of myself and found they are an improvement with this specific diode.

BTW I have a price winning collection of axial high quality (spacelab) caps. If you want some of those please measure the old ones and send me a PM.
Oh please... not more of this snake oil! There are exactly 3 reasons why a diode type may affect the "sound" of a circuit. [1] in an unregulated supply, if their lower forward voltage drop leaves more/higher voltage to drive the signal-path circuits. [2] if the switching transition has lower cross-over ringing, feeding lower hard-to-filter-out RF energy to the amplification stages, and [3] when reverse leakage increases ripple in delivered power, resulting in greater intermodulation distortion of well-balanced (yet still sensitive) amplification stage circuitry.

Note that [1], [2] and [3] are all negated by the use of series-fed high performance voltage regulators. The VR substantially drops the unregulated "reservoir" voltage to a near-constant level; its design specifically also attenuates ripple by at least 80 dB; design-choices that include snubber resistors in turn eliminate RF cross-over ringing or flyback noise. The use of larger caps both pre-regulator and post-regulator further drop feed-through RF, HF and LF noise by another 30 to 50+ dB.

So ... ANY "competent" diode will suffice. Specifically having Schottky-junction devices in THIS circuit can, and will do nothing whatsoever to the regulated, delivered DC voltage. Nothing. Further, there are snubbers in the circuit. This addresses flyback (and forward-charging) HF noise. Modifying the rectifiers might change it a tiny amount but snubbers+regulation sift that out quite effectively.

Don't change the diodes, is my recommendation. Actually - I'm not even sure I'd change the capacitors! Are they leaking? Is the preamp now plagued with audible 60 Hz noise (indicating capacitor failure), or perceptible intermodulation distortion? (indicating post-regulator cap failure) IF NOT ... then remember that "26 years" (as I recall the OP saying) is not a long time for modern capacitors to perform their duty. Yes, for pre-1970s equipment, and especially pre-1960s, 25 years would be entering the danger region. But not after the advent of competent electrolytic cap design in the early 1970s.

Sheesh. Snake oil.

GoatGuy
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Old 22nd July 2013, 03:02 PM   #18
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You're a funny guy. I am pretty much convinced that the caps need replacement after all these years. ESR measurement and a check of their value can confirm that. Of course one can wait till they fail but we would call that too late. Costs are low and life of the device will be prolonged so why not replace them ? Caps have become much better over the years but I would not use types with snake oil electrolyte. They sound awful. The ones with goat milk electrolyte sound much more organic.

After consideration I would not change the diodes as they all sound and measure the same. Any "competent" diode will suffice
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Old 22nd July 2013, 04:15 PM   #19
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OK jean-paul.

Change the caps. Maybe every 5 years, just to be sure. And get the yellow-stripe cryogenically treated matched cut-off Schottky diodes too, while you're at it. Don't forget to change out the interconnect wires from copper to solid silver, too! There's a lot of signal loss in untreated copper, Sir Snake says. Maybe replace the rubber feet on the exterior of the cabinet with the soft silicone acoustic isolators. And, perhaps consider replacing the transformer with a custom wound R-core job. Increases the accuracy of power delivery. Rhodium plated plugs, single-crystal power cords, and platinum-rhodium plated jacks. They're easy to replace, and look so much better.

Yes ... its funny. Snake oil usually is, when exposed.

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Old 22nd July 2013, 11:36 PM   #20
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Ha ha, you are so funny. Come one, you must know even better ways to ridicule matters that you don't believe. Trolling is the way to go when things go against a belief.

BTW don't know why you put my name in italics but that IS my name, sorry for that. I don't need to choose an internet name or any other camouflage, Goatguy.
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