Eros Coupling Cap Voltage Requirement

[Davenportt]

I read in some posts in this forum that 400v rating would be adequate for replacement coupling capacitor in Eros since 600v was supplied because they were at hand.  Would 300v be adequate?   V-Cap teflons only come in 300v at 1.0, which is why I ask.  I know that .47 would be okay to use, but still I'd like to know if the 1.0uf 300v would work?   

Thanks in advance,
David

[Paul Joppa]

During the startup transient, after the power supply comes online but before the shunt regulator pulls the voltage down, there will be a high voltage on the capacitor. No, I have not put it on a recording scope to evaluate exactly what the peak voltage will be, not have I done transient simulations. I just specified a cap I know will be more than adequate (630v rating). But the peak voltage could easily be at least 400 volts. Many caps can withstand a higher voltage for a few moments, sometimes listed as a surge rating. But I would not take the chance unless you are so wealthy that if they are damaged you can throw them away and try something else. How much are 1.0uF V-caps again? Per pair?  :^)

If the cap fails, it is likely to put a high voltage on the output, which might take out downstream components - preamp, power amp, speaker. Count those into the wealth requirement above.  :^)  <<-- some humor intended!

[Davenportt]

Thanks for the information.  Humor duly appreciated.

David

[milosz]

Current schematic shows 1.0 uF  400 volt capacitor- and the kit I recently bought indeed has a 400 volt cap for output coupling.

Paul, I assume that 400 volt cap must be sufficient, since that's what the kits come with now..... surely the Eros kit wouldn't be sold with a part that wasn't quite rated high enough and likely to lead to 200 volts DC on the output......?

[Paul Joppa]

Current schematic shows 1.0 uF  400 volt capacitor- and the kit I recently bought indeed has a 400 volt cap for output coupling.

Paul, I assume that 400 volt cap must be sufficient, since that's what the kits come with now..... surely the Eros kit wouldn't be sold with a part that wasn't quite rated high enough and likely to lead to 200 volts DC on the output......?

Dang, you are right - I was not careful enough. The circuit, which I drew, shows 400v so I must have thought that was adequate when I did the original analysis. The parts list says 630v, which was the basis for my defense of that value. But Doc B. and Eileen make the parts list according to what they actually ship in the initial kits; some parts changes happen according to availablilty (which has been very erratic the last few years). The circuit is more likely to show what I intended in the design phase.

I would still not be comfortable with a 300v part.

[milosz]

Well I have found a pair of NOS Nytronics paper-in-oil  1.0 uF / 400 VDC caps on eBay for not much, so we'll see how they sound.