Capacitor voltage rating

[triode]

Hi

Would it be too risky to use 400VDC rated cap for parafeed coupling cap?
The schematic says 388V on B+ but would the voltage jump higher when the amp turned on?

Thanks

[Paul Birkeland]

PJ recommends 630V for that position, though you could certainly go higher!

[Paul Joppa]

Yes, the voltage jumps higher at startup - up to 500v, if the power line is a little above average.  It jumps even higher if there are subsonic transient signals at the input. The voltage rating is a loose approximation in any case; lower voltage gives a longer life. I prefer to not exceed 80% of rated voltage when possible, at least for polypropylene or electrolytic caps. (Mylar needs more margin - IIRC 50% is safer.)

[triode]

Thanks PB and PJ
I guess I should steer away from expensive 400V

[Brissie]

Hi,
I was also looking at upgrading the parafeed cap in my MonAmours.
The standard 12uf is not that easy to find so I was wondering if it is better to get 10uf or 15uf in this position?
I suppose it won't make much of a difference but maybe there is a preference.
Thanks, Steve.

[Paul Joppa]

It is unlikely to make enough difference to be audible. If it were me, I would go for the 10uF.

Have you run the stock cap long enough (100 hours minimum) to be sure it has been broken in? That's advisable if you wish to compare sonic virtues.

[Ivan303]

Using a pair of horn sub whose amp is running off the second output of a preamp below 100Hz so really don't need (or want) anything below 50Hz going to or coming out of the Monamoures.

Could I safely lower the parafeed cap to 5uF or lower.

Lots of nice film caps at 650V or even 1000V out there in lower values.

[Paul Birkeland]

You could lower the value of the interstage coupling cap, 0.01uF would put you -3dB at 50Hz. I suspect if you decreased the value of the parallel feed cap by a factor of ten, you'd see similar results, though the parallel feed output stage interacts a bit with the reactance of what it drives, so this may be a good time to buy 10 different values of Solen caps from 1 to 10uF and just tack each one in to see what yields the best results, then grab your preferred fancy cap with that information nailed down.

[Ivan303]

You could lower the value of the interstage coupling cap, 0.01uF would put you -3dB at 50Hz. I suspect if you decreased the value of the parallel feed cap by a factor of ten, you'd see similar results, though the parallel feed output stage interacts a bit with the reactance of what it drives, so this may be a good time to buy 10 different values of Solen caps from 1 to 10uF and just tack each one in to see what yields the best results, then grab your preferred fancy cap with that information nailed down.

Thanks!
 
Best results by measurement  (I have Home EQ Wizard and a calibrated mic) or should I listen for something bad if the cap is too small?

The interstage coupling cap is already downsized a bit and is a Solen Teflon (green) at .047uf as Edgar Horns don't begin to go that low.  :-(

 One of the few upgrades I've done where there was a noticeable improvement.  OK, EML Mesh 2A3s are really good as well.  :-)

I really don't need to go that low as my preamp as two outputs and they are off a cathode follower so one has a big series cap (2uf?) that runs to the sub amp while the other has a .47 uf to go directly to the MonAmours.

Decent 2uF and 3uF 650V film caps are out there for 'reasonable' prices (cheaper than the green Solen teflon .047uf) so that would likely do it as far as a parafeed cap goes.

Not looking to cause and bad parafeed reactions just to save a buck or two.  There is NOTHING wrong of with the sound of the MonAmours as the are.

Have a Happy New Year!