Coupling Capacitors Voltage

[Pingu]

Hi All,
Just a thought really.
I’ve noticed that similar OTL head amps although using higher voltage coupling caps initially have had the voltage on theses measured at bellow 90v thus enabling 100v film caps to be used here. This gives a much much greater choice and of course a greatly reduced price too. Yes I know it’s a bit near the caps limit but it’s still within their spec.
So I was wondering if anyone has measured the volts on these capacitors.
Anyone know?
Martin

 

[Paul Birkeland]

They can run a bit higher than that. 

If you abandon the direct coupling on a Crack, the cathode voltage can be made much lower. 

 

[Pingu]

Not about abandoning the coupling caps just increasing value with lower voltage.  ie 220Uf  100volt
It would make lower impedance phones more compatible I think

 

[Paul Birkeland]

It would make lower impedance phones more compatible I think

This is one of the less understood aspects of the Crack.  If 220uF caps would make the Crack work well with low impedance headphones, we would pack the kit with them (it would make it much easier since there are already three 220uF caps in there for the power supply).  The issue is that the Crack has high output impedance, which will lead to bloated, distorted bass with low impedance headphones.  The Crack is also a bit current limited on the output, so there may not be enough power to properly drive low impedance headphones. 

100uf capacitors with 50 ohm headphones will be down 3dB at 30Hz, which isn't the end of the world; the other issues illustrated above will be far more audible.

 

[Pingu]

Thanks for the words of wisdom.
I see why no one has suggested increasing the coupling caps just upgrading them for film caps now.
Thank
Martin