[Kevinp]

There's a relatively well-known way to multiply AC voltage when rectifying to DC supply - just by using a few capacitors and rectifyer diodes. Has anyone (possibly audiophiles should stop reading at this point) used such a thing in a power amp supply - and if so did it work?

Bit ashamed to ask really, but I happen to have this nice toroidal looking for a use and also this subwoofer which needs a power supply....  :-)

Thanks
Kevin

[ctviggen]

Are you thinking of a diode rectifier?  If so, the basic diode rectifier just takes AC and rectifies the negative portion of the AC waveform.  By adding capacitors (or even a transformer), you get something close to DC. So, if you have 120 volts AC, you'll get 120 volts DC.

[randytsuch]

Are you thinking of a diode rectifier?  If so, the basic diode rectifier just takes AC and rectifies the negative portion of the AC waveform.  By adding capacitors (or even a transformer), you get something close to DC. So, if you have 120 volts AC, you'll get 120 volts DC.

Not quite.
In theory, if you start with 120 VAC, multiply by 1.4, and you end up with 168 VDC.
Normally, you would use a transformer/torroid to step the 120 VAC down to something lower, then rectify the lower voltage through a bridge, then caps, to DC.

Randy

[mgalusha]

Kevin,

I have built a tube amp that used a voltage doubler and it worked well. From what I understand using a voltage doubled power supply can result in much higher ripple. If I remember correctly this was because the voltage doubler operates as a 1/2 wave rectifer. In the amp I built the circuit had very good ripple rejection so this wasn't an issue. It may be OK for a subwoofer as well.  Don't forget the current capability is cut in half.

You might want to download the power supply simulator from Duncan Amps and play around with it on the  virtual bench first.

I did read an article in AudioXpress a couple of years ago that described a full wave voltage doubler. I never built one but it was an interesting design. A quick Google search turned up some info in Tube Cad on fullwave doublers. http://www.tubecad.com/january2000/page14.html

Mike

[ctviggen]

You're right -- forgot about the factor.

[Kevinp]

Thanks for the replies! The voltage doubler that Mike mentioned is exactly what I was talking about, although the matter of rectified DC being higher than the rms value of AC certainly plays its part too.

Thanks Mike, I hadn't considered the likely increase in ripple - good point! Possibly I need to think carefully about that. It may be that this places even more reliance on decent capacitors, and I was already wondering how much I'd really save over a new transformer, given the larger number of capacitors needed in a doubler anyway.  Its encouraging that it worked for your valve amp though, so if I do have a go I'll post any conclusions on the forum for general interest,

cheers
Kevin