Stax bias circuit

[dtroise]

Hi

This is my first post, I would appreciate opinions on why I have this issue.

The link below is the Stax energizer using Lundahl PP TX that I built with a pro-bias circuit. The only change was I didn't use the Lundahl power transformer or the oil caps, I used a magnetically shielded toroid TX mounted on top of the cabinet and poly caps, I also installed the 4m700k resistor after the last cap.

The bias volts are 575 d/c, here is the issue, when using my new 500 MK 11 headphones there is a plopping sound that starts in the left channel and then in the R channel, think of a dripping faucet in a cup of water, the L channel is about 60 cycles per minute and the R is less than half of that. The music plays and sounds wonderful and when turning the volume off the noise doesn't change.

When I turn the power off and let it play with the stored energy the sound is phenomenal.

I have two more pro-bias amps SRD 7 MK 11 and a 252 this does not happen with them. The other strange thing is that when I plug in my Lamda Pros there is no noise only crystal-clear music.

I believe it is safe to say that it is not the headphones and is something to do with the bias circuit picking up a 60-cycle noise from the electrical supply, however, this is a noise that I have never heard in audio. The electrical source for my audio equipment is fed from a distribution panel with an isolated earth ground star system and balanced isolation TX, the neutral is not tied to the earth.

Any opinions would be appreciated as I am stumped, thanks in advance, Donald.

the STAX Transformer www.audiodesign.com/my/stax_transf.html

 

[spritzer]

This bias supply will blow up your headphones very quickly so don't use it.  Everything is wrong with it so I'd completely scrap it

[dtroise]

WOW! Thanks, Spritzer

I was wondering if it was a correct circuit. Do you have any idea as to why it causes that dripping noise, is it the capacitor design? Would it be a problem to use the transformer wired as 250 volts in a standard Stax doubler circuit?