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

 

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

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?

All of that circuit is wrong so use that transformer and use the Stax circuit as found in the 007t or 717.  The schematic for the 007t is certainly out there.  Also, don't use caps larger than 100nf as that is plenty of storage for a bias circuit.  Stax use 10nf so that works just fine.  1uf or higher is utter madness.  

Ok, thanks again.