I have for sale a few of these bias boards which can be used to replace the bias supplies in any of the old Stax SRD boxes or used as stand alone units with any transformers you'd like. I've made a few versions of this circuit in the last couple of years for my own use and if I had any spares, sold them here. This latest version is basically the same circuit as the last couple of version but I've added a simple circuit so that LED's can be used as power indicators. This was needed since the wast majority of these boards weren't being used in Stax SRD-7's (the only stock box to have a neon power indicator) but rather with very expensive transformers and dealing with neon bulbs is a bit of a pain.
The basic functions of the circuit are the same as before, universal power input (100V, 117V or 230V all work without any modification) and all the boards can be fitted with a second output at a lower voltage via a voltage divider. They all come fully assembled and with the correct voltage divider resistors for the desired output voltage. This is an addition to the Stax Pro bias output (580VDC) which is always active (though you can just leave it unconnected). The board can also be fitted with a fuse holder but I most often leave them out or have an external fuse as it is by far the highest point on the board and that can cause issues.
As for choice of transformers, no need to stop with the old Stax units as basically any output transformer can be wired up to drive electrostatic headphones. I had one of my boxes at CanJam which had an earlier version of these boards and Lundahl LL1630 transformers (140$ each) and I've used far more expensive transformers then that with great results.
I'm asking 110$ for each which includes the Paypal fees and world wide shipping via the regular post. Tracking is available as an extra but it is very expensive.
