So I picked up a pair of Stax SR-40 on ebay.  I know they're electret and do not require a charge to be fed to them.  They have the standard 5 pin stax plug it looks like.  Can I use these with the current feedback electrostatic amp?

yes

be careful with the volume

Excellent...  Do I have to wire the jack differently?

You should be able to use it with any electrostatic amp.  Dr. Gilmore has suggested that you keep the level down in electret phones to below 200 volts, but that is still pretty loud.  The jack is wired exactly the same as with the standard Stax phones, but the bias pin is not connected to anything.

Edited April 25, 20179 yr by JimL

got it...  Now I must build it.

These are handy to keep around for testing amps as they indeed don't need a bias supply.  Just hook up a channel and you are good to go. 

That's what I was thinking when I saw them come up.  Since I'm going to start building the electrostat stuff I needed a set of test cans.  I just couldn't see hooking up a new pair of stax only to blow them up.  Definitely easier to swallow $70 vs $400 or more

There are those who would aver that your $70 earspeakers sound better than some of those uber$400 ones......

makes me regret not getting a Current Feedback Amp set in the last GB. 

shouldn't be horridly expensive to get a run made for the cfa, considering you need 4 an amplifier

The SR-40 is an electric model and needs no bias voltage. Since the one you sawing comes with the SRD-4, all you would need is a power amp/integrated amp/receiver and then you would hook up the SRD-4 to speaker outputs. The SR-40 would too work with any of the Stax amps. I have SR-80 and they have a very nice midrange, but are missing in bass and treble compared to best gaming headsets. I wouldn't pay more than $75 for them, and only if in excellent condition.