The Headcase Stax thread

[spritzer]

I don't think Warwick are doing so hot these days... 

I snapped this in Selfridges on Oxfordstreet yesterday and I might have been tempted as an insane collector if I didn't already own one of those piece of shit amps.  Well that and it sounds like shit... there is that issue too. 

Edited November 29 by spritzer

[mikeymad]

65% off?! - they must have low overhead.... 

[spritzer]

That's what I was thinking, the margins must be insane on these as its a store not really known for any good deals.  

Now I'm thinking if I did a deep dive on this earlier in the year when I got a set dirt cheap... or I just sent all of that to Kevin?    Well first off input, bunch of parts here USB xmos, A/D etc:

All of this leads to a pair of ESS 9028 dacs:

Not the best picture but that looks a lot like filtering to try and make up for the utterly retarded driver design:

Finally output stage... yeah this is pretty dire.  Remember this thing is 4k$... 

Now how does this thing actually work?  The clue is those two gray caps and the wires going to the headphone plug.  450V B+ on  a single rail so shall we say a maximum voltage swing of ~840Vppss and the bias is clearly 2000V.  The bias is superimposed on the audio signal after the output caps and then we have the grounded shield, that's it.  These are even simpler than what Koss were doing in the 60's where the back stator on the ESP6 (and 7, 8 and 9) are grounded but otherwise normal electrostatics. 

[Craig Sawyers]

I had a pair of ESP6's in the mid 70's. Those were the self energized ones with a transformer in each earcup? I remember that they were not light. Sounded good as I recall, but listening time was limited by the head crushing weight and the sweaty fluid filled earcups.

[spritzer]

Yup, transformer in each cut and weight is close to 1kg.  I rebuilt one 15 years ago and recently got the urge to mass with one again.  700V bias (well cut off so probably lower in practice) and I'm going to put new earpads and a headband on them.