Estatron Electrostat Energizer

[Jon L]

https://estatron.com/collections/all

Somebody who studied Head Case is now building and selling a 'stat energizer.  Kind of interesting because it's only $160.  Worth it?

[spritzer]

I have so many questions... why is the max bias 240V and why is there a separate 1uf cap for each channel?  The bias on Pro headphones is shared for both channels... so is this a normal bias only unit?  The specs list a 303 though so I'm confused. 

[Willem Brandsma]

Hello! I'm the guy who designed this thing. It has a max 240V bias because I assumed it would be safer, would provide compatibility with older Stax models, and shouldn't have any downsides aside from reduced sensitivity. There are separate 1uF caps on each channel because each channel has it's own biasing circuit. This was done to eliminate channel imbalance.

The port is a pro-bias socket because I realized that most people won't be using this to drive normal bias headphones, as none are currently manufactured, and I could reduce the complexity of the plug significantly by putting the bracing bolt in the center of it.

I have included a picture of the PCB board for your entertainment. The bias circuits are simple villard voltage doublers with a zeners to stop it from going too high. Whatever the positive voltage swing is the bias will be roughly double that. I can probably convert them to roughly 580V by simply replacing the zeners with higher voltage MOVs.

If you would like to test it yourself I would be more than happy to send one too you. I am also happy to answer any questions you have, and I am very open to criticism.

 

Edited Tuesday at 08:55 AM by Willem Brandsma
Changed picture to one that was oriented correctly.

[spritzer]

Thanks for the post and lots to unpack here.  The issue with using lower bias is less potential on the diaphragm and it has to be compensated to a degree with the drive voltages.  That really doesn't work so it opens up a can of worms with regards to peaks and spikes making it onto the drivers, causing damage.  It's all about balance. 

For me, 1uf caps are also way too big for what is supposed to be a high impedance circuit.  I'd then put a large value resistor between them and a much smaller cap before the ballast to limit energy transfer.  The choice of a Villard voltage doubler puzzles me as it is a terrible circuit with no real redeeming factors while it would cost next to nothing (even less) to use a far better circuit.  I'd be less worried about switching noise in the diodes etc. over what it is a bad circuit.  Smaller caps with cheaper diodes would work much better.  The bias is also summed so any benefits from channel seperation are along gone. 

One the Stax SB units they took took one AC line from each of the channels to grab the highest potential as the impedance of the transformer would minimize any channel cross talk. 

Thanks for the offer but I don't need anymore stuff.    I like the price and some of the ideas here but I'd switch to a better bias supply, maybe even a voltage tripler, with smaller caps and say a 200V limit on the input.