[Dusty Chalk]

Alright, this might be a totally ridiculous, stupid idea (and perhaps even a repeat -- if someone could find the thread, I'd be grateful, 'cause I looked briefly, but not being sure what key words to look for, found none), but I was wondering if a box could be constructed so that one could listen to their Stax (or other) electrostatic headphones such that they could listen to it with their regular headphone amp.

Here's a little more detail about my idea: the cords to electrostatic headphones basically consist of stereo sets of two types of current -- one is the regular signal, and the other is the "power". Now, the idea would be that the regular signal would be a pass-through to a jack that one could plug into a "regular" (dynamic) heaphone amp. The other would be the same as the "power" wires from an electrostatic headphone amp only, perhaps with a load across the signal wires (for example, the chintzy little amp that comes with the Baby Orpheus). Better would be to construct such a box so that the part of the electrostatic amp that amplifies the signal isn't there, so that that power is not wasted.

Thoughts? Perhaps I should move this to DIY?

 

[Sovkiller]

Look like a challenge for Dr. Gilmore to me.....

 

[thomas]

Disclaimer- I've never actually seen a set of electrostatic headphones in my life, so my description might not be completely accurate...



I don't think your descriptions of the cables is correct, AFAIK there's no way to send power on one set of wires and a signal on the other, and combine them together in a passive componenet like a headphone- only an active device like an amplifier can perform that function.

I believe the extra set of wires in electrostatic headphones is used to set a bias voltage across the driver (ie create the electric field by which the diaphragm is attracted/repulsed, analogous to the magnet in a dynamic headphone), and actually carry no current/power...Electret headphones, which work in the same principal as electrostatics, don't require the bias voltage because they have polarized electrets which create the electric field

The actual amplifiers used to drive electrostatic and dynamic headphones are also very different, owing to the different means by which the headphones create sound. electrodynamic headphones use magnetic forces, which are proprortional to current while electrostatic headphones use electrostatic forces, which are proportional to voltage...So dynamic headphones (and amplifiers designed to drive them) use very low voltages (~1V) and high currents (several mA) while electrostatic headphones use extremely high voltages (several hundred V) and extremely small currents...

So a dynamic headphone amp wouln't work with an electrostatic headphone, or vica versa...(though maybe a big 1000watt poweramp could work with electrostatics)

 

[Swampwalker]

Thomas- you are modest as you are knowledgeable. However, you can use a conventional amp with Stax 'stats if you use an energizer unit rather than a Stax or other amp. This supplies the biasing voltage for the diaphraghm (280 or 560v!!), while the signal amplification is passed through from your regular (not headphone) amp. Note- an RKV or Moretti or other amp with an impedanzer would work, as would a Microzotl w/o an impedanzer. The Stax energizers accept speaker level inputs from an amp and have a pass-thru with a switch to energize either speakers or Stax. I've used an energizer with some Lambda Pros and the differences between that and a 404/006t combo were subtle (although admittedly, I was using some pretty high quality amps that cost as much or more than the 006t, to drive the energizer).

 

[kevin gilmore]

A number of issues here.

There is a bias pin that puts a space charge on the diaphram. Its
typically580 volts or so and current levels so low that you cannot
measure it.

The stators of which there are 2 per channel require voltage
swings in excess of 200 volts each and in the opposite direction.
i.e. balanced.

So if you don't want to use a stax transformer box, the requirements
on the power amp are quite significant. It must have balanced outputs
and it must be of extremely high power to have enough voltage swing
to drive the headphone.

So for an example a krell fbp700cx power amp which is nominally 700
watts rms per channel into 8 ohms can put out a balanced signal of
about 100 volts rms. And therefore would actually work, but would be
way low in volume.

Older mcintosh stereo tube amps with 600 ohm output taps would
work great. You would need a pair of stereo amps to drive the
headphones. Balanced input only in this case.

Dedicated high voltage amplifiers are the only practical answer unless
you like listening to step up transformers.