Sony Electret headphones

Just paid 1 euro for a pair of Sony ECR-400 headphones. There is no power supply with them, does anyone have ANY info on these cans or the missing power supply (schematic).
In eternal hope Steve

Had them apart. Only two wires to each side. I they are true electret then I guess they dont need any polarizing voltage but they will be very high impedance. Does anyone know how these things are normally driven. I thought about a pair of 50ohm/ 50K mic trannys used backwards with a cap to couple them....
Steve

Apparantly, it originally came with a "box": http://staxt2.hp.infoseek.co.jp/stax8.htm

These "passive" boxes most often rectifies and voltage-doubles a part of input signal to generate the needed polarisation voltage. This is probably also why they need to be driven from a power amplifier output.

Don't expect too much from the mic-input transformers - they will not be able to deliver the signal levels you will need to use these headphones.

To test them, you could try maybe a 220:5V psu transformer. Take care - and limit current, or you will blow your amplifier and possibly the headphones as well..

There's good info on electrostatic headphones several places on the net..

Jakob E.

Jakob-

If part of the input signal was doubled and rectified then surely on a quiet passage you would have no voltage to power the headphones. Headwize.com's site is down today, bet the answer is in there, cant find any circuits anywhere else on the net.
Steve

Steve,

Naa.. There is no actual current draw - other than for the initial charging of the "capacitor".

I'm pretty sure this is how my Stax's works..

Jakob E.

Use a tube output transformer backward. Try 6K or 10K CT to 16Ω, at least 8 watts. Wire the 16 side through a 4Ω resistor to a 5W-50W 8Ω speaker amplifier.

The impedance really does dip to around 10K at the top of the audio band, and the reactive power can be well over 1 Watt. You can't drive these with headphone jacks. You need a loudspeaker amp. And in tests of one pair with the official box, a 20W amp was hardly overkill.

Aaaaaaagh, of course.Silly me, I was thinking of making a dedicated amp maybe with tubes so a polarising voltage would be no problem. A 30meg resistor from a 250v rail and leave it to find its own level. So you think they need a good voltage swing to drive them? what 30v 50v 100v. How about a 100v line transformer backwards. That would be audio grade too, would need a cap to isolate the polarizing voltage.
Steve

PRR,

Using your idea of a tube o/p transformer backwards, would that be directly connected to the phones or with a blocking cap. I am thinking of the polarizing voltage being shunted down by the transformer.

Steve

> making a dedicated amp maybe with tubes

For 1-buck headphones? Make darn sure they work GOOD before you go insane building an amp. Electrostats are not, in my opinion, that wonderful. And the electrets are generally considered inferior. And I know the electrets can be ruined with test-tones.

> So you think they need a good voltage swing to drive them? what 30v 50v 100v

400V RMS for many STAX, 800V RMS for the better-grade STAX. Sony did not break any laws of physics so they will be similar.

You are over-thinking the polarization. These are 2-wire electrets! You can't short the polarization.

[quote author="PRR"]> making a dedicated amp maybe with tubes

For 1-buck headphones? Make darn sure they work GOOD before you go insane building an amp. Electrostats are not, in my opinion, that wonderful. And the electrets are generally considered inferior. And I know the electrets can be ruined with test-tones.

> So you think they need a good voltage swing to drive them? what 30v 50v 100v

400V RMS for many STAX, 800V RMS for the better-grade STAX. Sony did not break any laws of physics so they will be similar.

You are over-thinking the polarization. These are 2-wire electrets! You can't short the polarization.[/quote]

Would a Stax SRD-7 and the Sony ECR-400 be compatible?
The connectors are different, could be for other than propritary reasons.
Normal headphones have normal connectors because it is hard to blow up earth connecting a set to some amp. But the electrostatics may not be that fun to connect between brands.

My Sony ECR-400 was bought in the past two weeks and just arrived this evening. Sounds great. Did cost me 42 GBP plus shipping. But they were complete, 1x Headphones + 1x Amplifier (called Headphone Adapter).

There are DIY projects on the web for Electrostatic designs but I would read some of the litterature on the subject before venturing into practical projects.

Over on http://www.audiocircuit.com/ you click on
Headphones, Electrostaic, Projects and also EPH-AR, for a projects with nice pictures.

Mikkel

Hi Mikkel,

Welcome to The Lab..!

Jakob E.