[nightfire]

Anyone here familiar with how electrostatic phones work: would it be possible to take a 100:1 step up transformer and use it on a powerful normal speaker amp?

Would this drive a pair of 'stats, or do they fundamentally work differently?

 

[akira]

Quote:

Originally Posted by nightfire /img/forum/go_quote.gif Anyone here familiar with how electrostatic phones work: would it be possible to take a 100:1 step up transformer and use it on a powerful normal speaker amp? Would this drive a pair of 'stats, or do they fundamentally work differently?

It works.
When building transformer adapter for stax, it is recommended to use transformer 8 ohm: 5k - 10k ohm, so it's app. 1:1000, not 1:100.

And of course you need bias. For pro model, it's 580V.
This link could be useful
http://www.head-fi.org/forums/showthread.php?t=22800

Akira

 

[spritzer]

You could always just buy a Stax adapter on ebay for 50$ and it is designed for this with a built in bias supply. It's easy to build a +580v bias supply for the older models.

 

[nightfire]

Innnnnteresting.

I didn't realize this was possible. I'm gonna find myself a used o2 then. If I can use my F1 clone to drive them with a transformer or adapter, this seems like a no brainer.

Even if it doesn't sound great, it'll be a nice intro to electrostats and I can buy a dedicated amp later.

 

[tyre]

Quote:

When building transformer adapter for stax, it is recommended to use transformer 8 ohm: 5k - 10k ohm, so it's app. 1:1000, not 1:100.

I think that's a little off. The turns ratio of a transformer is determined by taking the square root of the primary impedance divided by the secondary impedance, or the reverse in this case since this is a step-up rather than a step-down transformer.

I've measured the impedance of a pair of transformers pulled from an old energizer. The primary was 2.3 ohms and the secondary was 4500 ohms. So the ratio would be about 1:44 . The transformers were intended for some old electrostats though, so I couldn't say if that would be a sufficient step-up ratio for modern electrostats.

4500 / 2.3 = 1956

square root 1956 = 44

I also tried connecting the transformers up to an amp which was connected to my soundcard. Then I applied a test tone and measured the voltage across the primary as well as the voltage across the secondary. Dividing one by the other gave me the turns ratio. I ended up being about 1:53 which is a little higher than the calculated ratio. I guess that the difference could be because the calculated ratio was determined with DC resistance versus AC impedance.

 

[OtterMarc]

Quote:

I think that's a little off. The turns ratio of a transformer is determined by taking the square root of the primary impedance divided by the secondary impedance, or the reverse in this case since this is a step-up rather than a step-down transformer.

Tyre,

Wouldn't this be true only if the pri and sec windings were of the same wire gauge?
Also, impedance isn't resistance. I'm trying to understand better.
Thanks.

Marc

 

[macm75]

John Broskie's take on OPT's for stax...
http://www.tubecad.com/november99/page2.html
A real stax OPT application...
http://www.audiodesignguide.com/my/stax_transf.html