[tyre]

I was curious if it would be possible to make an electrostatic headphone amp using monolithic high-voltage opamps. Would the high gain needed roll-off the high frequencies if the opamp used didn't have a very high bandwidth? How high of a voltage gain would be needed to get sufficient volume?

 

[kevin gilmore]

You are going to need to find a device with at least a 700 volt
power supply range. Apex makes a number of parts that do this.
They are hybrids, not monolithic. And they are expensive. You
need 4 of them, 2 per chanel.

The required voltage gain is in the range of 600 to 1000.

The maximum voltage i'm aware of for a monolithic part has a
power supply range of 120 volts.

 

[tyre]

Oops, I used the word "monolithic" to refer to any type of non-discrete opamp, not realizing that there's a difference between "monolithic" and "hybrid".

I bought a few Burr-Brown 3583 FET input opamps for really cheap and was interested in using them. They are only capable of +/-150V though. There are some Apex PA97 opamps on ebay right now capable of +/-450V, but they have a class C output. Would it be possible to add some sort of constant current source on the PA97's output to bias it into class A?

 

[kevin gilmore]

Those burr brown parts are great stuff. Not exactly for this purpose
and as far as i know, no longer available. Lots of my instruments use
these as mass spec quad coil deflection. High frequency response is
a little lacking too. Would work, but not sound great, or get very loud.

That particular apex part is biased class C for a reason. If you try to
run them in class A they will burn up very quickly. There are versions
of those parts (pa96 i think, too lazy to look it up) that are A/B versions
with bigger pass transistors inside. If you can find them on ebay great.
But highly likely they are already burned up, as they are definitely static
sensitive. Otherwize you are going to pay in excess for $600 for 4 of them.

I'm working on a true electrostatic portable. It is many months away.
The power supply is the easy part. Getting any manufacturer to actually
make me some parts i want seems next to impossible. Is a micropower
900 volt pnp transistor so hard to make??

 

[Tachikoma]

Quote:

Originally Posted by kevin gilmore I'm working on a true electrostatic portable. It is many months away. The power supply is the easy part. Getting any manufacturer to actually make me some parts i want seems next to impossible. Is a micropower 900 volt pnp transistor so hard to make??

Could you make it with normal bias outputs too?

 

[kevin gilmore]

The voltage swing of the amplifier and the bias voltage have nothing
to do with each other.

I'm shooting for a 1300 volts peak to peak stator to stator drive.
(+/- 350 power supplies)

The bias will be adjustable between 500 and 600 volts.

 

[robzy]

Quote:

Originally Posted by kevin gilmore The voltage swing of the amplifier and the bias voltage have nothing to do with each other. I'm shooting for a 1300 volts peak to peak stator to stator drive. (+/- 350 power supplies) The bias will be adjustable between 500 and 600 volts.

[size=xx-small](Unashamably off topic and lame-)[/size]
I take it this isnt going to run on the same AA cells my cmoy is...

Rob.

 

[kevin gilmore]

Runs about 12 hours on a pair of aa nicads.

Production will be a single large Lithium ion battery. Should get
about 20 hours.

About the same physical size as an AE-1

It is highly unlikely that this will become a headamp product.

 

[Salt Peanuts]

Quote:

Originally Posted by kevin gilmore Runs about 12 hours on a pair of aa nicads. Production will be a single large Lithium ion battery. Should get about 20 hours. About the same physical size as an AE-1

Woohoo! This means a portable/transportable O2 rig for me in the future.