"High" Voltage Mosfet Amp

I have some

formatting link

and would like to make a simple mosfet audio voltage amplifier(common source). Possibly using drain feedback bias and/or source degeneration. The power supply is around 500V. Is there any difference I should be worried about from a similar low voltage case? I'm looking for a gain of around 20 with an input swing of about 1V max.

Reply to
Jeff Johnson
Loading thread data ...

Why bother with a 500V supply if you only need 20 volts of output swing?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
 Click to see the full signature
Reply to
Phil Hobbs

Audiophool syndrome ?:-) ...Jim Thompson

--
| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
 Click to see the full signature
Reply to
Jim Thompson

he

0

I'm confused, the supply is 500V, and the input is 1V with a gain of

20? Sounds like you need more gain. Can you post a pic of a schematic? What are you driving?

George H.

Reply to
George Herold

Sure I would like more than a gain of 20. 100 Ideally. If I use drain feedback bias there is no way to get past 30 since this would easily put me over the max V_GS of 30V.

Reply to
Jeff Johnson

"Jeff Johnson"

** That would be funny if he was not serious.

..... Phil

Reply to
Phil Allison

t

Yeah, I need to see a circuit.

Reply to
George Herold

.

ed

d

me

As a said to Phil, can you post a circuit?

Where's the load? What's the load? Why 500V? (that's dangerous)

George H.

Reply to
George Herold

he

0

You're not expect linearity with DMOS I hope. You might want to see who is left making fets with lateral current flow.

Reply to
miso

Are you trying to reinvent the Fetron, a high voltage FET with the same pinout as some well known triodes ?

Reply to
upsidedown

  • Nope, the wanker trying to re-invent the wheel.

He wants to make a square version.

BTW:

Fetrons used high voltage j-fets in a metal pack that typically simulated a

9 pin dual triode.

..... Phil

Reply to
Phil Allison

...a hopped-up pair of rollerskates...

Reply to
Robert Baer

f

He's probably trying to drive an electrostatic speaker. Quad Electroacoustics sold one for many years, and it was highly regarded - low frequency response is limited by the physical size of the speakers, and high end freaks filled it in with separate sub-woofers.

One of my ex-colleagues was quality control manager there for a few years, and was deeply impressed by the weird scheme that Quad used to get a minimally conducting film onto the moving membrane - think Gohm's per cm.

Back in the 1960's there were a bunch of articles about building your own electrostatic speakers, and the high voltage amplifiers to drive them. Quad just used step-up transformers, which made a load that many audio-amplifiers didn't like driving.

One of my ex-bosses - Ralph Knowles (now dead) - had a pair of Quad Electrostatics and had enugh money that hi-fi shops would try to sell him hi-end amplifiers to drive them. Most of the amplifiers were amateur-night rubbish.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

at

any

The Quad ESL63 had rather more than a transformer to drive the electrostatic moving parts

formatting link

The deformable membrans that moved the air were split into a number of concentric circles, and the voltages that drove each circle came from a passive RLC delay line in which a series of transformers contributed the inductance and some of the capacitance.

It's not surprising that Quad managed to make the input impedance look more of less resistive - once they'd got the delay aspect of the RLC network right, tweaking it to make the input look resistive can't have been all that difficult. There were certainly any number of parameters available for them to adjust.

During my - unsuccessful - job interview at Quad I got to see (but not to hear) the three dimensional analog of the Quad ELS63, which apparently worked, but couldn't be made cheap enough to sell.

-- Bill Sloman, Nijmegen

Reply to
Bill Sloman

Different subject, but if you want gigohm conductive glass, you can buy expensive stuff, or use welder's glass.

John

Reply to
John Larkin

Possibly...

Reply to
Jeff Johnson

Well, I don't mind a little bit of non-linearity... The datasheet shows it might be pretty bad though ;/

Reply to
Jeff Johnson

Interesting. I worked at FEI for a while and then afterwards helped develop a product, self-employed, to help extend the average life expectancy of their electron emitters hidden behind the wehnelt.

Jon

Reply to
Jon Kirwan

Interesting. Is it bulk or surface conduction?

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
 Click to see the full signature
Reply to
Phil Hobbs

Don't know, but I suspect bulk. Somebody told me this, and I thought I'd pass it along as a hint.

John

Reply to
John Larkin

ElectronDepot website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.