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Old 14th January 2013, 12:38 AM   #1
mixelle is offline mixelle  Ecuador
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Default Tube operating points help

Hi,

I am trying to design an amplifier for electrostatic headphones. Since it would be using high voltages I prefer to ask for help instead of experiment while finding the operation points for the output tube.

The idea is to use the sections of a 6BL7gta in push-pull sort of like this amplifier by Mr. Gilmore All-Triode Direct-Drive Amps for Electrostatic and Electret Headphones | HeadWize

The goal is to have 1400 volts peak to peak stator to stator capacitively coupled to the headphones. Since I yet have to design the phase splitter there is absolutely no constraints on gain, power supply voltage or if I need to use fixed bias.

I have built several amplifiers and designed a single ended tube amp. But this would be my first push pull project for design so I am learning.
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Old 14th January 2013, 02:22 AM   #2
DUG is offline DUG  Canada
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Quote:
Originally Posted by mixelle View Post
Hi,

The goal is to have 1400 volts peak to peak stator to stator capacitively coupled to the headphones.
Seems a bit much for headphones.

There is a very informative thread in the ESL/Exotics about ESL headphones that might help your design.

What you are doing is also on my (big) list of projects to do someday. (only I was going to try HV MOSFET's)

Keep us posted.
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Old 14th January 2013, 03:40 AM   #3
mixelle is offline mixelle  Ecuador
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Quote:
Originally Posted by DUG View Post
Seems a bit much for headphones.

There is a very informative thread in the ESL/Exotics about ESL headphones that might help your design.

What you are doing is also on my (big) list of projects to do someday. (only I was going to try HV MOSFET's)

Keep us posted.
Actually is not that much, here is a list with the voltage ratings of several amplifiers. 1400v p-p is the rating for the Stax T1 and the KGSS

Electrostatic Amplifiers Voltage ratings
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Old 14th January 2013, 05:43 AM   #4
DUG is offline DUG  Canada
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Interesting
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Old 14th January 2013, 05:55 AM   #5
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How much capacitance do you need to be able to drive?

All good fortune,
Chris
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Old 14th January 2013, 01:34 PM   #6
mixelle is offline mixelle  Ecuador
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How much capacitance do you need to be able to drive?

All good fortune,
Chris
I am modeling the amp around the Stax SR-307 so 120pF according to their datasheet
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Old 16th January 2013, 03:25 AM   #7
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I am modeling the amp around the Stax SR-307 so 120pF according to their datasheet
OK. Check my math: Max slew rate (at zero crossing at 20 KHz) is 2.8 exp8 V/S meaning a peak charging current of 33.6 mA. Here V/S = I/C.

All good fortune,
Chris

Last edited by Chris Hornbeck; 16th January 2013 at 03:27 AM.
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