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current feedback electrostatic amp

kevin gilmore

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  • 3 weeks later...

I wonder, would it be possible/practical to split the Blue Hawaii power supply in the same way that the GRHV power supply is split? I only ask because the split configuration provides so much flexibility, and the BH power supply is so much more affordable than the GRHV for projects like this and the SRX+.

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10k input resistor to ground, or relatively low impedance pot required, will up date board in a bit.

Just curious Kevin, but have you looked at putting the pot either midstage or at the output on your designs? I realize this is probably no-go on electrostats, but on the dynamic amps might loosen 10k only problems? I know Pass does this some, but requires even lower values (2k on Pass Aleph P pre for example). The guy doing the Neurochome HP-1 also seems to advocate this.

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On 2017/1/12 at 5:48 AM, kevin gilmore said:

seems linear systems is now shipping matched p-channel duals that match the lsk689 so jfet front ends may be possible again.

I assume you are referring lsk389? And matched p-channel means 2sj74 pair would work if I could find some real ones?

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11 hours ago, Pars said:

I think it is the LSJ489/LSK689 that are the matched pairs.

For a reverse taper pot, can't you just connect a regular log pot backwards (In to the pin normally grounded, ground the pin that is normally the in pin)? Or am I mistaken?

LSK489 and LSJ689 are the n-channel and p-channel FET duals respectively. 

Reverse taper wired as you described would work with linear taper pots. Not log.

Edited by Laowei
Corrected npn pnp
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  • 3 weeks later...
  • 3 months later...
On 12/15/2016 at 10:23 PM, congo5 said:

Finally... simple enough I can understand some of it.

Best $50 I have spent in a long long time (had a few parts already).

Having listened for a few hours now, Will describe the sound.

Fuck me.

You wouldn't happen to have worked up a BOM for either of the BH ultramini or the CFA boards would you? If not, I can get started on doing them, but will need some guidance on voltage/wattage ratings on the passive components.

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no on the CFA but its simple / not a lot of parts, used xicon 1/2W resistors, or RN60D

but have this on BHultramini its years old and think the trim pot is wrong, should be a pv36Y I think. see if the three pins are staggered or in a row on yours


check it against the, board some of it will help

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5 hours ago, MrSlim said:

Awesome, that will do the trick I'm sure.  Thanks!

I added some parts to mouser project

you still need to pick resistors, terminal blocks, transistor mounting hardware and maybe change the big caps

Mouser has some new 600v ones for the prereg side

 they are higher voltage than necessary for 400v supply's

also you can look over the KGSSHV BOM for ideas as many parts are similar


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Yes still like it, its different, darker but fun

last week > Megatron, BH and it

there may be some tweaks to the circuit that could be found

but not if no one builds it

Please try it before building it a home in a multi thousand dollar enclosure:mellow:


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  • 4 months later...
On 12/11/2016 at 9:54 PM, spritzer said:

The new layout is pretty much ready but might be a while until we release it.

Still interested in the direction you would take the board design.

and any changes or updates you might make.

  I'm fine with through hole parts as the footprint is already small,

but an ultra tiny amp would be Neat!


I used mine yesterday to power some DIY stats for testing, and although a simple plates are enough sink for testing its too hot for long term when jammed in a case.

So ordered some .7 C/W heat sinks for each channel.

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  • 2 weeks later...

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