current feedback electrostatic amp

[kevin gilmore]

that might be a bit low, certainly the 1uf caps are too big for the current board size

[kevin gilmore]

i was going to use the .47uf 600v caps, those are definitely too big

[spritzer]

The 1uf/450V caps I use are pretty small.  We might cram on some small film caps too if the board will allow. 

[spritzer]

I just finshed the board and we might be able to fit some SMD caps but through hole are out of the question. 

[congo5]

Working +-399vdc 18.5ma bias

lots of gain, power, noise free, good bass.

aluminum plate 57C  in center after 30min

[spritzer]

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

[JoaMat]

Nice!

18.5 mA through output transistors? Nearly 2.5 W each.

[congo5]

23 minutes ago, spritzer said:

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

if you want someone to test the new layout..........

[joehpj]

Is there any problem to set the mid point?

[kevin gilmore]

no way to set the midpoint, on congo5's unit, it is about 5v

(well there is, but its a pain, have to trim resistors)

[joehpj]

5V seems acceptable. I was thinking if someone was bad luck enough to have a bunch of sands far away from average hfe will be a pain to set the mid point.

Is it possible to put a svr somewhere to do the trimming job?

[kevin gilmore]

its a cfa and the gain is high enough that trimming is probably not necessary. But i will look into it

[congo5]

listening / measuring again.

on startup the outputs are positive, which is safe, good.

I added a fan to my heatsink plate, lowered temp = lower bias.

on start bias is ~13ma and climbs as it warms up. if my fan lets it.

which may be why offset is different today. and also running on mains instead of variac.

rails at +-394v, outputs to ground are all positive, 10v  and under.

no adjustment needed here.

I call this a Big Win  

Its to cold to feed ducks, glad I made this.

Thanks

 

[joehpj]

Bias current seems to have positive correlation with temperature. That means this amp may blow itself without adequate heat sink? Also, the performance will be different in winter or summer.

Please describe the sound.

Anyway, nice job. It's time for some fancy casework.

[congo5]

these are positive tempco devices, as are most things.

it does seem more sensitive to rail voltages.

Could that be a way to autobias the thing?

Do think it sounds better warm

I am in awe of the simplicity of the circuit vrs SQ

[congo5]

if you don't mind a warm case, this seems to be enough  heat sink 3.5" x 9" + case bottom

after one hour its 40 degrees rise from ambient 70/110

[spritzer]

The great thing about this amp is its simplicity and that it can be used with the affordable off the shelf Antek transformers.   

[congo5]

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.

[spritzer]

I need to prototype this one soon.  Just what I needed...more stuff to prototype...   

[nopants]

i have a 330v edcor left over which would be perfect for this project.

which psu version is that? i don't remember the lv electrolytic being situated like that

[congo5]

its from the KGST GB, bhultraminipsv4 I think

[sbelyo]

I think I want to dip into the electrostatic pool.  Is this a good place for me to start?

[sbelyo]

I'm hoping this stays somewhat simple.  I'd like to build one as my first.

[nopants]

only one HV power supply necessary, and 4 copies of a small board. Seems like it's either this or the SRX+

[gepardcv]

I'm intrigued by this design. Have to think about how to absolutely minimize chassis size with some small external heatsinks, and maybe use split GRHV PSU boards (not that there's anything wrong with the mini-BH, and it might win out for me in the end).

(Not that I need to make yet another electrostatic amplifier...)

Edited December 17, 2016 by gepardcv