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Kevin Gilmores Current Domain Electrostatic Amp

post #1 of 15
Thread Starter 

Hi All,

Has anyone built the above amp?. I did a few years ago and have just got back in to trying to setup

biasing following Kevin's procedure. There seems to be quite a large drift in output voltage at idle

measured between + and - Outputs. Both channels exhibit this variation. If you look at the meter over

a 5 min period this standing voltage varies from +10mv to say 900mv. Then will drift down again.

 Hoping someone or Kevin may pop in for some advice would be appreciated.

The amp sounds ok, really nice in fact.

Thanks

Les

post #2 of 15
Quote:
Originally Posted by iwik View Post
 

Hi All,

Has anyone built the above amp?. I did a few years ago and have just got back in to trying to setup

biasing following Kevin's procedure. There seems to be quite a large drift in output voltage at idle

measured between + and - Outputs. Both channels exhibit this variation. If you look at the meter over

a 5 min period this standing voltage varies from +10mv to say 900mv. Then will drift down again.

 Hoping someone or Kevin may pop in for some advice would be appreciated.

The amp sounds ok, really nice in fact.

Thanks

Les

 

Spritzer and Kevin will probably jump in soon, but if it's mV you're really fine for electrostatics. My electrostatic tube amp (also a KG design) runs at +- 1v and it's meant to run between +-10V.

 

Did you measure your DC offset (channel and ground)?

post #3 of 15
Thread Starter 

Thanks RiStar,

The offset to ground remains close to zero. It was just that Kevin's said his one only did +- 200mv over a month.When I was trying to adjust the pots I was just chasing myself.As it depended at which part of this cycle I did the adjustment. I have not checked this drift from output to gnd yet.

I also have built his Tube amp as well and that's still going well. Prefer the solid state one.

Lets hope someone else chips in but thanks again.

Les


Edited by iwik - 1/4/14 at 10:13am
post #4 of 15
Quote:
Originally Posted by iwik View Post
 

Hi All,

Has anyone built the above amp?. I did a few years ago and have just got back in to trying to setup

biasing following Kevin's procedure. There seems to be quite a large drift in output voltage at idle

measured between + and - Outputs. Both channels exhibit this variation. If you look at the meter over

a 5 min period this standing voltage varies from +10mv to say 900mv. Then will drift down again.

 Hoping someone or Kevin may pop in for some advice would be appreciated.

The amp sounds ok, really nice in fact.

Thanks

Les

Hi Les.

 

Came across this amp a few days ago and it looks an interesting alternative to a Tube Cad tube amp which I've partially built but never got around to finishing. I know that the 2SK389 are like hen's teeth and fetch silly prices so, have you used these or have you found an alternative? 

 

I did build a VSE RTP3C and successfully replaced the two 2SK170's on the input with an SSM2212. As the 2SK170 is, as near as damn, half a 2SK389, I just wondered if anyone had tried it.

post #5 of 15
Thread Starter 

Hi,

I built my amp a few years back, so used 389. They are available on ebay for $7.50. Although I expect something similar

could be found.

Try this

http://www.ebay.com/itm/1x-NEW-TOSHIBA-2SK389-BL-2SK389-BL-DIP-7-IC-CHIPS-/321114283329?pt=LH_DefaultDomain_0&hash=item4ac3e71d41

 

Les

P.S There are two better variants  Blue Hawaii and the KGHV you may want to look at.

post #6 of 15

you are chasing nothing, that imbalance would be difficult for even a servo to stabilize any better than that.

 

Quote:

Originally Posted by valve5425 View Post
 

Hi Les.

 

Came across this amp a few days ago and it looks an interesting alternative to a Tube Cad tube amp which I've partially built but never got around to finishing. I know that the 2SK389 are like hen's teeth and fetch silly prices so, have you used these or have you found an alternative? 

 

I did build a VSE RTP3C and successfully replaced the two 2SK170's on the input with an SSM2212. As the 2SK170 is, as near as damn, half a 2SK389, I just wondered if anyone had tried it.

 

yes you can use 2sk170s on the input, or the more-modern lsk389 if you don't want to deal with matching pairs yourself. on the kgsshv board there is a pmbf part whose full model number escapes me. Someone else has also met with success using a pair of bc550

 

I wouldn't use the 2sk389 unless you've got some old-stock blue hawaii boards and you were forced into that footprint

post #7 of 15
Thread Starter 

Thanks Nopants,

Just needed a bit of confirmation, still a bit green on this Tech.

This amp will keep me happy till I finish my T2.

Les

post #8 of 15
Quote:
Originally Posted by NoPants View Post
 

 

yes you can use 2sk170s on the input, or the more-modern lsk389 if you don't want to deal with matching pairs yourself. on the kgsshv board there is a pmbf part whose full model number escapes me. Someone else has also met with success using a pair of bc550

 

I wouldn't use the 2sk389 unless you've got some old-stock blue hawaii boards and you were forced into that footprint

Having both input transistors on the same die is the way to go.

I tried the pair of 2SK170s in my KGSSHV and there was signifigant drift that could not be zeroed-out.

YMMV - One could try glueing them together or some type of matching scheme.

 

So I bought a fistfull of LSK389s. Problem solved.

They also work fine on my old Blue Hawaii boards.

The footprint is different, but the LSK leads can be bent to accomodate it.

post #9 of 15

My Blue Hawaii has 2SK170's and it works fine. I bought a bunch on Mouser back when they were in stock and matched a quad. I do not have them in direct thermal contact and still only get 1-2V differential DC drift between seasonal biasing (usually re-bias for winter and summer as my common mode drift is about +-15V between winter and summer - which is not a big deal for electrostats but might as well bias it out since I can).

 

The two TO92's fit very conveniently into the 2SK389 socket, just have to figure out the pinout. There are no awkward crossing leads between the two 2SK170's.

post #10 of 15

Yeah I think a matched pair of k170's is fine, I think personally I would get lazy about matching though. Thermal bonding should go a long way- I'm pretty sure this is the cheapest "standard" solution to the input stage.

 

Valve, I think most people would recommend building the KGSSHV over the KGSS given the dea(r)th of 2sc3675s. There is also artwork out there, with multiple options to suit your needs.

post #11 of 15

The newer KGSSHV with schematics and art work is located at http://www.head-fi.org/t/582131/is-anyone-building-the-kgsshv


Edited by Bach911 - 6/29/14 at 12:30pm
post #12 of 15

I think these are all the current boards

http://gilmore.chem.northwestern.edu/boards/

post #13 of 15

Thanks for the correction. I am currently collecting the needed parts for the KVSSHV and will look for someone to make the boards with the Gerber files you provided. aquawayindustrial on ebay is sending 2SK389-BL. It is comforting to know I have latest files you created.   

post #14 of 15

none of the new boards are  designed for 2sk389 anymore.

 

use lsk170b singles, available from diyaudio.com or

lsk389b available from trendsetter

post #15 of 15

Thanks again for the correction. Bought lsk389b from trendsetter as recommended. Earlier bough 20 SK170 and tried to match with little success. Idss on 12 volts ran 0.03 to 0.15 mA. None would match below 10 percent. Maybe the lsk170 would match better than the sk170, but why take the chance. I will read all of the 29 pages from the "Is anyone building the KGSSHV?" tread so you are not having to save me from serious mistakes........not that I mind hearing from the creator of cool electronic designs and overseer of the NMR.

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