Kevin Gilmore Circlotron Output, Large Enclosure [high-slew] Electrostatic Amplifier

[JoaMat]

From silk screen I guess current on Circlotron driver board can be set to something like 10 - 25mA. Pro/con low vs high current?

[Victor Chew]

Kevin, what transformer specs are we looking at here.

I know that because of the high voltage and safety concerns it is recommended to have this is one box, but is it at all possible to have it in 2 boxes if we can find suitable umbilical cords and connectors to handle the concerns. I am asking this because of the weight and also future ease of repairs if anything needs attention.

[kevin gilmore]

10 ma for the driver is more than enough.

needs to be 3 transformers, 2 of which have 4 windings of 380vac each

the other is the kgsshv-carbon transformer

 

[JoaMat]

How much power will a single Nanotube draw at maximum?

[kevin gilmore]

so the default would be 25ma on the output stage and 15ma on the driver stage

so 90 watts for the output stage and 54 watts for the driver stage (both at 900/450v)

plus what ever differential on the power supply so close to 200W is probably right

[JoaMat]

Is it possible to have feedback from driver output instead of Circlotron output or will that just end up in a disaster?

[kevin gilmore]

i think so, but have not tried it.

the opto feedback controls the bias, so it should work in theory.

[JoaMat]

What is the procedure setting up the Circlotron using Offset respective Output Stage Bias trimmers?

[kevin gilmore]

set the pot for 9.5V output, it works backwards, lower voltage is more current

measure the voltage across either R6 or R7 and then adjust for 3V

adjust the balance pot for zero volts differential out

rinse and repeat

 

Edited October 20, 2015 by kevin gilmore

[JoaMat]

Thanks.

Just so I get this right. I assume it's 9.5V from pot to the opamp - not 9.5V from output of amp. R6 and R7 are 120 ohms? (I've a schematic showing 100 ohms) so that gives some 25 mA.

The 100 ohms pot for Offset is used when... just to get above in range?

[kevin gilmore]

9.5 v from the pot to the opamp.

production r6,r7 is 120 ohms.

the offset pot is set a little high so that the servo can bring everything into range.

[JoaMat]

/

Edited November 12, 2015 by JoaMat

[JoaMat]

A picture of my attempt to build a Circlotron driver.

 

Edited November 12, 2015 by JoaMat

[Kerry]

Nice! What servo are you using? Also, I have SMD parts for the 5pf cap and diodes. I've also been using the SMD version of the lsk389, just in case you're looking to get rid of more through hole parts.

Are those the 0603 LEDs?

[JoaMat]

As a Carbon amplifier I just use a trimmer to control the offset.

 

Yes, it’s 0603 LEDs – TLMS1100.

Edited November 12, 2015 by JoaMat

[sorenb]

The HV900 boards (from the Circlotron Group Buy) is working  

Has loaded it with 20k. When powering up, the amp-meter max out for a few secs, then drops to approx 1A, and finally settles at 180mA.

Using a 250VA from ToroIDY seems to run cool and silent.

Edited November 14, 2015 by sorenb

[sorenb]

how accurate does the 900V has to be?

I guess the HV900 should be equal to the drop across the positive HV rail and negative HV rail? does it have to be accurate, or is is just lowest denominator that rules?

Running both HV900 with 20k load for some hours, having monitoring of the drop across the SiC's, and it seems to fluktuate about 10V, and an average of 60V ... could one choose lower secondaries e.g.360vac rather? 

The ToroIDY 250VA (4x380 VAC) runs lukewarm and silent, so I guess 250VA is adequate but cannot be less. When loaded secondaries drop to +372VAC (230V mains)

Edited November 15, 2015 by sorenb

[Victor Chew]

Do let us know when you get music. And please do tell us how it sounds.

[sorenb]

23 minutes ago, Victor Chew said:

Do let us know when you get music. And please do tell us how it sounds.

Will do, but its probably gonna take a while.
I've finished all HV900 by now, and had them up and running in sets with 20kohm load for about four hours per set.
Both transformer and angle brackets only get lukewarm.

[sorenb]

Circlotron Driver board from the Group Buy is working.

As I'd like to test as much as possible before connecting everything, I'd decided to hook the driver up as an amp.

The Carbon V5 and Circlotron driver board are very similar although there are a number of differences that require a bit of tweaking to make it work.
The biggest difference is in the servo part of the driver board and since the driver board is missing the A06 -  controlling the current in the tail of the output stage directly from the opto - it is probably not possible to run the output stage at 20mA as it will exceed the opto current capabilities.

The pic shows (I believe) everything needed to 'convert' the driver into an amp - I haven't tried to get the servo to work though.

The important alterations is: (not including servo - amp only)

• NOT populating the 10k/10uF besides the opto terminal (until it is actually gonna be used that is)
• parallel the 500ohm in the tail of the output stage with 150ohm or thereabouts (I just solder one on top - easy to remove again)
• adding 2x (100k + 100k) for feedback.
• adding 2x 5k1 ballast resistors to the output

 

This is as I hook'ed it up, and dialed it in for 20mA operation - has ran for some days 24x7 without any problems.

For the servo to work a few changes in addition to the picture above is needed:

• the opto has leg2 tied to GND - this trace needs to be cut.
• Remove: the 47uF between the opto leg1 and leg2, and 5k resistor between OpAmp leg6 and opto log1
• Add: 1uF between OpAmp leg6 and leg2, 200ohm between OpAmp leg6 and opto leg 2, and GND to opto leg1

 

 

 

Edited October 4, 2017 by sorenb

[nopants]

On 11/15/2015, 6:43:50, sorenb said:

Will do, but its probably gonna take a while.
I've finished all HV900 by now, and had them up and running in sets with 20kohm load for about four hours per set.
Both transformer and angle brackets only get lukewarm.

Seems like you can shave off a bit of heatsinking if brackets are enough to keep the temperatures manageable

[sorenb]

If someone wants to power up the Circlotron using a variac it might cause a bit of trouble.
When powering up the driver it has B+ at the output until the driver output stage begins to conduct current, then it drops to some ~0V (if proper adjusted that is)
Having B+ at the input of the Circlotron output board will turn on the SiCs at full throttle going for 7,5Amps (900V/120ohm) ...however limited by the HV900 current limiter.
 

Better to power up the driver at full mains, and afterwards dialing in the output boards + HV900's using a variac.
That approach seems to work out pretty ok.

Only applies to the HV900:
For anyone building this Kevin recommends to increasing the current sensing resistor from 5,1ohm -> 12ohm to further protecting the output if something should go wrong.

/Edit: as per Kevins comment below.

Edited December 2, 2015 by sorenb

[kevin gilmore]

increasing the current resistors on the 900V supplies only.

[Tinkerer]

On 8/26/2015 at 11:45 AM, kevin gilmore said:

10 ma for the driver is more than enough.

needs to be 3 transformers, 2 of which have 4 windings of 380vac each

the other is the kgsshv-carbon transformer

 

So what would be a good va rating for the two 380VAC transformers to give a little headroom?

[kevin gilmore]

120 watts should be plenty

in other news soren found a problem with the turnoff condition.

easiest fix is a pair of back to back 12V zeners on the outputs gate to source

in addition because soren wanted the feedback at the driver board, there is this modification which actually reduces distortion even further and allows

direct local control of current in the output stage without a "classical" servo.

the carbon really is very stable over time without the servo, mine has drifted less than a volt with the servo removed.

so there will be another version of the output board.

http://gilmore.chem.northwestern.edu/circlotronoutputnew.pdf

 

 

Edited December 10, 2015 by kevin gilmore