Looks nice John. Maybe a bit more venting on the bottom and possibly top.  I found that the extra venting really helps.

@joehpj - I've used a 400VA transformer running on by BH which has 25mA of current on each leg and I consider that a bit overkill.  I would say 200VA should suffice and 300VA is more than enough for the Carbon at 20mA.  Haven't built it yet, so I'd also like to hear what others have used.

Ahh, also EI? toroid? R-core?

For a 300VA transformer, toroid ones can be easily mount in a case while EIs don't. But someone told me EIs are better for high voltage usage.

I'd go with toroid or r-core. 

I have the following transformer from Toroidy, based on prior discussions:

150VA

primary: 2x115V

secondary:

- 2x 335 VAC at 200mA

- 16-0-16 VCT at 500mA

 

Not enough for a Carbon at 20mA, you think?

Well with Toroidy one never knows but I'm running at 160mA on my way over spec transformers with no issues. 

10 hours ago, spritzer said:

I would move the transformer further away from the volume control as it is so prone to pickup noise there. 

Thanks guys for looking over the layout, I’ll have a look at the top and bottom vent pattern to increase airflow, I’m stuck with these amp boards as I’ve already part populated but as I’ve placed a milled 2.5mm cavity hole under each C2M1000170D on the heatsink mounting shouldn’t be an issue.

Birgir the transformer is encapsulated, I’m hoping to get away with that position, do you think there’d still be an issue?

...and my transformer based on previous discussions is 153VA based on the above said specs.

 

Edited January 21, 201610 yr by johnwmclean

Is the 400V PSU from KGST (KGBHultramini) able to power Carbon?

I've already built a 400V KGST. I wonder if I could just swap the output boards. I've checked the transformer. It was tight but should be OK.([email protected] , [email protected])

That wouldn't be a problem. 

Anyone that have tested the opto servo. How does it work?

6 minutes ago, JoaMat said:

Anyone that have tested the opto servo. How does it work?

seems to work fine (although the servo is a bit different on the Circlotron driver in comparison to the Carbon ... but close enough I'd say)

Thanks. Does it mean that you have zero volt offset even from the start?

 

I have the opto servo running. You have tot set offset to about 20V and when you engage to servo it will go to 0.

ref:

 

 

Edited February 9, 201610 yr by insanity

Thanks, so the servo keep the offset to zero from the start (except from the first seconds when power on) and further on without any fluctuations?

14 hours ago, JoaMat said:

Thanks, so the servo keep the offset to zero from the start (except from the first seconds when power on) and further on without any fluctuations?

Same question.

Though the carbon seems very stable without either servo - offsets start out under 20v and gets to less than 1v fairly quickly - not sure it is needed.

Also wanted to mention that this thing runs very hot (especially the 450v version).

 

I missed the group buy to get the amp boards for the KGSSHV Carbon, does anyone has any spare amp boards available?

I'm in the same boat. Any spare boards available, or any advice on where to go to get quality boards produced? Any help is greatly appreciated as I'm a bit new at this!

I've had good luck with iTEAD's prototyping service. Others have reported good results with Seeed Studio. PCBs from these manufacturers are not quite as nice as the PCBNet ones, but work fine for me on other builds. Just send them or upload Gerber zip files from KG's site (http://gilmore.chem.northwestern.edu/boards/). It's relatively inexpensive.

On 2/10/2016 at 9:00 PM, GeorgeP said:

Same question.

Though the carbon seems very stable without either servo - offsets start out under 20v and gets to less than 1v fairly quickly - not sure it is needed.

Also wanted to mention that this thing runs very hot (especially the 450v version).

 

EDIT: Got it all wrong. Post deleted.

 

Edited February 23, 201610 yr by mwl168

it looks to me like the opto servo needs the op27 installed as that is where it gets its sense power.

which is why to adjust to +20v and the opamp will invert that.

I did not get it going yet, but its so stable that every time I check it I decide to hook up the servo later....

 

Thanks Congo5. I was wondering the same thing (if OP27 is needed for the opto servo to work) after reading the schematic. 

I will install OP27 and give it a try.

One question, does the output need to be as high as 20V for the servo to work? Shouldn't 5V or so be enough for the OP27 to sense the differential? From the get go with the offset and balance pots centered, my Carbon has not seen higher than 15VDC offset.

Edited February 22, 201610 yr by mwl168

yea I don't know, the Carbon is my first time with this servo..
+20v would slam the opamp to its rail so instead of pin 6 adjusted for 0v it would be full negative output .

the 4n25 can swing 20v more negative than positive?

to bias the pzta06?

I do not understand............... but whats a few volts dc against a 580v bias.....

we will have to wait for the big boys to answer....

yes you definitely need the opamp, otherwise the opto has no drive.

Thanks Kevin. 

For clarification, my Carbon's output voltage as measured from the O+ to ground is about -14 VDC at start up. Do I need to adjust it to + 20 VDC at start up for the opto servo to work?   

the opto version only works in one direction, so the output needs to be at least +10 before turning on the servo

Thanks Kevin.

I experimented with the opto server tonight (this time with the OP27 in place) and here are my observations:

Without the servo jumpers in, I first adjusted the offset of both boards to be about +18 VDC at cold start, measured between the + output and ground (this applies to all subsequent measurement).

I then inserted the jumpers and powered on the Carbon with opto servo now engaged. The offset on one board measured -2.5 VDC right from the start, it dropped to about -1 VDC after 5 - 6 minutes, from there it hovers around -0.9 VDC, drifting about 0.5 VDC or so up and down. I measured again at 20 minutes and then at one hour marks with same results.

At the one hour mark, I adjusted the balance from around 2 VDC to within 0.5 VDC (absolute value). This brought the offset to hover around -0.1 VDC.

The other board exhibited similar behaviors but started with and ended at lower offset voltage. (Without servo, this board has always had lower offset and balance compares to the other one.)

It appears to me that the opto servo is working and it's effective from the very start although it does take about 5 minutes or longer to reach the lowest possible offset voltage. 

As I have mentioned in the past, the Carbon, without the servo, is very stable to start with. It seems to me the main advantage of the opto servo is to keep the offset at a low voltage from the start and settle it down faster. Without the servo, my Carbon typically takes between 15 - 20 minutes for the offset to settle. 

 

 

Edited February 23, 201610 yr by mwl168