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

[G600]

Anybody with a working build ?

[Tinkerer]

Sort of related to G600's question. Has anyone confirmed you can fit everything in a 5U case? I'll need to order my case sometime soon, and while my local machine shop will give me a pretty good deal on a custom if I have to get one, a modular 5U would still be quite a bit cheaper.

[Walter Reyno]

I was playing around with a drawing program, not being very precise/accurate, using dimensions from the 5U dissipante at diyaudio/modushop and the only way I could get the ten boards to fit inside at all was to mount them vertically with the caps oriented front-to-back. Then of course you also have to fit three transformers in there. I haven't ordered them yet so I have little idea how big they are. I didn't check for clearance but I imagine that jacks and power input might have to go in the middle because the boards fill most of the space along the sides.

[Tinkerer]

 

On 2/14/2016 at 11:02 AM, Walter Reyno said:

5U dissipante

You used the 400mm one for that stuff, not the 300mm right?

 

EDIT: Doesn't matter. Got my overspecced transformers in today from toroidy and they are way too big to make it work I think. Will take some measurments and double check later.

Edited February 17, 2016 by Tinkerer

[Tinkerer]

Got around to making a quick and dirty model using the 5U case internal dimensions and the measured dimensions of the boards, my toroidy transformers, and brackets and such. Looks like there's room but you have to make best use of the vertical space. I don't really know what affects what like the real gurus here but I just tried to keep all the PSU's together and give the stacked amp boards their own space in the corner, as well as left space along the bottom back of the case for power plug/fuse/inputs/outputs. There's an inch or so left near the front that you might be able to shift everything even further away from the transformers as long as you keep all the faceplate controls in the center. As is, there's space to have the jacks or front power button offset.

 

 

 

And model is here for anyone to play around with. http://www.mediafire.com/download/t7jk13n7s2ky166/Amp+mock+up+6.obj

[Tinkerer]

So I had a question about some Dale stuff I got from Mouser. Bought a few months ago but only really started going through it now after I got all my heatsinks and transformer stuff together. Online when I bought it, and on the label it says 1/2W-1W. But looking at the size of them and the data sheet it says rated for 1/4 watt. They're CMF60 series. Had a few of my xicons that showed up too small as well. None of the bags are opened. I don't know what I can do or exchange at this point, but I want to make sure I'm not stuffing boards with parts that aren't going to cut it, even if that means rebuying/returning some things. I'll go reference the Carbon BOM for anything that crosses over that can help, but I thought I would post here in case there were any obvious pitfalls I'm missing.

Also a dumb question but what is the brand/label series for the bright red power resistors with the marked bands? I took a shot in the dark and wound up with some of those chalky looking BC ones. But with the circuit needing them increased to 12ohm, I needed to buy new ones anyway so I wanted to make sure I got it right this time.

 

EDIT: Probably a mislabel on the mouser end. I accidentally even got a couple itty bitty CMF55's stated to be 1/2W. Guess that's a lesson to me to read more carefully instead of just searching by voltage, type and power rating when shopping for resistors.

Edited March 30, 2016 by Tinkerer

[mypasswordis]

I also don't get why the RN60C is labeled 1/8W on mouser... the only difference between C and D should be less temp drift. All the CMF60 should be fine to 1/2 watt and CMF55 to 1/4. The datasheet does say the CMF55 is rated for 1/2W at <70C.

Not sure which bright red resistors you are talking about, got a pic? The 12 ohm 3W resistors I am using in the current limiters for a different power supply are CPF312R000FKB14 but they are orange.

[JimL]

Part of it is what conditions you are running.  If you look at the specifications sheets, you will see that an RN60 resistor has a power rating of 1/8 watt at 125 degrees centigrade, and a power rating of 1/4 watt at 70 degrees centigrade. So the power spec is "derated" at higher temps, which is not unusual.  Which is where the confusion comes in - which is correct?  If you're running the inside of your equipment at above boiling temps and need military grade reliability, then 1/8 watt rating for an RN60 is the way to go.  If you're running stereo equipment inside your house, 1/2 watt rating is perfectly fine.  At least, that's the way I read it.

[spritzer]

That's it, it's all about the different temperature rating.  RN60D should be rated at 1/4W as this is mil-spec and made by a lot of companies (well used to at least). 

[G600]

Any progress on this powerplant ?

[sorenb]

for those who have the first output board and needs to 'convert' to the latest corrections Kevin did

Edited May 25, 2016 by sorenb

[Tinkerer]

Cool. Was hoping for a summary. Last correction I recall seeing here was just the back to back zeners.

 

Also belated thanks on other help earlier. It was exactly what I needed, especially the CPF312R000FKB14 for the power resistors.

Edited October 19, 2016 by Tinkerer

[Tinkerer]

Bumping this back up to the top with a few more questions before I start hooking things up and hoping they don't explode.

 

On the 4N25 opto relays. The ones I got didn't have the little notch to show direction. So I compared them to my Opamps and just used the direction of the printing on the top to determine which way to slot them in their sockets. Is that right?

 

I have 6  6"x12" vertical heatsinks with 3" fins in my case to dissipate the heat from the boards which are mounted to 1/4" angle brackets. With 10 boards, not counting the onboard GRLV, I can stack two on every sink with one free space left on each side. My question is how best to mount the ten boards for best heat dissipation and the least interference. I thought maybe this way so I could get at both the output and driver boards from the top to adjust them while it was running.

 

Related to the driver board. With the new output boards, what needs to be changed/left unpopulated/jumpered on the driver board for the driver to function correctly, if anything.

 

What is the voltage I should be aiming for on the test points to have the correct current set on both the driver and output boards?

 

Is 20awg thick enough for the 900V lines? I have some 4kV wire laying around in that size.

 

Some of the AC runs will be a bit long on this amp because of the size of the case and transformer placement. Other than twisting the leads, should I also do anything like get some braided shields to sleeve them in and ground that to chassis, or is that overkill?

 

Last, about what size fuse is needed for this amp? VA rating of all three transformers I have put together is 1000VA, so even though they're overbuilt that would still be what? 10A?

[sorenb]

On 10/19/2016 at 10:19 PM, Tinkerer said:

On the 4N25 opto relays. The ones I got didn't have the little notch to show direction. So I compared them to my Opamps and just used the direction of the printing on the top to determine which way to slot them in their sockets. Is that right?

4n25:you have 'diode' (A->C) from 6->4 and 6->5, and 1->2, also see the datasheet

On 10/19/2016 at 10:19 PM, Tinkerer said:

Related to the driver board. With the new output boards, what needs to be changed/left unpopulated/jumpered on the driver board for the driver to function correctly, if anything.

feedback is missing and servo is missing input, as it is no longer comming from the output board

On 10/19/2016 at 10:19 PM, Tinkerer said:

What is the voltage I should be aiming for on the test points to have the correct current set on both the driver and output boards?

8mA for driver and somewhere >20mA for output board depending on your heatsink and crazyness I guess ;o)

On 10/19/2016 at 10:19 PM, Tinkerer said:

Is 20awg thick enough for the 900V lines? I have some 4kV wire laying around in that size.

I use 18AWG but don't see why 20AWG should be enough though

On 10/19/2016 at 10:19 PM, Tinkerer said:

Last, about what size fuse is needed for this amp? VA rating of all three transformers I have put together is 1000VA, so even though they're overbuilt that would still be what? 10A?

using 240V (2x250VA+210VA) using 2.5TA on each

Edited October 21, 2016 by sorenb
Updated according to the latest output board

[Tinkerer]

 

13 hours ago, sorenb said:

feedback is missing and servo is missing input, as it is no longer comming from the output board

Right. What I'm asking is with the servo not getting input and not really doing anything, should it be bypassed completely? Or do the boards work fine if you just wire it up normally like this?

 

Also, just double checking, but the Output low voltage input is supposed to be -15VDC like the silkscreen says right? I know the corrections posted higher up the the thread for the original output board are different than the current version we have, but I figured it's worth being sure.

[sorenb]

Seems ok.
I'd kept feedback on the driver itself, and feed the servo from the driver board as well.
As far as I remember 2x 1M from the SiCs of the driver combined into the OpAmp and the +input grounded.

[Tinkerer]

So mostly the driver board mods back on page 2?

200K from each SiC to the feedback terminal to keep feedback on the driver, and 2M from each SiC into the OpAmp for the servo? Then use the Output stage bias trimmer to short the servo input+ to ground?

What about the other resistors and diodes in that post like the 100V diodes and the parallel reistors? Are they necessary or just part of converting the driver board into a standalone amp?

Just trying to understand since I'm kind of a neanderthal when it comes to figuring this stuff out. I can monkey something together and follow instructions but actually knowing how everything operates is usually beyond me.

[sorenb]

Yep.
diodes are protection for the opamp. Probably Kevin left those out since the servo input original was suppose to come from the output board via optos and thus not needed.
the parallel resistors is there to raise the current but not needed here.
 

[Tinkerer]

Got some parts in from mouser and altered one of the amp boards. Guess there's really not a prettier way to do it unless you run all the wires underneath. Just double-checking one last time before startup. Pretty sure I did this right, but better safe than sorry. The +15 and -15 go to the rails right? And the hanging end of the 25K resistor goes to ground.

 

Edit: turned it on, both LED's came on and nothing exploded. Gonna count that as a win. Checking the current and balance now.

Edit 2:  Okay. Current set to 10mA via .5V across the 50R. Default was around 15mA for both channels, that bracket got warm quick. I had to back the pots way off. Funny because the power supplies are almost dead cold all day long. Transformer was only lukewarm after all the testing.

Edited October 29, 2016 by Tinkerer

[sorenb]

On 10/29/2016 at 2:05 AM, Tinkerer said:

Got some parts in from mouser and altered one of the amp boards. Guess there's really not a prettier way to do it unless you run all the wires underneath. Just double-checking one last time before startup. Pretty sure I did this right, but better safe than sorry. The +15 and -15 go to the rails right? And the hanging end of the 25K resistor goes to ground.

 

Edit: turned it on, both LED's came on and nothing exploded. Gonna count that as a win. Checking the current and balance now.

Edit 2:  Okay. Current set to 10mA via .5V across the 50R. Default was around 15mA for both channels, that bracket got warm quick. I had to back the pots way off. Funny because the power supplies are almost dead cold all day long. Transformer was only lukewarm after all the testing.

Feedback loop seems way too long - having it implemented at a separate board might not be the best of ideas.

[Tinkerer]

Could you be more specific on why? The feedback was on a whole different board previously (output board), and would have had even longer connections that way.

Edit: I just mean, is it that it can pick up noise or that the added capacitance of the wire mucks with something, I really don't know. I can add shielded wire if its the first but there's really not a solution to the second other than a shorter path, which would be pretty ugly point to point but easily doable.

Edited October 31, 2016 by Tinkerer

[sorenb]

two resistors in series, with some isolation ...the shortest distance bewteen the drains and feedback terminals...I did it on the backside

[Tinkerer]

Okay, so I'm getting into the bolt down stage (everything tested but the actual circlotron output) while I wait for final parts on my outer panels and I needed to double check some layout stuff.

How much does it actually matter to have the transformers as far as possible from the PSU's? The easiest way to wire this would be to have the PSU's in the back, the transformers up the middle and the Circlotron output stage nearest to the front panel. This thing is spacious enough I'm hoping it's a nonissue compared to smaller amps.

I was going to mount the potentiometer in the back and have a rod run through the length of the amp to the front panel. However, this means it will be running directly over the top of the three transformers. Though as you can see from the picture, it will be about 8 inches above them. How much of an issue will that be? Is it still better than having the potentiometer in the front and a really long ass run for the audio input from the jacks?

 

Excuse the half finished case and the backwards potentiometer but should give a sense of the spaces involved. 12U, a real tub for sure.

[Tinkerer]

Almost forgot, this is why the potentiometer has to be at a certain height no matter what kind I use or whether it's front or back. I'm using the old upper fan vent as the volume knob location. I backed it with frosted lexan and will put led's in the 4 central holes to make the whole cutout area glow softly. The knockout panel on the bottom will have the headphone jacks.  I know people don't usually go on about casework stuff until its done, but since this is a particularly large one I thought it might be helpful for anyone else trying to get one of these together in one box, especially if you want to shove a GRLV in there. Heck, those normal-looking stand feet are a full 2 inches across.

 

[Tinkerer]

While I'm waiting on someone with some knowhow to chime in about the internal layout questions I asked, progress continues on the case. First side panel is mocked up minus the LED indicator for the hole.