The servo I did was for the KGST.

I had a couple of issues with it. I just happened to be working on it this weekend. I solved one issue that caused it to shut down at very high volumes.

I still have a small oscillation of 100mV around 6.7MHz. It's common mode so I don't think it affects the sound.

I'll publish the Ltspice files on the KGST thread later tonight.

I have some ideas of how to adopt it for the KGSSHV, but this amp has much less voltage between the bottom rail and the top of the servo.

Thanks Kerry. 

 

Pardon an ignorant question, but your servo design, when adopted for the KGSSHV, supposed to work on top of the built-in servo? 

No. It's a very different design and runs standalone.

Would need new boards or possibly a daughter card.

As promised, here are some pics of my build. I am embarrassed to post these pics but did not want to be disrespectful and anti-social    

 

This is my temporary housing. I can now start to think about what to do with chassis(s) for the amp. At this time I am leaning toward a 2-chassis route where the transformers and PSU are housed in a separate box. I plan to visit Taiwan later this year and hope to check for available options when I am there. For now, I needed to put the modules in a case so I can listen to it - did not like the idea of having modules operating on 400V + sitting all over the table connected with loose wires    I still have lots of work tidy-up the wiring. 

Edited April 19, 201511 yr by mwl168

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Edited November 11, 201510 yr by JoaMat

And, finally, how many Mouser orders does it take to build a KGSSHV? 

 

 

Nice. No reason to be embarrassed

Congrats

@joamat - I've got to figure out if the servo is possible and stable first. I can post some ideas if you'd like to experiment a bit.

I'm very interested in your servo, so ideas and information are welcome and I'm sure builders out there are equally interested.

I published the schematic for the KGST w/ servo in the KGST thread here: 

 

Congratulations on the build mwl168 and happy to hear it's making sweet music. May i ask what temperature your reading on the heatsinks as they look pretty small.

If he runs it stock it should be enough sinking, the original full-size offboard build was overkill

Just some centre drill bits and an automatic centre punch nothing too exciting, my drill press is a Ryobi from Bunnings as well and it sure is quirky...

Which automatic centre punch did you end up getting? I'm keen for one

If he runs it stock it should be enough sinking, the original full-size offboard build was overkill

Ah thats good to know. 

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Edited November 12, 201510 yr by JoaMat

Congratulations on the build mwl168 and happy to hear it's making sweet music. May i ask what temperature your reading on the heatsinks as they look pretty small.

Thanks!

 

I see that nopants already answered your question but I can confirm what he said.

 

I am running 120R for the R5/R6 on the amp which should yield about 9mA output current. At this setting and without the chassis cover on (as is in the photo I posted), the heatsinks are only slightly warm to the touch when the ambient temperature was in the 65 F range. This does surprise me a bit as the heatsinks, as you said, are on the small side. Sorry I don't have the device to accurately measure the heatsink temperature.

 

In the coming days or weeks I may try to lower R5/R6 to around 100R just for experiment sake. This should bump the output current slightly to 10mA as I've read here and I'll see how much that affects the heatsink temperature. Putting the cover on will also be another factor which I need to do soon.

 

As I've said in my previous post, the operating temperature affects the offset quite a bit (as does raising the output current based on what I read here). I know you have the same boards I used for this build so may want to consider lower the value of R26 (2K) to give better range for offset adjustment

 

Best!

 

 

 

See my update on heatsinks temperature in post # 4482

Edited October 19, 201510 yr by mwl168

I've been really busy today. Below is KGSShv converted to Carbon with some daughter boards. The big one on left channel is servo Kerry style. Amp has been running for one hour and it seems to work.

 

 

IMG_1407.JPG

Is this the same build as the one you posted before? At what current did you configure the output stage?

I've been really busy today. Below is KGSShv converted to Carbon with some daughter boards. The big one on left channel is servo Kerry style. Amp has been running for one hour and it seems to work.

 

 

IMG_1407.JPG

 

Awesome

 

Do you have a scope you can throw that on?  We can tweak some of the values if needed.

 

I'm guessing you were able to recalculate some of the values in the voltage divider chain.  I love that you can turn ideas into practice so quickly.

 

EDIT:

I'm guessing you added this servo to the third stage (same place the POT was) and not the output stage.

Edited April 20, 201511 yr by Kerry

Just want to say that it’s Kerry’s KGST that inspired me to build this offset servo. The KGST version Kerry built is very impressive. Use of smd parts and the offset servo is IMO a step forward.  I’ve spent some time to figure out how to get a working offset circuit (studied pictures of Kerry’s KGST).

Edited November 14, 201510 yr by JoaMat

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Edited November 11, 201510 yr by JoaMat

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Edited November 11, 201510 yr by JoaMat

Do you have a scope you can throw that on? 

 

Sorry for slow respond. Yes I have an oscilloscope, something UNI-T - red thing - but I don't know how to use it and I 'm to scared to stick my nose in high voltage area with it.

I am running 120R for the R5/R6 on the amp which should yield about 9mA output current. 

 

 

Is this  http://gilmore.chem.northwestern.edu/boards/kgsshvproductiondualmot.PDF the schematic for this rev 0.91 board? Sorry if this is a daft question.

that schematic is close enough

 

 

i'm redoing the kgsshv-carbon board for current parts, i added the cascade current source,

is there anything else people might want?

Edited April 21, 201511 yr by kevin gilmore

Sorry for slow respond. Yes I have an oscilloscope, something UNI-T - red thing - but I don't know how to use it and I 'm to scared to stick my nose in high voltage area with it.

It seems like tying the reference up the way you did should work fine. I've modeled that approach before.

Glad it seems more stable.

Regarding the scope, I only wanted you to look at the outputs. You would ground the clip on the probe and measure each leg of the amp.

PM me if you'd like and we can walk through the process. I think I have a solution for the oscillation in the KGST but need to try it tonight.

I've been eyeing the stereo board version of the KGSSHV, and debating between building it next, or a KGST. Decisions, decisions.

 

For the lower-voltage versions of the KGSSHV (like the 400V stereo), a couple of things I never quite understood (and would appreciate a link back upthread, since I seem to have missed this info previously):

 

1. What transformer specs do I need for a 400V version?

2. What parts need to change on the PSU board (I'm looking at kgsshvpsminifinal)?