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kevin gilmore

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I'm still waiting for a transformer but as of now, I've gotten the PCBs completed.  What I'm wondering now is what are the proper power-on and setup procedures?


This is what I'm thinking.  Some dumbness/ignorance here so feel free to correct me:



Connect transformer to 115/230v AC mains via input recepticle with fuses

Connect 280VAC and 30VCT to the PSU

Do I need a dummy load on the PSU before powering on?  What can I use?

Power on, measure DC outputs, measure Bias voltage using the Bias test point.

Adjust trimpot as needed.  What does the trimpot adjust?

All the GND connections go to chassis ground?



Leave the servo opamp out.

Connect the DC power inputs.

Connect the AC Heaters.

Insert tubes.

All the GND connections go to chassis ground?

Do I need to connect the outputs?

Do I need to connect the inputs?

Adjust the balance.

Adjust the offset.

Power off and insert the opamp.


Check heatsink temperatures.


Am I missing anything?



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No load for the PSU needed.  It's regulated so you will see pretty much the same numbers with and without the amplifier boards present. 


The trimpot is a voltage divider and thus adjusts the bias supplies voltage doubler potential. 


All the GND connections are connected together on the ground plane on the PSU PCB.  These aren't connected to chassis by default so you need to run a wire to the chassis, either direct or through a ground loop breaker. I for one always go direct. 


For the amp boards, each one has one wire to the PSU ground, don't connect them to the chassis as that will generate ground loops.  No need to conect input or outputs when testing


Also remember to power off before inserting the servo opamp.  Better yet would be tom use the jumper in the position marked "servo"

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How much bigger is this amp is to your current KGSSHV mini offering Birgir?  How about the sound?


Here they are together.  KGSSHV mini quite a bit smaller. 




As for the sound they are very similar.  The ST is a bit warmer and more fluid but that's it. 


Aside from the transformer being larger than specified, are there any issues (or benefits) with using a larger transformer?


Just look at the Antek units as they are all oversized so the pro's are less heat, less noise from the transformer but the negative is more inrush current and more overhead for the PSU to deal with as heat. 


Nice work!

On your PS, are you simply bolting the two FQPF 9N90C mosfet voltage regs to the chassis as a heat sink?


Yup, it uses the chassis as a heatsink but this is a special version of the PSU. 

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I called Antek last July inquiring about their out of stock AS-1T275 and was told it would be in the "next shipment" in the first part of September. Called today, and it is not expected to be in stock until their "next shipment "in November.

So I went with a custom SumR.

Going to stuff everything in the same case as Birgir. Its my first electrostatic amp, and you know what they say about imitation. :)

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There are several of these same Chinese made cases on Ebay.

This was the least expensive when including shipping in US that I found.


One word of caution, by the inside dimensions on the ad and seeing Birgir's build, its going to be a TIGHT fit.

Edited by Laowei
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Looks to be the same case but I just pulled them from my pile of boxes.  A note though, the KGST boards from the group buy will not fit in this box.  The ones I used were specially made to fit it and they just barely do so. 


Also it runs hot... too hot.  Chassis is at 43°C above ambient so I'll have to fabricate new top panels for these amps. 


The fuse rating depends on the transformer used.  The amp draws about 60W. 

Edited by spritzer
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My KGST is up and running. Got the transformer yesterday from toroidy. As expected it is dead silent. Everything seems to work fine, no explosions. Balance and offset can be zeroed. Haven't had a chance to connect a source and headphones yet. I'll probably do this on the weekend. Uncased pictures will follow on the weekend. 

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