Laowei

I have a balanced Schiit Gungnir DAC in my main system and will hook it up soon and listen to 96/24 downloads. Even now, the KGST and SR-207 in mono via iPod sounds very promising. Surprisingly in mono, it sounds more open with low level detail than my current LCD-3F. Guess you could say I'm liking it. More to come as I get both channels up, get the upcoming Schiit statement DAC and more a more high end Stax set. Thanks again to Kevin and Birgir for all the work this design, and Headinclouds for putting on the GB. I am enjoying building this amp and exploring the new for me Stax universe.

Listened to one channel of my KGST last night. First time I ever heard a Stax, even if only a lowly SR-207. Source was an iPod Touch with its crappy digital attenuation playing MP-3 compressed files. It sounded pretty good actually, which I attribute mainly to the KGST. Originally I wired up one channel, and dialed in the balance and offset. Warmed up for a half hour and reset the trim pots. Powered down and hooked up the iPod, powered up and listened. Nice and quiet. Then I powered down and wired up the other channel. Could not get either to balance or get to zero offset. Tracing voltages, one of the first channel's CCS plate loads was acting up -could not get a stable voltage. Powered down and using my Fluke as a diode tester, found a problem with that one IC, compared to the other 5 in the amp. Unwired the first channel, and the second channel was able to balance and zero offset. Listened to that channel, and everything was nice and quiet there too. Listened for about an hour to mono..... Ordered some more 10m90s and other parts from Mouser this morning.

Thanks Kerry and Birgir. Did not want to try powering everything up at once, even with a variac. I don't like bright flashes, loud BANGs, and letting the smoke out of the transistors (along with tripping home circuit breakers). Trying to take a systematic approach to powering up for the first time. At least powering up the LV first should get the front end CCS LEDs to light. HV to be added in time..... I have a healthy respect for that. Yeah, the case will eventually have lots-o-holes. Thinking both top and bottom plates to have them above and below the heatsinks and tubes. Also a heat isolator if needed between the PS and amp boards. Going to have to get it up and running first and then decide on what it will take. A lot more work to do.

Got my amp and PS boards stuffed and soldered. Got my transformer 2 days ago and case yesterday. Everything in the photo is only trial fit and not screwed down. Getting ready to test the different power sections, and wonder if I can test the +/-15VDC circuit on the amp boards without +/-350VDC active. Thanks again to Kevin and Birgir for all the fun.

Thanks. Now I can order the wire I need.

I have found in photos on other DIY Stax amps that the Stax jack has Grey, White, Orange, Yellow and Blue wires soldered to its pins. The photos are none too clear and cannot see which goes with which. Is there a L+, L-, B, R+, R- convention to the color code that is used? Like to keep things as standardized if possible.

Looks like I get to start my own pile of boxes.

There are several of these same Chinese made cases on Ebay. This was the least expensive when including shipping in US that I found. http://www.ebay.com/itm/251509708498?_trksid=p2055119.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT One word of caution, by the inside dimensions on the ad and seeing Birgir's build, its going to be a TIGHT fit.

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.

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

Boys and their toys.

For HV tubes amps, I use a variac to slowly bring up the power for the first time and monitor the voltages. Keeps things from going BANG!.

That hole is used to route the wires to the screw terminal block for the floating tube heaters.

Did the same on my KGST BOM too. Caught it before I ordered.

FWIW: Kevin's BOM lists 4x OP07 a single opamp, and your Mouser BOM lists 2x OP275GPZ, dual opamps with a different pinout.

As a noob to building amps to power electrostatic headphones, I found this linked thread started by Birger very helpful in my upcoming build. A lot of valuable info is there for the reading and a great reference. For the other noobs building the KGST.

If you cannot get the tubes' offset adjusted with the 1k trimmer and the 1k5 resistor, try resizing the 1k5 resistor down to give more adjustment range. From what Geoff was mentioning it sounds like a tube to tube variation problem, it may or may not be needed on an individual amp. First see if you can get the offset properly adjusted with the 1k5 resistor. BTW Geoff, that photo looks nice. Quite inspiring! Working on my Mouser parts order as I type. Thanks for the PCB group buy. And thanks to Kevin and Birger for the design and prototyping.

That's the resistor marked 1k5 on the boards (3k5 on previous virtual versions) next the 1k offset trimpot?

FYI Power transformer with shipping quotes I received to the same specs as above: SumR: $94.00 plus $30.00 shipping to US Toroidy: €75,80 plus €45 shipping to US. Shipping is a killer for me with Toroidy.

The KGST is an evolving work in progress, so there is no one single BOM. Use the value printed on the PCB (1K5). That is correct for the revision the board was made to.

KGST PCBs in da house. They look great. Thanks Headinclouds!

That sounds great Geoff. Many thanks for doing this group buy. Kevin or Birger, what is the max P-P output voltage of the KGST with 350V rails? ~850-990V? Also what is the KGST's gain? I am trying to map out the gain structure of my system. Thanks.

The black looks great, Birgir.

Sweet! Great job!

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