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After almost three and a half months, the KGST is finally in operation, and is sounding great. Thanks to all who have responded to my questions and given guidance. I am really surprised at  how good t

Thanks to the NYC Spring Meet yesterday, I was motivated to finish casing up my KGST.  I'm very happy with the result.  The chassis is 7" x 12.8". Perfect for my night table   Here's the beast in i

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Any suggestions on how to best place the power supply and amp boards before I start drilling? Transformer's place is given, and maybe the power supply should be placed at the back too with the amp boards facing the front (right). Thinking of hum and heat issues. Tubes will fit inside the box but I suspect holes on top lid above the tubes would be beneficial - top lid only has those small ventilations on the sides. Depends how hot the KGDT runs.

 

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32 minutes ago, mdr30 said:

Transformer's place is given, and maybe the power supply should be placed at the back too with the amp boards facing the front (right).

Difficult to see from the pics how much space you really have, but FWIW this layout would probably be my starting point.

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  • 4 months later...

As there is one more KGDT being built I thought I'd post some pics. I went with Jose's suggestion regarding the placing of the amp boards, seems to be the best compromise.

I had concerns with the AC heater leads but no hum. A modest +/-300V but very nice with normal bias Stax. And 6/12V tube rolling possible.

 

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  • 4 months later...
On 9/12/2017 at 6:51 AM, spritzer said:

First thing I'd check is a cold solder joint or something like that.  Then measure the pots and see what they are doing when you turn them. 

Hi Sprizter,

I would like to check if the volume control on the KGST can be adjusted individual, just like typical Stax amp. As my left ear is slightly unbalance from my right.

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4 hours ago, spritzer said:

On the ones I build that is not possible.  Those dual split shaft pots are impossible to get outside of ordering thousands of them at a time. 

Thanks for the info. I have just bought a KGST s/no. 34 from a fellow head fi forum member. So, I would really appreciate if you could advise me how to adjust zero and balance for the tubes. And any other tuning that must be done and check, before listening. It's shipping from Switzerland to Australia. The average incoming voltage is around 240V at my place.

I'm currently using my Stax 727II with feedback mod, driving L-700.

 

Cheers

Tachi

 

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The balance and offset adjustments are the same as the for the Stax SRM-T1 so all the same applies.  The pots are marked on the PCB so its easy to spot which is which. 

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6 hours ago, spritzer said:

The balance and offset adjustments are the same as the for the Stax SRM-T1 so all the same applies.  The pots are marked on the PCB so its easy to spot which is which. 

Ok, got it, thank you.

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  • 4 months later...

Hi folks,

How long does the tubes in the KGST usually last? Mine has started making "tube noises" from time to time, in both channels, most notably after power-up. It goes away after some time/warm up. I have cleaned the pins and tightened the sockets, but no change.

 

 

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  • 7 months later...

Hi,  I am a newbie to this forum and I am late to the party. I only find out this forum and thread recently. I have a Stax Lambda (non pro version) for many years and have been using a SRD-7 to listen to music. But I have always wanted a direct drive amplifier for this headphone. So when I found this forum and the KGST thread, I was thrilled and decided to join the party even its late. I have contacted Birgir recently and bough a set of boards from him. 

I know I will need help for this community to put this amp together and I am reaching out to the members (especially the experienced and advance members) who have much more experience in this than me to give me a helping hand, much appreciated. I do have some experience in building amplifiers (tubes included).

The first help I need is to find the most recent schematics for the KGST amplifier and its PSU. I know there has been some revisions since the beginning. If someone can point me to where I can find them, I would greatly appreciate. 

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Hi Matthew,

I'm in the same boat, I recently got the boards from Birgir and I'm currently building my BOM plus learning a lot about electronics as I don't want to build it just for the sake of building it, but also understand what it does. I have drawn the schematics on a sheet of paper but they need tiding up, so if someone has an electronic version I would not mind.

Cheers,
Arno

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An we are three! I do nto have the boards yet and would be grateful if Birgir coudl sell a set to me as well.

I have been hapy with my three stages 300B SE + transformer (built by myself) for long time but the KGST seems to be still the golden reference for staxes. Kind of gave up the idea to build one as the last group buy has been lon gago.

Kevin loaded all the diagrams in a share when he retired, but not sure if that are still up to date.

Biggest concern of mine woud be components availability. Is there a recent verison of KGST with currently on the market components?

 

Antonio

 

 

 

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Going by memory, the only obsolete part on the KGST is the 2SK170 JFET which is still available at BDent. Stay out of eBay, etc. - most advertised out there are fakes.

I personally do not consider KGST the golden standard of  Stax amps but it's easy and low cost to build. 

One other easy to build Stax amp that uses all current parts is the all solid state electrostatic current feedback amp. 

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Listen guys. The info's in here, you've just got to hunt, start building and then shout out when disaster strikes!

Built mine 4 years ago, and I'm old, so I've forgotten a lot since then, but to get you started here's a list of questions and answers, and other info I cobbled together after trawling through the posts. Might be useful. I've also attached a schematic I have in my files as well.

If you know where you can get a quad of 6s4a's from, don't tell anyone else, just let me know!!

You'd have to check through the posts for any significant changes over the past 4 years.

FWIW, I got my custom TX at a good price from Toroidy in Poland. It's worked a treat, but there are plenty of other places out there.

Good luck!

@matthew-levi Thought everyone was using the KGST with Pro output?

KGST circuit.jpg

KGST info addendum.pdf

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9 minutes ago, valve5425 said:

Listen guys. The info's in here, you've just got to hunt, start building and then shout out when disaster strikes!

Built mine 4 years ago, and I'm old, so I've forgotten a lot since then, but to get you started here's a list of questions and answers, and other info I cobbled together after trawling through the posts. Might be useful. I've also attached a schematic I have in my files as well.

If you know where you can get a quad of 6s4a's from, don't tell anyone else, just let me know!!

You'd have to check through the posts for any significant changes over the past 4 years.

FWIW, I got my custom TX at a good price from Toroidy in Poland. It's worked a treat, but there are plenty of other places out there.

Good luck!

@matthew-levi Thought everyone was using the KGST with Pro output?

KGST circuit.jpg

KGST info addendum.pdf 116.85 kB · 1 download

Thank you for the amp schematic. Do you know where I can get the PSU schematics. I have looked thought the dropbox and Google Drive posted by KG but does not seem to be able to locate the PSU. I thought there are others who have build non pro version. BTW, your info addendum is very useful, thank you for that.

 

 

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Kevin designed multiple PSUs for Stax amps over the years.

I believe the board shown in matthew-levi's post is what's called BH mini PSU. It's the simplest, lowest cost to build PSU. The schema show in decoherent's post looks like the GRHV psu.

Either PSU will work but the GRHV is much more stable and much lower noise but also much higher cost and larger in physical size. 

Edited by mwl168
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