kgst

[insanity]

Update: When i short the inputs the amp is silent. Must be noise from my test source then (Yulong D100 mk II). Doesn't really compare to the Invicta which is my usual source. 

Edited September 21, 2014 by insanity

[Laowei]

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.

[GeorgeP]

nope.

[Laowei]

Thanks.

Now I can order the wire I need.

[headinclouds]

I must chip in here  There is no official convention.  I have a sort of mnemonic way of doing it.  Bias is always white.  Left channel has two colours with L in such as blue and yellow. The brighter being the more positive so yellow is the + output.

 

The right channel has at least one colour with an R in such as grey, and the brighter one is pink or similar.  This aids in checking you have it connected up correctly.

 

It's pretty too. 

[spritzer]

I just use what ever I have at hand.  It will change now as I run down the old supply of wire and switch to the new stuff

[chiguy]

So I finally received my transformers.  I've built 2 KGST PSUs and all of the measured DC voltages seem to be within a few volts of what's expected. However, the -350V line is off on both PSUs.  One PSU stabalizes at around -366.6VDC and the other PSU stabalizes at around -360.2VDC after about 10/15 minutes .  The +350V lines are +353VDC and +356VDC.  The transformers I have measure around 320VAC with no load on the HT lines.

 

Is this something to be concerned about?  Anything I can do to bring it down a bit?

Edited September 30, 2014 by chiguy

[mypasswordis]

Check the zener diode string and swap as necessary so that they add up to the right amount. Can use dy294 to test the zeners if you have one

[spritzer]

Yup check the zener string.  I just looked over the layout file for the PCB and didn't see anything wrong. 

[chiguy]

Thanks for the advice!

 

It was pointed out to me that with 5% zeners, 350 x 1.05 = 367.5 and yup, I am using 5% zeners.  I guess I got unlucky.  =\

 

What I'm currently using:

http://www.mouser.com/Search/ProductDetail.aspx?R=Z4KE150A-E3%2f54virtualkey61370000virtualkey625-Z4KE150A-E3

http://www.mouser.com/Search/ProductDetail.aspx?R=Z4KE100A-E3%2f73virtualkey61370000virtualkey625-Z4KE100A-E3%2f73

 

I guess I can order some more zeners test for the best ones.  I can't find anything that are better than 5% at 1.5W. 

[chiguy]

A side question, would there be any benefit in adding a GND binding post like what Stax does on their amps?

http://www.mouser.com/ProductDetail/Johnson-Emerson-Connectivity-Solutions/111-2223-001/?qs=sGAEpiMZZMuIC3ROaEqRYQyfaKnYG3ZM

[mypasswordis]

I would simply buy and test some 91V zeners to replace the 100V ones.

[spritzer]

A side question, would there be any benefit in adding a GND binding post like what Stax does on their amps?

http://www.mouser.com/ProductDetail/Johnson-Emerson-Connectivity-Solutions/111-2223-001/?qs=sGAEpiMZZMuIC3ROaEqRYQyfaKnYG3ZM

 

I don't see any reason to do that. 

[justin]

I would simply buy and test some 91V zeners to replace the 100V ones.

 

this, the voltage of zeners will be higher when they get hot

[spritzer]

When dealing with stuff 91V zeners are good to have around. 

[kevin gilmore]

if you want a rock solid and stable to way less than 1% power supply

you have to build the original kgsshv supply trimed down for voltage.

its probably not necessary unless you really want the extra stability.

[chiguy]

Thanks everyone!  I've ordered some zeners. 

 

I didn't think having +/- 350VDC on the dot was terribly important, I wasn't expecting such a difference in range however.  While testing last night, part of me was thinking "just plug the amp boards in, what's the worse that can happen?"

 

On that note, what would happen if I ran the amp boards with my power supplies as they are now?

[kevin gilmore]

as long as the zero and offset are right, it will work fine.

 

should work fine between +/-350 and +/-400

[Laowei]

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.

[nopants]

curious as to how it sounds over the mergertron

[Kerry]

I turn on my +/-15 supply before I turn up the HV and have had no issues. You should be fine to test the LV first. Don't do the reverse though.

[spritzer]

No problem testing just the LV side of the amp alone but it won't tell you much aside from "didn't blow up". 

 

I would recommend holes for that chassis... a lot of holes.  Either that or dial down the current for the CCS as it should get very toasty. 

[Laowei]

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.

Edited October 6, 2014 by Laowei

[spritzer]

Mine have a lot of holes underneath the boards so that's a good way to go.  Still the KGST runs very hot but if heat ever becomes a real problem you can cut the current to through the tubes a bit. 

[chiguy]

How does one reduce the current in this amp?