The ultimate DIY? A Stax SRM-T2!

[kevin gilmore]

the parts stuffing is on page 3

http://gilmore.chem.northwestern.edu/staxt2nc3fdh3.pdf

if the active batteries are not conducting then many of the led's will not be turned on.

Adjust RV2 to decrease the resistance, (i think)

When things start to conduct, small changes will cause the amp to flip flop back

and forth. Until both sides of the amp are balanced. Its a bit tricky, but once

you figure it out, its not too bad.

Yes the led's run at low currents. But from the picture i posted, they do in fact light

up pretty well. Definitely not dim.

Also measure the voltage across R42. If its zero, then there is a problem with the 2sk246

Edited July 3, 2010 by kevin gilmore

[Inu]

Working!

Cause

Position of the RV2 (10K) was way too low.

Voltage starts moving from 8K to 10K position.

As matter of fact, I used 2SK246BL instead of GR. I used lower idss group from my stock but it was not low enough.

While investigating, sparked somewhere in the Active battery area and all of 2SK216 and 15V zener diodes in R-channel went to heaven.

I need to find out the place that sparked.

I can sleep tonight.

Thank you for all your help.

http://picasaweb.google.com/inuponken/T2#5489547000733455298

[Bidoux]

I know it isn't liked here to say it, but I do think all these builds are awesome !

The only thing I regret is the position of the tubes. I would have personnaly prefered the small tubes in the front of the big ones ; maybe the layout was not possible this way.

[spritzer]

That layout would make no sense at all since the output sockets are at the front and the inputs at the back. Why run wires back and forth just for the look?

Ohh and I'm glad it worked.

[Craig Sawyers]

Semis just arrived, with the only waited for item being the 2SC3381GR. Luckily judging by Inu's post I've got 2SK246GR and not BL.

At least I can stuff every semi not heasink mounted (apart from the '3381s) now.

[struts]

Working!

As matter of fact, I used 2SK246BL instead of GR. I used lower idss group from my stock but it was not low enough.

[url=http://picasaweb.google.com/inuponken/T2#5489547000733455298]

Good job you mentioned this Inu, I was also thinking of 'cheating' and using BLs. Can anyone here point me at a source for the GR version?

[kevin gilmore]

I love it when a plan comes together...

The whole design of the amp is to minimize the lengths of the audio traces.

So the pot is in the back, the input tubes are in the back, signals go from the

back to the front and then out the front hole.

There are lots of amps that do it backwards, which makes no sense.

The BL vs GR version thing completely makes sense.

Even at 8k, there is still plenty of adjustment room, because once

you get it to turn on, on that pot, .25 turn is all that should be needed.

Edited July 3, 2010 by kevin gilmore

[luvdunhill]

Good job you mentioned this Inu, I was also thinking of 'cheating' and using BLs. Can anyone here point me at a source for the GR version?

I can supply you with some if you cannot find them elsewhere. These are a "standard" with many of the Borbely designs, used to cascode the input JFETs to "enable" them to work at a higher voltage.

[struts]

I can supply you with some if you cannot find them elsewhere. These are a "standard" with many of the Borbely designs, used to cascode the input JFETs to "enable" them to work at a higher voltage.

Most kind, luvdunhill! I may take you up on that if I can't locate them nearer to home.

[Bidoux]

It makes sense, Spritzer and Kevin Gilmore.

On Woo audio 6 or Woo audio 3 it is the way I described because the pot is not "extended" like you did, so the inputs are in the front in some sort of ways.

[struts]

Most kind, luvdunhill! I may take you up on that if I can't locate them nearer to home.

Got them (Nikko Electronics). Now my problem is the FQP8N80Cs. Mouser is out and not expecting stock until December(!) and Digi-Key has a minimum 1000 order. Any suggestions folks?

[Inu]

Got them (Nikko Electronics). Now my problem is the FQP8N80Cs. Mouser is out and not expecting stock until December(!) and Digi-Key has a minimum 1000 order. Any suggestions folks?

I bought them from here.

I'm using FQPF (mold type) version.

FAIRCHILD | FQPF8N80C | FQPF8N80C Series N-Channel 800 V 1.55 Ohms Mosfet - TO-220F - Future Electronics

[url=http://www.futureelectronics.com/en/technologies/semiconductors/discretes/transistors/mosfets/Pages/9586512-FQPF8N80C.aspx]

[struts]

I bought them from here.

I'm using FQPF (mold type) version.

FAIRCHILD | FQPF8N80C | FQPF8N80C Series N-Channel 800 V 1.55 Ohms Mosfet - TO-220F - Future Electronics

Many thanks Inu.

[Inu]

Many thanks Inu.

Ebay

Power Mosfet 8N80 8A 800V 35nC 13pF DMOS TO220 Metal x4 - eBay (item 180460936754 end time Jul-23-10 17:07:00 PDT)

[Craig Sawyers]

Good job you mentioned this Inu, I was also thinking of 'cheating' and using BLs. Can anyone here point me at a source for the GR version?

ELECTRONIC COMPONENTS, SEMICONDUCTORS, PARTS, TRANSISTORS, INVERTERS, TRANSFORMERS | DALBANI

[Voltron]

Congrats Inu and KG!

[struts]

ELECTRONIC COMPONENTS, SEMICONDUCTORS, PARTS, TRANSISTORS, INVERTERS, TRANSFORMERS | DALBANI

Thanks Craig, I subsequently found this in one of your earlier posts. This is a really excellent source, one for the Rolodex.

[spritzer]

I just bought from them for another project. Very quick shipping.

[struts]

Ebay

Power Mosfet 8N80 8A 800V 35nC 13pF DMOS TO220 Metal x4 - eBay (item 180460936754 end time Jul-23-10 17:07:00 PDT)

Even better, although Scott just beat you to the punch on this one via PM. Apart from instant availability the really great thing is that these ebay sellers usually have incredibly low shipping fees. For instance this seller charges $3.90 worldwide, about 1/10th of Future Electronics' min delivery charge to Sweden

Just don't know how Spritzer does it, he must be paying the same or more than me. I'm guessing shipping fees are going up end up being about 25% of the cost of his amp!

Thanks for all the help guys.

[Craig Sawyers]

Got them (Nikko Electronics). Now my problem is the FQP8N80Cs. Mouser is out and not expecting stock until December(!) and Digi-Key has a minimum 1000 order. Any suggestions folks?

Or www.rswww.com at 99p each, their part number 671-5199 - where I got them from. Their website is down at the moment - they often do site maintenance at the weekend.

[spritzer]

Just don't know how Spritzer does it, he must be paying the same or more than me. I'm guessing shipping fees are going up end up being about 25% of the cost of his amp!

Yup and add to that a lovely 60% tax since any electronics here are a luxury commodity...

[Craig Sawyers]

Well, apart from the 2SC3381 both boards are now completely stuffed.

I'm getting a little wary of pushing those into the holes though. Although KG opened them out a tad, just enough to leave some plating on the inside of the holes they are still reportedly a very tight fit. The holes seem to be a tad under 0.6mm - a #74 perhaps (0.57mm). I need to stock up on carbide circuit board drill bits anyway, so I have put a couple of 0.65mm on the list. Across the corners of the square pins is 0.63mm (2SK389's actually measure 0.59mm) - so an 0.65mm should work nicely.

The downside is that 0.65mm will definitely take out the hole plating - so I'll have to carefully solder both bottom and top side pads. I'll report back once I have the drill bits and the 2SC3381.

[kevin gilmore]

One person has just canceled, so there is one more set of boards/chassis available.

First person to PM me gets it. But it still will be a few months and it will ship as a complete

set. (figure about $1500 plus shipping)

[kevin gilmore]

Morphsci is today's winner...

That went fast.

[Inu]

Replaced 2SK216s and 15V ZDs.

Both CH are working now.

If I connect 100V taps to the connecters on the PCB, regardless of RY, HV appears on secondary of HV trafo.

20V(120-100)from LV trafo.