The ultimate DIY? A Stax SRM-T2!

[ujamerstand]

partsconnexion is in GTA.

Edit: for some reason I thought you were in Canada, nevermind!

Edited April 27, 2011 by ujamerstand

[HAL 18000]

Hi all,

I finished to read the thread. I think I will have to read everything again because it is a bit dense for me.

Anyway it was quite interesting, and I am going to build this T2.

That is going to be my first DIY project. I am not a total newbie, I do soldering sometime and I did have quite a lot of electronic courses during my studies, but I don't remember much now.

- PCB boards: I will need to have the PCB boards built. The latest files I found are from Kevin post :

Correct me if I am wrong, but these are the files I have to send to the PCB manufacturer?

I did a quick check and there are a few options available:

- PCB boards: Material: FR4 seems the most common

- Finish: HASL lead free, Electroless Gold RoHS, Electrolytic Ni/Au RoHS, Chemical Silver RoHS

- Copper Weight (oz per sq ft): from 0.5 to 5.0

- PCB thickness (mm) 1.6, 2.5

Can someone explains me what should I choose?

- Components:

- Many links to components retailers has been given in this thread, I bookmarked them.

- One thing I am wondering about is the transformers. I am living in the UK like Craig so I may get the same transformers, but what if I want my T2 to work on 110V and 220V?

- It looks like most of issues are related to defunct/counterfeit components. I think it is a good idea to test them individually. I have a basic multimeter which measures voltage, current, resistance and continuity.

What sort of good multimeter would you recommend me? There are several references to a curve tracer for transistors, is it absolutely necessary?

- Chassis, heatsinks: Well, at the moment, I don't know how I am going to do that. I even don't know where to start. I don't remember having seen details on how to build them. Any help will be highly appreciated.

And congratulation to Kevin for his work on this DIY T2 and everybody who already have a working unit!

[Craig Sawyers]

Hi all,

I finished to read the thread. I think I will have to read everything again because it is a bit dense for me.

Anyway it was quite interesting, and I am going to build this T2.

That is going to be my first DIY project. I am not a total newbie, I do soldering sometime and I did have quite a lot of electronic courses during my studies, but I don't remember much now.

- PCB boards: I will need to have the PCB boards built. The latest files I found are from Kevin post :

Correct me if I am wrong, but these are the files I have to send to the PCB manufacturer?

I did a quick check and there are a few options available:

- PCB boards: Material: FR4 seems the most common

- Finish: HASL lead free, Electroless Gold RoHS, Electrolytic Ni/Au RoHS, Chemical Silver RoHS

- Copper Weight (oz per sq ft): from 0.5 to 5.0

- PCB thickness (mm) 1.6, 2.5

Can someone explains me what should I choose?

- Components:

- Many links to components retailers has been given in this thread, I bookmarked them.

- One thing I am wondering about is the transformers. I am living in the UK like Craig so I may get the same transformers, but what if I want my T2 to work on 110V and 220V?

- It looks like most of issues are related to defunct/counterfeit components. I think it is a good idea to test them individually. I have a basic multimeter which measures voltage, current, resistance and continuity.

What sort of good multimeter would you recommend me? There are several references to a curve tracer for transistors, is it absolutely necessary?

- Chassis, heatsinks: Well, at the moment, I don't know how I am going to do that. I even don't know where to start. I don't remember having seen details on how to build them. Any help will be highly appreciated.

And congratulation to Kevin for his work on this DIY T2 and everybody who already have a working unit!

[Voltron]

Welcome to Head-Case, Hal. Take a few minutes and read your welcome PM linked in my signature and others'. You will hear this from people far more knowledgeable than me, but you are making a huge mistake by choosing a complex, high voltage amplifier as your first DIY project. Listen to them. Heck, it looks like it took you two tries just to make an account here.

Edited May 2, 2011 by Voltron

[Craig Sawyers]

Sorry 'bout the random repeat. Too much booze - hic. You've sure picked a toughie to build as a first major project!

- PCB boards: I will need to have the PCB boards built. The latest files I found are from Kevin post :

Correct me if I am wrong, but these are the files I have to send to the PCB manufacturer?

You need the Gerber files to send to a board house.

I did a quick check and there are a few options available:

- PCB boards: Material: FR4 seems the most common

- Finish: HASL lead free, Electroless Gold RoHS, Electrolytic Ni/Au RoHS, Chemical Silver RoHS

- Copper Weight (oz per sq ft): from 0.5 to 5.0

- PCB thickness (mm) 1.6, 2.5

Can someone explains me what should I choose?

Kevin ought to commernt here abuot what he specified. But standard is FR4, 1oz copper, 1.6mm thick.

- One thing I am wondering about is the transformers. I am living in the UK like Craig so I may get the same transformers, but what if I want my T2 to work on 110V and 220V?

All you need to do is specify what primaries you want, and Paul will wind according to your spec. Bear in mind that 110V is usually 60Hz, so you ought to specify that too. Also, I guess that you want two windings that you either connect in series or parallel.

What sort of good multimeter would you recommend me? There are several references to a curve tracer for transistors, is it absolutely necessary?

I'm getting worried - to build the T2 you ought not be asking questions like that. It is difficult to build, demands someone who knows what they are doing, and is highly lethal if you don't know what you are doing

Are you sure that you want to tackle this as a first project?

[kevin gilmore]

My boards were 4 oz copper.

Lil-knight's boards were 3.5 oz copper.

A person here did in fact build the T2 as his

first DIY project. And succeeded. But he had

help from above.

This thing is a whole bunch of work and even more

if you are doing your own chassis.

[HAL 18000]

Thanks for your answers and warnings.

-Complexity is one thing. With work and patience it can be overcome and I am willing to do that. Actually that is where is part of the fun . It will take many month without a doubt, but I am not in a hurry. I will reopen my electronic courses material if necessary (I never thought I would do that for a hobby). Also I am single so more time to spend on it .

Hazard is another thing. It is always around, even someone here received a shock while building the T2 (Inu I think ). Some times ago, before I got an interest in the T2, I read someone speaking of its B22 amp and the danger of high voltage but I did not gave much interest at this time.

I will do searches to understand what are the risks. It is definitively something not to be taken lightly. Do you have some documents/links describing the safety rules when working on high voltage circuits?

- In my office there is an area where technicians do calibration (and repair maybe) on test and measurement equipment for telecommunications. I will have a chat with them one day to see what sort of equipment they have, perhaps I will see intersting things.

- Why using aluminum for the heatsinks and not copper? As far as I know copper has a superior heat dissipation capacity. Is it a matter of price or is it easier to work with aluminium?

[deepak]

Copper is to put it in New Englander terms, wicked expensive at the moment

[HAL 18000]

Indeed. I checked the prices, copper is around 4x more expensive.

So far 5 T2 have been "officially" finished, what is happening with the remaining set of 15 boards/chassis sent by Kevin? Have they been quietly completed or are still work in progress?

[nattonrice]

It is a pretty massive undertaking to "stuff" the board let alone finish it.

I like to think of my self as pretty experienced and I'm still trying to track down a problem in my -500v supply (not having much time doesn't help this).

With the sort of questions you are asking I'd approach this project with a lot of care.

[Craig Sawyers]

With the sort of questions you are asking I'd approach this project with a lot of care.

Check.

Took maybe ten hours or more to completely stuff the amp board. Then another two or three to stuff the power supply. Hell, it must have taken a day or more just to purchase all the components - even with KG's excellent BOM. Probably another six hours plus to make the umbilicals. Add a bunch of time to wire the chassis to the boards. Then 20 to 40 hours to track down the counterfeit 2SC3765's and do a major re-build of the main heatsinks.

I reckon 40 hours plus to build this sucker - when you know what you're doing. And that was with KG's chassis kit and boards. Then the same amount of time again to fault-find (yeah - I was unlucky with crap transistors. And happen to have a curve tracer to diagnose the problem and know how to use it).

The equivalent in other areas of endeavour would be to chose an Aston Martin or a V12 Jag as your first car to rebuild and restore. And before you ask - yes I have restored my V12 Jag (but that cost **a lot** more than the T2, and took two years). I have a *very* understanding wife

And it is lethal (as are all electrostatic headphone amps) - in the T2 some parts have way upwards of 1100V from one place to another, and enough current available to stop your heart .

[pedefede]

OK - got most of the parts finally ... so soldering has finally begun !!

(It will probably last long, as im building at least 5 projects simultaniously....)

I noticed Inu "lifted" a lot of components .. especially the zeners and diodes - while Kevin mounts most components on the PCB surface. I suppose its probably a heat issue.

But (besides its easier), the PCB also holds a groundplane to shield some noise ...

So is there any reason to lift other than the power-resistors?

peter

[Kerry]

News from the build front...

I just powered up the PS and everything looks good

I took a few shots. First up is the patch to squelch the oscillation. I used Teflon coated wire and tried to run it so it would cross the least number of traces.

Here's the money shot of the rails before I mounted the board in the chassis. Note that I actually mounted everything in the chassis before I attached the rails so that everything would fit once the transistors were soldered in. This was recommended earlier in the thread.

I ended up with the 7721-3PPS insulating washers, but did have to drill out the IXCP10M90S and MOSFETs with a #28 bit and deburr them. All the transistors / regulators were mounted on aluminum oxide thermal pads (4171G). I was then able to use stainless steel (black oxide coated in my case) hardware with worrying about an electrical breach to the mounting rails.

Here's another shot of the mounting rails after it is placed in the chassis. Note that I tested all of the components before I put anything onto the board. I matched the current regulators for the current limiting in each of the four supplies (I'm sure I did not have to do this). Also, I checked the hfe on the 2SC3675 transistors and picked values between 41 and 47. I wanted to keep the higher hfe transistors for the batteries.

Before testing the supply I checked the transformers (first ohms then voltage). Everything from SUMR came in just fine. Said a prayer and powered on just the positive rail. Everything checked out.

Next I disconnected the positive rail and checked just the negative rail. Wow, that worked too

Finally, I applied power to both the positive and negative rails and everything check out. Note that the -260 volts is a combination of the 500, 60 and 300 supplies on the negative rail.

I've still got to scope the supply to make sure that there are no oscillations, but I'm not too worried about that.

Not done yet, but I wanted to thank everyone for posting their issues and solutions on the thread. It really made a big difference for me.

[Voltron]

:jbl:

Beautiful work Kerry!

[blubliss]

Very nice!

I guess I am the only one who used plastic screws, hope that will be all right in the long run?

My T2 (which is on right now-lunch break) also approves of your work

[Kerry]

I think that Inu also used glass filled nylon srews. He's been running for a while now. It's all within spec, I just wanted more headroom.

[blubliss]

Mine are plain nylon from McMaster-Carr.

[Horio]

Great work Kerry. Looking forward to more pictures as you progress.

[Craig Sawyers]

Great looking job Kerry! Good luck with the main board, and looking forward to hearing a report on what it sounds like in due course.

[ujamerstand]

Congrats! Good luck on the amp side of things! (Not that you'd need it. )

[livewire]

Nice!

Cant wait to see more positive progress.

[Lil Knight]

Beautiful work, Kerry!

[justin]

I think that Inu also used glass filled nylon srews. He's been running for a while now. It's all within spec, I just wanted more headroom.

have you found those smaller than a #6?

[chinsettawong]

Nice work!

[Kerry]

Thanks.

Regarding the glass filled screws, I've only seen them in #6 and up. I just looked on McMaster and they have Tephlon at $3.50 per (ouch!). They have regular nylon, but I also noticed that they now have polycarbonate in size #4 rated to 212 deg F.