The ultimate DIY? A Stax SRM-T2!

[peranders]

I think this will have no impact at all when it comes to heat transfer but I'm glad if you prove me wrong. How much power will you dissipate in the transistor?

[iwik]

Did any one bother to check the 2sk246 fet before soldering it in?. If so how did you test it.

By the way also any body thinking of these 2sa1486 which i think HKsouce sells then i think

they are Fake breakdown at 400v, cant remember where i got mine from .

Les

Edited May 4, 2016 by iwik

[johnwmclean]

16 hours ago, peranders said:

I think this will have no impact at all when it comes to heat transfer but I'm glad if you prove me wrong. How much power will you dissipate in the transistor?

Better thermal conductivity due to finer surface smoothness is a well established proven fact.

Whether I can prove there is a benefit is not my concern, my primary reason for employing this strategy is to have a potential that is advantageous rather than hindering.

Very little work and material is required to achieve this, so why not?

 

[JoaMat]

Here is an original T2 with Kevin’s optocoupler servo. Servo is on a small board, replaces one of the 2SC3675 in Darlington pair.

Works well…. so far.

[Kerry]

Working on the face plate for the T2.  I made the jacks and the boards and milled the face plate out of .5" stock.  It's blind mounted from inside the chassis.

I'm just about ready to wire this up. 

EDIT: I also need to add the hole for the POT.  I've got a bit more milling to do on the face.

Edited May 18, 2016 by Kerry

[johnwmclean]

I’m always amazed by our much fine detail must go into work like this. Beautiful Kerry!

[GeorgeP]

Kerry, is that pot cut out for an Alpha or one of the small TKDs? I thought you were going with a board mounted pot earlier, but may be misremembering.

[Kerry]

9 hours ago, johnwmclean said:

I’m always amazed by our much fine detail must go into work like this. Beautiful Kerry!

Thanks John. I've always been impressed by your build as well.

18 minutes ago, GeorgeP said:

Kerry, is that pot cut out for an Alpha or one of the small TKDs? I thought you were going with a board mounted pot earlier, but may be misremembering.

No, it's for a digital encoder so I can use the new version of the digital attenuator. I have couple of different style  encoders that this pocket will accommodate. 

The attenuator will mount over the board where the POT mounts are. I'll probably make up a board to make this easier.

Edited May 18, 2016 by Kerry

[JoaMat]

 

14 hours ago, Kerry said:

Working on the face plate for the T2.  I made the jacks and the boards and milled the face plate out of .5" stock.  It's blind mounted from inside the chassis.

I'm just about ready to wire this up. 

EDIT: I also need to add the hole for the POT.  I've got a bit more milling to do on the face.

I agree with John. Amazing front plate you have done, Kerry.

 

Today I built a T2 servo on a small board. It’s now doing service on an original DYI T2 and seems to work OK. If it really works the layout will be implemented in a new version of DIY T2. Also give me opportunity to learn milling PCBs on a small CNC machine – indeed a funny toy. Did a small mistake - can you find error in below pictures?

[Inu]

[JoaMat]

Yep, that’s right.

Tried to be smart. Set the cut depth to shallow at first. Ordered the machine to clean up a small area…. and at the same time it cut the trace near that pad. Learning by doing...

[headinclouds]

That's good work Joamat.  A fine example to us.

and Kerry great stuff, are you doing that on your own milling machine?  One of the "rules" I adopted from the outset was no screws should show on the front panel.

It is a costly process and requires heavy material but looks good.

[Kerry]

Yes.  I used my mill for this.  My version 2 mill is fairly solid and as long as watch the speeds and feeds, I can mill 1/2" plate no problem.

[Kerry]

Working on casing the power supply now.  The first two images are renders from Fusion 360 (love this program for CAD/CAM)...

I got the transformers from Richard at SumR.  I added a winding to the LV transformer for the +5V I use for the control circuit/relay as well as the Arduino and digital relay.  I also removed a winding on one of the HV transformers since it's not used and adjusted some voltages.

Just finished testing them in the new setup and so far so good.  I've still got to test everything under load before reconnecting to the amp. 

The face plate is a temporary while I mill the final one.

 

[chinsettawong]

Great job putting everything together in such a tight space.  Looking forward to seeing the finished amp.

 

 

[GeorgeP]

^ this! Awesome work as always!

By the way, what switch are you using there?

[johnwmclean]

Such fine work, loving it!

[Kerry]

The switch was this one:

http://www.ebay.com/itm/161443985922

[luvdunhill]

Kerry, for all that awesomeness, I still can't get behind: transformers in the rear (which stacks under the input stage and near PSU output connectors) and mounting transistors that way (versus angle bracket). Just my $0.02 though, beautiful work and what an amazing assent as a DIYer

[spritzer]

He could put a steel plate in the lid of the PSU, that should take care of the transformers. 

[kevin gilmore]

mu metal is even better

[spritzer]

Indeed, works wonders on this stuff. 

[JoaMat]

5 hours ago, luvdunhill said:

Kerry, for all that awesomeness, I still can't get behind: transformers in the rear (which stacks under the input stage and near PSU output connectors) and mounting transistors that way (versus angle bracket). Just my $0.02 though, beautiful work and what an amazing assent as a DIYer

Transformers in the front (other reason than above though). You like the wiring? Size is huge.

Angel brackets adds to much thermal resistance and add space.

Edited May 25, 2016 by JoaMat

[Kerry]

Thanks for the comments above    I do appreciate it since I'm always looking to do better.

I was thinking of putting the transformers in the front, but I couldn't fit the power inlet and output comfortably with the board layout.  I can think about this as a future revision.  Currently, I've got about a 4" gap between the top of the transformers and bottom of the inputs when the units are stacked, which helps a bit.  I've also got about 2" between the transformer and output and I will shield the output cable leading to the output.  Transformers are shielded too.

Additionally, I added shielding (tied to chassis/earth on the PS side) between the AC in the umbilical and the DC outputs.

I can look into mu metal / steal as well.  This seems like a great solution.  What about a steel mesh (just thinking of air flow)?

What's the specific concern on the transistor mounts?  I know there are more screws if I want to remove the board, but I did like the idea of saving space and also that there was one less component between the transistor and the sinks.  I considered mounting the transistors to a 3/16" flat plate and mounting the plate to the sinks, but it just felt like a lot of extra machining and I didn't have a clear goal for it in mind.

EDIT: One other thought/question.  I was going to solder the transformer leads for the filaments directly to the output jack.  If I need to replace that transformer for any reason I could simply cut the leads and splice the new transformer in.  I don't love this, but it's not that much work in the grand scheme of things just in case the LV transformer blew out in the future.

Are there any good suggestions for in-line connectors?  For the output filaments, they'd need to be able to handle the -500V to chassis/input filament isolation.  This feels like a bit of over-engineering, but this whole build is about that :)

Edited May 25, 2016 by Kerry

[kevin gilmore]

i soldered the filament wires directly to the jacks.