The ultimate DIY? A Stax SRM-T2!

[n_maher]

That looks fantastic Inu! Can someone explain to an idiot about the TRS jack though?

It's the panel bearing for the shaft extension kit, looks a lot like the front a Neutrik jack so the mistake is understandable.

[Craig Sawyers]

Based on the assumption that KG's knob is 1/4" (waits for the inevitible comments...), since the panel bearing specced is for 1/4" rod, I need to transition from 1/4" rod to 6mm shaft for the DACT.

I've therefore bought a 6mm shaft coupler (Rapid Electronics), and will ream half the length out to 1/4". I could of course turn the 1/4" rod down to 6mm at one end, if I had a lathe (but I don't), so adapting the hole size in a coupler is much easier.

[Inu]

I used http://www.custompowdercoating.com/

They did good job with reasonable price (less than $200 for all).

Yes, I placed R81 and R82 on the back.

[Craig Sawyers]

I used http://www.custompowdercoating.com/

They did good job with reasonable price (less than $200 for all).

Yes, I placed R81 and R82 on the back.

Did they mask casework areas that are in electrical contact?

[swt61]

It's the panel bearing for the shaft extension kit, looks a lot like the front a Neutrik jack so the mistake is understandable.

Ah, that makes perfect sense. I couldn't for the life of me figure out how a TRS jack was going to work on an electrostatic amp. So the shaft goes into the bearing and back to the attenuator, gets locked down into the attenuator, and then the knob goes onto the shaft end? Very nice setup, wasn't aware they worked that way.

[kevin gilmore]

Well pretty close. The shaft is machined single piece out of the knob material. Then there is a coupling right behind that

to the extension shaft, and another coupling to the pot. Depending on which pot you get, the second coupling needs

to be a different diameter on the pot end. The picture posted previously showed this.

http://gilmore.chem.northwestern.edu/t2chassis29.jpg

[swt61]

Ah, thanks Kevin. That's an elegant design!

[Inu]

I need to order another 450V 680uF.

Won’t fit if height is 50m/m, need 45m/m.

The edge of front panel touches the head of capacitors.

Panasonic 450V 680uF (35mm x 45mm) is out of stock...

Craig,

How about your EPCOS caps?

[Craig Sawyers]

I need to order another 450V 680uF.

Won’t fit if height is 50m/m, need 45m/m.

The edge of front panel touches the head of capacitors.

Panasonic 450V 680uF (35mm x 45mm) is out of stock...

Craig,

How about your EPCOS caps?

Maximum EPCOS height above the board is 47mm. How about slightly shorter spacers? Specced ones are half inch, so would 10mm work better?

[Craig Sawyers]

Well pretty close. The shaft is machined single piece out of the knob material. Then there is a coupling right behind that

to the extension shaft, and another coupling to the pot. Depending on which pot you get, the second coupling needs

to be a different diameter on the pot end. The picture posted previously showed this.

http://gilmore.chem.northwestern.edu/t2chassis29.jpg

I wondered what the second coupling was - that is a really neat design, and keeps visible shaft grub screws completely out of the equation!

With the fancy Alps, you have to go *up* from 1/4" to 8mm, whereas with the DACT you need to go "down* to 6mm.

[Craig Sawyers]

Maximum EPCOS height above the board is 47mm. How about slightly shorter spacers? Specced ones are half inch, so would 10mm work better?

Scratch the 10mm comment - the board height is fixed by the heatsink bracket position.

[Craig Sawyers]

Another UK source of UNC fixings, including black, in various headstyles and 1/8" length increments http://www.modelfixings.com/

[Inu]

Maximum EPCOS height above the board is 47mm. How about slightly shorter spacers? Specced ones are half inch, so would 10mm work better?

The space between PCB and edge is 49m/m so your EPCOS are safe.

I uploaded more pics.

[nattonrice]

Just got my traffos =D

Oh and fuck me my mouser bill is rather weighty...

Birgir, did you get your chassis parts?

[kevin gilmore]

Birgir did get his chassis parts

evidently i messed up on one of the stax jacks...

[nattonrice]

In that case let the obligatory "pics or ban" comments begin!

Was there a problem with the replication?

[Craig Sawyers]

Just got my traffos =D

Oh and fuck me my mouser bill is rather weighty...

Birgir, did you get your chassis parts?

FWIW my total Mouser bill was

[spritzer]

Here is a quick snapshot I took before I packaged it all up again for storage.

The heatsinks look great, beyond great even but the other panels are a bit flat. Also notice the small marks on each end of the panels which go right through the finish.

Yeah, one of the Stax jacks is messed up but I'm too tired to take a picture of it.

[kevin gilmore]

Not sure what happened with the stax jack. it may have been one of the first 3 that i did, and maybe

i machined it a bit too fast. From now on i will test the fit before i ship any more stax jacks.

The problem with teflon is that it likes to get out of the way of the end mills as it is being machined.

Maybe i bumped the speed knob...

It will be replaced. When i send birgir his "custom pure titanium" knob.

Hopefully the material for that will be in the end of this week.

Yep we are at the silly stage...

Need to find a 2 inch cube of aged lignum vitae.

[n_maher]

Need to find a 2 inch cube of aged lignum vitae.

GENUINE LIGNUM VITAE Wood Turning Spindle Blank Lathe - eBay (item 190409818674 end time Jun-30-10 17:55:49 PDT)

You might be able to work around the heart check.

[kevin gilmore]

I don't believe the moisture content for one second. I have lots of lignum vitae here, after

you take the wax off, it usually takes about 10 years for it to be usable and it shrinks

well over 10%. My wonderful hardwoods store went out of business last year, so no

more of the exotic stuff for me till i find some place else where i can look at the stuff first.

[luvdunhill]

I always test the AC out of all transformers first.

And unloaded power draw checking for shorted turns

did you test the transformers with a load as well (rated maximum load or actual load?)

Also, thanks for the transformer specs. Could you also give us the maximum gauge that each lead can be (so, pad diameter) and the maximum lead length we need?

[luvdunhill]

.. and one more thing. Is there a preferable relationship to the primary entry point and the secondary exit point on the toroid? 180 degrees? 45 degrees?

[Craig Sawyers]

did you test the transformers with a load as well (rated maximum load or actual load?)

Also, thanks for the transformer specs. Could you also give us the maximum gauge that each lead can be (so, pad diameter) and the maximum lead length we need?

One additional thing that is worth mentioning to a transformer manufacturer is that some of the windings float at high DC. Specifically the heater windings to the EL34's (-500V), and two of the HT transformer windings are referenced to -560V or -500V. So those windings in particular need an insulation barrier - just overlaying one secondary over another probably won't work (it *should* in principle, because winding wire is good for more than that - but not if any insulation is compromised through nicks during winding, or just thinned because of winding pressure).

[kevin gilmore]

I tested at 10% over maximum rated load (which is dc because its pure class A)

out of the power supply with a stack of resistors.

The leads out of the high voltage transformers are 14 inches long.

And yes you have to tell them to do 600 vac wire for all of the transformer windings.

Which SumR does anyway i think.