Stax amps parts specs

[Earspeakers]

Because I am a bit anal about this I have a TorqueLeader torque screwdriver for precisely this application.  My T2 a la Gilmore design has been working with that arrangement for three+ years without missing a beat.

 

Hi Craig, 

  What setting do you use on your screwdriver?

[Craig Sawyers]

I just followed a data sheet I found.  An interface with heatsink grease is actually pretty insensitive to torque, but I think I used 5in/lbs and conical washers (AKA Belville washers).

 

Datasheet attached

AN1040-D - heatsinks.pdf

Edited March 3, 2015 by Craig Sawyers

[mwl168]

The ceramic insulators I bought are only 1mm thickness. Are they safe to use for the KGSSHV application?

[GeorgeP]

The ceramic insulators I bought are only 1mm thickness. Are they safe to use for the KGSSHV application?

part number?

[mwl168]

Sorry, bought them off eBay - don't have part number. They are listed as TO220 insulator.

[Earspeakers]

Sorry, bought them off eBay - don't have part number. They are listed as TO220 insulator.

 

Can't tell you if they're OK if you don't have the part number and the specs. 

 

Probably OK, but who knows for sure. 

[mwl168]

I intend to use the ceramic pad together with the PPS shoulder washer Kevin suggested. This way, the transistor should be completely insulated from both the heatsink and the bolt used to secure the transistor to the heatsink.

That being said, I am trying to locate sources for thicker ceramic insulators that do not require me to buy them in huge quantity. Better safe than sorry.
 

 

Edit:

 

Found AAVID aluminum oxide ceramic insulators at both Mouser and Digikey:

 

4170G: 19.3mm x 13.97mm x 1.57mm (L / W / Thickness), center hole is 3.68mm diameter

 

4171G: 16.51mm x 12.7mm x 1.778mm, center hole is 3.81mm diameter

 

This should work well with either 7721-3PPSG or 7721-10PPSG shoulder washers. 3PPSG bushing is 3.18mm in length and 10PPSG is 2.41mm, both with 3.56mm outer diameter.

 

Trouble may lie with the transistor's tab hole diameter which (based on data sheet of 10m90s and 01n0100d) can range from 3.53mm to 4.08mm. 

Edited March 3, 2015 by mwl168

[Craig Sawyers]

The ones specced in the Kevin's T2 parts list were 4171G.  Mine measure 2.03mm thick.

[iwik]

Hi Craig,

Nice to see you active again. Re transformers, iam currently building the KGSSHV and I see

SumR Transformers are questionable(reliable). I am not sure I want to go this path(have his T2 ones).

Thinking of going the path you did with Paul. Can you offer any extra specs I should state

to help ensure a long life from the Traffo?.

Thanks

Les

[Craig Sawyers]

Apart from electrical spec (currents, voltages) the main one is to make sure that the wire insulation spec is compatible with the temperature of the Tx's.  The T2 clone ones, even from TEC (Paul Houlden), run HOT.  That is as much a consequence of the available space in the original chassis as anything else.  If you have more room, or mount the Tx's in a separate case, overspec the VA and they won't run so toasty hot.

 

Main things to remember are (1) heater windings are easy - it is just AC, so the VA of those windings is straightforward (2) All other windings look into capacitive input filters, and the VA rating of the windings that feed those need to be much higher - a factor of two is typical, but you have to simulate the precise set up to get the real factor.  This is because of the pulse-like charging currents (2) mechanical hum is a big thing - it is difficult to get a toroid to be quiet.  A typical problem arises when a US transformer manufacturer (like SUMR) designs for 60Hz and then exports to Europe where we have 50Hz. You need a bigger core for 50Hz than 60Hz to prevent the core going towards saturation and buzzing.

 

But talk to Paul - he was head designer at Avel back in the glory days, and was responsible for power transformers in just about every piece of high end kit (Krell etc) through the 80's.  He does an audiophile mains Tx now - I have a custom pair in my current multichannel amps (active XO) and although they are 700VA you have to press your ear up to them to hear anything.  The ones he did for the T2 are silent too.

[luvdunhill]

I believe the issue has less to do with the manufacturer and more to the issues that Craig brings up regarding the difference between DC current draw and AC current draw. Too many people think that if the circuit draws 100mA then that's what the transformer needs to be spec'ed at, when it's much more complicated than that. Then they claim using "massively oversized" transformers as a feature when likely they just stumbled upon the right number. Also, failure to specify a particular temp rise and then holding the vendor to that number is another problem.

[chiguy]

I used transformers from Avel Lindberg for my KGST builds and they buzz a little bit.

[Craig Sawyers]

Avel ain't what they used to be.

 

There are only two good toroid manufacturers in the UK - Paul Houlden of TEC (no website), and Terry Monaghan of Canterbury Windings http://www.canterburywindings.co.uk/.  For EI transformers, audio, phono Tx's and transformer volume controls again in the UK, Sowter are the one to go to http://www.sowter.co.uk/

[iwik]

Thanks Guys,

So when Kevin says for the KGSSHV traffo:

i spec'd 100 ma per high voltage winding, just in case you want to turn the bias up a bit.

Is this Dc or AC draw?.

Les

[kevin gilmore]

100ma AC

 

it sure would be nice if transformer manufacturers would understand

that what i want is a specific DC current, given a diode bridge and a capacitor

and then calculate what the peak AC current is, then build the transformer

that way.

 

But none of the manufacturers seem to have the slightest clue.

[iwik]

Thanks Kevin,

I want to get one made and hopefully they will better understand. Thinking of going to the UK

where Craig Sawyers went.

Les

[luvdunhill]

100ma AC

it sure would be nice if transformer manufacturers would understand

that what i want is a specific DC current, given a diode bridge and a capacitor

and then calculate what the peak AC current is, then build the transformer

that way.

But none of the manufacturers seem to have the slightest clue.

Electra Print did. Ironically he stopped selling custom power transformers because the customer didn't understand how to spec a transformer.

[Craig Sawyers]

100ma AC

 

it sure would be nice if transformer manufacturers would understand

that what i want is a specific DC current, given a diode bridge and a capacitor

and then calculate what the peak AC current is, then build the transformer

that way.

 

But none of the manufacturers seem to have the slightest clue.

That's for sure.  

 

Last Tx's I specced I tried a different approach -  I told Paul that the winding X was going into (eg) a full wave bridge rectifier and 47,000uF of reservoir from which 5A average current was taken, and let him work back from that.  In fact I think I sent him a schematic which showed that.  What arrived certainly seemed to do the job with zero mechanical buzz and runs really cool.

[nopants]

If you commissioned the T2 tx's from Paul he should have those specifications on file too right? I have a set of SumR transformers but maybe it might make more sense to commission his work for 60Hz duty.

[Craig Sawyers]

Yes he should; mention my name to jog his memory.  At 60Hz the core losses will be a bit less, so they should run a tad cooler.  He did mine with a potted centre and a clearance hole (I think M6), so you need a correct length nut and bolt. Looks neater than the dished washer sandwich.

 

His email is [email protected], phone +44 1989 566710

[nopants]

Thanks Craig, sent him an email. I guess I was first in line and the price may or may not come down depending on who decides to commission a set.

[iwik]

Be interested to hear Pauls response as I was about to contact him.

[nopants]

"Yup, we can make them for you. I'll have to get a UPS quote for delivery to California. Craig mentioned that there might be other people in the states who require this set of transformers. Obviously the more orders, the cheaper I can make them, So price I quote you will be worst case, and if I get more orders soon, then it'll be cheaper !!"

[Pars]

You should see if he can use Royal Mail or something that would hook up with USPS. Not likely, but with UPS you could get hit with customs. Of course, I could be wrong

[iwik]

If we are talking about the KGSSHV traffo then I would be interested. Would need him to

send to NZ, no need for double handling eh.

Edited March 6, 2015 by iwik