Stax amps parts specs

[Craig Sawyers]

Bear in mind I'm back on head-case after a 2-year absence.  We're talking the 3-transformer set for the KG SRM-T2, or more recent design uplift.  From what I can see the KGSSHV is a single transformer.  Am I correct?

 

No reason that Paul couldn't make that one though - but from the most recent pics on the KGSHV thread that looks like a pretty decent looking transformer with centre potting.  So why change?

[iwik]

Which make of Traffo are you talking about Craig?. Ive seen the Polish one and Sumr.

Sumr seems to be mentioned as having failures and Buzzing. How bad this is the $64000

question.

Be great to know just how many of Sumr transformers are good. Is it just that Richard

has had the Lions share and that's why we are seeing these come up more often.

[spritzer]

More than half of my SumR transformers buzzed and about a quarter are simply unusable.  One of them melted through the insulation and shorted to the chassis... 

 

I've had some up and downs with Toroidy but they are mostly good. 

[GeorgeP]

My Sumr T2 transformers have been silent and trouble free for nearly 2 years. The KGSSHV transformers, on the other hand, seem to be prone to developing a low level buzz, as do a lot of other toroids I have heard in other audio equipment over the years. I have been lucky enough to not have experienced a sumr meltdown, but have heard of it from other sources as well. Certainly not an unblemished track record.

[nopants]

There seem to be quite a few options available if you wanted to use an off-the-shelf solution for the KGSSHV, it might not make sense to go the custom route, SumR or otherwise. Not to derail this thread too much but you can always use Birgir's 12VA Triad part + Edcor 330Vac for 400V operation with the BHSE supply. With the fancier diff amp affair there are several options for 450V / 500V operation from those same suppliers. I think Hammond also has some offerings which fit the bill.

 

I am pinging Paul because I did similar due diligence for the T2 transformers and just getting the appropriate voltages/currents out of commercial products would probably cost more than the custom route- not to mention second-order effects that Craig and others have touched upon.

[nopants]

Paul got back to me, 195 GBP for the transformers before shipping to the staes, which as some predicted is a killer. 

[Craig Sawyers]

I've just checked back, and in 2010 the three T2 transformers cost 161 GBP, so he has increased price as per inflation over five years.  Paul's design runs with a temperature rise at the surface of 42C above ambient, which is bang on his design goal.  The wire insulation is rated up to 120C so they are well within.  Although they are the same diameter as the SUMR, they are taller (60mm as compared with SUMR 40mm) so the SUMR ones will definitely run hotter.

 

I got Paul to do mine for the same reason - shipping the SUMR Tx's to the UK was the killer.

 

Anyway, your call.

[nopants]

Thanks Craig, I provided the number for other interested parties, not to call out the price (it's actually more reasonable than I was expecting). That shipping to the states is heinous though. I brought up Par's suggestion to Paul but the price ended up being more than UPS.

 

I'm going to go ahead and put the 25% deposit towards getting them made. I take it you didn't have any issues with fit inside Kevin's cases?

[Craig Sawyers]

In Kevin's original T2 clone PSU case - no.  Diameter was chosen to fit.

[iwik]

Got a price from Paul for the KGSSHV,

2 x 485 @ 130ma and 16-0-16 @500ma

Price  85GBP and as much again for shipping to NZ.

Quality is what I am after so one pays.

Les

[spritzer]

485V is very much on the high side.  Your pass transistors will get very, very warm indeed.  450V would be the max for a +/-500V amp.  Up the current a bit instead. 

[iwik]

Hi Birgir,

Here is what Kevin stated on the I'm on a roll thread Post #582

 

 

 

"Whether you run the output at 450v or 500v, you still need about 625 vdc unregulated for the bias regulator.
So 485 vac (center tap is better but not required) is the target input voltage"

 

Thoughts please before I order.

Les

[nopants]

450vac

[spritzer]

It's ok to just do the calculations...    625VDC*.707= 441VAC.  

 

Edit:  The 450V version doesn't need this much as it has a voltage doubler which generates the bias voltage which is then regulated down to 580VDC

Edited March 17, 2015 by spritzer

[iwik]

Thanks all ,

450v it will be. Re read and somehow I missed the "BIAS Regulator" and read this as something else.

Hopefully Paul will make a decent traffo for me.