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The ultimate DIY? A Stax SRM-T2!


spritzer

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That's good  news. And yes, current limiting is happening. It is the 30ohm on the -500 that does it - drop it to 25 or thereabouts.

On Paul's T2 traffos, someone else from that same buy is getting a lot of hum as well. My set is quiet though, so go figure.

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Well the hum thing is pretty disappointing.  Every transformer that Paul has wound for me is as silent as the grave - including the T2 ones.  When he was head designer for Avel Lindberg in the 1980's through to mid 1990s he designed transformers for Krell and umpteen other high end and pro audio companies.

If you are getting hum, seriously please take it up with Paul - he will be more than keen to sort it out.  I'll mail him and let him know that there is a problem in advance.

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A DC offset on the mains can cause hum.  Usually caused by a local industry pulling power out on half cycles, so either the top or the bottom of the mains waveform is flattened (but not both, or not equally).  What happens is that the effective DC offset biasses the core of the transformer, and you hear harmonic distortion through magnetostriction in the core.

There is a good article, and method to remove it here http://sound.westhost.com/articles/xfmr-dc.htm

Basically two big electrolytics in opposed series, or back to back parallel, with diode clamps across them.  In series with the live power.  Worth a bash since some have silent transformers and others don't, which could well come down to local variation of mains quality.

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1 hour ago, MLA said:

I'd forgotten that there was a kit.  I've bought things from these guys before - and they are very cheap and exceptionally high quality.  Multilayer 4 oz copper is kind of standard. And they do the lowest noise variant of the Jung super-regulators.

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George's suggestion to up the current limit worked like a charm, everything's up and operational. 

 

Sounds good, a bit of popping/clicking but nothing too noticeable. How should I go about tracking that down? For my personal use I don't know if I care enough yet, but I might try to fix it when I redo the internal wiring/etc.

Knob courtesy of insanity, I probably should have measured it before sticking it on

Operational_T2.jpg

Edited by nopants
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Only change to PSU was reducing +250V to +150V.

For amplifier I changed batteries from 740V to 640V. Also the 68V grid voltage was reduced to 33V, but that is taken care by the resistor on the small board with two 2sc3840.

Maybe one should build a modified T2 with lsk389 for input and EML 20B-V4 for output....

Edited by JoaMat
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  • 2 weeks later...
On 6 mars 2016 at 8:00 PM, Craig Sawyers said:

I'd forgotten that there was a kit.  I've bought things from these guys before - and they are very cheap and exceptionally high quality.  Multilayer 4 oz copper is kind of standard. And they do the lowest noise variant of the Jung super-regulators.

... not quite. The DCT02 has two layers and 105 um (3 oz.) copper. The small super regulator boards has 4 layers with 70+35+35+70 um. All high current tracks are doubled = 140 um if you add both of the sides. At the moment two designs have 4 layer boards.

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  • 2 weeks later...

IMG_1449.JPG

T2 with Emission Lab’s EML 20B-V4. Transformer to left is for filament 4 x 5.0V. Adapters are made by some help of a 3D printer, Teflon tube sockets, slauthered Neutrik XLR connectors, two pole male connectors. All held together with really good Loctite super glue.

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