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The ultimate DIY? A Stax SRM-T2!


spritzer

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Interesting question, I was wondering that myself.  The T2 current sources are pretty sophisticated, but without measuring their dynamic impedance I don't know if using cascoded MOSFETs would give a higher dynamic impedance, which would be the reason for making a substitution.  My bias is that the closer the  current source/load is to a perfect current source the less it should contribute to the sound.

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I've been looking to get some of the original T2 boards made for myself (in 3oz copper & 2mm thick). It looks like the only way to do it at a reasonable price would be to do a run of boards. So I've been talking with headinclouds about doing it through his PCB supplier and at 10 sets it'd be about £100. At 20 sets it'd be about £80. This doesn't include shipping or paypal fees. Still have to work out exact details, but under $200 is definitely possible at 10 sets. Anyway, pm me with your interest.

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There have been some posts lately about cascaded current source. With reference to JimL's srx schematic and the srx layout made by Kevin - I made a couple of small boards, surface mounted dn2540 along with some resistors and replaced the two 10m90s resistors.

 

Edited by JoaMat
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JoaMat,

Very nice adaptation  One caveat, the 10M90S is designed as a current source, so I presume that the choosing the current setting resistor can be done using the graph in the data sheet.  However the DN2540 is not specifically designed as a current source, so I have found there is more variability in the current from one sample to the next if you're using the same value resistor.  This is why in my schematic I use a pot for fine-tuning the current, and also a current sensing resistor (10 or 100 ohms) to set the pot to the desired current.

 

I would also be interested in hearing about any subjective changes you hear after the mod, since in my SRX mod I never tried the 10M90S by itself.

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  • 2 weeks later...

I've been drawing up some panels recently, figured some others might be interested.

 

post-3922-0-92968600-1420182504_thumb.pn

post-3922-0-99239000-1420182509_thumb.pn

post-3922-0-54524400-1420182513_thumb.pn

 

Still have to triple check things, but I'm pretty sure I have all the critical measurements right.

 

Some folks have expressed interest in another small board run, but not quite enough though. I'd like to avoid fronting the money myself & selling extras later if possible. So unless someone has a boardset (amp v1.07/psu v1.15) they'd be willing to sell I'll have to figure out what to do about PCBs later.

 

Anyway, would anyone be interested in some quad RK50's? onlinecomponents.com has a decent discount on them if at least 5 are ordered.

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The closest in dimension to the original heatsinks I've been able to find (cheaply) were from conradheatsinks. So there'd be a seam from joining two 200mm heatsinks, and I'd have to cheat a little with some spacers on either side of them to get the required 16.2" inside length. I drew the top cover to hide those seams, really. That and I happen to like how how the vitus amps look. ::)

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