The ultimate DIY? A Stax SRM-T2!

[JimL]

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.

[s_r]

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.

[chiguy]

Are these the boards using updated sand?

 

Sorry, I not sure which original board you're referring to.

Edited December 18, 2014 by chiguy

[s_r]

It'd be for the boards with the old sand.

[G600]

I'd be in for Joamat's T2 if there is a run.

[spritzer]

Those boards aren't ready for full release and I doubt we are going to clean them up.  I also have my reservations about the mod going too far in some aspects so I will rather work on the new T2 version for Kevin and I. 

[G600]

Sounds good Birgir.

As long as they use actual sand...

[JoaMat]

/

Edited November 11, 2015 by JoaMat

[spritzer]

Mostly to do with the 10M90 CCS.  Works just fine but I fear it might change too much how the amp performs over the stock CCS.  As I have thousands of 2SC4686A's and 2SA1486's using it isn't a problem. 

[GeorgeP]

Would the 4686's be in place of 3675?

[kevin gilmore]

yes the 4686A parts would be in place of the 3675. And since they are isolated, they are easier to mount.

The only parts that would not be isolated are the j29 and k216.

 

In a couple of places the 1486 can be replaced with the ksa1156 because they are used at only 250v.

And those are fully isolated too.

[nopants]

lower cob than the 3675 if the sheets are to be believed

[spritzer]

One of the CCS 3675's shorting to the heatsink was what killed my T2 so they aren't welcome. 

[JoaMat]

/

Edited November 13, 2015 by JoaMat

[kevin gilmore]

not sure those are real, the price is way to cheap.

I paid about $1 each for the real ones from mouser.

[JoaMat]

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 November 12, 2015 by JoaMat

[chinsettawong]

Wow! Nice!

Edited December 23, 2014 by chinsettawong

[JimL]

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.

[s_r]

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

 

 

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.

[nopants]

I like it, but doesn't the top panel imply you want to do something specific for the sinks?

[s_r]

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.

[spritzer]

Good luck getting any reply from Conrad as they have gone into full radio silence mode. 

Edited January 2, 2015 by spritzer

[GeorgeP]

Are there no off the shelf solutions that do custom lengths greater than 400mm?

[iwik]

S_r,

I have a set of these boards, if interested pm me.

 

Les

[bravi]

New member here. Pl pm me if anyone has a set of boards. Upgrading to SR009 after living with 407/SRMT1 combo for 7 years.