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The ultimate DIY? A Stax SRM-T2!


spritzer

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Now I have two competing fantasy images of Craig: either he's in blissful audio Nirvana playing music nonstop and achieving new levels of awareness --or-- he's been electrocuted by the T2. I know the reality is more mundane, but whenever this happens that kind of thing runs through my head. :jacob:

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I wish no word “2SC3675” or “2SK216” in his next post.

Now I have two competing fantasy images of Craig: either he's in blissful audio Nirvana playing music nonstop and achieving new levels of awareness --or-- he's been electrocuted by the T2. I know the reality is more mundane, but whenever this happens that kind of thing runs through my head. :jacob:

I think it may be as simple as he can't post anymore without breaking Inu's wishes :D

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Omygod. I'm speechless and breathless - I've really heard nothing to compare with this. I could witter on about speed and clarity, and the tendency to listen to things far too loud because there is zero listening fatigue.

Looks guys - I have a BH, and bloody good it is too. But KG's recreation of the T2 is simply in another league.

OK - the right channel has noticeably hiss, but that is because I need to frig with the battery voltage a bit on that channel. What I need to do is stop listening for long enough to pull the lid off again.

Mind you - it served up a bit of a fright. I'd had the thing on/off/on/off etc as I was messing around trying various cures for the 650kHz problem with no mishaps. Put all the covers on, heaters came up, but when the HT came on the fuse blew. WTF??? Tore covers back off to find the gremlin. There wasn't one - the 2AT fuse I had in the IEC was clearly not man for the inrush job (6.3A in there now) - but it waited until I'd put the gadzillions of screws in before it gave up the ghost.

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Omygod. I'm speechless and breathless - I've really heard nothing to compare with this. I could witter on about speed and clarity, and the tendency to listen to things far too loud because there is zero listening fatigue.

This is a way better way to explain the tendency to crank the volume. No fatigue of any kind, even at ear bleeding levels.

And i can listen for many hours at levels way louder than i should.

I've been thinking quite a while on this, what i would do to make anything that would be better than this

and i just don't have any ideas.

I'm still running on a 2 or 2.5 amp fuse, it has never blown.

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Just for the record, there were three mods to the power supply and amp:

(1) The power supply mod developed by Kevin and Inu to make it stable

(2) Adding precautionary 750 ohm resistors in series with the gates of all K216's

(3) Adding 5pF 1kV caps (I used ceramic, Inu used mica) across the 100k feedback resistors. That was also an Inu mod.

(1) and (3) are essential IMHO. (2) is discretionary - these resistors were not present in the original from examination of the photos.

It has already been said - this sucker runs real hot. Once it has been on for a few hours the heatsinks, front panel and top plate are toasty.

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solid state front end is definitely doable. Cut the +250 to +100, use 2sa1486 as cascode transistor, cut R6 in half and

use everyone's favorite n-channel front end fets. Add zener at junction of R9 and R10.

change out the fet and led's in the batteries for the precision regulator and a resistor, remove one adjustment.

might have to fiddle a bit with the range on RV1.

Neither should make any change in the sound whatsoever. But its not better.

There is no suitable 1kv + transistor to replace the output tube.

But if anyone knows of anything suitable please let me know.

Something that can handle at least 20 watts with 500 volts across it.

Cathode of output stage with tubes is possible but then the -500 would

have to be -600 or more, then remove Q26,27,28,29 this would likely

change the sound a bit. All the output current would have to go thru

this tube, and thats a bit much for the kind of tube you would need to use.

Still nothing really stands out as any better. Just maybe a slight bit simpler.

If you think this thing gets hot, you should have touched the original.

No practical way to replace the active batteries with a tube. Gas tubes

have too high an impedance.

Edited by kevin gilmore
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Just for the record, there were three mods to the power supply and amp:

(1) The power supply mod developed by Kevin and Inu to make it stable

(2) Adding precautionary 750 ohm resistors in series with the gates of all K216's

(3) Adding 5pF 1kV caps (I used ceramic, Inu used mica) across the 100k feedback resistors. That was also an Inu mod.

(1) and (3) are essential IMHO. (2) is discretionary - these resistors were not present in the original from examination of the photos.

It has already been said - this sucker runs real hot. Once it has been on for a few hours the heatsinks, front panel and top plate are toasty.

Thanks Craig for summarizing. Very glad you got everything working :)

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I think that those things are going to perform very poorly at 20 ma, but i'm willing to

give it a try. Gate capacitance not too bad. Now to find someone with the things

in stock.

Would be neat to run the things at 100ma, but you will need a fork lift to move the

required power supply... Figure about 800 watts with the current sources.

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