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spritzer

The ultimate DIY? A Stax SRM-T2!

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What was your +200 and -540 adjusted to in order to get 708v? And were your mods needed to achieve this?

I have 2sk246 BL grade and 10k fixed resistor instead RV2 in source 2sk246.

In any case, does not necessarily turn exactly 708V. Less than 730V is already very good sounding.

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Maybe it helps:

Add 750-1,5k series resistors in gate all 2sk216. For me it was awesome helpful.

Add 0.1uF MKP or NP0 capacitors parallel 22k resistors in batteries.

 

Also for fantastic sound I turned batteries to 708V.

Much like this then (pic is of Inu's T2)? Would all the 2SK216's need this or only Q5/Q6 & Q26/Q27? D'you happen to have a part number for the .1uf caps?

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Much like this then (pic is of Inu's T2)? Would all the 2SK216's need this or only Q5/Q6 & Q26/Q27? D'you happen to have a part number for the .1uf caps?

Yes, same as Inu's mod. For confidence, do for all 2sk216. The resistors can be cheap 25-50ppm grade.

 

I have Vishay MKP-1837 0.1uF from partsconnexion. You can use any film/ceramic capacitors. This mod can be used if the previous mod has not helped.

Sorry for google translate.

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I've put in some 1k xicons in series with the K216 gates now. It hasn't solved the problem, but it appears to have helped somewhat. The noise on the left channel is noticeably quieter than on the right now. Guess it's time to grab some caps to put in parallel with the 22k xicons in the battery.

edit: Actually I'm not sure it changed the noise at all. It's been a while since I listened longer than a minute to the T2 due to the noise.

Edited by s_r

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They're all (raised) xicons. A scope might help pinpoint the problem but it's been years since I used one (and not with anything high voltage). As it stands right now it's just a heavy, expensive paperweight. :unsure:

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Sure, we always need something better.

That said, nothing blew up, adjusting the batteries was very easy, and I didn't knew I would go that far without electric trouble.

Seven months sourcing and testing parts... only a few steps away from music !

Edited by G600

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1 hour ago, G600 said:

Sure, we always need something better.

That said, nothing blew up, adjusting the batteries was very easy, and I didn't knew I would go that far without electric trouble.

Seven months sourcing and testing parts... only a few steps away from music !

massive achievement! I guess a thorough and careful approach pays off ;o)

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2 hours ago, G600 said:

Sure, we always need something better.

That said, nothing blew up, adjusting the batteries was very easy, and I didn't knew I would go that far without electric trouble.

Seven months sourcing and testing parts... only a few steps away from music !

C'mon, pick it up J-D! Why no music yet?

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Nope, I only adjusted the batteries, no idea of the offset.

Outputs not wired yet too.

And DAC not in the same room.

And.... :D

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3 hours ago, G600 said:

Sure, we always need something better.

That said, nothing blew up, adjusting the batteries was very easy, and I didn't knew I would go that far without electric trouble.

Seven months sourcing and testing parts... only a few steps away from music !

Not really about something better, those things are unsafe and can kill you.  There is probably no protection inside them so you could kill your self or even blow up the amp. 

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5 hours ago, spritzer said:

you could kill your self or even blow up the amp. 

Your choice of words clearly shows your priorities. :D

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Hehe true but using cheap meters at these levels is no joke.  No protection circuits, the insulation in the leads is an unknown quantity and the actual measured value can be way off.  Doesn't mean you have to go nuts, I have some 100$ B&K Precision meters here that are just excellent. 

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I stocked up with Fluke meters during my build.  Three NOS 8060A's and and a second hand 87V.  All from eBay for not much at all.  And then I made up some custom PTFE leads to interface with the test point jacks I used on the board, so I could monitor battery voltage on both channels simultaneously.

The Fluke's were one of the best purchases I ever made.  Trustworthy, bulletproof - a joy to use.

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I used to cal them for about 20 years.

The first handheld flukes had a problem with the LCD displays when used in highly humid conditions and we used to replace them with tropicalised dilsplays.

Nowadays they are just excellently built throughout.

The funny thing was, some (and only some) of the cheaper multimeters were more accurate than the flukes, but they seemed to only last a few years and they never showed up for calibration.

The Flukes used to show up regularly for years unless they met with an accident like being run over by a tank or dropped from a very great height.

Edited by wink
Shpiilenk

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What voltages would you consider OK

- between + and - output

- between +/- and ground

- difference between batteries ?

I can dial the outputs to less than 100mV between them at the expense of a little difference between batteries.

And the outputs are 14 to 16v above ground, except for one that is only 1.6V. I guess this isn't good...

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Pretty much anything around 30v and down is fine. Don't worry about the batteries being exactly 740v - in fact I am only aware of them not being absolutely perfect.

But worrying about fine adjustments without plugging in a set of earspeakers at this point is premature (unless you are lucky and your t2 is silent without having to do some adjustments to the pots).

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Yep, pretty sure of that.

I think I have spotted the difference that can explain why I have one output stuck at 1.6V above ground. Control picture courtesy of Inu.

Could you guys confirm this is a board bug ?

Sans titre.png

UNI_6633.JPG

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No board bugs in your version - pretty sure Inu's boards were from the initial run before the corrections were made. But your board is 4oz copper which means everything needs to be extra-perfect.

 

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Sorry, maybe I wasn't clear.

I can't understand why I don't have a trace here : 

Sans titre.png

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Yes, your board is missing a trace in that spot. You have the slightly shrunk version. Looks like the trace got dropped somehow.

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