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stax t8000 clone (well sorta)


kevin gilmore
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Good thing we have so many DIY choices. (Thank You Kevin!).

I must say I would expect more from Stax.

Any idea what's going on with those guys?

Their purchase by Edifier was supposed to infuse cash into their business in order to come up with new products.

 

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its clear that more than one person spent a bunch of time on this. 14 different circuit boards, 2 piece custom extrusion for the front, all chassis pieces painted aluminum etc. So a lot of money spent. Too bad the design is 20+ years old. Too bad they refuse to do a regulated power supply. Too bad they won't make it big enough to do 20ma output stage current.

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What does prevent Stax from doing some innovations, like Sic FET or Circlotron ? Same question about regulated PSU and moar current capability...Japanese pride ? Design philosophy to keep it "simple" (let's say conservative) and with a small enough footprint ?

Ali

Edited by Ali-Pacha
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17 hours ago, mypasswordis said:

If they really wanted a small footprint they would go SMD on everything so they could have enough space for a regulated power supply, or at least use some bigger caps than the tiny ones in the T8000. And the more current the amp draws, the higher the ripple on the rails...

Speaking of which...what capacitance are those PS caps in the T8000?  When I refurbished my T1 I substituted 330 uf/450V caps for the original 100 uf ones.  Dunno if it made a difference but it couldn't hurt.

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I can do that

so on the t8000, there are places to install jumpers, evidently because stax was not sure of what tubes they would be able to get, and so they setup the jumpers to do things like 12ax7. Problem is that (waiting on final confirmation from birgir) for the 6922, the 2 x 6.3v filaments are wired in series, so not only do each section of the tubes have to be super well matched, but filament current between the 2 tubes also has to be matched, and the common connection (its a voltage gain of 1000 remember) increases cross talk.

so 2 x LDO regulators, set at 6.3V each

 

 

Edited by kevin gilmore
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What's the current of -15V? I was thinking of using some ultra low noise LDO instead of GRLV to shrink the footprint.

If I have to compromise one lead of the umbilical because of not enough lead for the TS. Should I use one 1085 for the front end tubes or tie F- to GND?

I have 10 leads in total. +-400/+100/-15/GND/bias/6.3VAC are 8 already.

 

For the tubes, I think 6922 will be a better choice because of higher max voltage for longer life. 6DJ8 is pretty limited.

I was thinking using some 6H23p though.

Edited by joehpj
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3 hours ago, kevin gilmore said:

in other news, going to 24V instead of 15V for the jfet input based versions of everything also makes the front end amplifier slightly more linear

Very cool! Which part of the spectrum benefits most?

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It would be fun to create a modern T2 in a chassis not much larger than the T8000 just to fuck with Stax.  Naturally SS output as it is just better.  ;)

Also I just wanted to add it here that the PSU caps in the T8000 are indeed 220uf/400V, same exact units as used in all the other Stax amps.  The heaters are run at 6.3V but I need to measure it to me certain.  The PSU feeding them has 10V caps it is very plausible... 

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