Stax SRM-700T and SRM-700S

[Hugo]

Two new amps have just been announced:

https://stax.co.jp/products/srm-700t/

https://stax.co.jp/products/srm-700s/

Edited October 17, 2019 by Hugo

[Jonny]

For people, who prefer english
https://stax-international.com/products/srm-700t/
https://stax-international.com/products/srm-700s/

[spritzer]

These amps just make me sad...  Same basic stuff as the 006t and 727 but at a much higher price.  Resistor plate loads at 300kYen?  Seriously? 

[joehpj]

They claimed the 700s has JFET VAS stage. Any opinion?

[spritzer]

Clearly a jfet input but I didn't see the see any mention of a jfet VAS stage.  If this is the same as all the pervious Stax amps (which I'm pretty sure it is), then that would be a 700V jfet...which doesn't exist. 

[Hugo]

21 hours ago, Jonny said:

For people, who prefer english
https://stax-international.com/products/srm-700t/
https://stax-international.com/products/srm-700s/

Thanks. I didn’t realize they had the info in English.

Edited October 18, 2019 by Hugo

[joehpj]

On the 700s page.

●New semiconductor driver with J-FET in the amplification stage
All semiconductor driver unit that has adopted custom-made low-noise dual FET at the first stage, and for the first time in STAX driver unit history J-FET has been employed at the second stage.

 

After so many years, Stax finally ran out of the long obsoleted Toshiba JFET. The 700t is more like a change that has to be done eventually. But still for some unknown reasons, they still refused to employ CCS in their tube amps. And the second of the 700s stage is quite interesting for me. It's so sad that it hasn't been a lot of innovations since the old Stax gone broke, so minor changes now become news.

Edited October 17, 2019 by joehpj

[chinsettawong]

Could it possibly be this kind of JFet?

[spritzer]

Could be.  It is clearly a SMD part but most of these are also available in those packages but one wonders why...  I doubt Stax are using any of these new fangled "non Japanese" parts as they just switched to On Semi out of necessity but yeah... who knows. 

[Pars]

3 hours ago, joehpj said:

After so many years, Stax finally ran out of the long obsoleted discontinued Toshiba JFET.

Fixed that for you. They sure as hell aren't obsolete...

[spritzer]

I found these on the official Stax sale site so a bit more info:

So...this is a 007t with inferior tubes (they can handle less power than the 6CG7) and the same 47k plate load.  Not sure whey they fuse the B+ on each triode but that's clearly what's going on. 

Now for the SS:

Not enough detail to see the VAS but this is clearly a take on the T8000 and 717 so resistor loaded VAS.  You can spot the power resistors behind the VAS heatsink. 

[kevin gilmore]

so the 700s

power supply voltages are exactly the same as the 717 and 727

from the transformer yellow,green,yellow go to full wave bridge rectified and regulated to +/-15

blue black blue (the filament supplies on the 700t) rectified and added to Vh- to make the - boost supply

white red and brown orange are the 2 high voltage windings full wave rectified into CRC making +/-350

output boards identical to the t8000 each board has 3 x 2sc6127 and 1 resistor

vas boards have 4 x 2sc6127 (2 x Darlington pair) and 4 x 150k/2W current source (on main board)

vas is driven from dual low voltage n-channel jfet. (red heat shrink) (previously dual npn transistors) 

front end identical to 717/727 with dual n-channel jfet

so about 99% identical to srm717 with non-obsolete parts and change of vas stage driver from bipolar to jfet

on the D50 the front end jfet is known to be sourced by linear systems. So likely the k170 are also sourced by linear systems.

so the 700T

absolutely identical in every way to the srm-007t (and srm-t1 etc) with 2 x 6sn7 replacing 4 x 6cg7

plenty of room for replacement constant current sources to replace the mills load resistors

both are priced the same, between $2895 and $2995

 

 

[garageboy]

So the srm500t (using 6cg7) has potential to supply more power than the twice the price srm700t?

[spritzer]

No, not at all.  The 500t is more similar to the 600ltd amp with presumably a bit lower rail voltages but still the same circuit as the T1. 

I have a 700t here and it is terrible in stock form, just awful.  Utterly lifeless but adding a CCS really transforms the thing into something decent.