STAX SRM-1

[setaria]

Dear All,
I need schematics of STAX SR-1 neither SR-1 MK2 nor SR-1 MK2 pro. Mine is SR-1 without any suffix. It was released in 1979. Dislike SR-1 MK2 or later brothers, it has JFET differential amplifier followed by 2SD594 amplifier and finally 2SC1828 emitter follower output. I've drawn most of (but not all) of the circuit by inspecting the board, but I wish it confirmed with your help!

 

[chrisng]

There's schematic for the STAX srm-1 from Audio-database.com but no component values.

 

[setaria]

Thanks, chring. These drawings without component values were used in the leaflet of SRM-1 in 1979. I got some but not all values as in the attached diagram. I am not so sure about the values. The designer preferred serial connections of devices, probably considering the high signal voltage. The circuit is much simpler than later versions that use folded cascode amplifiers in order to connect electrostatic headphones without capacitors. But I like the simplicity of SRM-1. Can anyone correct the values?

 

[ericj]

The mk1 SRM-1 is pretty rare as i understand it. You might try contacting Birgir at Mjölnir Audio - I suspect he's owned one, probably refurbished one. He's been posting as "Spritzer" on audio fora for at least 20 years. He may have posted something about it on head-fi or head-case.

 

[ericj]

Oh hey, came across this thread where the good Dr. Gilmore commented on a mk1:

https://www.head-fi.org/threads/need-some-suggestions-to-recap-stax-srm-1.905395/

 

[setaria]

Thanks, ericj for providing valuable information.
I tried to read color codes of resistors and have drawn tentative schematics. Still it may have some wrong values or wrong connections. Any correction or comments are welcome. It looks very simple. Mine is over 40 years old, but works reliably. I just recapped it. It doesn't have a folded cascode amplifier or a current mirror circuit, but it sounds pretty good.

 

[Pars]

This info is for a mkII, but might help some. Head-case is where to ask as birgir (spritzer) and Kevin G hang out there. Head-fi is generally a waste of time.

https://www.dropbox.com/scl/fi/8b0t....pdf?rlkey=glz2ojmhutusntws2dae3loi0&e=1&dl=0

 

[setaria]

Thanks a lot, Pars. I got a STAX SRM-1 MK2 P.P. a year ago. It was worn-out with dust but I fixed it. The MK2 series have more sophisticated or complicated circuits than the original SRM-1. SRM-1 is much simpler and more stable. They sound similar at least for me!