STAX input voltage question


This is my very first thread posting, so please be tolerant if I sound stupid (but I really AM! lol). I acquired a STAX SRM-1/MK-2 and before turning it on, I want to make sure that the voltage is set to 117V. There is no jack in the back of the unit where voltage is switched between 100V, 117V, 220V, 240V. And, there is a sticker on the back that says "AC 100V Only". Can I obtain a jack to switch to 117V or am I already there or should I get a new hobby? I will likely have lots of dumb Stax questions but this one is paramount at this point. Thank you in advance for any advice.
ill

Showing 6 responses by spritzer

There are many different versions of the SRM-1 Mk2 and some have a voltage selector and some do not. It could even be hidden inside but you can never know with Stax. Since it says 100v only on the back then the amp is Japan spec and probably configured for 100v only. Pictures of the inside of the amp will help, especially of the bottom of the main PCB.

If you want to talk more about Stax then I suggest you hop over to www.head-fi.org as there are quite a few of us Stax-o-philes there.
Glad to help or bring you deeper into the headphone madness. I've got it pretty bad with more the 40 electrostatic headphones, some 7 amps and 20+ adapters.

I'll see you in the Stax thread on head-fi
What the voltage selector plug does is rearrange the primaries of the transformers so they are reflect the input voltage. It's hard to tell if Stax changed the transformer or if the bypassed the selector switch or if it was some after market mod. The best way would be check if the backside of the socket is wired the same i.e. the same wire from the transformer goes to the same pin on the socket on both units and if there are the same internal connections on the back of the socket. Pictures would be great of both units.

Regarding the shocking part, yes it is a definite possibility but the fuse will protect you. When I'm testing "uncertain" amp I stand well away and turn them on with a switch on an extension cord.
Since the voltage selector plug is lost, a former owner may have bypassed it since the amp will not receive any power if it isn't there. There are 4 primaries if I remember it correctly, two 20v and two 100v, but I could be wrong.

I don't have any of my tube amps up for sale any time soon since two of them have only been with me for a week. I can recommend the best amp for the job though based on the headphones you will be using. Any one of the Lambdas needs a pretty basic amp compared to the SR-007 Omega II. I use a EL34 based Blue Hawaii as my main amp and it is larger then many power amps but still isn't powerful enough for the Omegas so I'm working on a 845 based design.
Since your 100v amp has a plate over the voltage selector that changes everything. Thats how Stax shipped the 100v amps back in the 80's so they could be converted at a dealer but not by an individual. The simply configured the primaries correctly and then bypassed the need for a plug. There should be the same transformers in both units, if they are the same version (A,B or C in front of the serial number), so there should be a sticker on them with the name "Bando" and then a serial number. If they match then you can hook up the voltage selector as on the 117v unit and then make the same connections internally as the plug would do. That should do it.

I have a T1, mine is modded with most of the wiring replaced with silver and WBT silver RCA jacks, and both the Lambda Pro and the Lambda Signature. The T1 is the work horse of my setup and is turned on 24/7 and it sounds great with most of the Stax models except the tougher loads such as the Omegas, Sigmas and the 4070. It is a clear step up form the SRM-1 Mk2 and it's easy to hear how much better the Lambda Signature is compared to the Pro's.

Happy to help out a fellow Stax nut.