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.
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 as there are quite a few of us Stax-o-philes there.
Thanks so much Spritzer for the info and advice. You are my VERY FIRST thread/blog/forum (whatever you call this thing) contact/friend/advisor! I just signed up with head-fi. Yes, I will likely have more questions, as I seem to have been re-bitten by the STAX bug, after it lie dormant for over two decades.
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
Thanks much Spritzer. I hope I figured a way to better articulate my question.
I have two STAX SRM-1 Mk2 units. One is 100V for Japan and the other 117V for USA. The serial numbers are surprisingly close and the voltage selectors themselves look identical (but are wired slightly differently). The 100V unit has no jack in the voltage selector on the back. The 117V unit has the voltage selector jack in place and pointing to 117V. The 117V unit will not power up without the jack in place. I don't like the idea of trying to power up the 110V unit with the other jack inserted in it pointing to 117V. When I look inside, I see that there is a slight difference in the color coded wiring schemes (btw: these 2 units are amazingly close in serial number). Can the 110V unit be wired to the same color coding scheme as the 117V unit with expectations of it working (at 117V assuming that I find and insert another jack)? Or, are their other internal differences?
Another idea would be to permanently wire it for 117V without having to find another jack (IF there are no other internal differences)?
Can you tell that I am not a 'techi'?
My wife has a technical question for you also: "Will I get SHOCKED?" lol
Thanks much!
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.
Spritzer, Both transormers and wires look identical. But the wires leading to the back of the selector switch sockets are wired differently (2 wires go to different pins, as I recall). This is where I was asking if wiring the 110V unit the same as the 117V unit would convert it to 117V.
I can take some photos but will have to borrow the right camera to do it.
btw: My ultimate goal is to find as perfect a tube STAX as I can afford. If you have anything in your arsenal that you might like to sell, let me know thru email. Thanks much again.
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.

It is the 100V unit that has the voltage selector plug missing and it WILL operate. I bought that unit brand new, from a reputable dealer circa 1986. The packaging seemed factory fresh but I guess someone MIGHT have removed the plug before selling it. I can't imagine that they would have modified any internal wiring though. Also there is a very 'original' looking plate screwed over the voltage selector switch.
It is the 117V unit that will not operate with the voltage selector plug removed. Does that info change what you said before?

On the subject of a tube amp: I am considering an SRM-T1 for either my Lambda Pros or for Lambda Signature Pros that I have access to. What do you think of that combo and do you think that my 61 year old ears could hear the difference compared to what I have? I do love the detail of STAX and the sweet sound of tubes (at least when listening to McIntosh tube amps through speakers).

Thank you again so very much for all of your advice.
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.
YOU da MAN!!! Thanks again for the valuable info. All pretty good news too, if I understood correctly. I can make a lot of progress just on what you have taught me here. Would you please email me at so that I might ask a quick question about price of a couple of items that I am looking at? I have more STAX questions but will let you rest a while after having put you to so much explanatory effort. lol
Thanks again....!!!
Email sent. Resting is overrated anyway.