Theremin doesn’t really work anymore. Been in storage for years.

Hello!
I’m so excited to have found this site!

I really hope I can get some insight and/or guidance. Maybe someone with experience will be excited by my conundrum. 

I bought a Moog Etherwave Theremin many years ago. It was in storage for many years because…life just kept me away from making music. 

I pulled it out recently, and it does not work properly. 

First, the output is very quiet, no matter how loud I turn up the amp. 

Second, the volume antenna doesn’t seem to do anything no matter how I turn the volume knob or how close or far I am from the antenna. I can grab it, and the volume doesn’t change at all. 

Lastly, it doesn’t seem to have the same tone range when affecting the tone arm. I have to be fairly close to it to make any change, and then it only changes very little. I can affect the sound more by turning the pitch knob back and forth. 

I cleaned the case and antennae really well and opened to see if there was anything really obvious. There’s no bulging capacitors or lose connections that I can see. 

Does anyone know where I might start to investigate or fix it. I see people tuning this and that inside, but I’m afraid I’m not that knowledgable about electronics to know what I’m doing. However, I have a multimeter and soldering iron, and can follow directions very well. 

Any help is greatly appreciated. 

Thanks!

Use your multimeter to check the voltage coming out of the wall wart.  It's rated 14 volts AC, so I'd expect the peak to be somewhat higher than that.  Check between pins 1 and 2 or 1 and 3. 

If that's OK I'd check the regulated power rails inside.  There's an 8 pin expansion connector that where pin 1 is ground, pin 5 is -12V DC, pin 6 is +12V DC.  If you can't reach those easily, these voltages should also present on the control potentiometers.  There is +12V across the brightness pot, and -12V across the other pots.

If those are OK there is a method to defeat the volume side control to check the pitch side, but I'm not sure what that is (maybe connecting pins 2 & 6 on the expansion connector?  Don't do this without confirmation from someone else here though).

After that I'd say you probably need access to a scope.

Hello rdarwish,

I can fix any of my own stuff but reluctant to troubleshoot for others because there can be many unknown variables.

It will get fixed, so do not start changing the inside until you get an expert opinion, now that I think about it with theremins everyone is an expert.

Can you solder, do you have any of those wires with alligator clips on both sides.

Where are you located, this is just my obsession.

Do you have the swizzle stick tool used for coil tuning. Don't use it.

Do you have a small analog AM Radio as you might pick up a signal near the pitch rod if you are tuned to about 850 khz which is the third harmonic up.

The radio is a safe thing to do, have the lid on the box.

Christopher

Thanks for the replies. I understand what you are both saying in theory, but I’ll have to do a little homework to be able to put it into practice. 

I can solder, I’ve done tiny projects and repaired a few things through soldering when it was an obviously broken connection. 

I’ll have to look around for a radio. Would a clock radio work?

I don’t have those wires with the alligator clips, but I could get them. 

I’m in Chicago, but I have a car, and I’d be happy to mail it off to get it repaired; I really don’t want to lose the thing. I’d pay for the repairs as well of course, but I’ll try to see what numbers I get with the multimeter as soon as I can. 

Thank you both for your kind replies. I really appreciate it. I’ll report back after I check stuff out. 

Have a good day, it’s boiling here in Chicago!

Does Moog do repairs, that would be safest.

Otherwise the best part of the EtherWave is the box and you can stick my boards in there.

www.Hwy79.com

Christopher

Hi!

It’s working again!

I’m not sure what happened, but I opened it up to take measurements, pretended I knew what I was doing, and when I turned it on, it’s almost working as good as new. The volume antenna works perfectly now and the volume knob does what’s expected. 

I still feel like the pitch arm doesn’t have the range it used to, but I may just be remembering incorrectly. 

So, getting me to stick stuff in there seems to have jostled something or jump started something or I don’t know what, but it’s working again! I’m so happy, all the repair places were so expensive and I really didn’t wanna throw the thing away. 

Thank you so much for your help!

Have a great day!

This is great success. What it tells me is your issue is mechanical. The first thing I would do is use the proper potentiometer cleaner in a spray can and spray your potentiometers. DO NOT USE WD-40.

Christopher

I just ordered some 

I’ll let you know if it makes a difference. Thanks for the tip!

Hello!
I received the contact cleaner and sprayed the heck out of the whole inside. 

It seems to have made a huge difference, and the pitch arm is working so much better now. The range was only like 6 inches last week, but it’s about 2-3 feet now!

Thank you so much for your help, you really saved me a bunch of money and saved the theremin from sitting in the basement or trash for all time. 

I really appreciate it so much!

Thank you 

rdarwish,

I wanted your theremin to be irreparable so someone could stick my stuff inside for a Classic Theremin experience.

I always say get a sound sample, from that you can tell who Lev Sergeyevich Termen invited and that is not many for 2020.

Christopher