Readjusting the volume oscillators (2022 Theremin)

Hi all, this is a repost because I posted the original in the wrong forum section. 

I’ve been playing my theremin for just under 3 years and I’ve always had my volume control knob all the way to the left. This works well for me when I’m playing at home with headphones and gives me just the right distance to control the volume well. However, whenever I connect into a sound system or amp that has a much louder minimum volume than my headphones, the distance I lift my hand to get to maximum volume is way too small and is difficult to control.

I’ve read the manual instructions for readjusting the volume oscillators and I have the little red plastic tuning thing. I’m just a bit nervous because also in the instructions it says that incorrect adjustment can render the instrument unplayable and isn’t covered by the warranty. Does anyone have any advice for readjusting the range on my volume loop?

Thanks everyone!

Hi Finn, let us look at the whole set before doing a re-adjustment of the volume part of the theremin. If the volume range with headphones is right, but with an external amplifier not, because the gain is to high, you should reduce the input gain of the amplifier. If the amplifier has only the aux in and no loudness control an active or passive input mixer or divider can help. For example the JHS Little Black amp box, passive with single jack in / jack out. Alternativ a guitar amp, with a gain control knob. 

I wonder how you play at home with headphones. If you don't have then a connection to earth via an external amplifier, the theremin is wether not really easy to play nor sounds good. Grounding only via the cheap and inferior power supply is highly inadvisable.

Hey Pascal, thanks for taking the time to troubleshoot and help. Currently, I can’t really check if the amps I have access to have gain control, I do know that the sound system I can connect to, the gain can pretty easily be controlled. In terms of grounding I still don’t 100% understand how to do it/how it works. My issue with grounding is that I’m currently living and playing in Nepal, where pretty much no buildings are specifically grounded. I haven’t really had any issues with tone or background sounds from what I understand to be “bad grounding” so far, but if there’s an opportunity to improve my sound or the volume loop stuff I’d love to take it. 

Thanks again for your input.

I'm not entirely sure I understand the problem correctly: The Theremin has a good volume response with the “VOLUME RANGE” set to the far left when you use headphones. As soon as you switch to external amplifier mode, the hand distances between very loud and very quiet are too short, regardless of where “Volume Range” is set?

The headphone output is always active, even if AUDIO OUT is muted with the MUTE button: When you use headphones, is an external amplifier with a jack cable still connected or not? If not, the pitch and volume settings shift because the theremin is less well grounded. The manufacturer recommends using a grounded amplifier.

Sorry, I probably wasn’t as clear as I should have been. When I’m playing with headphones, I don’t have an amp connected. Also, when I’m playing with headphones, it’s plugged in at the headphone port facing me. The volume range is good when I’m using this setup. I didn’t know that the pitch and volume setting drift so much based off amp connection, so thanks for that new information. I’m not really sure if my amp is grounded or not though. How can I tell?

When you're wearing headphones you're probably grounding your body better (or more correctly, referencing your body to the Theremin) which could be another factor in all this.  Grounding is a very basic and critical thing for Theremin operation.  In the US anyway, Moog Theremins ground through the AC connection, something you can check with a DMM.  If there is no ground connection on the Theremin AC cord then it can't ground that way (same for the amp) and you should then ground it via the amp or other means.

I originally bought the theremin in the US, and I’ve been using the same power supply, so my guess is that I am grounding either through my body or somehow through the power supply. I probably have a DMM lying around somewhere that I can test with.

Another issue that I’ve been having, that's less important is when I try to play in a certain room at school, I can only get this horrific grainy sound and my pitch knob also doesn’t work very well. The room is slightly underground, but I'm not sure if that plays into the grounding or something. It’s not a site issue because I can play literally anywhere else and have it sound fine.

The grainy sound is likely mains hum intermodulation.  If you could provide a sound sample I could examine the spectra and confirm this.  My Etherwave used to do that when placed too close to AC wires in the wall it was positioned near.  Perhaps the outlet in that room isn't grounded very well, or has a small voltage on its ground.

Back to the initial problem, new adjustment or not, and if so, how. 

You could hang temporarely a small stripe of aluminium foil, for example width 5 mm, length 50 mm over the volume antenna, the filter resonance now shifts a bit and the volume range too, at the same position of VOLUME RANGE. If you feel it is better for your playing, the adjustment with the calibration tool should be some degree clockwise. If not, counterclockwise. 

Highly recommanded: mark the initial position with a permanent marker on the drew pen. Be carefully, the sensitivity to the result is high.

Here an example how the adjustment works on a coil with a slotted core. 

Next picture shows, how much "play" occure before a position change of the core is made. 

Users Manual: Only small adjustment are ever required. 

I've found it helpful to wrap a short piece of tape around the "swizzle stick" with the ends stuck together like a tiny flag.  This gives a good visual of how much you're rotating things.