Problems with Tuning and Testing of my EW Plus

Posted: 10/14/2017 6:02:12 PM

Joined: 9/12/2017


After several problems while constructing my Theremin Kit (wrong screws, so I had to drill my own M3 holes, a missing thread reducer for my mic stand, and because I overturned the connectors to the antennas and damaged the wood cabinet a bit, 3 extra lockwashers to hide that part) I am finally in the Tuning and Testing section. Before I installed the Theremin on my mic stand, I can't adjust the tuning controls to get something useful.

But with that stand i managed to get to point 13) where I should get a level of -2.5V to +4.5V and +7V when touching the pitch antenna. For me its -1.9V to +4.9V, also +4.9V when touching the antenna. The manuel says it will vary a little, except thats over 2V. Is this still ok?

Also the gate signal in 11) is always 9.5V (when away from volume antenna) regardless of proximity to pitch.

My biggest concern though is that it sounds horrible, I turned all knobs and tried to figure out how to produce a more harmonic noise, but I don't get it.


Some additional information/questions:

I just have an EW Plus and a mic stand, no amplifier. I tried to connect it to my soundcard but don't know where to plug in exactly. There was a level displayed for my EW, however I couldn't get a sound out of my boxes.

So I just plugged in my 12€-In-Ears with an 3.5 to 6.3mm adapter and get a sound, but its hurting me... ;-(

Do I have to use special shielded cables for everything? Since if I squeeze my headphone cable at any point, the pitch drops to a deeper level. What advices can you give me?


Please help!

Posted: 10/14/2017 10:56:25 PM

From: Colmar, France

Joined: 12/31/2007

Your story reads like you should better trash that kit and buy a readily built instrument... Remove the 3 lock washers, I suppose they are in metal, thus these will add electric capacitance which can lead to unwanted effects. I think the screws were ok, but these are not M3 but imperial, so there was for sure no need to drill M3 holes. The Mic stand thread adapter can be bought for $1.50 in every music store round the corner.

Most important thing : It is normal that it sounds horrible through that integrated headphone output. And with only a headphone connected, the Theremin will never sound nice and behave stable, so you can’t tune it that way.

Like old radios from the 1930s and 1940s, a Theremin which has a similar principle of operation needs to be grounded. This is normally done by connecting the audio output via a 3 or 5 meters long shielded 6.3mm audio jack cable to a suitable music instrument amplifier which will provide grounding to the connected instrument through the three prong wall plug. Without grounding, the Theremin will not be stable, can often not be tuned (floating rf potential) and you will hear a distorted sound and sometimes even ghost tones.

Like for all electronic equipment, you should understand that the price for the instrument is only a small part of the total spending for the whole chain. A $500 instrument needs at least a $200 combo amp or active leaker do get everything out of it, but one might also spend $1000 for a professional music reproduction system.

Normally, if everything is well done, the EW Standard an Plus Kits work pretty well out of the box since the circuit board comes pre-adjusted, so it’s always a good check to set it up correctly on a mic stand and a clear radius of 1.5m or 6ft around, connect it with a shielded cable to a suitable grounded instrument amplifier and try it out without fumbling with the internal inductors. Especially if you aren’t an experienced RF tech, you risk to make things worse turning these. 

Check the volume response and the pitch range (or better have it checked by an experienced Theremin player) and report eventual anomalies here. Then, the pros might perhaps help you tou get it back in tune.

Posted: 10/18/2017 1:21:20 AM

Joined: 5/8/2017

Thierry is correct, and headphones connected directly to a theremin are generally a disaster, unless it is one of them new fangled fake theremins.

GROUND the instrument and GROUND yourself.

It may actually start to work somewhat then. But I wouldn't bet money on it.

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