Grounding and Alternatives.. Yes, a repeat performance! ;-)

Hey everyone, 

I've recently gotten into theremins and have greatly enjoyed reading all of the discussions on this site, I hate to drag up an old thread but I had one question about these ground antennas if anyone happens to see this.

Would it possibly be dangerous to couple a player directly to the ground on the theremin via a conductive bracelet around the ankle? I'd like to use something like this https://www.amazon.com/Rosewill-Grounding-Alligator-RTK-002-Detachable/dp/B004N8ZQKY, but can make a conductive mat ground antenna instead if there are any valid safety concerns.

Welcome scimonet,

An analog theremin needs a good earth ground for two specific reasons whereby a digital theremin needs only one to complete the circular capacitive feedback loop.

The wrist strap looks like the right idea but this particular one has a 1 meg resistor in series with the connection to you. This defeats the purpose.

Analog theremins use a radio frequency wave shape to get that natural beautiful sound. The RF energy needs to escape the circuit by way of a direct earth ground to avoid unwanted distortion in the final audio waveshape.

PS: earlier in this thread I am RS Theremin debating with FredM, I changed to oldtemecula when I was given the secret of theremin.

Christopher

Hi scimonet,

That cable has significant resistance.  You could instead try grounding yourself to the Theremin through a small capacitor such as 0.01uF = 10000pF, which is a lot bigger than hand capacitance so it should look more or less like a short to the Theremin.  XC = 1/(2*pi*F*C), so the impedance of 0.01uF @ 60Hz looks like 265k ohms (probably enough to protect you from mains shocks).  And at 200kHz it looks like 80 ohms (way lower than your body resistance).

AFAIK there is no hocus-pocus going on with RF and such, so I wouldn't worry about that influencing the sound or anything.

Ah thank you, hadn't realized the cable had such a high resistance. Perhaps could use the <10kΩ wrist strap in conjunction with dewster's idea. I should mention that I was considering these solutions for a digital theremin (Open Theremin v3 powered by 5v 500 mA power supply), so much less concern than with mains.

Hi scimonet,That cable has significant resistance.  You could instead try grounding yourself to the Theremin through a small capacitor such as 0.01uF = 10000pF, which is a lot bigger than hand capacitance so it should look more or less like a short to the Theremin.  XC = 1/(2*pi*F*C), so the impedance of 0.01uF @ 60Hz looks like 265k ohms (probably enough to protect you from mains shocks).  And at 200kHz it looks like 80 ohms (way lower than your body resistance).AFAIK there is no hocus-pocus going on with RF and such, so I wouldn't worry about that influencing the sound or anything.

So just one of these, an alligator clip and some copper wire around the ankle maybe? https://www.newegg.com/p/2CS-001X-00003?item=9SIA86V2Z07949&source=googleshopping&nm_mc=knc-googlemkp-mobile&cm_mmc=knc-googlemkp-mobile-_-pla-srad+tech+ltd-_-ec+-+passive+components-_-9SIA86V2Z07949&gclsrc=aw.ds&&gclid=CjwKCAjwlovtBRBrEiwAG3XJ-_GSI4m_J5OMPDX3jekq4ZZT3YpUWk3HGn1XToyYFDLip4ObKMZyyhoCVY0QAvD_BwE

Hello bendra,

That link is for 100 pieces when in reality with the Open Theremin I doubt even one is necessary unless there is some 50/60 hz noise issues.

Christopher