Open Theremin V4 - grounding Problems?

Posted: 8/29/2023 8:01:29 PM

Joined: 8/29/2023

i recently got an Open Theremin V4. I am trying to set it up properly. But i am not happy with the sound.

I use a guitar amplifier.
I tried to use the Theremin in different Rooms. After a 10 minute heat-time i start the callibration function.
When trying to play the Theremin, the Pitch-Distance is very low. 20-30cm. When i go further, the sound is very low and not very clean. I dont get clean deep tones.

Grounding suggestions from Manual are:

Use any of the following methods to ground your theremin.

1. Use a grounded audio cable. If you connect your theremin to a mixer or amplifier that is grounded, the theremin is grounded through the audio cable.

2. Use a grounded power supply. You can power your theremin through the USB plug (by a device like a computer or a power adapter with USB connector) or by a separate power adapter. If the power supply is grounded the theremin is grounded as well. Notice that many USB power adapter and power supplies are not grounded.

3. Use a separate grounding wire. There are soldering pads on the open.theremin.Uno board where you can connect a extra grounding wire. Attach this wire to a grounded metallic object in your room (like a lamp or a water tube)

As is life in germany we have 2 pins in our plugs, so there is no Pin for ground. I am not sure, but i think method 1 and 2 are out.
So i have soldered a 1,5 flexible cable to the ground-hole at the V4. The cable is 4 meters long and has a aligator clip on the other side.
I am not sure where to connect the aligator clip. I tried it on metal at Windows because i don´t have any metal on the floor. I tried to ground the aligator clip with myself, but the sound doesn´t get any better.

Is their any tutorial for setting up the V4 properly or can anybody help me and give me some tipps?

Thanks for every hint.
Best regards,

Posted: 8/29/2023 8:40:11 PM

From: 30 km south of Paris (France)

Joined: 12/23/2022

Hello Sebastian,

I'm surprised that you have 2 pin plugs in your house.
Unless it is a very old house, you must have 2 pin plugs with a ground connection on two sides.
This is called type F plugs and sockets.
Here in France, we have type E, which is similar to type F, but with a male ground connection pin on the socket, and female on the plug.

Here is a typical E-F compatible plug.

And here, a F type socket. This is what you should have in your house.

Posted: 8/30/2023 7:54:53 AM

Joined: 8/29/2023

You are right. Thats the plug we have.
But how can i connect my groundwire from the V4 to it?

One Pin is phase and the other is 0 (Nullleiter)

Posted: 8/30/2023 8:08:41 AM

From: 30 km south of Paris (France)

Joined: 12/23/2022

Yes !
You can use a separate plug only for grounding.
This is what I do with my Etherwave.
I use a plug with only a ground wire connected to it.
The other end of the wire is actually connected to my mixer.
The mixer ground and the Etherwave ground are connected through the audio cable.

Here are my plugs.
From left to right : 1-Mixer power supply, 2-Etherwave power supply (both with no ground), 3-grounding plug.

Posted: 8/30/2023 12:29:57 PM

From: The East of the Netherlands

Joined: 6/18/2019

Hi Sebastian,

You could connect the aligator clip to a metallic/unpainted part of a central heating radiator if you have those in your house.

Posted: 8/30/2023 7:08:38 PM

Joined: 8/29/2023

You could connect the aligator clip to a metallic/unpainted part of a central heating radiator if you have those in your house.

As we have underfloor heating, its not possible. But in the manual they say, i could connect it to my Lamps.

I tried André´s suggestion.

Hope u can see the pictures.

My jack cable to the mixer is a bit cheap i guess. I use an small to big jack converter, but the cable does not fit properly. So i ordered me a new jack cable from small plug to big plug.

So my first test with the new grounding was not succesfull. The sound volume was very low until i hold the jack cable. But even then, the sound was not very clean in the deep tones.

I will report, when my new jack cable is here.


My setup looks like this:
Ground from V4 to Plug-PE Type F into power outlet.
Jack cable grounds mixer with V4.

This is my little chaotic testroom. Still my pitch-arm goes from 0 to 20-30cm.  Higher distance makes the tone unclean.
I read from other users of the V4, that they have a pitch-range from 0 to 80cm.

What could else be wrong with my setup? Maybe my room is to chaotic?

Best regards and thanks for any help,

Posted: 9/26/2023 6:47:34 AM

Joined: 8/29/2023

No Progress from my side.

Does anybody have any more Ideas what i can do or what is wrong?

Maybe i expect to much from the V4, but i read so many good things about the v4.

Best regards

Posted: 9/26/2023 6:52:29 AM

From: 30 km south of Paris (France)

Joined: 12/23/2022

Did you receive your new cable?

Posted: 9/26/2023 7:00:54 PM

Joined: 8/29/2023

Yes. My configuration looks like in the last picture.

Posted: 9/28/2023 10:06:23 AM

From: 30 km south of Paris (France)

Joined: 12/23/2022

Can you make a video and post it here ?

What power supply do you use to power the theremin ?
Since the Open theremin requires a USB-C 5 volt supply, you probably use a cellphone charger.
This type of supply is a switching power supply which may interfere with the theremin oscillators, with funny audio results.
Try to use another supply which might work on a different frequency and create less or no interference.
Ideally, use a linear (non switching) power supply.

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