OpenTheremin "from scratch" with through-hole PCB/parts?

Posted: 6/17/2024 10:18:47 PM

Joined: 6/17/2024

Hello Theremin World!

After playing around with building several toy theremins many years ago, I've decided to return to the hobby with a goal of building a quality playable instrument.

Given I'm in the software industry and already have Arduino coding skills, I'm drawn to using the OpenTheremin project as a starting point. However, I don't just want to buy a pre-assembled board, if for no other reason than I like doing things the "hard" way and want to learn, and have the ability to make custom changes over time. I have PCB-making skills and equipment. Also I hate SMD soldering!

So I'd like to design an OpenTheremin PCB for use with through-hole parts. I've seen references to others who have done the same and it seems straightforward, but can anyone point to any specific guidance or pitfalls on going this route? Specifically I'm wondering:

1) The only part in the BOM that doesn't have a through-hole version or close alternative seems to be the BB914 varactor diode, and I wasn't able to find another varactor/varicap with similar properties. Is the best bet just to use the SMD version here with a SOT23 to DIP adapter?

2) There is also no direct through hole equivalent to the SMD CC453232A inductor (1mH, 40 ohm) however there is a close match in the B82141A1105J000 axial RF choke (1mH, 33 ohm); any reason this substitution could not be made?

3) I see lots of references to board layout being critical to the OpenTheremin sound but without a lot of detailed guidance on what to avoid. Are there specific components that shouldn't be near each other on the PCB?

Any other tips/tricks on building a from-scratch OpenTheremin would be appreciated!

Posted: 6/18/2024 12:10:04 AM

From: Northern NJ, USA

Joined: 2/17/2012

Professor, before you invest a lot of time and effort in this, maybe just buy one to see if it's what you're looking for?

But if you go this route, maybe separate the coils and antennas more.  And off the shelf coils tend to be a problem in terms of Q and thermal drift.

Posted: 6/18/2024 12:30:46 AM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014


The synthesizer version of the theremin does not use anything Leon Theremin discovered or constructed, they just exploit the Theremin family name. Going from Analog to Digital lost more than was gained and added unnecessary complexity to something that by nature is simple, yet not easy.

You should think more seriously about where you want to end up. Thank goodness you did not say you wanted to do your build in surface mount or I would not have responded.

I wish you the best


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