Equivalencies for Pop. Electronics Theremin

Posted: 4/29/2015 5:16:48 PM

Joined: 4/28/2015

While i was redrawing the schematic i noticed that an newer version of the shematic and PCB have some errors:


1-in the pcb file , the resistor labeled R7 (between R6 & R8) should be R5
2-in schematic , C12 is marked with a + simbol , leading to think it is electrolitic capacitor.
3-in schematic , C4 has no + simbol , leading to think is not an electrolitic capacitor


i can confirm error 3 from previous popular electronics pcb here:

i hesitate about error 2:
in this same older file :: there is a (+) near C14 or C15:   Are C12 C14 & C15 0.001 electrolitic or not??? 

error 3 i confirm is electrolitic..


Finally about the coils  , i think  SLOT TEN-5-14 are not available anymore... Any other source for coils ??

Thanks for reading... Hope this helps anyone making this circuit ...



Posted: 4/29/2015 5:18:36 PM

From: Colmar, France

Joined: 12/31/2007

The SLOT TEN-5-14 are still available and may be ordered directly on the Coilcraft website! ;-)

The 0.001uF = 1nF are not electrolytic but ceramic.

Posted: 5/1/2015 11:35:31 AM

Joined: 4/28/2015

Hello :

i will use coilcraft SLOT TEN-5-14 coils , this is my updated pcb before layout.
I will probably change connectors , and place averything carefully...

This is the updated schematic will all  today equivalents..


let me know if you see any errors , sugestions are also accepted..

the PCB maker always make 5 boards minimum , so i will be glad to share some PCBs ;)

PCB type : standard FR-4 2 layers.


i have some trouble finding this type of capacitor in SMD package:

4.7pF  Polystyrene capacitor    
60 pF 
 Polystyrene capacitor (alternatives 56pf or 68 pf)

is posible to replace with ceramic type or other?  even in through hole are not simple to find...
Please advice!!


Posted: 5/1/2015 2:42:24 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

valpoder said: "let me know if you see any errors , suggestions are also accepted.."

Over the years I constantly say don't buy or build any theremin design including an original RCA if no sound samples are available. Can you direct me to one SWTPC theremin sound byte. I did enjoy building their strobe-light kits back in the '60s. I believe they were out of Arizona.

Miss those days ......... not really. lol


Edit: Found what I was looking for, the Theremaniac theremin is based upon the '67 SWTPC design and Mr.Collins always had a sweet theremin sound. How the oscillators are buffered my limited knowledge does not allow me to see. I do have one in a drawer somewhere.

Posted: 5/1/2015 3:21:56 PM

Joined: 4/28/2015

Hello Christopher

Its an honor to read your post , i remember visiting your website back 10 years ago !! 
i understand what you mean , but this circuit is sort of a challenge for me ... Also i have all the gear to test the circuit so it will not be a problem to debug..

I think it would be great to have a small and compact theremin to build , all with easy to find parts.

Cheers back there in california !!!
ill be happy to send you a pcb , just for laughs !!!

Note::  i will probably use NPO caps for the 4.7pF and 60 pf as they are recomended for frequency stability!:!!

Posted: 5/1/2015 4:35:21 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

Valpoder said: "Its an honor to read your post , i remember visiting your website back 10 years ago !! "

It would be an honor, for me too, to get one of your PCB's. Ten years makes us older, it has been a good journey and we both have evolved. My theremin knowledge was developed listening to everyone at TW, even when I was being ornery. Over twenty unique people pass by TW and my website daily without stopping to say hello. They have interest in building a theremin. You might have the modern design they are looking for.

My eye hand coordination is not good enough for the new surface mount stuff, then throw in the shakes. lol

A really good idea is if your pcb design allows it to be configured as a stand alone Volume Control if not building the full theremin. There is a real need for this so think about it! Every pitch only theremin could use it plus other applications.


Edit: With a stand alone volume control the normal audio output jack would be stereo. Output on the tip and input on the ring, ground on the sleeve. A jumper would be used on the ring when used for volume only. Also a stereo cable allows the theremin to plug into the computer sound card without shorting issues. In a volume only use a breakout cable  plugged into the output jack. Stereo jack  STX 3120-3B preference from Mouser.  Just a Thought

Posted: 5/2/2015 7:15:29 AM

Joined: 4/28/2015

volume control output is a very good idea: it could be used for synthesisers and guitar effects:

how would you implement volume control? from which node/signal? should i add a buffer?  

if the circuit works , i would probably make complete populated boards , so no need to worry about shaky hands..  ;)

but before all that , i will get hands dirty and make this circuit work ... but it looks good  ;)

cheers !!

Posted: 5/2/2015 2:46:01 PM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

I always thought the SWTPC volume section would be interesting to try as a stand-alone volume control. In my style of electronic design I would breadboard the section to clarify the approach, not smart enough to just interpret a schematic with confidence. Your IF transformer coils might be too close together. If so it will distort your audio wave shape into a mousey sound rather than a mellow sound.

Without bread-boarding I am lost, only then do I draw circuit boards which then lead to schematics so everyone else can follow my thoughts.  As an original designer this is backward from those who just copy a design.

I only do one side PCB cause that is all my free software from 15 years ago allows, I'm to old to change. Then I home etch my own boards to proof them for about $1. Then I furnish iron-on PDF so anyone can make what I make or then maybe I buy commercial boards with my generated Gerber files.

* You are at the point your theremin pc board should take shape to fit an enclosure, I like Pac Tec, some have a 9v battery compartment slide door.

Throwing out thoughts to see what sticks. LOL


Posted: 5/3/2015 11:50:11 AM

Joined: 4/28/2015

>> Your IF transformer coils might be too close together..

even if they are well  shielded to ground ?  
which ones are too close? L3 L4 & L2 at the right side of the board ?
you are right , they are a little close , i will try to respect original position and proportions...

>> Without bread-boarding I am lost 

I understand what you mean , but since all is SMD , no bread-board is possible.
I will limit to make miniature version of the known to work circuit , and then try too experiment with your 
volume control output idea later on...  its just a prototype for the moment , i will improve the board in the next stage...

I am very confident it will work , also , mostly because the board will have a tight ground plane in both sides ;)
By the Way i use Eagle cad soft which is also free to use in small boards like this...

Thanks for the feedback
It loooks good !!


Posted: 5/5/2015 6:13:03 PM

Joined: 4/28/2015

The coils are here!!!  Coilcraft SLOT TEN-5-14 !!!!

i work some more on the pcb before sending it to FAB !!!

 EDIT: a first prototype of 10 PCB where sent to factory today !!!  
its very pretty 8.5x3.5 cms double layer board!!!

Boards will arrive in the following days... !!!!

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