SC/Jaycar kit-Maxie's mods advice wanted

Posted: 3/11/2005 4:52:54 PM

From: Noo Yawk Citay

Joined: 3/6/2005

Thanks for the tip on the auto-bypass for the 9V battery. I'll check that out. Also, I will be trying the loop volume antenna. I believe the Kees Enkelaar unit is based on the SC board and it has regular antennas. I do plan to add the mods noted above, incl. an adjustable volume sensitivity. Hopefully that will work. And a much bigger box to minimize ingteraction of the volume and tone!
Posted: 10/16/2005 3:31:54 PM

Joined: 4/28/2005

I notice a discrepancy between Maxie's text and pictures.

In the text (towards the end of the article), Max writes, "Next I created a low-pass filter between the MC1496 and the LM358 by putting a 100 k trimpot in series with the 0.1 uF capacitor....."

However, those are not the values in the circuit diagram. A 10 k ohm trimpot and a 1 uF capacitor appear between IC1 and IC2 (

Does anyone know which was Max's final revision? Perhaps someone who knows Max could ask?



Also, the sound files at the end of the article can be found on another site. It really doesn't sound too bad for such a simple circuit:

Posted: 11/14/2005 7:31:07 PM

From: New Zealand

Joined: 11/10/2005

Hi, I am also building a Jaycar theremin. However, I have relativly little experience building electronics, but i was thinking of doing max's mods. I should be able to handle the mods that involve changing the value of the resistors ect. But, I was thinking of doing the other mods when it is close to complete, because by then i would have had more experiance with electronics. I was wondering how diffucult it would be to do the mods in the later stages of construction or even do the mods once the theremin is complete.?

thanks, Andrew
Posted: 11/17/2005 2:45:58 PM

Joined: 11/2/2005

So, where is Max's webpage? I have seen it referenced numerous times, but I cannot find a working link.

I am sure it is under my nose somwhere, but I have a big nose....

Posted: 11/17/2005 4:11:13 PM

From: Sammamish, Washington

Joined: 2/13/2005

His page went offline a few months ago. He gave me all of his content, but I've only been able to put a little of it back online here - much of it was copyrighted material/schematics that I don't have rights to republish. The Jaycar mods article can be found on the Jaycar page in our Theremin Gallery.
Posted: 3/18/2010 11:17:32 PM

From: Mexico

Joined: 3/18/2010

Any one who can help me in theremin mods. I have follow the instruccions from max´s mods but i can´t with the tuning, it sound´s like a fuzz scream and i whant a violin sound please help me...
Posted: 3/19/2010 5:15:41 AM

From: Colmar, France

Joined: 12/31/2007

The Jaycar will, due to its circuit design, never produce a nice violiny sound. Even if you add the oscillator coupling mod in order to sharpen the waveform a bit, this will only affect the lower or lowest range. You could make the coupling stronger, but this would result in a total loss of the lower range while the waveform in the higher register would still not be enough sharpened.

During the weekend I'll have a look on some other of my documents - perhaps I'll still discover another modification which will be more helpful than the simple skewing by Maxie.
Posted: 3/19/2010 7:23:23 PM

From: Mexico

Joined: 3/18/2010

Hi Thierry-min, i appreciate if you could help me with this issue, i know that probably i can´t get an amazing sound, but at least, some playable sound, with a good octave range.
I notice that if i touch some resistor near T1 and T2 with the telescope anntena included in this kit the sound gets better but just while i´m holding it because if i left it once again this horrible fuzzceamingsound.
The wire "L" shaped from Max article does not work for me i don´t know why.

Thank you so much for your help....
Muchas gracias...
Posted: 3/24/2010 6:33:45 PM

From: Colmar, France

Joined: 12/31/2007

You told that the sound of your theremin is screamy but it shouldn't. My first advice for all theremin modifications is: make sure that it works at 200% correctly before modding it. In its unmodified state, the Jaycar theremin should have a very smooth timbre similar to the Henk-theremin in this video ( If yours hasn't, make sure that
a) you use a good and stable power supply
b) remove the internal speaker, it's crap and will not allow to hear a difference in timbre!
c) connect the theremin with a suited RCA to 1/4" adapter cable to a reasonable amplifier. The output level of the Jaycar is somewhat higher as the Moog Etherwave, so you risk to overdrive a guitar amplifiers input which creates still more distortion. A keyboard amplifier or the CD input of your Hifi system will give better results.

When you start modding, you should understand what you do before you take the soldering iron into your hands: The L-modification creates a capacitive coupling between the fixed and the variable pitch oscillators. The effect is that if both oscillators ar working at almost the same frequency (very low audible tones at the output), one tries to pull the other which deforms the waveform slightly and gives a more stringy sound, but only for frequencies below 150Hz.

A better way to change the timbre is to act on the waveform independent of the actual frequency. The loww-pass filter in the output circuit will nevertheless vary the timbre, so that it will be somewhat smoother for the highest audio frequencies (>1kHz). How to act on the waveform? It's simple: as soon as the the sine waves are deformed, i.e. clipped, you'll get a different timbre. Symmetrical clipping gives rather a wind instrumental timbre, asymetrical clipping gives a rather stringy sound (like the RCA theremins). You can obtain the latter by desymmetrizing the symmetrical mixer IC MC1496 by adding some offset voltage to one or both of its inputs, so that it is easier saturized for on half of the sine wave than for the other. Please let me a few days for designing the additional circuitry, because one has to take great care to not to destroy the mixer by over-biasing it. This will give you the time to rework your theremin for proper operation in its original state. ;-)
Posted: 3/24/2010 7:50:34 PM

From: Mexico

Joined: 3/18/2010

The circuit was working fine with his known limitation after any modification but any way i´ll re-check all. I have one extra Jaycar theremin without any modification, it is working fine, so in case I need it, i´ll have a new opportunity to restart this modification or to blow it up :-) (joke)
Working on, thank you for your time and help.


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