Add waveform and brightness

Hi,

i have a simple question :)
How can i add a control for brightness und wand waveform to the 145 Theremin?
http://home.att.net/~theremin1/145/145.html
http://home.att.net/~theremin1/145/145schematic.gif

Well the i hope the building is simple too :D
If someone has an idea - I'm a totally noob, please talk like to a baby^^

MFG,
Nils

I would not advise you to build this Theremin if you want tone control and you are a 'noob' without good electronics knowledge.. I can give advice, but it is likely you will not understand it, be able to implement it, or(most important) be able to experiment and make required changes.

I would advise going for an established Theremin kit which provides the tone control/s you want.

BUT - If you do continue with this one - any distortion / waveshaping applied to the inputs to the hetrodyning mixer (A) and (B) on the schematic will change the tone.. Alternatively you can modify the tone after the mixer.

Well, ok i'm not a completely noob, some years ago i built this thing, but its not working anymore and i think there are many mistakes on the board.

This time i make an etched one.
I meant i'm a noob in understanding electronic circuits. But i can built them, look at this multieeffectboard for guitar i made (still not in a box):
http://nils.neuenwal.de/HPIM3109.JPG

This is my first 145 Theremin 4 years ago:
http://nils.neuenwal.de/HPIM0605.JPG
http://nils.neuenwal.de/HPIM0606.JPG

But if you have an idea, you have to tell me exactly where I have to change something^^

Yeah, my idea was to change the signal at TP2 at Q13. Q13-gate is just the change of V, Source there comes the signal.

I have oscilloscope and everything here. WIthout it, i would never ever have built the first one ;)

ok - The problem is this..

Principles on how to implement tone control is general - and can be applied to various Theremin builds..

But the deatails of actual modifications required for any particular Theremin require specific circuits and / or component values suited to that Theremin..

Working out the required modifications, calculating required component values, and supporting the testing / development / debugging of such a modification is beyond the reasonable scope (in my opinion) of a forum like this - certainly beyond what I have time to do.

See Building a Theremin (http://www.thereminworld.com/forum.asp?cmd=p&T=3867&F=1) and its follow on here (http://www.thereminworld.com/forum.asp?cmd=p&T=3906&F=1) where there is discussion regarding waveshaping.. Devise a scheme, then post your schematics and we can comment on them and try to help.

[i]"But if you have an idea, you have to tell me exactly where I have to change something^^" [/i] - Sorry, I cannot do that - YOU need to bring your level of competency up the the point where YOU are capable of doing it for yourself, with gentle non-specific help.. If you want to make original modifications to a circuit, YOU MUST understand enough to be able to deal with the difficulties which WILL occur!

Fred Mundell
Fundamental Designs Ltd.
Electronics Consultant.
<- See Profile Image for Email.
Designer of Theremins and other alternative electronic music controllers and instruments.

From the original Theremin here a quote:
"The VCA is deliberately designed to distort the
difference frequency waveform, thereby adding
desirable harmonic content. The BRIGHTNESS
and WAVEFORM potentiometers vary the biases on
the VCA input, which change the way in which the
audio waveform is distorted. The BRIGHTNESS
potentiometer determines how much the waveform
is distorted, and therefore the amount of the total
harmonic content. The WAVEFORM potentiometer
determines which harmonics will be strong, and
which will be weak. It is similar to a Rectangular
Width control on analog synthesizers.
The entire theremin circuit runs on ± 12 volts, which
is supplied by a simple, small power supply. Total
current consumption is about 30 milliamperes."

Well..that does not seem to be difficult, but where are these possibile points in my schematic?

http://home.att.net/~theremin1/145/145audioampandvreg.gif

In the pdf is also a schematic of the original Theremin, but i think you know it.
http://www.moogmusic.com/manuals/HotRodEtherwav.pdf

I was going to post the following link to the ASSORTED QUESTIONS forum, but it seems that topic is now closed.

This is a comparative linearity (range and spacing) chart for the Ethervox, RCA, Etherwave and Etherwave Pro theremins within an 18 inch playing arc. I made this several years ago but since we had been discussing linearity, I thought it might be of some interest to new Theremin World members who hadn't seen it.

I should add that the Etherwave I used in the chart was purchased in 1996 and it is possible that the linearity of newer models is improved. You can clearly see how the spacing between the notes closest to the pitch antenna are seriously "pinched".


http://www.peterpringle.com/linearity2.jpeg

[i]
Well..that does not seem to be difficult, but where are these possibile points in my schematic?[/i]

You are looking at an EW VCA / distortion, and wanting to put this into your Arthur Harrison circuit?

You need to take the post-mixer audio, scale the signal levels to match the EW signal level requirements.. Take the volume CV from the Harrison circuit, scale this to match the EW VCA CV requirements.. Then build the EW VCA and feed these (modified / corrected / scaled as required) CV and Audio signals to the EW circuit.

If you cannot follow this, or do not know where to pick up the post-mixer audio, or what shifting / scaling is required for the audio and volume CV, its probably better to give up and build the entire EW circuit.. There is a full article including construction details / layout etc Here (.PDF) (http://www.cs.nmsu.edu/~rth/EMTheremin.pdf)

Just as an addition my Layout for the 145 Theremin (with common small coils):

http://nils.neuenwal.de/pcb1.jpg
http://nils.neuenwal.de/layout.jpg

The layout is tidy - what PCB editor are you using?

Couple of suggestions.. I would avoid right angles / corners as much as possible - particularly on any tracks carrying high frequency.. shorten the length by curving tracks or using gentle angles.

Also.. You have enough space to increase the width of your tracks in places, and I would do this .. not too gross (you dont want to increase capacitance to adjacent conductors) but a bit thicker could reduce possible problems from track inductance.

I would also remove any "islands" in the copper fill - have the fill connected to 0V, and where this is not possible, remove the island - islands can increase capacitive coupling between tracks with undesirable results.

Well after all parts were soldered nothing but one oscillator was running. But exactly with the values of the calibration.

After a while i found that two tracks were broken, now the other are running too. Very nice waves. Now I am at TP2 and TP5 and i think there are some broken tracks too. Or i have to replace some caps. I'll see.

But I made a fault and the eyes where to small and it was difficult soldering the parts. Next time bigger eyes.

http://nils.neuenwal.de/HPIM3508.JPG

[EDIT]
Well at all it is running now. But i will replace the BF410C with the 2n5484 soon to get better waveforms and better control i hope. The amplitudes are very low. But still the sound is nice, everything works fine. Here are some (all of it) pictures:

http://nils.neuenwal.de/HPIM3509.JPG
http://nils.neuenwal.de/HPIM3510.JPG
http://nils.neuenwal.de/HPIM3511.JPG
http://nils.neuenwal.de/HPIM3508.JPG
http://nils.neuenwal.de/HPIM3507.JPG
http://nils.neuenwal.de/PCB1.JPG