Continuation of "TOKO Inductors Needed for EM Theremin"

[i]Would switching the 5mH and 2.5mH totally mess up the volume controls? [/i]

I don't know. You have to try it. I would
be surprised if it *totally* messed it up.

[i]I interpreted the 5mH as being bigger; is that correct?[/i]

If the inductors are built using the same
core than the 5mH inductor requires apx 40%
more turns. The inductance is proportional
to the square of the number of turns. To get
twice the inductance requires sqrt(2) * number
of turns.

[i]I've been trying to tune the pitch, and when my hand touches the antenna, it jumps to a very high "ping" like note. I've tried to change this, but it seems like changing it sacrifices sensitivity of pitch. What should I do?[/i]

Don't touch the antenna ;-) Without seeing
the board layout it is hard to say. Is your board
layout similar the board in the EM article?
Is there other metal near the oscillator?
How did you layout your coils? The EM article
recommended a specific spacing *and* orientation.
To determine the orientation you need to look
at the direction of the coil winding ( I am
not sure if the coil is marked).

(* jcl *)

The only metal on the box besides critical parts is two small hinges, two small latches, and nails and screws. If you would like pictures, you could give my your email address and I'd be happy to send them to you.

The layout is similar- each "functional block's" components are close together, and the FPO is far away from the VPO, and there are just a few other differences. I guess my main question is is it normal to have the Theremin play a much different tone while the antenna is touched?

Do you have any suggestions for as to why the volume isn't working?

Does the pitch oscillator play fine until
you touch the antenna? You should draw a distance
vs frequency graph. Plot the distance for each
octave change. I am not sure how many usable
octaves this design should have but 3-4 sounds
reasonable.

For the volume oscillator check all of the bias
points of your transistors. Use an oscilloscope
to check the fixed and variable oscillators.

(* jcl *)

Yes, it plays fine and has a large range until I touch the antenna. I think that I haven't tuned it quite well enough. Does the pitch jump on your theremin?

Adjusting P1 while I touch the antenna actually does change pitch- my mistake.

I think I'll take another shot at re-tuning...I only have a lot of sensitivity in the lower frequencies.

The front panel pots are wired in parallel, correct?

What are "bias points"?

Thanks,
Dan

Yes it is normal that directly touching the antennas gives strange effects. Just do not touch them!

As I wrote in the other Thread, only L7 is critical and must be a 2.5 mH coil. The other three are in series, the order may be mixed up.

[i]What are "bias points"?[/i]

There are various points around the transistors
that are labeled with voltage values. You
should verify that the correct voltage is
at each point.

(* jcl *)

The tuning section in the Hotrodding Etherwave manual and my do it yourself article make the tuning sound like the tone should be 3.5 octaves above middle C when you touch the antenna, and then decrease steadily from there. Instead, should it be 3.5 octaves above middle C (3000Hz) very close to the pitch antenna?

I checked all the bias points, and the only ones where I had a bad reading were at the emitters of Q6 and Q7. I read an infinitely small amount of negative DC voltage.

When you touch the antenna you are adding a large
capacitance. You should expect a large change.
If you are getting a usable pitch range prior to
touching the antenna I would not worry about it.

A reading of zero sounds like there is an open connection.

(* jcl *)

It seems that the volume oscillator is working, but not with optimal Parameters. I would check if the emitter resistance on Q6 and Q7 is really 2.2 kOhm (colour code red-red-red) and not by mistake 22 kOhm (colour code red-red-orange).

jcl- It's not quite zero voltage, just over.

The color code is definitely red-red-red. Is there anything I should check around U3 that could be causing a problem? The volume potentiometer doesn't even make a change.

Also, if I turn the resistance of P1 down, the zero beat gets further away from the antenna, but there is also a point where if I turn P1 very far down, the pitch increases as I move away from the antenna. Is this normal?

I measured the DC voltage at pin 12 of U3, and it was a consistent -12VDC while I changed L11's inductance to it's max and min. There was also no change in voltage when I brought my hand near the volume antenna coils. Could this mean that I did in fact mix up L7 through L10. It is a wire coming from these coils that goes to the VCA, so that makes me think it could be the root of my problem- is that a false assumption? Would having the wrong inductances in the volume antenna circuit lead to the incorrect voltages at the emitters of Q6 and Q7? My meter isn't sensitive enough to check for the resistance across the coils, and there is no spec sheet that denotes the size of windings; for all I know, they could be mixed up... Would it be worth soldering them in the other way? Turning P2 also had no effect on the voltage at pin 12.

Thanks,
Dan