Continuation of "TOKO Inductors Needed for EM Theremin"

Du kannst das auf deutsch erklaeren, aber ich bin ganz sicher, dass dein englisch besser als mein deutsch ist. :)

I think I may use a switch to cut off a ground, but I've already finished the box, so I may just put a switch on the circuit board in the inside of the box. The setting for this switch would be a little more permanent, so I'm not too worried about having to open up the box to access it (I do have hinges and latches, so it's easy to open anyway.) This switch would be analogous in function to a trimmer I suppose.

Is signal ground the same as grounding through the amp?

A few posts ago I asked about the places on the schematic that are labeled as either +12V or -12V. Are these inputs from the power supply or just places to take voltage readings?

Also, when wiring potentiometers, how does it work with the three different solder terminals?

Thanks,
Dan

[i]I think I may use a switch to cut off a ground, but I've already finished the box, so I may just put a switch on the circuit board in
the inside of the box. The setting for this switch would be a little more permanent, so I'm not too worried about having to open up the box
to access it (I do have hinges and latches, so it's easy to open anyway.) This switch would be analogous in function to a trimmer I suppose.[/i]

You may want to try it before you make more work for yourself.

[i] Is signal ground the same as grounding hrough the amp? [/i]

Usually the amplifier will tie signal ground to earth ground.

[i]A few posts ago I asked about the places on the schematic that are labeled as either +12V or -12V. Are these inputs from the power supply
or just places to take voltage readings? [/i]

The points labeled +12V or -12V should be connected to the appropriate power supply output. Reference voltages are usually indicated with an
arrowed line or a squiggly line. Check out the -0.6V reference voltages in the oscillator section.

[i]Also, when wiring potentiometers, how does it work with the three different solder terminals?[/i]

Usually the center pin is the wiper. This is easy to check using an ohmmeter.

(* jcl *)

Is signal ground the ground that I need to connect to the grounded points on the schematic? Will the theremin work with regular speakers without an amp? If I don't use an amp, will it work without any signal ground?

I don't think it would be much work for me to just break the ground wire with an SPST switch on the circuit board, or is there a complication I'm overlooking? Otherwise, I'd have to completely remake my front panel and add another hole for an external switch.

Thanks

I started another thread about a few problems I've had with the circuit, and I mentioned L11 being the Coilcraft substitute with a 30 Q-min instead of 60. I have already but it into the circuit, but it wouldn't be hard for me to swap out. Could the Digikey part # TK1421-ND work as a better substitute? In the other thread, I wrote how I wondered if the substitute was causing my problems; is it worth switching out the inductors or is the inductor most likely adequate and unrelated to my problem?

Thanks,
Dan

I would say that, theoretically, the Q-factor of a coil is not so important in a theremin's oscillator design, since the Q-factor influences the bandwith of the tank circuit, which is important for radio reception (separation between stations). But the Q-factor has no influence on the oscillator's frequency, which depends only on the coils' inductivity.

So I would say that if the inductivity is correct, the theremin has to work. Maybe that, depending on the oscillator's design, a higher Q-factor gives more thermal stability, but has nothing to do with the elementary function.

Sorry, once more, for my bad English, I hope you can understand what I wanted to tell. If not, don't hesitate to ask me.

What do you mean by "thermal stability"? I think the inductor has a very wide range, so should I try the volume function on different ranges of that inductor?

Also, Thierry, do you happen to know how I can tell the difference between the 5mH and 2.5mH coils?

Thanks a ton,
Dan

"thermal stability" means that the volume oscillator's frequency may vary with the temperature. Almost all oscillators have this effect, but with a lower Q-factor it may become a little bit more important. But after studying the schematics of the EM theremin, I think this will not have audible effects.

Normally, these adjustable coils have a tuning range of +/- 10% while fabrication tolerance is also +/- 10%. On the ninth page of the 10 page article in the left column, the adjusting of L11 is described. As long as you may tune it as it is written, the coil you use is fine.

How to distinguish the 2,5 mH and the 5 mH coils, was that your question?

If there aren't colour code rings as on the resistors, you may take your multimeter and mesure the resistance of the coils. Those with the slightly higher resistance are the 5 mH coils (this is the polish wet finger method, but it works... :-))))

ok, now, here in western Europe, it's almost 1 AM, so please be patient if you have further questions. You'll have to wait a few hours.

If both the 2.5mH and 5mH inductors are the
JWMiller parts you should me able to measure
the difference in size. Otherwise look at the physical specification in the datasheet.

If the coils are manufactured with the same
core measuring the resistance should also work.

(* jcl *)

Would switching the 5mH and 2.5mH totally mess up the volume controls? I interpreted the 5mH as being bigger; is that correct?

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?

Also, with the pitch control turned so that the resistance is at a minimum, the pitch decreases as I move my hand towards the pitch antenna, and then there is no noise until I touch the antenna, which is the same high note.