EM/EW Theremin Linearization Coils

Hi,

I am new to the board and interested in building the EM/EW Theremin circuit. I am wondering: is it possible to replace one or more of the 10mH (6306/1535G) coils with two 5mH (6304/1535D) coils in serial? What effect would it have to replace two of the 10 mH coils this way, for a total of 5 pitch linearization coils instead of 3?

Related question: It seems that in 2018, both the Hammond and original Miller fixed coils are extinct and nearly impossible to source. Has anybody modified the circuit to use more readily available inductors?

Thank you all!

Been a while since I last looked, but the Bourns 6300 series of "Varnished Chokes" were still orderable.

Using more 5mH in series would probably work too.

I haven't been able to find any after extensive searching, and according to this document, Bourns stopped shipping them last year. So I figure the supply is limited to whatever is out there, and once they're gone, they're gone.

Since the EM/EW project is pretty much the only option to DIY a two-antenna instrument, I hope someone will adapt the circuit someday to use currently available components. Or fill that niche with a new project/kit design.

And thanks for the vote of confidence on using an alternative coil configuration.  In a similar vein, what about using a 5 mH coil instead of the two 2.5 mH ones for the volume antenna? Is it bad to have fewer than 3 coils/would linearity be negatively affected?

"I haven't been able to find any after extensive searching, and according to this document, Bourns stopped shipping them last year. So I figure the supply is limited to whatever is out there, and once they're gone, they're gone."  - aerorad

Oh dear, that is bad news.  I wonder how Moog Inc. will source these parts in the future for the EWS and EW+?

Since the EM/EW project is pretty much the only option to DIY a two-antenna instrument, I hope someone will adapt the circuit someday to use currently available components. Or fill that niche with a new project/kit design.

I believe ILYA is working on a design that uses smaller inductors and dividers, and if I were building analog Theremins that's definitely an angle I'd pursue. That way the equalizing coil could easily be a DIY air core.

And thanks for the vote of confidence on using an alternative coil configuration.  In a similar vein, what about using a 5 mH coil instead of the two 2.5 mH ones for the volume antenna? Is it bad to have fewer than 3 coils/would linearity be negatively affected?

Stringing more, lower-valued inductors, together is probably safe, but I wouldn't go the other way without characterizing the self-capacitance.  Obtaining lower self-capacitance is generally the reason for using multiple inductors.

Just wanted to add that there's nothing magical about these inductors in terms of Theremin use.  It's true that their construction yields a fair amount of inductance for their size, but at the expense of temperature dependence (drift), self capacitance (the need to use many in series), and lower Q (reduced resonance / peak antenna voltage).  They can be huge, but Theremin used air cores here for practical reasons.  Radio designers are usually more concerned about size than anything else, hence the dearth of inductors that are appropriate for Theremin use.  After much fruitless searching I gave up on it a long time ago and started winding my own.

Your points about these particular inductors are well taken, but I am an electronics hobbyist, so I doubt I will be winding coils or characterizing self-capacitance any time soon! For that reason, I've been trying to gather the originally-intended components (or at least close alternatives), since from the other posts I’ve read on here, this circuit seems not to be very forgiving of substitutions. I’ll move forward with the build if I eventually find the coils. In the meanwhile, I have been studying the many discussions on here about building the EM/EW, and trying to absorb some of what has been said by yourself and the other more technically-inclined posters.

BTW: anybody know if there has been a "definitive" PCB layout uploaded for the EM/EW ? I think the one in this thread is the most recent, but it seems that there were a number of changes suggested after its posting.

Also curious to know if there is a recommended schematic to start from, considering that there have been many versions over the years. Is it the one in this thread?

I know I have strayed quite a bit from the original topic, but I am also trying to wrap my head around the power situation ... I understand that the EM/EW requires a connection to earth ground, and that this can be supplied either solely by an audio connection to a grounded amplifier (as in the original EM article) or the power plug itself (as in the "hotrodding" article and henceforth), and that issues can arise when both connections are present simultaneously.

I want to avoid using the Moog PSU and DIN connector; it just feels proprietary and limiting (and expensive) to me. Could I use something like this PSU, with the understanding that I won't be able to use headphones or ungrounded amps with the theremin? Are there any other caveats with that approach?

The Cui-Stack PSU referenced in the EM article has an output of 12VAC; why do the newer ones put out 14VAC, and which is better (or does it matter)?

Finally, could someone please explain why the 3-pin DIN connectors are necessary, if two of the pins are tied together as shown on the schematic in the "hotrodding" article?

Thanks!

Hi! An interesting approach to the question of the power of the theremin! If you want, you can implement your idea, but it is much harder than the other way: you do not like the DIN connector or expensive adapter with such a connector?.. You can take a suitable adapter. if it is adapted to the conditions of your country, cut his power Jack and put in place a new male DIN connector, soldered 2 wires to pins 1 and 3. pin 2 can be left without connection. Now you have your chosen power supply unit, but with a different connector, namely DIN. Grounding will be done through a shielded audio cable going to the sound amplifier. PS: 12 volt output AC adapter will give less voltage headroom for adequate operation of the stabilizers on the PCB of the theremin. Therefore, an output of 14 volts AC is used.

The Jameco wall wart is AC to AC so it may work.  Not sure why the EW uses a DIN connector, I'm generally against that sort of thing, especially when it comes to power delivery, though I suppose they had to get the ground in there somehow.  Probably used two of the pins to ensure the ground was as low impedance as possible.

I recently studied the original Moog 110 volt 60Hz adapter... It has 3 pins. One of them is earth. This wire goes from the outlet to the theremin via pin 2. 1 and 3 pins to supply AC power to the thermo-box.

I assume that the Moog adapter must have the third prong for connecting to earth ground through the wall outlet, but I haven't seen photos to confirm that online. That's rare for an AC adapter, in the US at least. I'm still confused why the connection to the theremin itself has 3 conductors, particularly if two of them are AC.

@Valery: You make a good point about attaching a DIN connector to the end of an appropriate PSU. if I already had an Etherwave with the DIN socket, I'd probably do that, but since I want to DIY, I'd rather replace the DIN with something more standard. And thanks for confirming that the 14V supply would be better!