Chokes for '96 theremin build

Hi, I have wanted to build the theremin that was in the 96' electronic musician article for years and have finally gotten around to doing it. All of the parts were easy to find (caps, resistors, diodes...) save for the inductors, (as I'm sure most if not all of you already know). I have been searching for the chokes but every time I think I have found one (mouser, digikey, etc.) the parts themselves turn out to be obsolete. I was trying to find the data sheets for the old inductors in an effort to find currently available equivalents when I came across this theremin forum. I found some posts in this site concerning sourcing of the chokes but for the most part, they were from years ago and as such have obsolete links or point to obsolete parts. It has been a long time since I was in school for electronics and remember very little about inductors and was wondering if anyone had information about cross-overs for the 11 inductors specified in the parts list (10 mH (4), 100 pH variable (2), 2.5 mH (2), 5 mH  (2), 68 uH variable (1)) to components that are currently available. After reading a number of posts it's obvious that many of you have a tremendous amount of experience in these builds and so I joined thinking that maybe I could pick your collective brains. Any help would be greatly appreciated!
Thanks,
Ken 

Hi Ken,

I think you are running into the same problem that a few others here have brought up - the lack of availability of some parts, primarily the inductors.  I think within the last two years I was still able to freely order the 10, 5 and 2.5mH inductors from Newark or Mouser, and when I went to order more they were gone. I wish I had bought more at the time.  But let's look at what you are facing.

First, the theremin in that article has evolved into the more refined contemporary design used in the Etherwave Standard and Plus, and I have an annotated schematic here that reflects the 211-J version of the main board which is current within the last few years.  The current Etherwaves have replaced the obsolete Toko variable inductors with Coilcraft parts, which are still currently available although you may have to order directly from the manufacturer since these are not stocked at the usual sources.

The bigger problem as you know will be the those fixed inductors.  Some can be found by watching eBay, and there may be some out there right now although not necessarily under the JW Miller name (use Bournes or Hammond in your searches, or just the number).  But I believe that the updated schematic uses one or two other small fixed inductors that may be equally difficult to find.

If you are adventurous and in this for the learning experience and are willing to breadboard this up piecemeal and wind your own inductors, you could conceivably come up with your own alternatives for the hard-to-find parts. You will have to recognize that the obsolete inductors can't be replaced with other parts of the same value; the original multi-section pi-wound inductors are unique in that they have high self-resonant frequencies (SRFs) that the common small molded axial and radial leaded parts of the same inductance values do not have.  Nothing is impossible to replicate, but the substitutions would mean that you would almost certainly need access to some basic test gear including an oscilloscope.  It would no longer be a build project where you could simply follow the plans and Bob Moog's tune-up procedure and expect it to make music. 

I should note that within the last 2-3 years I was able to purchase main boards and the CV boards (for the EW Plus) in small quantities directly from the Moog factory for around $70 each, which is a pretty amazing price when you compare that to the cost to build the boards.  I don't know the current situation with some of these parts being obsolete, but perhaps they have a lifetime supply and will still sell the boards.  Moog has always been very nice to deal with by phone and they seemed more than happy to sell the subassemblies at the time.  That may have changed but it would be worth a try if you wish to go that route.  There is still plenty to learn about theremins even if you start with a factory board and work backwards. 

But I understand the urge to do it all yourself too.  However getting a theremin to work can be a little frustrating, and if you make some part substitutions and on top of that are working blind without much test gear, the reality is that you might be better off starting with a simpler design or a currently available theremin kit that contains all the parts.

Hi, 
Thanks very much for the detailed reply. I will certainly check with Moog about an EW board (probably cost me >$70 in parts to build one). Obtaining a board would certainly be easier than prototyping one and I'm not looking forward to winding my own inductors nor am I equipped to do it. 

BTW, do you happen to have a parts list for the EW 211-J schematic and what is annotated about it?  You also mentioned that in the updated schematic there are 1 or 2 fixed inductors but I counted 6. Are you referring to a different schematic than the one you provided the link for? 

Incidentally what is the CV board as opposed to the main board? Does CV refer to daughter boards for the inductors? 

In terms of theremin kits, that is how I originally started my theremin quest. However, I never found any that provided functionality that was similar to the one in the original schematic.
 
As a side note, I have a scope, signal generator, component testers, etc.

Cheers,
K

I don't have a parts list.  This is just a schematic for an older Etherwave design that I modified to match one of my newer boards.  The annotations are the notes in red that I added to show values or part numbers that were blank.

I was referring to the schematic that I linked to you. I think L12 and L13 are some small single-section pi-wound inductors and L14 is an axial leaded encased inductor.  These were not used on the 1996 design but you would need these as well if you were to build the current one.   These are in addition to the three fixed inductors on each antenna, so I guess that makes nine fixed inductors unless I've forgotten something or added wrong.

The CV board is a narrow SMD circuit board that was added behind the front panel pots to turn the Standard Etherwave into the Plus version.  It provides standard pitch and volume control voltages compatible with analog synthesizers to allow the theremin to be used as a controller.  The basic theremin doesn't use it.  It also has some (very little) circuitry for pitch preview.

Thanks. Tomorrow I'll give Moog a ring and see if they are still making their boards available.
Cheers,
K

Let us know if they still do this.  I'm curious if they are tightening up due to parts shortages.

Let us know if they still do this.  I'm curious if they are tightening up due to parts shortages.

Hi,
Sorry I didn't get back to you sooner but I thought I had (memory is apparently shot, ugh).
I got in touch with moog but unfortunately, they no longer sell their boards.
I did however come across a theremin kit sold by Paia. Do you have any experience with their theremax theremin product (see link below)?
https://paia.com/proddetail.php?prod=9505KFPA

Cheers,
K