Build Project: A Moog Melodia Replica

Posted: 8/5/2019 12:48:35 AM

From: 60 Miles North of San Diego, CA

Joined: 10/1/2014

People please get a grip, the theremin is about a controlled flowing sound, not the look of a box with stencils. Add in a good Therminist and some will experience the magic of what it is all about. If something of value exists then post a sound sample. The theremin is a simple device.


Posted: 8/5/2019 4:56:23 AM

Joined: 11/25/2017

I'm so impressed with your work, pitts8rh!

Posted: 8/5/2019 11:32:41 AM

From: Minnesota USA

Joined: 11/27/2015

I appreciate the kind comments. 

"Add in a good Therminist and some will experience the magic" -Christopher

To oldtemecula, it's spelled "thereminist", and if you have something substantial to say, come out with it.  If all you can offer are these tiring passive-aggressive snipes, then I would invite you to vigorously GFY.

Posted: 2/21/2020 9:13:32 PM

Joined: 10/23/2014

Absolutely beautiful build. It makes my original Melodia look kinda crummy by comparison. Maybe I'll get around to cleaning up the case one of these days. Have you added the electronic components to the case?

Posted: 2/22/2020 12:07:53 PM

From: Minnesota USA

Joined: 11/27/2015

"Have you added the electronic components to the case?" - senior_falcon

Not yet, I'm embarrassed to say.  I still have to make something to do a correct honeycomb/progressive wind for the adjustable coils and the long fixed inductors. This is something that I have been looking forward to doing for a long time when I get a breather from the D-Lev project.  Even though I could have scramble-wound the coils by hand a long time ago, this Melodia project has always been about replicating the real thing as accurately as possible rather than just getting it done (even if it takes a long time to do so).

About two months ago I did get started with the progressive winder for the two fixed Melodia inductors by machining an encoder wheel and making an optical interrupter that I added to a 5C 3-jaw chuck mounted on a spin index.  The chuck would hold the long ferrites and I thought I could use the hand crank on the spin index to hand wind the coils.  The whole spin index was mounted on the table of a CNC mill, and the optical encoder was fed into the same encoder input on the mill that is normally used for the handheld encoder.

My idea was that I could just let the encoder pulses from the rotation of the hand crank push the milling machine table left and right to accomplish both the task of creating the honeycomb wind and the slower progressive movement down the length of the ferrite, all movements being dictated by gcode programming.  I would just feed the wire out from a simple stationary wire guide mounted to the head of the milling machine.

This all sounded good in my thought experiments, but during test it failed for two reasons.  First, the transport on the milling machine could not keep up with the rapid x-axis motion required for the honeycomb wind, and second, the bearing friction and the mass of a 4" rotating chuck completely obliterates any of the sensitivity that you need when hand winding something like #36 gauge wire.

One thing I did learn out of all this is that the CNC mill would be able to do the slower task of providing the lengthwise translation required during winding.  So the next plan is to build what is essentially a mechanical Morris Coilmaster type of geared arrangement to do the honeycomb wind.  This winder would be mounted on the CNC table to provide the slow translation of the honeycomb wind down the length of the coil, which I know it will be able to keep up with.  Since this is a one-use project I'm just going to 3D print up the gears and cams out of plastic.

So after all of these excuses the short answer is no, I haven't made any real progress on adding parts, but I'm looking forward to it because it will be like building a Heathkit when I get there.  Making the theremin work may be a challenge though, because my adjustable coils are going to be best guesses.  I don't think I know what the actual inductances of those coils are, and if you remember the ferrites that I used inside the homemade coil forms are just best guesses.

But thanks for your long term interest.  I'll get there, but I'm working more slowly these days.

Posted: 11/3/2020 2:20:08 PM

From: Minnesota USA

Joined: 11/27/2015

Question: I am wondering if anyone out there with knowledge of the Moog Melodia would happen to know the inductances of the coils.  This would include the short and long ferrite core antenna inductors, and the nominal value or range for the tunable coils.  Bob Moog's build instructions describe the number of turns and type of wire to apply to the forms, but since I built my own tunable cores and I had to take what I could get for big ferrite cores I can't necessarily go by these instructions.

It's time for me to finish this project after a very long haitus to work on Dewster's D-Lev.  I'm still heavily into that but I'm going to see if multitasking works.

I'm in the process of making a honeycomb coil winder that will also have the reciprocating wire guide riding on a geared lead screw that should allow it to make the "progressive" wind that is used on the Melodia's antenna inductors. This is an original design, although the honeycomb section is based on the Morris Coilmaster, using the same gear ratios.  I don't know if it's going to work, but at least there will be a lot of moving parts to watch when I turn the crank.

I had several false starts on this project, first planning to go electronic with stepper motors and an arduino, but then settling on a purely mechanic contraption with gears and cams, mainly because I like contraptions.  This thing is starting to look like the old Hasbro "Mouse Trap" game.  But it doesn't have the bathtub or shoe yet.

I'll be posting some pictures in a few days.  I have no idea what gear ratios I need for the progressive winds, so I'll be starting off by winding string coils.  I've been wanting to get past this coil-winding hurdle for a long time, because all the hard work on the replica is done and the rest should be fun.

So if anyone has any inside knowledge of the Melodia I would be interested in hearing from you!

Posted: 12/6/2020 8:07:05 PM

From: Minnesota USA

Joined: 11/27/2015


I'm still finishing a write up for the coil winder (the thing that allowed me to finish this) so I don't have any words yet to accompany these teaser pictures, but I'm pretty impressed with how it plays so far.  Pretty amazingly simple design, I think.

Posted: 12/6/2020 8:36:25 PM

From: Theremin Motherland

Joined: 11/13/2005

Well done!

Does the piano hinge connected with chassis?

Posted: 12/6/2020 8:58:01 PM

From: Minnesota USA

Joined: 11/27/2015

"Does the piano hinge connected with chassis?" - ILYA

No, it's just close.  The chassis that I made came out a little wider than it should be.  There should be a small gap at the rear.

Posted: 12/7/2020 3:00:54 AM

From: Northern NJ, USA

Joined: 2/17/2012

Beautiful!  Very nice looking progressive wind EQ coils!  And the variables are really gorgeous!  What are you using for coil dope?  Are the insulating tubes on the resistors and such stripped wire insulation?

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