Moog Melodia

Posted: 5/7/2012 12:50:52 AM

From: Pittsburgh, Pennsylvania

Joined: 1/1/2011

Last week I had a going away party for our doctor at work and naturally everyone was interested in my theremin.   One of my co-workers upon seeing me play said  "I'll be right back....I have something for you to see!"   Thirty minutes later he showed up with a Moog Melodia in it's original box!  As the story goes his grandfather put it together and it was in his basement for many years.  Since neither of his grandparents are alive no one remembers if it ever worked.

I bought a 4 - AA battery box at Radio Shack, and connected the red positive wire to the switch and the black to the other ground terminal in the original battery holder.   Along with that I bought an RCA to 1/4" audio cable to hook to my amplifier.   There is a slight "pop" from the speaker when I turn it on but no other sound.  

The case is in almost perfect condition with no scratches and the original finish is nearly perfect......the antenna and volume plate is in perfect condition also.  I believe the main problem is that the theremin was in a damp enviroment in the basement so there is some corrosion on the inside of the metal circuit box and the wires and soldier on the transistors.  However the volume and pitch tuner knobs seem to be in excellent condition.  I used tuner cleaner on them along with the on/off switch.

Possible problems I see:

(1) The theremin never worked from the time it was built. (Which explains no one remembering it.)

(2) The dampness ruined the components and/or some connections.

(3) The 4 AA batteries are not enough to power this model.

Aside from the above, could I have overlooked something simple?

Is the theremin even worth rebuilding....or would it make a better wall ornament for the music room?

Thanks for your thoughts!




Posted: 10/23/2014 4:43:09 PM

Joined: 10/23/2014

Just fired up my melodia after quite a few years.  To answer your questions:

It is definitely worth working on to get it working, and it should be fairly straightforward to do so. Do not use it as a wall ornament; it cries out to be played.

4 AA batteries are fine for powering the melodia.  One thing that can be confusing is that the magazine article shows the circuit with NPN transistors. My melodia uses 2N414 PNP transistors and so the batteries must be installed so the the positive side is at ground, not negative as is shown in the magazine schematic.  (I don't know if all melodias use PNP transistors - mine is a later one.) The actual schematic is shown in the construction manual, so look to that for your guidance.

It could be that the switch has corroded, though your cleaning should take care of that.

Since this is a 2 year old thread I will wait for feedback from you before going any further.



Posted: 10/23/2014 5:27:06 PM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

A repost from Levnet on Oct. 9, 2014

Even our beloved Bob Moog got caught up in the compulsion to complicate and sonically alter his early theremins. Take for example the earliest Moog theremin, the Melodia. Only four individual, removable (plug-in) transistors, a few coils and a battery case to provide stable self power for portability.

Rob Schwimmer uses his Melodia extensively, and those who have heard it marvel at its sound. It doesn't even have a volume loop; only a square brass plate on the side of the cabinet as a sensor. Another advantage to the Melodia is, by inserting various transistors into the pitch sockets, the tone can be changed which allows the owner to customize the sound over a small range. Simple, neat and easily serviced using the Instruction manual provided in the original kit. Which, by the way, was easy to follow during assembling of the instrument and alignment. If you buy ANY other commercial theremin, no schematic, no tuning instructions and no detailed parts list.

      If this is progress, I'll have none of it.

Uncle Howie 

Posted: 10/25/2014 12:52:01 AM

Joined: 10/23/2014

I am enjoying playing the Melodia again.  I had put it aside for a number of years after getting an etherwave standard. Now that I am using it again I have found it to be more linear than I remembered. It can play almost an octave lower than the etherwave (without the ESPE01) and sound good doing it.  Playing it is much like playing the Etherwave and I have no trouble going from one to the other.  I will say that it's a good thing the pitch trimmer knob is so large because it is very sensitive to adjustments. 

I see that Thereminworld does not have a schematic for the Melodia.  I did some searching on the internet and could only find the article "A Transistorized Theremin".  As noted above, this is not exactly the same as the Melodia. Besides the use of PNP transistors and reversing the diodes, there are changes in the values of some of the resistors. I can scan the two pages in the kit assembly manual with the schematic and parts list and post them here if there is any interest.

And I have a favor to ask: My assembly manual for constructing the Melodia kit begins at page 3. I would really appreciate it if someone who has the complete booklet could scan the title page and pages 1 and 2 for me so I can replace the missing pages and make my documentation on this instrument more complete.

Posted: 10/25/2014 5:01:13 AM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

Hello falcon,

Here are scanned 1961 article pages I saved that Maxie Baar did way back when. He was a fun theremin designer. If you make scans of what you have and they are different I can add them to this webpage if you emailed them to me. Also you could add them to the TW photo album. Looking closer at the Melodia it is a great starting point for any new designer. This design uses all NPN transistors.

Melodia Schematic updated


Posted: 10/25/2014 5:08:25 AM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

This is the article I thought was the Melodia:

But it uses PNP..


Also real interesting that the bass goes lower - but looking at the schematic, I think this makes sense - C4 and C5 couple to the lower Z emitters so there is probably a lot less oscillator locking.

The tuning is adjusting the antenna capacitance at the most sensitive point, but this confers a big advantage over the EW design.. If T1 and T2 are correctly set, then the linearity of the instrument will be optimal regardless of the environment, because one is actually tuning the "antenna" .. But being 1.5pf - 5pf I expect this control will be extremely sensitive!

Anyone wanting to build this may find getting these variable capacitors difficult - I have used my screw adjustable antenna for circuits like this, changing the antenna length acts as a variable capacitor without reducing sensitivity. For the loop I did the same sort of thing except that the adjustable "antenna" was in fact grounded and placed behind the loop horizontally, so that I could add / reduce capacitance seen by the loop.

" I can scan the two pages in the kit assembly manual with the schematic and parts list and post them here if there is any interest."

Yeah, I would be really interested in seeing your version! - Also, I would love it if you could post these to the Element 14 library ;-)

Oh - and welcome to TW ;-)



Posted: 10/25/2014 1:36:13 PM

Joined: 10/23/2014

Both those articles are the same: "A transistorized theremin by Robert A. Moog" which was published in Electronics World, January 1961.  If you look closer at the schematic or check the data sheet on the transistors you'll see they are NPN.  The docs that came with my melodia have a reprint of that article and a different manual for assembling the kit with a check box for each completed step.  

Years ago I installed a 4 AA cell battery holder inside the instrument to replace the original battery holder that takes a 6 volt battery that is no longer available.  I clearly marked on the new holder what the polarity of the cells should be.  When I tried to get the melodia working recently I installed the batteries as marked and for some reason couldn't get any sound at all.  After checking that the battery was actually providing power to the circuit I got out the magazine article and found that the battery polarity was wrong.  According to the article ground should be negative with +6 volts supplied to the circuit. So I turned the batteries around and still had no sound. Hmmm... I thought perhaps a transistor had failed and looked into getting some replacements and learned that they were NPN transistors

The next day I got out all the docs on this critter and for some reason went to the kit assembly manual and was astonished to find the schematic there calls for the positive terminal at ground and -6 volts provided to the circuit. Also, PNP transistors are shown in the circuit. So it seemed that my original markings were correct after all.  After turning the batteries around again, this time the melodia came to life.  Why that did not happen the first time is a mystery - perhaps oxidation in one of the transistor sockets, a dirty switch or ??

Mine was built from a kit some time after 1964.  The instrument has the newer moog logo with a circle around a note which was first used in 1964.  I have no idea whether older melodias use PNP transistors or if they match the magazine article. If there were two different versions it might explain why some of them sound different from others.

The local boy scout troop is having a haunted house tonight and the melodia will be there making woo-woo sounds, but I should be able to do some scanning tomorrow.

Posted: 10/25/2014 1:52:48 PM

From: züriCH

Joined: 3/15/2014

give the kids the woos of their life. i only found this:  at about reply #17     it's about the npn pnp transistors. and also a link to the coils. any way worth to have a look. and a wooie time.

Posted: 10/25/2014 5:22:08 PM

From: Eastleigh, Hampshire, U.K. ................................... Fred Mundell. ................................... Electronics Engineer. (Primarily Analogue) .. CV Synths 1974-1980 .. Theremin developer 2007 to present .. soon to be Developing / Trading as . ...................................

Joined: 12/7/2007

"If you look closer at the schematic or check the data sheet on the transistors you'll see they are NPN. " falcon

Apologies! - you are right - dont even need to look at the transistors, the supply connections say it all!

I did have a Melodia schematic with PNP's but have absolutely no idea where it is now - I used to collect every design of Bob Moog's I could lay my hands on, right back to the early '70s.. But I wasn't interested in theremins then so I may well have given it to a tech college with a mountain of books and magazines I left behind when I came to the UK. I remember getting the copy from another student who had bought one -

Chances of me finding it are less than my chances of winning the lottery I dont play.. Sorry.


(and to be honest, it was a long time ago.. I remember clearly they were PNP's - but I wouldnt gamble more than a fiver on this being true - )

Posted: 10/25/2014 6:42:50 PM
RS Theremin

From: 60 mi. N of San Diego CA

Joined: 2/15/2005

falcon said: "I can scan the two pages in the kit assembly manual with the schematic and parts list and post them here if there is any interest."

The more places these are available I think the better.

I can organize the info I collected today on the Melodia, then see if Google gives me a top spot in search. (-'

You got me curious to why the change to PNP. My first thought is Bob Moog wanted to use germanium for a certain character and PNP were most available.

xther: your webpage  at about reply #17  find was excellent, it reflects a more supportive and gentle forum with people posting on the day Robert Moog passed away. I wish I was in contact with that NewYorkDave, I think we have something in common.



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