Schematic Variations

Posted: 2/26/2008 6:23:30 AM

From: Yorkshire

Joined: 2/26/2008

I have been comparing the schematic for the Etherwave Theremin (as found in the MoogMusic manual: "Understanding, Customizing, and Hot-Rodding Your Etherwave Theremin" dated 2003) to the one published in the February 1996 edition of Electronic Musician. The hot-rodding guide mentions that the Etherwave's board was updated in July of 1996 and the schematics are clearly closely related. There are some differences which I understand, but a few have left me a little confused. I have enough experience with electronics to follow the schematics and build the circuits, but not enough to really know what is going on or what effect the differences have on the instrument.

The Feb 1996 Electronic Musician article (EM96) -
the 2003 MoogMusic Understanding, Customizing, and Hot-Rodding Your Etherwave Theremin manual (MM03) -

The differences I have noted are as follows
C1, C5: 3900pF in EM96, 3300pF in MM03
C2, C6: 22pF in EM96, 15pF in MM03.
C10, C11: 1uF polarised in EM96, 0.47uF (only shown as polarised on the board diagram) in MM03. Additionally, in EM96 C11 was connected between the emitter of Q5 and 0v while in MM03 it is connected between the emitter of Q5 and +12v.
C13: 1uF in EM96, 22uF in MM03.
C14: 2200pF in EM96, 1800pF in MM03.
C15: 0.01uF in EM96, 6800pF in MM03.
C28-30: not present in EM96, C28 connects pin 12 of U3 to 0v (thanks to therem13 for alerting me to that one in his "TOKO Inductors..." thread), C29 and C30 are located within the power supply circuit.

R14: 560k-Ohm in EM96, 1M-Ohm in MM03.
R27: 100k-Ohm in EM96, 150k-Ohm in MM03.
R35: 1.8M-Ohm in EM96, 4.7M-Ohm on MM03.
R36: 1.8M-Ohm in EM96, 1M-Ohm in MM03

L5, L6: 100uH in EM96, 47uH in MM03.
L11: 68uH in EM96, 47uH in MM03.
L12-14: not present in EM96, inline with L5, L6 & L11 respectively.

Of all these changes I only really understand those to the arrangement of the coils, while it is the change to C11 which confounds me the most.

I am planning on building a Theremin (for my self to play, I'm too old for this to be a school project!) based upon these designs, but at the moment I cannot be sure that either is mistake free.

Any help with understanding these differences will be gratefully appreciated, I look forward to hearing from all you experts.

Posted: 3/20/2008 3:00:28 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

Would be happy to help - but cannot get the pdf links to work..
Email me the pdfs (see my picture) and I will look over them

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