How do I distort thee, let me count the ways PART II

Posted: 4/22/2009 7:44:17 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

[i]"My friend wants to know what are the external potentiometers in thh glasgow theremin, the potentiometers which have to be controlled by the user"[/i]

Your friend really needs to work this out for himself! - If he does not understand the function of the potentiometers in the circuit, he has no chance of getting this completely cr*p design to work!

This design is NOT presented in a way which is easy to follow, and leaves out lots of essential information, and in some places is just plain BAD!

For example - there are potentiometers across the shmidt (4093) oscillators for tuning them - These are shown as 20k, and would probably be "potentiometers which have to be controlled by the user" (one to set the pitch osccilator frequency, one to set the volume oscillator frequency) - but these are shown as 20k and have no series resistor to limit the range and/or limit the current/frequency.. Also, these potentiometers are connected to the most highly sensitive part of the circuit.. The wires to connect these are antenna! - at MINIMUM one needs the potentiometer connected to the gate output, with a series resistor (probably 15k and change the potentiometer to 5k) on the board.

Other potentiometers relate to the bias voltage for the VCO, and other VCO functions, and the VCA and its functions - These can be evaluated without needing the Theremin (oscillator /mixer side) running (feeding a voltage to the CV connection point and feeding CV to the VCA), to see whether one wants them as user potentiometers or as presets.

The Glasgow Theremin was not published as a construction project, in my opinion it is an awful design, and really should come with a health warning.. "Warning - This design is intended to put people off building Theremins, can cause mental health problems or at least severe frustration and depression, and will result in a virtually unplayable instrument if one eventually gets it to work - If you do get this Theremin to work as a playable instrument, You are obviously competent enough to have designed your own, better instrument - and this would have been quicker than correcting / modifying this cr*p design!"

Fred Mundell
Fundamental Designs Ltd.
Electronics Consultant.
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Designer of Theremins and other alternative electronic music controllers and instruments.
Posted: 4/22/2009 8:58:51 PM

From: Colmar, France

Joined: 12/31/2007

Fred is absolutely right and I'm happy that I haven't been the one to tell this first.

a) By studying the data sheets and application notes of the VCO and the VCA an experimented technician would have found out the impact of the potentiometers on the circuit.

b) The Glasgow Theremin is an experimental project and was never intended to be built as a musically playable theremin. It is rather for people who experiment with different theremin technologies in order to see what one can theoretically realize.

Normally I would say that the first theremin one builds should be a kit which has already been built some hundred times, so that one can be sure that it has a useful design.

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