Completely newbie planning to build EM theremin

Posted: 5/13/2014 8:44:33 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

"However, if i do use a tantalum capacitor, how will i place them on the board?" - Blala.

In terms of polarity, my understanding from looking at the circuit, is that Q5's Emitter will always be below 0V, and the junction of R11,R12 and R13 will never be below lower than Q5's emitter voltage - so if connecting one end of C11 to ground, this should be the -Ve end, but if connecting it to +12V, it should be the +Ve end.. and the -Ve end of C11 should always connect to the emitter.*

C29 and C30 - well, C30's +Ve end goes to the input of U1, and C29's -Ve end goes to the input of U2.. But really, you dont want tantilum capacitors for these! - 470nF 50V ceramics are fine! - voltages here just make tantilum a complete waste of money IMO.

Think about an electrolytic as if it was a diode - Put +V on its -V end with its +V end more negative, and it wont behave like a capacitor, it will conduct - but unlike a diode, this conduction is extremely likely to damage it.. An electrolytic only behaves like a capacitor when its +Ve end is more positive than its -Ve end.

You can only use electrolytics safely where you can be sure it is always biased in the right direction - any AC which "unbiases" it and causes "reverse" conduction will cause the circuit to misbehave and could damage the electrolytic and even the circuit.


*Please dont take this as gospel - The EW tuning circuit has changed on later builds, and I have not played with the EW tuning circuit.. Have only started tinkering with a real EW board.

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