[sdiy] What's wrong with this picture?

René Schmitz uzs159 at uni-bonn.de
Sun Jun 23 13:24:32 CEST 2002

Hi Hallvard,

At 02:30 23.06.02 +0200, Hallvard Tangeraas wrote:
>Bipolar power supply? You mean like +15V, -15V and 0V?
>I tried running it off a 9V battery (thinking this should work since the
>operating range of the TL-082 is 4-15V and the LM-741 is 5-18V).

What you say is true, but the circuit needs a third voltage halfway between 
the potentials of "+" and "-". This third voltage is GND. (There are ways to 
simulate that with a single supply, a voltage divider buffered by an opamp can 
generate this third potential.)

As a first shot one can try two 9V batteries in series:
     + -       + - 
o----| [---o---| [-----o
+9         GND         -9

Although the sine shaper will not work properly, because the oscillator doesn't 
have the right amplitude. But for a test its not a problem, the sine will be 
more like a triangle. 

>>(Pin 5 and 4 are tied tothether on IC 1, break up that
>OK. No problem.
>>use the trace in the middle where the R2, R6, and the diodes meet as your
>In other words:
>After separating pins 4 and 5 of IC-1 (TL-082), should I connect pin 4 of
>the same IC to -15V and leave the rest as it is (connected to the "-" power
>supply pin, but instead feeding 0V/GND to it?).
>What about IC-2 (LM-741)? Should I remove pin 4 from the GND tracks on the
>PCB as well, and instead connect it to -15V?

No. The rail labelled "-" becomes the -12V rail. The one in the middle is the 
new ground rail. Pin 4 on IC 1 is already connected to "-" and pin 4 on IC2 is 
connected to "-", so thats ok.

As the circuit is currently the only connection between "-" and all points that 
ought to be at GND, is thru that connection between pin 4 and 5 on IC1.

So there is nothing to do except breaking up the trace, using a bipolar supply, 
and soldering the GND lead to the rail with R2, R6 and the diodes.

>Is there any way I can use the circuit with a battery (i.e. a 9V battery as
>mentioned above)? Alternatively I can use the vocoder's power supply as it
>has +12, -12 and 0V lines.

If you already have the bipolar 12V then use that. (I just said 15V because my 
psu is 15V.)


uzs159 at uni-bonn.de


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