MOTM

To the experts (which is most everyone here but me),

I working with a small circuit that I would like to add voltage control
(e.g., lfo, env.) through an attenuating pot.  When negative voltages
(e.g., from an lfo waveform) enter the circuit they 'screw things up'.  Is
there a "simple" way to restrict the incoming voltages to positive
voltages only?

Thanks, Jeff

At 4:25 PM -0500 2004/04/16, Jeffrey Pontius wrote:
>To the experts (which is most everyone here but me),
>
>I working with a small circuit that I would like to add voltage control
>(e.g., lfo, env.) through an attenuating pot.  When negative voltages
>(e.g., from an lfo waveform) enter the circuit they 'screw things up'.  Is
>there a "simple" way to restrict the incoming voltages to positive
>voltages only?
>
>Thanks, Jeff

Simplest way is to use a diode. But you may still get a small 
negative voltage equal to the diode's forward voltage drop, around 
0.65V. Can your circuit handle a small negative voltage of -0.65V?

Either a half or full-wave rectifier will do it.  For a half-wave 
rectifier circuit, look at the CV processing circuit on Ken Stone's 
Voltage Controlled Divider:

http://www.cgs.synth.net/

A half-wave rectifier will simply cut off the negative voltages, but 
allow all positive voltages to pass through with as much accuracy as the 
resistors in the circuit allow.  The rectifier circuit uses one TL072 op 
amp (both sections).  A full-wave version is also doable with one dual 
op amp.  The full-wave will invert any negative voltages and make them 
positive.  Use whichever circuit meets the need.  See Electronotes for 
FW rectifier circuits.

-Richard Brewster

Jeffrey Pontius wrote:

>To the experts (which is most everyone here but me),
>
>I working with a small circuit that I would like to add voltage control
>(e.g., lfo, env.) through an attenuating pot.  When negative voltages
>(e.g., from an lfo waveform) enter the circuit they 'screw things up'.  Is
>there a "simple" way to restrict the incoming voltages to positive
>voltages only?
>
>Thanks, Jeff
>
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> 
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