[sdiy] blend or dry wet circuit for synth levels?

[Scott Gravenhorst]

Dan Snazelle <subjectivity at hotmail.com> wrote:
>
>
>i want to find a method or a circuit for a situation where you 
>have an fx processor that you want to have a DRY wet knob on the 
>front which goes from INPUT Only to FX only. 
>
>can anyone think of any good examples of this? i had assumed i 
>would to use an opamp circuit of some kind but have no idea how 
>to go about doing this. 
>
>maybe even a dual ganged pot with the pots wired in reverse and 
>the 2 inputs both go through a summer? (So when you turn it UP 
>the other input gets turned down?) would that work? 

Sounds like you're describing a pan pot.  I think that can be done with
one pot:

  DRY ----+
          |
          >
          >
          ><-------- OUT
          >
          >
          |
  WET ----+

Obviously, there is coupling between DRY and WET through the pot.  That
may or may not be a problem.

A dual ganged pot would provide isolation between DRY and WET, but is
more expensive and would require an opamp.  Each pot would be wired as
a potentiometer, but the pot endpoint terminals would be reversed from
WET to DRY (WET hot on one side, DRY hot on the other).  The output of
the two pots (center term) would go through equal size resistors into
an opamp summer.  The output of the opamp would be the panned mix of
WET and DRY.

WET ---+
       |
       >
       ><---\/\/\/\---+---\/\/\/\----+
       >              |              |
       |              |     |\       |
       |              |     | \      |
   +---+              +-----|- \     |
   |   |              |     |   >----+------>
   |   |              |  +--|+ /
  gnd  >              |  |  | /
       ><---\/\/\/\---+  |  |/
       >                 | 
       |                 gnd
DRY ---+
 
    ganged pots



-- ScottG
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-- Scott Gravenhorst
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