[sdiy] Mixing between two audio-sources..

[Jerry Gray-Eskue]

<Hi guys..

I'm looking for a way to mix two different audio signals. In the end
it's going to be a voltage controlled dry/wet
control for an effect loop.

The SSM2024 datasheet has something like that. However, I'm a bit unsure
if this circuit isn't oversimplified. I'd like to have equal volume over
the whole sweep-range for the cases where the two audio signals are
identical.

Any idea how to do this?

Cheers,
  Nils>


Nils,

	The SSM2024 may be hard to get, but if you have one you should be able to
set it up as in fig-24 of the Data Sheet with the some minor changes.

Replace the 100k pots with your voltage source (0 - 5vdc) using a opamp
unity gain buffer for one side and an inverting opamp unity gain (-1 gain )
for the other side. This should give you a log sweep from side to side that
to the ear will sound like a smooth pan.

If you want to mix down to one channel out add an opamp mixer to the two
outputs.

Either setup uses half of the chip so you could build a dual unit with one
SSM2024.

>From the Data Sheet:

"For this example, the control voltage is developed using a
100 kW potentiometer connected between +5 V and ground.
This configuration results in attenuation only. To produce both
gain and attenuation, the potentiometer should be connected
between a positive and negative voltage. The control input has
an impedance of 5 kW. Because of this, any resistance in series
with VC will attenuate the control signal. If precise control of
the gain and attenuation is required, a buffered control voltage
should be used."

You may want to look into using the +- voltage control option. If you are
using a 0-10v Control Voltage you can use an Opamp to convert to +- 5v just
use a mixer setup ( gain of 1 ) with a fixed -5 as one input and the control
(0-10v) as the other.

Jerry GE