Trimpot on Corrrral Chorus?

[dpresley58]

Was wondering what I'm looking for when adjusting the trimpot on this unit... No voltages were given, so didn't know if I'm just tweaking for chorus effect, or if there was something a bit more empirical for it.

Thanks in advance.

[Mark Hammer]

The delay chip requires that the audio signal be added on top of a DC bias voltage.  The trimpot feeds that DC bias voltage to the MN3007 input through the DC path of R9/R10/R11/R13.

When the bias is set too high or too low, the MN3007 will not pass signal.  When it is just a bit high or just a bit low, it *will* pass signal but with poorer audio quality.  When you hit it on the head, the sound quality will clear up.

Ideally, one observes the signal on a scope and tweaks based on observed waveform quality.  If you are working by ear, it CAN be set properly, but it is best to remove impediments to being able to hear differences in audio quality. So here is what I'd do:

1) Set rate to slowest and depth to minimum.  This should still produce clocking of the delay chip but much less or no pitch wobble.

2) Either don't install or simply unsolder one end of R21.  Alternatively, if you have installed the vibrato option, set it to vibrato rather than chorus, so you hear ONLY the delayed signal.

Now, as you adjust the trimpot, you will hear changes to the quality of the delayed signal ONLY, allowing for more accurate adjustment.  Solder R21 in place or flick the switch back to chorus, and away you go..

[dpresley58]

 
Thanks, Mark. -Just- what I was looking for.