chorus to flanger mod

[brett]

I believe that it's possible to convert my Boss CE-3 chorus to a flanger.  Is it a simple conversion and is it worthile (ie does it make a good flanger?).  Or should I buy a second-hand flanger?

[Mark Hammer]

Flangers and chorusses do share common chips, and are similar enough that one can be turned into the other in a pinch, but you need to keep the following constraints in mind:

1) Time shift is not feature shift.  You can create a chorus tone from flanging by increasing the time delay a bit, and create flanging from chorus by reducing the time delay.  Unfortunately, chorus units have no regeneration capability (which involves more than a simple component change to create), and flangers are expected to cover such a wide range of modulation rates that the typical LFO setup ina chorus will likely be insufficient.  Fortunately that latter one usually involves just a toggle and a cap change i the LFO to "fix" but in a BOSS chassis there is the trickier issue of where you put such added controls.

2) Filters matter.  The lowpass filters in any BBD-based pedal are usually intended to provide maximum bandwidth while protecting against aliasing and clock noise bleedthrough.  Since the clock runs slower in a chorus, the filters are tuned to a lower corner frequency than they would be in a flanger (where the clock runs at a higher frequency to produce shorter delays).  So if you were to do your damndest to get a slow "jet plane" flange out of your CE-3, chances are that it would come up short because the filters in the delay path don't permit the device to produce notches  very high up in the audio spectrum.  There is really no way this can be easily or conveniently altered into a hit-one-switch-to-make-it-a-flanger function.

Within those limits though, all that is really necessary to make it do different tricks is to change the small value capacitor nearest the MN3102 to something half that value, or alternatively lift one end of it, solder another same value one in series, and wire up a SPST toggle to shunt the second cap like John Hollis did in the Zombie.  I did this in my Zombie and it moved the sweep into a very pleasing "slow Leslie" range that is clearly different in character and tone from the usual chorus sound.

[brett]

Thanks heaps for the advice Mark.  Sounds simple enough, so I'll give it a go.

cheers