More fully featured chorus

[spargo]

Does anyone know of any available schematics for a more fully featured chorus pedal? I recently came across the Cosmichorus and would love to build something like that, that goes beyond a rate and depth control.

[Mark Hammer]

"Full-featured" is a relative term.  When I make/mod a chorus, I usually find a couple of things beyond rate/depth to be helpful.  Most of the things added are geared towards letting the chorus be subtler.

1) Being able to dial back the amount of delay signal at the point where dry and wet get mixed together is often helpful.
2) Being able to apply the delay to only the mids and highs is helpful to reducing audible "wobble" to a chorus.  Bass sounds better this way when chorussed too.  Find the cap that sets the low-end rolloff on the wet signal and drop its value by about 80% or the common value closest to what's there (e.g., if it's .033uf, then go with 6800pf).  I find that's a good starting point.
3) Most 2 knob chorus pedals only really differ in terms of what delay range they cover.  That's the basis of their "personality".  Apart from that, generally the same LFO, same BBD and accompanying filters.  So find the cap beside the clock generator (MN3101 or 3102) and play with the value.  Usually it'll be in the 470pf, or lower, zone.  Smaller values will shorten the delay range, larger ones will extened it and "thicken up" the sound.  Don't diverge too far from the original value, or you may experience audible misbehaviour.  I ofteninstall a toggle to switch ranges.  But be careful with wiring; you don't want clock signals being picked up by the audio path.
4) Any chorus pedal will produce vibrato if you eliminate the dry signal.  Find the resistor that carries the dry sgnal to the mixing point and install a toggle to lift it.

[Processaurus]

2) Being able to apply the delay to only the mids and highs is helpful to reducing audible "wobble" to a chorus.  Bass sounds better this way when chorussed too.  Find the cap that sets the low-end rolloff on the wet signal and drop its value by about 80% or the common value closest to what's there (e.g., if it's .033uf, then go with 6800pf).  I find that's a good starting point.

That just reminded me of an idea I had a while back, to make two controls, like the Big Muff Pi panning tone control, but that controls the mix of the dry vs the chorus mix (dry+wet) separately for treble and bass frequencies.  Here's a quick drawing:


The crossover point could be moved around easily with some different values.  I was thinking the Wet+Dry inputs could be just wet, for some weirder, vibrato sounds when the controls are past the 50/50 mix you'd then get at 12 oclock...

[earthtonesaudio]

That's awesome, Ben.  I wonder what that would sound like...

[Mark Hammer]

Interesting idea.  Looking it over, I'm thinking maybe the 470k mixing resistors in the mixing stage are a bit on the high side to result in an audible change from the 100k adjustment pots.  Besides, you're going to lose a lot of signal via the filters.  Did you maybe mean for them to be 47k?

[Processaurus]

Interesting idea.  Looking it over, I'm thinking maybe the 470k mixing resistors in the mixing stage are a bit on the high side to result in an audible change from the 100k adjustment pots.  Besides, you're going to lose a lot of signal via the filters.  Did you maybe mean for them to be 47k?

I made the summing resistors a spindly 470k because I didn't want to load the BMP tonestack either through each other or through the opamp's output coming back through the resistors.   They could very well be less with no ill effect.  Just wasn't sure what interactions a lower resistance (preferable for noise considerations) set of summing resistors would bring, so I sorta followed the 10:1 rule for impedance and made that stage high.  Maybe someone could quell my fears in that regard...

It might be better to scale down impedances all around, like making the tone pots 10K rather than 100K, but this should be workable enough to see if this type of control makes some musical options.