Can I mod my Chorus pedal?

[Kerosenetrewthe]

Hello, first post here. New to pedals and modifications and its looking like it might be an addicting thing to venture into.

I have an older Ibanez Stereo Super Chorus. I use it for bass and when engaged it sucks my lows right out. Is there a way I can modify the pedal so it doesnt cut all my low frequency out? Changing a cap or filter or something?

Thanks for any advice given!

[ninoman123]

Increase the input or output cap? I dont know the circuit so it might be more to that but that would be a good place to start.

[Mark Hammer]

Looking at the schematic for the SC10 Super Chorus, there are a LOT of caps that stand to have an impact on retaining low end.

That being said, there is not much point in trying to retain low end for the delayed portion because: a) low end is where the pitch wobble lives, and pitch wobble is as bad for bass as it is good for gutar, b) the design does very little to keep the high amplitude bottom end from distorting the BBD.  So, the optimal path is to do what you can to keep bass in the clean path rather than look for it in the delay path.

Here there are 3 caps that MAY have an impact, but it is unlikely that they will because the low-end rolloff is already pretty low.  The .047uf input cap keeps the low end rolloff well below where your bass ends, and C18/C20, which block any DC on the clean signal from entering the mixing stage at the output, also roll off bass well below where you are likely to hear it.

So, no, I don't see much latitude for doing what you want to do.  Maybe we need more information to pin down what's going on.

[Kerosenetrewthe]

Thanks for the information you posted. I think Im going to see if I can add an EQ pedal inline with the chorus. Bump some of the bass up. See if it kills the chorus shine too much. It may.

Then maybe i'll do some experimenting with the cap filter.

[Mark Hammer]

One possibility to consider is the role that the cancellations/notches produced by the chorus have extended far down enough in the spectrum that some of the bass is being cancelled.  Just exactly how that could happen to bass but not be a problem for guitar is something I haven't quite wrapped my head around yet, but for the moment let's assume it to be true for what-if thinking purposes.

There are two ways to reduce the amount of cancellation created in that range.  One is to shift the time delay to a slightly shorter range so that notches are not created in the bass region, but remain largely in the zone of the harmonics or at least upper notes.  The second way is to leave the delay range where it is and simply trim off the deep bass content from the delay/wet signal before it gets to the mixing stage.  

The idea behind both of these is that if there is little or no bass content in the delay signal then cancellation can not occur, or at least will be reduced enough to make a difference.  It is my understanding that sometimes when time-based effects are said to be for bass that some circuit changes like these are part of it (e.g., Boss Hi-Band Flanger).

Changing the delay range can be done 2 ways, although one of them seems unavailable for the SC10.  Normally I would just counsel you to change the small cap adjacent to the MN3102 chip for a smaller value, but in this case, that cap is 5pf.  That doesn't leave a whole lot of room to experiment with before you run out of values!

Fortunately, the SC10 has a trim pot on board which adjusts the clock range.  That 50k trimpot is tied to R43/R42.  In theory, you should be able to tweak that trimpot to shift the delay range so that it doesn't sweep down into the bass and produce these hypothetical cancellations.  The SC10 already comes with a chassis-mount manual delay control that provides a DC offset to the clock.  This is complemented by the trimpot which adds another DC offset.  This is quite similar to what you'll see on analog synth modules, where there are dual DC-offset controls - one for "tuning" or "prepping" the module, and the other for working with and changing the sound.

To try using the trimpot, do the following.  Set the Width control and Manual Delay Time controls to min.  With the guitar (or better yet, a white noise source like the hiss between radio stations) plugged in, SLOWLY adjust the trimpot until you start to hear a shift in tone.  Now bring the width up and see if this yields the difference desired.

The other approach - that of leaving the delay where it is and tinkering with wet bandwidth - involves replacing a pair of caps with smaller values.  These would be C13 and C14, both of which are .068uf caps.  Swapping both or one of them for something like .01uf will likely take out a significant chunk of low end from the wet signal, but leave the mids and highs intact.  You should get all the swirl you expect but the bass should sound more intact, and less "wobbly" because more of the pitch-shifted bass is taken out of the wet signal.  If you want to help this along, R23/R30 (both 82k) set the wet level at the mixing/output stages.  If they were a little larger, that would put the wet signal a little more in the background.  You will note that the SC10 lacks any control for adjusting the wet level.

Hope this is useful information.

[StephenGiles]

Dog walk AND swimming today!!! At least I can sit down now and laze about. Mark, I'm sure I've seen variable capacitors in a catalogue which go down to zero, but where? - that is the problem.
Stephen