BOSS CE-3 Vibrato Mod

[Joe Kramer]

Hi Friends,

The CE-3 is a good candidate for a vibrato mod for two reasons: it already has a wet-only output, and it doesn't kill the dry signal when you hit bypass, as would happen if you did a vibrato mod on something like a CE-2.  There's a way around the bypass problem with a CE-2, but it takes more parts.  With thanks to Dirk Hendrik, here's the CE-3 schemo:

http://www.dirk-hendrik.com/BossCE-3.zip

The problem Geoff Hunter and I were working on a while back was, how to get a sine wave from the CE-3 LFO, since the stock triangle wave is too extreme for a nice vibrato sound.

Now that problem is solved.  Here's a simple way to get a reasonable sine wave out of the LFO.  It's just a matter of some series resistance from the LFO output, and then some clipping diodes to 1/2 V, like this:

Code Select Expand

                 10K-100K

LFO output --------N N N---+-------------> to Depth pot
(Pin 7 IC5)                |
                        +--+--+
                        |     |
                        |     |
                        -     v  clipping diodes/LEDs
                        ^     -
                        |     |
                        +--+--+
                           |
                           V
                         to 1/2V


Apologies for my shaky schemo.  Finding the right resistance and diodes is a matter of tweaking, so YMMV.  About 47K with a pair of small LEDs worked pretty well for me, but depending on your choice of diodes, a range between 10K and 100K is reasonable.  Keep in mind, too little resistance and the diodes crunch the wave into a near-square.  No resistance at all and the LFO will stop oscillating.  Too high a resistance and the diodes won't conduct, so you'll get no waveshaping and a smaller output from the LFO.  Also, different diodes will give VERY different results.  Several pairs of 1N914s or combinations with 1N34s will work, but'll take up more room than a single pair of LEDs. 

I cheated a bit by using a scope to look at the LFO waveform while adjustng the series resistance.  If you don't have a scope (or free software like Visual Analyzer--highly reccomended!), you can use a 100k pot or trimmer and adjust by ear until you get both enough depth for a decent chorus sound and a smooth enough waveshape for decent vibrato.  There's a happy medium to be found if you decide you like the effect.

As for construction, there's no need to attack the main PCB to do this mod.  The resistor and the diodes/LEDs can be attached to the small PCB that connects to lugs of the DEPTH pot.  The CW outside lug comes directly from pin 7 of IC5, and the CCW outside lug is 1/2V.  Voila.

You'll might find a slight loss of depth with this mod.  I don't miss it myself, and find I rather like the chorus sound better with the sine waveshaper.  If you want more depth, you might try using a bigger value pot for the DEPTH control, like 1M or so.  This puts less load on the LFO and gives a bigger pk-pk wave, but might also require you to re-adjust your series resistance some.

Thanks to Geoff Hunter for his early work tracing out the CE-3 PCB before I got hold of a factory copy.  Thanks also to Paul Perry for pointing out to me the influence of the series resistance and the load in this app.

Happy Modding,
Joe

[midiez1997]

good day!
can I listen to the results of the mod somewhere?