CE-2 Chorus, switching controls

[cab42]

A couple of months ago, I built a CE-2 and I really like it. I built on a Tonepad pcb and included a mix control, vibrato switch and depth switch.

There is a setting that I use a lot, with rate and depth almost all the way down. I considered adding an extra footswich for switching between a preset and the controls or two sets of controls (only rate and depth, not mix).

I believe the switching is pretty straightforward with a 3PDT and if I want a led 4PDT. HERE's how I plan to do it (Lfo section from the Electrosmash schematic):



But 4PDTs are expensive and while searching for solutions I found the Analogman Bi-chorus. It seems to do exactly what I want, and from this image from the Analogman site, it seems that the switching is done with a 3PDT including LED. Mono version on the left.



How is this done? Is it possible or Is he using two separate lfo's?

[Scruffie]

You don't need to switch the 4.5V on both sets of controls, just change your switching round a bit.

[cab42]

You don't need to switch the 4.5V on both sets of controls, just change your switching round a bit.

Thanks, Scruffie. I have been staring at my drawing since you answered, and I can't get my head around it. Do you mean ditching the lower switch and only switching the wipers? But wouldn't that introduce parallel resistance from the switched out potmeters messing with the values and taper?

Or do I miss something?

[PRR]

> can't get my head

[Mark Hammer]

Given that the speed of the LFO depends on how fast the 100nf cap is charged up, would it make sense to use a trimmer to bridge the 1M input resistor and achieve faster speeds with an SPST switch?  The caveat is that it would not simultaneously change depth.  But it would sure be simpler.

[anotherjim]

Changeover switching - you can invariably leave one terminal of each path permanently connected together. So with a pot, it's only the wiper and the "hot" end needs switching over.

There might be cases where the disconnected circuit causes problems because it's radiating signal via the common connection into nearby circuits, then you might have to switch the common out and also switch that disconnected path to ground to stop the radiation. In this case, the common is the 4.5v Vref which should have a low AC impedance to ground so no extra switching should be necessary.

[cab42]

Thanks for help, suggestions and explanation.

I'll try to experiment with the lfo speed, maybe replacing the vibrato switch. I considered removing that anyway.

[Mark Hammer]

So I was just monkeying around with my CE-3.  It is very similar to the CE-2 circuit in most ways relevant to this thread.
The 1M current limiting resistor shown as R32 in the Boss service manual for the CE-2, and in your drawing, is supposed to be 1M also in the CE-3.  Much to my surprise, it was 820k.  Just for the heck of it, I replaced it with 680k, and as expected, it increased the maximum speed.  I don't personally have any need for foot-switchable speed presets, but the value of that resistance IS worth tinkering with.

As an aside, I was also surprised to find the current limiting resistor for the status LED, which was supposed to be 3k9 on the service manual schematic, was actually 1k8.  As it was rather dim, I changed it for 1k.  Still not bright enough for stage use, but tolerable for now.

[cab42]

Thanks, Mark

Interesting information. I found a couple of old threads about the CE-2, and as far as I can see you can change the speed range either by changing the the resistor or the cap. By lowering the resistor you will extend the range of the speed and by changing the cap you will shift the range of the speed. Is that correct?

On another note: I added a mix control, as per the Tonepad schematic. This blends in more clean sound so that fully clock wise it is a 50/50 mix. Would it be possible to replace the mix pot with a 1M pot ( and remove the other 470k resistor) so that fully counter clockwise is clean, and fully clockwise is vibrato. 12 o'clock would then be 50/50?

[Mark Hammer]

Others may have their own preferences, and I see enough commercial designs opting for a wet/dry blend control, but I like a dry-lift toggle for vibrato, and a wet-level pot, rather than a wet/dry mix control.  I see a rationale for being able to dial back the intensity of a chorus effect and make it subtler, especially for bass players.  But I see precious little useful terrain between 50/50 dry/wet and 100% wet, so being able to dial in 70/30 wet/dry holds no appeal for me. YMMV

As for LFO speed range, note that cap changes shift the whole range upwards or downwards.  There may be considerable overlap in the speeds attainable with cap-value X vs Y, but if you aim for faster speeds, you sacrifice lower speeds to get it.  With the resistor change one tends to also potentially lose a littl.e at the slow end, but you gain more at the fast end when doing so.  Besides, caps don't always come in the values you want, whereas a simple 1M trimmer will let you get exactly what you want.