Build Your Own Clone Message Board

Hi
Just finished my Mimosa. Sounds and works great.
I want to build another one for a friend. But with the possibility to add a switch so he can use it for bass AND guitar.
There's 3 caps (C1, C2, C3) involved that have different values.
It this doable?
I know how a 3PDT switches work, but I'm still struggling with what can and can't electronically be done.
For instance, if it were resistors instead of caps, i presume it can be done with a 3PTD. But since I don't really know how caps work... I have some ideas, but it's hard to explain without a drawing
Can someone tell me if it's possible with a single switch?
Also, a switch won't be handy IF you need to reset the internal trimpot every time.

Best regards!
Tom

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The switching logic with capacitors would be the same as resistors -- they are both impedances. However, you could get some popping noise when switching capacitors depending on how charged up they are when switched.

Also, it may pay to be careful about wiring layout. Too much stray coupling between wires and other circuitry sometimes can cause problems. Often a good strategy is to lay it out physically as much as possible like the schematic, keeping wiring and components near the inputs of high gain sections away from the outputs. That type of thing is a general principle. If you try something and suspect layout problems, often moving wires and parts around a little will cause changes in symptoms. If so, you are probably looking around close to where the problem is.

There's nothing magic about the 330n caps used in the bass version--the idea is to go up to a value high enough to let the bass frequencies through, so going a bit over that value is no problem. And since the capacitance of two caps in parallel is equal to the sum of their value, I would recommend wiring up a 3PDT toggle switch to put a 330n cap in parallel with each of the original caps. That will simplify the modification vs. wiring it to switch between two sets of three caps.

I'd recommend mounting the 330n caps on a piece of perf board and wiring the three of them to the throws of the 3PDT on one side and one leg of the original caps on the other. The three poles of the switch are then connected to the other legs of the original caps. Be sure to mount those caps to the PCB sitting up high enough to leave some exposed leg to solder your wire connections to.

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“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

I think I get it! Thanks!
I'm planning to buy a breadboard so I'll try it out there first.

About the bias trimpot, 2 more questions:
1/ when switching from "bass" to "guitar", do you think I'll have to change the trimpot setting, or does this have nothing to do with it?
2/ I have a multimeter (but still no pro in understanding all this pedal hocus pocus). How do I measure 1.5-1.7V on the source of Q2? I suppose I have to measure DC voltage, put one 'probe' to the S eyelet, but where do I put the other probe?

(I think I could really use some breadboard-time to start to know how these things work and I ordered an oscilloscope to help me understand more)

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I don't believe the caps should affect the trimpot setting to any significant extent.

The red probe of your multimeter should go to the indicated transistor leg and the black probe goes to ground. I generally just stick it in one of the four corner screw bosses, since the enclosure is grounded.

_________________
“My favorite programming language is SOLDER” - Bob Pease (RIP)

My Website * My Musical Gear * My DIY Pedals: Pg.1 - Pg.2

Thanks!

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