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Internal Trimmer on Face of Pedal?

farwest1

Member
If I wanted to add an internal trimpot to the face of pedal (instead of inside enclosure) is it just a matter of drilling the case and inserting a pot of the same value to the underside of the board?

In this case, schematic calls for 100k trimpot. Could I use an A100K pot instead?
 

phi1

Well-known member
Yep that’ll work. Use a pot with solder lugs and just attach with wires to the 3 pads for the trimmer.

Trimmers are typically B taper. Is there a reason you want to use A taper?
 

farwest1

Member
Yep that’ll work. Use a pot with solder lugs and just attach with wires to the 3 pads for the trimmer.

Trimmers are typically B taper. Is there a reason you want to use A taper?
Thanks! B taper works—I'm a noob and didn't realize trimmers were normally B taper :)
 

Chuck D. Bones

Well-known member
I have done this. Sometimes a taper other than B will have a better feel, you'll need to experiment to find out. Also, some trimmers, the bias trimmers in SoB for example, only produce useful sound over a portion of their range. You may still need a trimmer to go with your front panel pot. That's what AnalogMan did with the Sunface.
 

farwest1

Member
I'm thinking specifically of the gain trimmer on the Magnetron Delay. Seems like it would be useful to have a knob and adjust in real-time.
 

farwest1

Member
If I want to attach a regular pot to internal trimmer pads on a PCB, how do I know which lead goes to which pad?
 

Chuck D. Bones

Well-known member
The middle pad on the trimmer will go to pin 2 on the pot. The other trimmer pads go to pin 1 and 3 on the pot. There are a couple of ways to figure out which pad goes to pin 1 and which pad goes to pin 3.
The easy way: Temporarily wire the pot to the pads and see if the rotation is forward or backwards. If the rotation is correct, you're a good guesser and the pads are wired correctly. If the rotation is backwards, swap the pin 1 & 3 wires at the pot.
The harder way: Trace where the trimmer pads go using visual inspection, the schematic and an ohmmeter. Study the schematic to figure out which way should be clockwise rotation.
 
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