# Internal Trimmer on Face of Pedal?



## farwest1 (Apr 12, 2020)

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?


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## phi1 (Apr 12, 2020)

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?


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## farwest1 (Apr 12, 2020)

phi1 said:


> 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


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## Chuck D. Bones (Apr 12, 2020)

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.


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## farwest1 (Apr 12, 2020)

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.


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## farwest1 (May 22, 2020)

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?


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## Chuck D. Bones (May 22, 2020)

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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## farwest1 (May 22, 2020)

Thank you!

and the lazy way: wire it up however and just keep it if it’s reversed?


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## Chuck D. Bones (May 22, 2020)

Sure, why not.


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## moonlightpedalbuilds (May 23, 2020)

farwest1 said:


> 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.


I did the same to my magenetron delay. I placed in top row mid


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## farwest1 (May 24, 2020)

pedjok said:


> I did the same to my magenetron delay. I placed in top row mid


Same! Planning to box and test tomorrow.


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