# Trimmer question



## potierrez (Feb 13, 2020)

Hello!

There are many pedals with internal trimpots like son of ben, super 64 overdrive or similar circuits.

How do i know values of voltage and where i have to measure it?

I don´t find it at the building docs.


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## Robert (Feb 13, 2020)

It varies between circuits, and sometimes to taste.

Most of the time you'll bias a JFET (J201, etc) so the drain measures around 1/2 of the supply voltage (typically 4.5V for a 9V pedal).

It's not an exact science, sometimes they'll sound harsh or sterile at this point and you'll have to tweak by ear (The M800 is a good example)


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## potierrez (Feb 13, 2020)

Thank you!

I thought that maybe some of them would have certain values at the factory. In the cheesemonger it is okay to tweak noise gate to taste but in the overdrives I thought it was something more sensitive to different values.


I'm thinking of building blue shoe but I'm not convinced about the possible trimmer setting . . .


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## zgrav (Feb 13, 2020)

No doubt the commercial pedals are supposed to have the trim pots set consistently.  But in general that setting is just what someone else thought sounded the best.    The suggestion to set it so the voltage is half of the incoming voltage and then tweak it by ear is very practical and will serve you well.


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## potierrez (Feb 13, 2020)

zgrav said:


> No doubt the commercial pedals are supposed to have the trim pots set consistently.  But in general that setting is just what someone else thought sounded the best.    The suggestion to set it so the voltage is half of the incoming voltage and then tweak it by ear is very practical and will serve you well.



Thank you!!


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