Mini-Me Puzzle (solved)

[Anonymous]

Built probably 10 Mini-Me pedals and I have one that works great but the speed control acts like a logarithmic pot.  That is it takes much more clockwise turn to bring the speed up to fast than my other Mini-Me circuits.  It is a C1M pot like the others…..wonder if the pot is bad or has the wrong taper.  All other components are correct.  Would this be the pot itself?  Just that most of the speed bunches up toward the end of the clockwise turn when compared to my others.

[Billy]

If you haven’t already check the resistance throughout the pots rotation see if you get any strange readings

I’ve had a few duff alpha pots lately

I’d also check the caps that work in conjunction with the pot C20 and 21 in particular

[Anonymous]

Billy, Thanks.  I’ll check those out.  Probably not be easy to pull the pot out.  Still works properly just the taper is bothersome.

 

Thanks for the response

 

Hank

[Anonymous]

I see that the European pot code for an anti-log pot is the letter “F” while the American code is the letter “C”.  The European code for  a log pot is “C”.

Is it possible that you actually have a log pot installed instead of an anti-log?  If so, reversing lugs 1 and 3 may help.

See this:

 

http://www.resistorguide.com/potentiometer-taper/

[Anonymous]

Wilkie, It’s a C1M. That being said, it acts like a log pot. Reversing the lugs would be tough as it is a POB mounted pot…

Thanks

Hank

[Anonymous]

Board mounted?  OK.  NEVER MIND!  🙂

[Billy]

I know it’s of no use now but I’ve been using a great tip from Cybercow Mark when using board mounted pots just solder the very tip of the lugs in initially to test the circuit, making them much easier to remove for debugging etc

As I said I’ve had a few problems recently with Alpha pots bought from reputable suppliers usually intermittent ie check ok then go to infinate when rotated resistance readings changing and so on

Bunching up in my experience usually means a duff pot or incorrect taper or resistance somewhere I don’t know if mixing up R23 47K and R25 470K would do that but easy to miss when you’ve checked values a few times

[Anonymous]

Billy, Thanks  checked R23 and R25….correct.

Went ahead and clipped the C1M pot at the right angle of the 3 lugs, leaving the vertical portion of the lugs. Heated from the front side and pulled each out. Used a desolder pump and reinstated the holes in the board. Soldered in a new C1M and it works…..Not recommended for the weak of heart. Definitely. As you said, a “duff” pot.

Thanks all for the input.

Hank

[Author]

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