Potentiometer question

[thedwest]

I just got my order in from Tayda and they put a500k pots in a bag marked for a1m pots. My question is, aside from waiting until I get the right pot, could I substitute a b1m or a500k and make either work in place of the a1m? This is for the Son of Ben preamp pedal.

thanks

 

[moonlightpedalbuilds]

You will be short on the drive. At maxed setting, it will only give you half the drive. you can probably insert a 500k resistor before pin 3 or after pin 2 of the 500k pot. If you have two 500ks you can series them so you can still get the full range. Or just wait for your replacement pot.

 

[phi1]

Since the drive pot is wired as a voltage do wider (like a volume pot) in this circuit, 500k would still give you the max drive.

But it would affect the tone. C3 and the drive pot form a high pass filter (bass cut). So changing to 500k would change the frequency of this filter.

1MB will work exactly like a 1MA, just with a different taper. So it will be a little harder to dial in just right at low gains.

 

[thedwest]

Thanks for the info. Out of impatience, I went ahead and used the a500k. Definitely a bad choice. Just turning the drive knob to 1 made it super loud and aggressive, leveling off about halfway. So from 5 to 10 there wasn't much of a difference. I'll try the b1m since i have a bit before the right pot gets here.

 

[phi1]

Just for the sake of correcting myself, I took another look and I think 500k was will be les max gain than 1M because R6 is so high, so even at Max gain it’s forming a voltage divider with R6. And it will affect how that treble compensation network sounds (C4 and R7). Regardless, I’d say try 1MB like you’re planning to do.