Mysterioso gain and volume pots: linear vs log?

[DaveTV]

I just finished a Mysterioso build and I'm liking what I'm hearing so far. I noticed for the linear-tapered gain pots, the distortion suddenly jumps towards the end of the pot's sweep, making it somewhat challenging to dial in the distortion to taste. Would the gain pots benefit from being log (audio) tapered? What about the volume pots?

I've always wondered why the Blackstone pedal uses trimpot-type controls instead of more standard pots and knobs. It seems to me that this would make the Blackstone less tweakable on the fly. However, assuming the Blackstone uses linear pots like the Mysterioso, I wonder if the designer thought it best to make the Blackstone more of a set-and-forget type of pedal. Basically, find the sound you like and leave it like that.

[mjg]

If the gain is jumping up too quickly in the most clockwise positions, I think you want a reverse log (type C) pot. 

An audio taper may actually be worse than linear, as they will change more quickly in the clockwise positions. 

Try it out and see...these things can come down to personal taste.

[mauman]

+1 to mjg's post.   When set at 12:00 noon (50% rotation), the percentage resistance for each pot taper is: Log/A = 10%, Linear/B = 50%, Anti-log (C) = 90%.  So from 12:00 noon to fully clockwise, you're adjusting the top 90% on an "A" taper pot, the top 50% on "B" taper (what you have now), and the top 10% on "C" taper.   The "C" taper gives you the finest adjustment (slowest change) at the top end.  The "A" taper give you the same fine adjustment on the bottom end.

Regarding output/volume pots, I almost always use "A" taper even when "B" taper is specified.  Same range, just a taper that approximates the ear's response better than a linear pot.

[jimilee]

I used a b taper pot for the volume in the blueprint, cause I ordered the wrong taper. Unity is at 9 o'clock.


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[Bio77]

Instead of swapping the pot, you could try soldering a resistor that is 1/5 (100k here) the value of pot between legs 2 and 3 (might be 1 and 2, you need to study the circuit.  One gives you an A taper the other a C). No teardown necessary.  I've done that before and had some success.  Here's the link where I learned this trick:

http://www.geofex.com/article_folders/potsecrets/potscret.htm

[madbean]

What Bio77 is pretty much the best thing to try, I think. Reduce the value of the pot to spread the control over a larger range (since the gain pot works by reducing resistance). 100k, 220k, 470k would be the values to try. If you used PCB mounted pots you can even wrap the resistors around the pins first to test before soldering anything in place.

I agree the Blackstone is very fussy on its gain range and no doubt it was intended mostly as a "set and forget". The pot controls have special made caps that can be adjusted with a guitar pick which isn't too conducive to endless tinkering.