Multi Turn Volume Pedal

[kdj432]

Someone asked me if it would be possible to build a stereo volume pedal using 1 or 2 multi turn pots which he wants to control with a hand crank, I was discussing it with an engineer friend and he said he wouldn't do it with anything lower than 1meg which doesn't seem to be available also other values seem to be super expensive.

[robthequiet]

If you have mechanical diy abilities, you could always use gears, as in trucks and drones.

[wavley]

I use 50k and 500k 10 turn bourns pots all the time for precision bias supplies at the day job all the time, I don't see why you couldn't use those, they're not cheap, but at around $10 they're not bank breakers either. 

Doing two with one crank requires mechanical skill though.  Never looked to see if they make dual pots.

[PRR]

Welcome.

Try with 100K or 500K.

I assume this is a electrical engineer, and concerned about loading the guitar. Valid, but we also have to drive the load, drive line capacitance, and hold hum down. 100K will shave guitar top-ring, but many amps do that without being "bad". 250K or 500K may be fine also.

Rather than gears, I would do 2 pulleys and a string. Look inside old radios. The hand-knob turned 7 times around while the tuning cap turned a half-turn. Often a 3" wheel on the tuner and the knob shaft turned down to 0.2". A spring INside the large pulley held tension on the string (inside so rim friction held against tuning action). A key-word is "dial cord".

[kdj432]

He is an electrical engineer but he's also an amp builder so I'm not sure where his sense of adventure went.  I would have to use two pots to achieve stereo signal wouldn't I?  the guy that wants this pedal is able to 3d print a crank, he just needs to know what type of shaft I'd be using.  as far as I can gather this guy wants to be able to do a long fade out live (uses a lot of loopers).  it sounds to me if I use between 100k and 500k I may be losing top end signal?  this guy is afraid of that so I guess I would need to buffer this pedal.

[samhay]

>I would have to use two pots to achieve stereo signal wouldn't I? 

Nope - that problem was solved many moons ago if you are willing to use conventional potentiometers (cf. multi-turn trimmers).
Look for "dual-gang" potentiometers.

[robthequiet]

Occurs to me that a slider might be considered. Wonders of studio mixing have been done with 120mm faders on the console.

[PRR]

> this guy wants to be able to do a long fade out live

[wavley]

He is an electrical engineer but he's also an amp builder so I'm not sure where his sense of adventure went.  I would have to use two pots to achieve stereo signal wouldn't I?  the guy that wants this pedal is able to 3d print a crank, he just needs to know what type of shaft I'd be using.  as far as I can gather this guy wants to be able to do a long fade out live (uses a lot of loopers).  it sounds to me if I use between 100k and 500k I may be losing top end signal?  this guy is afraid of that so I guess I would need to buffer this pedal.

Well, if he's fading out loopers then the signal is going to be actively driven and I doubt that you'll lose high end signal.  Ernie Ball volume pedals are passive and 250k, 500k, or 25k depending on the model.

Paul is right, look at old FM tuners for doing this, also look at Ernie Ball volume pedals because they use a more simplified version of the string method.

[wavley]

>I would have to use two pots to achieve stereo signal wouldn't I? 

Nope - that problem was solved many moons ago if you are willing to use conventional potentiometers (cf. multi-turn trimmers).
Look for "dual-gang" potentiometers.

This is what Paul was getting at with the FM tuner, instead of a tuning cap only moving a half a turn for 7 turns you can use a log pot, cheaper and easier.  Audio through a 10 turn pot is tediously slow, probably even with a crank.