I'm sure most of us have encountered a build that required a trim pot: a small potentiometer that is soldered directly to the PCB, often intended to make some one-time adjustment that accounts for variability in another part of the circuit (e.g. bias), or maybe some kind of tuning that is expected to be very infrequent.
The most common kind of trimpot part I've seen called out for effect pedals is the Bourns 3362 style. These are single-turn pots (meaning you can make at most one full rotation of the potentiometer; actually, I think it's more like 300 degrees of rotation, so really just shy of a full rotation). Depending on the pot's value, these can be quite coarse in terms of how precisely you can (or can't) dial in a resistance value.
But there also exist multi-turn trimpots: the ones I've seen have a little screw that can be fully rotated several times. And at least for the ones I've used, these offer much more fine-grained control over the values you can dial in.
My main questions are along the lines of how these pots fare over time:
Clearly, given the same amount of rotation in a single-turn vs multi-turn, the actual resistance change will be substantially less in the multi-turn pot. My thinking is that the multiturn trimmer should therefore be more resiliant to environmental factors.
Another thought is, with the single-turn pots, you could probably make them a bit more resistant to the environment by putting a drop of glue on them. But if they will drift over time regardless, then future re-adjustment becomes much harder or impossible. (You might as well simply aligator-clip the pot in place, find the right resistance value(s), and hard-solder (a) precision resistor(s) in place.)
Naively, it seems like multiturn trimpots would generally be better, but I'm guessing there is probably some tradeoff of which I'm not aware.
I would assume that, in general, a good design takes the "slop" of a trimpot into account. Meaning, trimpots are presumably low tolerance parts (probably 10-20% like the big pots we use externally on effects), and if your design requires 1% resistance value tolerance to be achieved via trimpot, it's probably not going to work. However, what prompted these questions is my experience building the Aion Amethyst (Boss DM-2). Basically, to correctly bias the v3205, I felt a multiturn trimmer was necessary, and even with that, the it was a fairly narrow range that I felt sounded right.
The most common kind of trimpot part I've seen called out for effect pedals is the Bourns 3362 style. These are single-turn pots (meaning you can make at most one full rotation of the potentiometer; actually, I think it's more like 300 degrees of rotation, so really just shy of a full rotation). Depending on the pot's value, these can be quite coarse in terms of how precisely you can (or can't) dial in a resistance value.
But there also exist multi-turn trimpots: the ones I've seen have a little screw that can be fully rotated several times. And at least for the ones I've used, these offer much more fine-grained control over the values you can dial in.
My main questions are along the lines of how these pots fare over time:
- Does either style drift over time? Is one more likely to drift than the other?
- Can environmental factors affect trimpots? Specifically the kinds of environmental factors that come into play in an effect pedal: heat/humidity changes, vibrations, impact (e.g. being dropped)?
Clearly, given the same amount of rotation in a single-turn vs multi-turn, the actual resistance change will be substantially less in the multi-turn pot. My thinking is that the multiturn trimmer should therefore be more resiliant to environmental factors.
Another thought is, with the single-turn pots, you could probably make them a bit more resistant to the environment by putting a drop of glue on them. But if they will drift over time regardless, then future re-adjustment becomes much harder or impossible. (You might as well simply aligator-clip the pot in place, find the right resistance value(s), and hard-solder (a) precision resistor(s) in place.)
Naively, it seems like multiturn trimpots would generally be better, but I'm guessing there is probably some tradeoff of which I'm not aware.
I would assume that, in general, a good design takes the "slop" of a trimpot into account. Meaning, trimpots are presumably low tolerance parts (probably 10-20% like the big pots we use externally on effects), and if your design requires 1% resistance value tolerance to be achieved via trimpot, it's probably not going to work. However, what prompted these questions is my experience building the Aion Amethyst (Boss DM-2). Basically, to correctly bias the v3205, I felt a multiturn trimmer was necessary, and even with that, the it was a fairly narrow range that I felt sounded right.
