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04-16-2025, 12:35 PM
Hi Guys
The comment that "I could hear the amp at about 9-o'clock" suggests that there is a dead spot in the sweep at the quiet end (CCW).
That got me thinking about the actual resistance values of the pots I am using. Measuring a handful of them they are quite varied and the 12-0'clock half-way position is not actually one-tenth of the total end-to-end resistance; rather, it was usually a bit higher. These are "average" pots which tend to have 20% tolerance. Like every other "log" taper pot, it is not actually a logarithmic-valued track but a series of linear sections, which is easier to manufacture. With enough sections there is adequate response for most applications.being log,
I grabbed some other pots that are typically thought to be much better (conductive plastic instead of carbon), but their values were varied and within 20% of their rating.
I grabbed a stepped resistor style pot used in hifi equipment. This is not a true Alps, more likely a clone. In any case, the switch has forty or so positions with a resistor soldered between them. It comes down to the designer doing the math correctly to attain a proper incremental resistance sweep and net value desired. Here, the overall value was off by about 10% but the half-way sweep is right where it should be at one-tenth of the total. These stand a chance of being more consistent from unit-to-unit, but that depends on the tolerance for the resistors used.
The Alps pots are 2-section as they are intended for use in a stereo. This is actually okay for a Power Scale installation where we can effect a single-knob solution for any amp that has a Schmitt splitter AND pre-PI-MV, and for any amp using a concertina.
Over the years I have been adjusting values within the Power Scale kits to try to have the broadest range of control, good low-level resolution and optimal mosfet heat dissipation. With normal pots made by Humans it is nearly impossible to achieve all three at the same time. One solution, is to add a trimpot that would allow the installer to optimise the sweep for the specific amp sample combined with the kit component tolerances. However, I have found that trimpots are best avoided on kits whenever possible,
The comment that "I could hear the amp at about 9-o'clock" suggests that there is a dead spot in the sweep at the quiet end (CCW).
That got me thinking about the actual resistance values of the pots I am using. Measuring a handful of them they are quite varied and the 12-0'clock half-way position is not actually one-tenth of the total end-to-end resistance; rather, it was usually a bit higher. These are "average" pots which tend to have 20% tolerance. Like every other "log" taper pot, it is not actually a logarithmic-valued track but a series of linear sections, which is easier to manufacture. With enough sections there is adequate response for most applications.being log,
I grabbed some other pots that are typically thought to be much better (conductive plastic instead of carbon), but their values were varied and within 20% of their rating.
I grabbed a stepped resistor style pot used in hifi equipment. This is not a true Alps, more likely a clone. In any case, the switch has forty or so positions with a resistor soldered between them. It comes down to the designer doing the math correctly to attain a proper incremental resistance sweep and net value desired. Here, the overall value was off by about 10% but the half-way sweep is right where it should be at one-tenth of the total. These stand a chance of being more consistent from unit-to-unit, but that depends on the tolerance for the resistors used.
The Alps pots are 2-section as they are intended for use in a stereo. This is actually okay for a Power Scale installation where we can effect a single-knob solution for any amp that has a Schmitt splitter AND pre-PI-MV, and for any amp using a concertina.
Over the years I have been adjusting values within the Power Scale kits to try to have the broadest range of control, good low-level resolution and optimal mosfet heat dissipation. With normal pots made by Humans it is nearly impossible to achieve all three at the same time. One solution, is to add a trimpot that would allow the installer to optimise the sweep for the specific amp sample combined with the kit component tolerances. However, I have found that trimpots are best avoided on kits whenever possible,
