Another issue is that you didn’t show the exact circuit being used with the switched resistor ladder. If it’s switching the audio directly, then there may be a noticeable shift in the volume. However, I seem to remember that this was being used with a vacuum tube based organ, so I’m wondering if the switched resistive ladder may have been controlling the gain of a variable mu vacuum tube. This would allow a time constant to be implemented such that the volume change may be rather slow (e.g., more of a swell than a switch).

As for building a discrete resistive ladder, that shouldn’t be too much trouble with only 16 levels. It may not even be a major problem, at least for onesie-twosies, with more levels, where you could hand pick the resistance values for the resistors being used. But, I certainly wouldn’t want to put a design like that into production with discrete components. Of course, you could use a packaged resistive network, where the resistors are matched.

As for using an analog optical sensor, that might actually work reasonably well, if you picked the correct type of optical sensor, although designing the optical path might be a bit of a trick (especially making it stable enough so that mechanical motion didn’t affect the volume). Phototransistors tend to be rather non-linear, but something like a Cadmium Sulfide photocell might work well.

Dave

What I should say, then, is that this pedal is large and unwieldy, has to be mounted on a stand because of the way the electronics enclosure hangs down, and is at a steeper angle than I like for a standalone pedal; and that I’ve already borrowed a sleek standalone pedal; so I’m not highly motivated to pursue confirming that this one would work. Fair enough?

Haha the translation is hilarious. “What is asking screams” -> “It’s begging for it!”

http://pepevi.blogspot.com/2008/07/abrir-el-precinto-invalida-la-garanta.html

For convenience, here’s the Google translation to English.

Thanks, Jose!

I never got to listen to this organ much before it was retired, but if it really only had sixteen discrete volumes, I’d be a little surprised if I couldn’t have heard the levels change as it was used. I know you can get high-resolution optical encoders that would offer many more than sixteen levels, and I’d wonder about using one to drive a digital pot, rather than a DIY ladder, which would seem awkward to build with as many steps as I think I’d want.

I’d also wonder about using an optointerruptor (or optoreflector) in analog mode, moving a slightly noncircular cam through it. You could shape the cam for whatever response curve you wanted; but I don’t know whether the optical sensors would be predictable enough to use that way?

All that still feels like overkill to me, though. My experience with stereos and guitars and synthesizers and amps suggests that pots are good enough — good enough to be in the preamplification stage of a transistor/IC circuit, anyway — especially if used regularly so they don’t get “crusty.” Do you disagree, or are you focusing more on higher-power applications?

However, as one commenter points out, high power potentiometers were usually made by winding nichrome wire around a ceramic (or other high temperature insulating material) as a former, and using a sliding contact. That works, at least for power control, but as the windings age, the resistance may become nonlinear, and you may experience problems with intermittent contacts, which would introduce dropouts and noise into an audio signal (Not good for an organ!).

Carbon composition potentiometers have been available since at least
the early 1940s (and, probably the 1930s or even 1920s). But, they, too, experience a wear and noise problem.

The advantage of the switch approach is that it should be reasonably immune to noise, especially if the switch contacts are appropriately composed/plated. Additionally, with the correct selection of resistors, you can obtain any type of slope you desire (which is especially important for volume controls, since volume is inherently non-linear, e.g., audio taper). That’s not easy to do with a wire wound potentiometer, and, while it can be done with a carbon composition potentiometer, those still have problems.

For a modern approach, rather than going with a potentiometer (noise, wear, taper, etc.), I think I’d look at using some type of optical encoder driving some logic that controls a resistive ladder (e.g., Optical encoder controlled by a microcontroller which drives an array of (matched) MOSFET switches driving a resistive ladder. Or, something like that.).

Dave