Build a $5 Analog Programmer
After building a few voltage controlled signal processing devices optimized for maximum versatility, I unexpectedly found myself using a few "pet sounds" over and over again rather than taking full advantage of the various controls. With my analog delay, for example, I use automatic-double-tracking, flanging, and slap-back echo regularly, and I usually set up the controls the same way every time I use these effects. I began to realize that some type of programmer would save me a lot of time, but couldn't justify a complex digital design when all I needed were a few preset analog voltages. So, I came up with the simple - but effective - analog programmer shown in figure 1. It's very easy to build, draws virtually no power, and generates four different "programs" of two control voltages each (with two toggle switches selecting the appropriate program). For those who suffer from digiphobia (an unexplained fear of digital circuitry), this is an easy way to come up with a computer-less programmer.
A 4052 IC is the electronic equivalent of a DP4T switch. Program switches S1 and S2 specify the four "positions" of this "switch" (see Table 1 for how the settings of S1 and S2 correspond to which trimpots connect to the control voltage outputs). You simply adjust these trimpots the way you would adjust a pair of normal panel controls; in fact, one of the programs could select the front panel controls instead of the trimpots, so that you have the choice of three pre-programmed settings along with normal front panel operation. What could be simpler? An interesting bonus of using an analog design is that it never forgets (as some digital programmers have been known to do), and it can also program audio or sub-audio signal levels as well as DC voltages. (However, these signals must not go more than 0.7V below ground in order to work right with the 4052; you could use a bipolar ±7.5V supply to handle bipolar audio signals, but then positive control voltages would be limited to +7.5V.)
Construction consists mainly of wiring the trimmers to the 4052 chip. I used some miniature trimpots available from Digi-Key, to minimize expense and circuit board size. I strongly advise using a socket for the 4052 (and any other chips you use, for that matter) as it is subject to damage from static charges. Using sockets also allows you to salvage chips from obsolete circuits without having to desolder them; in fact, without fail, every circuit that I have built that didn't use sockets has come back to haunt me in one way or another.
You could take this whole idea further and use 4051s (SP8T analog switches) with three program switches to get 8 presets instead of 4. Once you get past a certain level of complexity, though, a digital approach is more reasonable.
By the way, even if you don't build this project I suggest that you get some of these chips and experiment with them. There are so many things in musical electronics that can be done with analog gates. I have used them to select between different effects loops, and have also wired up a circuit to allow me to switch between different master volume levels on my Marshall amp. If you start playing around with some of these chips, I'm sure that you'll come up with ideas of your own. In any event, happy programming.
Feature by Kirk Austin
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