This is a ribbon controller built to control the Tube
The controller consists of a wooden dowel attached to an old lamp stand, with a belt stretched along the top side of the dowel. The silver box near the top contains the electronics and controls, while the black box near the bottom contains the power supply transformer. As well there is a cow bell and wood block mounted on the same stand about 2/3 of the way up from the bottom.
Here are the construction details:
A 2 foot long piece of 1 1/2 inch diameter wooden dowel was mounted horizontally on the top of an old lamp stand with some angle brackets and wood screws. Along the top of this dowel a length of 1/2 inch mylar adhesive tape was applied. Then graphite powder (the type for lock and key lubrication) was rubbed into the mylar tape until the total resistance from end to end was about 100K ohms. Next, a belt was trimmed to the same length as the dowel. Then a 1/2 inch wide strip of brass shimstock was glued down along the center of one side of the belt. The belt was then attached to the top of the dowel at either end with washers underneath, so that it was suspended over top of the mylar/graphite tape with the brass strip facing down. Electrical connections were made using ring lugs on one side of the assembly.
Next, a basic sample and hold was built for the controller using a FET and a few op amps. The circuit is similar to that which Eric Barbour uses for his keyboard controllers, with a few mods and additions. The electronics was installed in a nifty little plastic box and attached it to the stand just under the ribbon controller. It has three controls; pitch, which offsets the CV output; width, which increases or decreases the CV output range; and glide, which is a basic portamento. There is one LED for power and another to indicate triggering (bright flash) and key down (dimmer steady light). As the whole circuit is just running on a single 15 volt supply, CV output range is from about 1 to 14 volts, which works well with my tube oscillators but which could also be adapted to solid state oscillators if required.
Initially there were problems with false triggering, particularly when using drum sticks. It was discovered that after the belt was struck, it would vibrate somewhat akin to a guitar string, so that other points on the ribbon that had not been struck would sometimes make contact. Tightening the tension on the belt was considered, but would make the controller less sensitive, particularly at each end, which should be avoided. So instead a strip of 1/4 inch wide weatherstripping foam was attached to the underside of the belt on either side of the brass strip. This way the foam was the first thing to make contact with the dowel, keeping the brass strip from falsely contacting. This completely eliminated the false triggering, without noticeably effecting the sensitivity.
Then it was found that while it functioned great when playing by hand, when playing quickly with drum sticks the controller would frequently miss the impulses. It appeared that the sample & hold circuit just wasn't fast enough. So, instead of attempting to build a faster sample & hold, the ribbon itself was modified to give a longer "key down" time. All that was necessary to accomplish this was to peel off the mylar/graphite resistive tape strip from the dowel, place two layers of double sided foam sticky tape down instead, and reapply the resistive strip back on over top of the foam tape. This way, instead of the drum stick reaching "end of travel" just as it makes the electrical contact on the ribbon, the stick makes electrical contact and holds it while the ribbon sinks into the foam. This produced long enough impulses for the sample & hold circuit to capture every time, and eliminated that problem. The ribbon now has less sensitivity when being used by hand, but The Peasant intends to use only sticks with it anyway.
Inside the Control Box
For sound clips of the ribbon controller in action go to the Vacuum Tube Synthesizer page.