Theremax DIY case/enclosure guidelines

Technical notes, diagrams and schematics for the Theremax series of PAiA products.
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Theremax DIY case/enclosure guidelines

Post by PAiA-Scott »

Theremax, custom case?

Upon completion of the circuit-board kit wired to its control and connector panel, basic operational tests can be made that will make any needed trouble-shooting easier, and, work as a point of reference should operation be hampered once it is fit in its case. With the output patched to an amp/speaker, apply power and tune and test the operation with the antennae leads spread-out into open space and not near power wiring or panel metal, on a piece of wood, cardboard, or plastic. Even without antennae it should tune and respond to your hands moving to or from the ends of the antenna cables. Then, put in a case like is shown in the assembly instruction manual with wood panels, a metal front-panel and an aluminum base and with the antennae attached in their clamps it will tune and operate as intended. It is normal and likely the tuning procedure will need to be performed as the unit is fitted into its case, and, as the location (and the variation in distance from the floor) changes, though the panel trim controls will often be enough adjustment to compensate for site differences.

In our kit, the board is placed up off a metal (aluminum) case-bottom via the #4-40 mounting screws/nuts and 3/16" spacer (about 4mm). A solder eyelet is under the nut at one corner of the board with the power supply minus pole and wire G (and the panel LED ground wire) which puts this whole bottom at zero potential or ground/circuit-common. This works as a local load to the four oscillator circuits and helps stabilize them somewhat. The metal front-panel being grounded or not is not so important, but circuit board wire SG goes to the panel connectors and controls joined by a solid-bare wire. The case bottom and panel are keep away from the antennae and mounts. The case bottom is closest at about 3" or 7-8cm.

It is best to not have metal too near the antennae, it will work to couple them to each other, or, to ground if the metal has a connection with the circuit board point G (0vdc/ground/circuit-common). If the panel with the antennae mounts is metal, the antenna lead must pass through a hole that is about 1/4" or 5mm and then the closest the clamp or antenna can be to the metal is about 1" or 2-3cm. Consider too, case materials or finishes might be conductive or with low resistance to the RF energy at the antenna cable ends and mounts. For example, a project sent here for service was determined to be suffering from excess loading of the RF oscillation due to the black paint on the inside of the case having a high carbon content and it working as a resistor between the antennae mounts the grounded metal case bottom (and, between the connected first and fourth oscillator circuit-sections). Be mindful too, that the antennae should not extend too near metal shelving or metal in tables, or appliances plugged into the mains outlet, as these are extensions of earth ground and a load to the RF energy.

As for the antennae, ours are metal rods (1/8”, 2-3mm, diameter). We have used copper for them, but now use brass. I have seen units in for service where the builder has elected to use aluminum rods and these were OK--also plumbing fittings. The loop for the volume antenna is to concentrate the field and the affect the hand has on the field. It is better to not have to move the volume hand so much. Then, it is easier to hold a steady pitch with the other hand. A plate or a spiral can be used too. I built one into a red, plastic pencil-box. I used a metal tray to mount the board and controls, pushed the hot iron through the box to allow the control shafts to extend through, mounted a 9pinD connector for the power, controller, and audio connections, and RCA phono connectors for the antenna mounts. These connectors didn't turn out to work so well as the antennae twist in the connector with metal rods in them, but they're OK with the lengths of red insulated wire I have in place now. They're each formed into spirals.

Below is a link to a photo of a completed kit and front-panel assembly showing the way the wires should be smoothed, formed and routed to be away from the parts in the four oscillator circuits and the antennae cable ends. ... scaled.jpg
Scott Lee