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Rotary Speaker - isolation cabinet - Part 4

Part 4

Here's the control box...

At it's heart are the guts of a Pioneer MA-12 mic mixer with a spring reverb:




I kept the electronics and discarded the case. I made some small adaptations - removing the unnecessary features such as the tape/source selection and associated inputs and outputs, and adding wiring to bring the controls off the PCB for mounting in the new casing.

The mic that I installed in the rotary-isolation cabinet is one of these...


...a National electret condensor mic. I'd separated the mic from the power unit thing, which takes an  LR44 1.5v button cell battery, in order to install that part in the control box. Luckily, by tracing the PCB of the MA-12 and testing with a multi-meter, I could find a suitable point to tap power for the mic and so do away with the need for batteries.

The above, however, forms only one half of the unit - the output side of the things. The other side is the input and speed control for the rotor. For this, there are three components; the motor speed controller, a small  amp to drive the speaker and a mic pre-amp which can be switched into the input stage should the sound source require it. These 3 components were built from kits purchased at Akizukidenshi in Akihabara, Tokyo. In addition, I built a simple LED blinker using a 555 timer that gives a rough visual indication of the rotor speed, although it's perhaps more decorative than functional.

These parts thus form the input side of things and are powered separately from the output. Keeping the two sides apart makes it far easier to avoid issues of ground hum and interference - especially with mic signals and the long cable connecting the control box to the isolation cabinet. I therefore put a power supply together using the guts of a 12v AC-DC adaptor and a series of regulators. This provides 9 volts to the motor and the amp, as well as 6 volts for speed controller/LED blinker and the mic pre-amp.

Here are the guts:


I included one final feature - an option to bypass the input amplification and plug straight into the speaker. This might provide a better solution for guitars using an external amp, for example.

The casing for the control unit uses my usual MDF, paint and lacquer methods...here's a selection of images at various stages of construction:






I gave it the name "Isospin" (isolation cabinet + spinning speaker) which has something to do with nuclear physics and quantum numbers.




video demonstration:

Comments

  1. Patrick Bartmess14 July 2019 at 06:24

    This is such a genius conception. I love the mechanical means of effecting sounds. Your finishing details are, as always, immaculate. Even down to the texture of the case - it looks like something that would be nice to rest your hand on as you play.

    ReplyDelete

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