national radio – battery bowered portable mutant synth

AJ’s Mum gave me this old AM transistor radio when we were cleaning out her garage, and being a curious sort of monkey I had a poke around inside it the other night to see what I could find with an eye to some sort of circuit-bending hi-jinks.

(click all pics to open bigger pics)

As it’s all made from discrete components rather than integrated circuit chips there are lots of easy access points to tap wires onto, and I found that by connecting various points in the circuit (more or less at random) I could get it to produce nice big fat square waves at various frequencies. Oh joy!

I didn’t really stop to figure out why or how the noises were being created as I was too busy soldering up the connections I liked before I lost track of them, but it mostly involved tying one leg of the biggest capacitor to a bunch of other points. I’m sure someone can tell me why these things happen – for now I’m just happy that they happen

I settled on four frequencies which I found to have the most pleasing relation to each other and which I thought would be most useful musically; essentially two notes a few steps apart, and another two notes a couple of octaves up and a few steps apart. The radio’s volume control acts as a master frequency control, sweeping from high (in the low volume position) to low (in the high volume position).

Next, some switches to turn the notes on. The board pictured above is a control panel, either from a CRT monitor or a TV (probably a monitor judging by the gorgeous beige knobs) and is conveniently furnished with four tiny momentary switches. This suits my needs perfectly; as you can see from the first picture the radio is pretty small and I was keen to keep it pocket-sized and portable.

All the extraneous parts of the control panel were removed but I left one small potentiometer attached. I also added a toggle switch which turns on a drone frequency. The other switches cut the drone off while engaged. The small potentiometer acts as a fine tuning control – it sweeps about half an octave – but only when the drone is engaged.

I thought about mounting everything nicely but I kinda like the Frankenstein look of the wires hanging out. Besides, this meant not breaching the original casing at all which I quite like.

The control panel is just hot-glued onto the front. I’ll put rubber feet on the back so it sits nice and firm.

Of course the other cool thing about this one is that it has it’s own amp and speaker so you can play it at the beach. Oh yeah, and the radio tuner still works so you can mix in AM static and signals as well. Or just, you know, listen to the radio.

AJ now claims it was her radio all along and not her Mum’s. She’s not getting it back. It is now a member of the Miniature Portable Plastic Battery-Powered Orchestra.

Audio and video demonstrations to come…