…infringing patents (probably)

by Stephen Hobley on November 23, 2011

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I’ve been meaning to build one of these for ages.
Can anyone guess what it is?

It’s not a Taser, or one of those shocking buzzer things – the clue is that the coils are well “potted” and have very different gauges of wire.

Mystery device Mystery Item, back view

Answers on a postcard please, or in the comments…

UPDATE : Correctly identified as a “guitar sustainerizer” otherwise known as an Ebow.

The circuit is a simple audio amplifier based on the LM386 (or in my case the NTE823) IC.

The two coils are taken from old telephone pickups – one (input) has a small rare earth magnet on the back, the other (output) was unwound and rewound with about 300 turns of #32 wire – this coil now has a resistance of just under 8 ohms. I tried a 4 ohm output coil, but the IC got too hot so I doubled the turns.

Note – I recently found a better candidate to make the coils with – tiny PC speakers.

The input coil has a resistance of 250 ohms – this is probably too high – I read somewhere that 50 ohms is probably better – so I may remove some of the turns on the coil.

Tomorrow I’ll publish the circuit and the etch mask, along with a video of the device in action.

…and here’s the patent :-)

UPDATE2 : Here’s the schematic, placement and etch mask – click to enlarge

Guitar Sustain Schematic Guitar Sustain Components Guitar Sustain Etch Mask

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{ 10 comments… read them below or add one }

Roy November 23, 2011 at 5:27 pm

some sort of high-voltage thing – I wonder what the green wires connect to

Stephen Hobley November 23, 2011 at 5:33 pm

Good guess, but it’s just 9v – it has an audio application.

Todd Harrison November 23, 2011 at 5:44 pm

It is a electromagnetic pendulum driver for a clock. One coil picks up the magnet on the pendulum and then triggers an ever so slightly offset one shot kick push in the second coil to keep the pendulum swinging and the clock running in good time. You potted the coils because you wanted low noise in your pickup and thous better timing for your driver.

Todd Harrison November 23, 2011 at 5:46 pm

But then that is is not an audio application so I guess I have to retract my idea.

Todd Harrison November 23, 2011 at 5:52 pm

You’re building some kind of a guitar string pickup amp that has a high and low freq response mix using two coils which respond slightly differently for a single string.

Stephen Hobley November 23, 2011 at 6:01 pm

oooh that’s so very close…

I’m going to have to film this thing in action, so it might be tomorrow before I reveal what it is…

Doug November 23, 2011 at 6:19 pm

You’re generating an electromagnetic field to vibrate a steel string (like what would be found on an electric guitar or base) but doing so at a small enough voltage so that you aren’t inducing current in the guitar pickup.

Stephen Hobley November 23, 2011 at 6:23 pm

Yes I am – just like one of these…


…only for $90 less. But to be fair to the makers of the above, the device works better than mine, with minimal noise – but this is only version 1.0 after all :-)

Roy November 25, 2011 at 1:12 pm

Cool – I misread the part number as NTE 523 (“High Voltage Tripler”). BTW the patent is long expired.

Jorge October 20, 2013 at 4:35 pm

Could you post the size of your printed circuit?

What a good post you have here, thanks :P

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