Alumitone Pickup Design Revealed

[mac639]

Thanks Bent.
Are you sure it was 4.97 ohms, not 4970 or 4.97K ohms? As I'm sure you know, regular pickups are anywhere from about 7500 ohms to 17000 ohms or so. Without getting into too much electronics lets say you need something over 1 volt to drive the amp to a reasonable volume. To get that much voltage you need to with that low a resistance(impedance) you would have to either increase the current produced or increase the resistance. This is just your old OHMS LAW (E=IxR) E=voltage, I=current and R=resistance. Actually there are other factors involved when you're working with audio frequencies but in theory anyway it's pretty much the same thing. On a regular pickup the number of turns of wire that interact with the magnet at any given instant will determine the amount of voltage produced, i.e, more turns more voltage. And pickups are basically a "voltage" generator and produce miniscule current. The end result with 4.97 ohms resistance you will have almost no output voltage to feed into the amp. Other than that, no you really can't measure the Peak to Peak AC voltage with the multimeter too well. I have a high quality Fluke electronic meter and it doesn't tell you too much. Of course you'd have to have the pickup on a guitar and strum the strings to have it respond to the string vibration to produce a signal (voltage) anyway since it doesn't do anything just sittin' on the bench. Sorry for the long winded writing. I still say there must be a transformer in there somewhere to increase the voltage. It'd be like an audio transformer with the secondary winding which would have few turns and be connected to the one turn coil, and a primary winding with a lot of turns that would be connected to the output jack and amp. That would increase the voltage available at the output by perhaps a factor of 100 or more.

[Bent]

Mac, yes of course it was 4.97K ohms..sorry about the goof.
I had an email from Alumitone a while back concerning another pickup. The tech told me that the reading should be around 5K OHM

[Georg]

Bent, pretty difficult to measure output from a PU with a voltmeter. The voltmeter impedance must be reasonably high and you need a form of "tone generator" to electro-mechanically emulate a vibrating string at various frequencies. An oscilloscope set to sample and hold the instant output from a source, is what we normally use for such measurements.

The resistance you measure across the Alumitone's output is pretty low, as it should be for a "current to voltage step-up transformer." No surprises there.
I bought an Alumitone last March in Dallas, but it's in Norway and I'm in the US so can't check up on anything.

The principle behind the Alumitone is described well enough in the links in this thread. Same principle was/is used for lowZ moving coil Pick Ups for record turntables, used by real HiFi connoisseurs (like myself). We often replaced the step-up trafo with a super-low-noise pre-pre-amp stage for even better result though

The principle can also be used to turn the strings themselves into "moving coils" and only leave the magnets in the position where we normally place the PU. The steel bar we use shorts out the strings so not sure if it will work well (noiseless) on steel guitars. It works perfectly on regular guitars fretted with fingers though, and they have metal frets...