Does anybody know how Lace "Alumitone" pickups work?

Question

I'm an amateur guitar maker and I've made a few coil pickups in the past, but Lace's Alumitone pickups are what really interest me, and I really want to try to duplicate them. What I know is that they utilize a single "knot" of aluminum to create a current-based signal rather than a voltage-based one. What I'm trying to figure out is how the pickup's small secondary coil works (Resistive properties? Is it like a mini Rogowski coil? What is a Rogowski coil?). Any info about the pickup's inner workings is welcome.

Answer 1

From what I can tell (looking at the Lacemusic.com site), it is a current transformer that is not 100% coupled as a normal current transformer would be.    Current transformers are typically 1 turn of heavy gauge wire (that you want to sense the current passing through) coupled to 1000 turns of small-gauge wire.  Perhaps you have seen an "Amp Clamp" on a multi-meter.  That's the same principle.

A very large magnet (2 of them) compared with the small cylinder magnets of standard pickups, induces larger eddy currents in the strings, which induces a larger current in the loop of aluminum.  That's one turn which is picked up by the multi-turn smaller coil underneath.   1 turn of aluminum is almost a dead short, so the voltage induced on the 1 turn is extremely low.  If there are 1000 turns on the secondary coil, the voltage is multipled by a factor of 1000, while the current is divided by a factor of 1000.  There are losses involved to the numbers aren't that exact.  And for this setup it looks like the coupling is not anywhere near 100%.

Since they can wind fewer turns on the secondary than a standard pickup, the impedance is lower which is advantageous in many other ways (possible better frequency response, more voltage to the amp input).

I might get one for my bass, because I have a terrible problem with noise and hum pickup.  That's another thing -- the secondary coil is naturally shielded (mostly) by the aluminum to reduce noise and hum.  It is also wound 90 degrees mechanically from a standard pickup to further reduce noise.

Thanks for the question and letting *me* know about these pickups.

.