Alumitone "Current Driven" design?

Olie Eshleman · From: Seattle, WA

I may be too ignorant to understand the forthcoming replies, but my curiosity will be my best weapon against possible ignorance, so here goes....

First of all, i love these Alumitone pickups, hi-fi but with a pleasant 'warm' character. I've noticed a small transformer on the underside of the pickups thin body, and the website says:
"This radical departure from pickup design is aluminum based, rather than copper. Result: less resistance, higher output coupled to a "current driven design" as opposed to conventional voltage based pickups."

The thin body and the thin gauge aluminum wire part all fit together and make a sort of sense to me, but that last part about the "current driven design", can anyone explain that? and why is it better or worse, or what are the pros and cons of such a departure?

Jason Hull · Posted 8 May 2011 2:15 am

It's marketing hype, especially the use of the word "driven" (action = good). All pickups function with voltage and current. The difference is the impedance of the pickup and the amount of voltage and current it can develop. Of course the sound changes, but voltage and current are still voltage and current!

Georg Sørtun · From: Mandal, Agder, Norway

Well, I am not going to reverse-engineer (and destroy) my Alumitone to check up on details, but its "one turn pick-up coil loaded by a step-up transformer" does indeed make it "current driven" in my book. No matter how one throws the voltage and current around when it comes to PUs, the term "current driven" definitely isn't "a hype" for Alumitone PUs.

AFAICD, there is next to zero ohm in the actual pick-up coil, so one has to draw the current generated in it by the strings disturbing the magnetic field in order to get a signal. The voltage in that one turn pick-up coil is too low to be of any use, but the current is "relative" high.

Next step is to convert the current to a high enough voltage, which is where the step-up transformer comes in. The current then goes down by (ideally) the same amount as the voltage goes up, resulting in a more normal signal-level under normal - medium to high - load introduced by the regular input/buffer-amp and/or volume pedal.

The step-up transformer itself, and the way it is coupled to the pick-up coil, reintroduce some of the frequency dependent signal shaping we know from regular PUs, but this signal shaping is or can be kept small and much easier to tailor since the step-up transformer can be kept small. As a result we get more of what you recognize as a "HiFi signal" representing the actual string vibration, instead of a signal that is highly shaped by more or less hot-wound coils in regular PUs.

The closest HiFi equivalent you can find is probably the "moving coil" PU put on record turntables for true vinyl-connoisseurs. These moving coil PUs were also "current driven" - had very few windings to keep the weight down - and needed a load and a step-up transformer or a very high quality linear "pre-pre-amp" stage to get the voltage up to usable levels for the regular RIAA input.

Another truly "current driven" PU found on a very small number of 6 string guitars, is where the (metal) strings are coupled to act as PU "coils" in magnetic fields. The strings then have to be electrically loaded, and the resulting AC-current from vibrating strings over the load has to be "transformed" to a high enough voltage to be of use. Haven't seen such a construction for the last 25 years or so, but they sound wonderfully natural and prove that you don't need a large coil to detect variations in magnetic fields - a piece of wire will do if you can step up the signal enough later on. Simple physics really, but not so straight-forward to turn into something usable.

Ken Metcalf · From: San Antonio Texas USA

This is the way I see it.. Very Happy

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Georg Sørtun · From: Mandal, Agder, Norway

Olie Eshleman · From: Seattle, WA

Ask and you shall receive. Thank You Georg!
I get it, I think......
Anyway, whatever they did I'm sold. Thinking this would be a great acoustic guitar pickup, but it doesn't look like lace is making an Alumitone sound hole pickup. A band mate got their 'ultra-slim' for his resonator guitar and it sounds pretty good, but it doesn't appear to utilize the same technology described here: no transformer.

Bob Hoffnar · From: Austin, Tx

It looks like a perfect candidate for a second neck pickup that could just slide in.
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Georg Sørtun · From: Mandal, Agder, Norway

James Mayer · Posted 9 May 2011 4:27 pm

I attached the single coil version to my cumbus.

Steve English · From: Baja, Arizona

How is the p/u wired to the steel?....red/hot, black/ground?

If so, what are the green and white wires for?

Jerry Overstreet · From: Louisville Ky

Steve, only 3 wires on the Alumitone for steel.

Orange to hot.

Solid green and wht/blk tracer both to ground. Wiring diagrams at http://www.lacemusic.com/wiring/wiring.php

The splittable humbucker style for 6 string guitar does have a 4th solid white wire that routes to a switch.

Jason Hull · Posted 10 May 2011 1:30 am

Georg Sørtun · From: Mandal, Agder, Norway

Randy Beavers · From: Lebanon,TN 37090

Georg, thanks for the explanations.

Isn't this step up transformer design similar to how a microphone works? The little transformer is about the size of the one found in a Shure SM-57.

Georg Sørtun · From: Mandal, Agder, Norway

Randy, I interpret it that way, but, since I only have tested one Alumitone for 10 string PSG and base my interpretation on the principle Lace refers to in their minimal description, and how I personally would have built such a device, I can't say for sure what role(s) each part play in raising/shaping the output for use on various instruments.

Back in the early 80s I designed and tested minimal-turns PUs for single strings, working in the 3 to 10 turn range for the actual pick-up coils. Loaded and amplified my prototypes sounded and measured excellent, but it was difficult to get hold of truly low-noise ICs to build pre-pre-amp circuits to fit a (string)number of coils and amps into the space of a regular PU so I discarded the idea as "successful but impractical". Step-up transformers was not even an option, as they "colored" the signal too much IMO. That was then... Smile

T. C. Furlong · From: Lake County, Illinois, USA

I wonder if the pickup would work at all if the transformer coil were positioned remotely. Somehow, I think it wouldn't work. Thoughts anyone? Georg?
TC

Georg Sørtun · From: Mandal, Agder, Norway

TC, with the secondary coil(s) laminated on/in the main coil(s) ... no, they can't be separated, only extended and modeled to further shape the output.

T. C. Furlong · From: Lake County, Illinois, USA

So the step up transformer needs to be located in the field of the magnets. Right?
TC

Georg Sørtun · From: Mandal, Agder, Norway

With the aluminum skeleton forming the main coil(s) and the secondary coil(s) being laminated (integrated) into the skeleton, it seems slightly wrong to think about the secondary coil(s) as "just" a regular step-up transformer, although it does indeed "step up" the voltage. A secondary, multi-turn, coil is driven by the current produced in the main, single-turn, coil - hence the term "current driven", producing a suitable high voltage over the specified load. This does of course mean that (enough of) the secondary coil has to stay in the current-field of the main coil, in order to transform current into voltage. Shielding the secondary coil inside the main coil means it will only pick up the current produced in the main coil and will be pretty insensitive to external fields/noise. The single-turn main coil is in itself pretty insensitive to external fields/noise - it short-circuits them, so the construction of the Alumitone is pretty neat.

To expand on how it works: the magnets are there (only) to create the magnetic field that the strings vibrate in, as for any electromagnetic PU. Vibrating strings in the magnetic field produce current across the surface of the main, aluminum, coil, and this in turn produces voltage in the integrated secondary, copper, coil(s) tailored for the signal-level, frequency-range and load each PU model is made for.

Steve English · From: Baja, Arizona

How tall is that pickup and who's got the best price on them?

I'm trying to figure out how to get one to fit my little Stage 1.2 Very Happy

Jason Hull · Posted 11 May 2011 4:38 pm

Here are the dimensions:

http://www.lacemusic.com/wiring/pdf/BB_specs.pdf

Bent Romnes · From: London,Ontario, Canada

I have been testing the Alumitone on my 10 string BenRom pedal steel for the last few months. At the same time, I tested a Truetone single coil and one of my homemade single coils as well.

I have always liked the sound of the single coils the best. But my area seems to be a breeding ground for electrical interference as Georg can attest to.
We know what that does to single coils.

I jumped at the opportunity to try the Alumitone. Peter den Hartog generously offered to lend me his.

As I said, single has been my sound preference, but the Alumitone comes very close. Lo and behold, it is also totally quiet, not a hiss. I am starting to like it Smile

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Steve English · From: Baja, Arizona

Wonder if I could grind an 1/8" off the bottom of the legs?

Is that solid metal?

Olli Haavisto · From: Jarvenpaa,Finland

I Dremeled the legs to fit it in my Williams. I`m not sure how much.
I would guess that any length is OK as long as you don`t damage the electronics.
1/8 is probably OK.
Pretty vague, huh Very Happy

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Olli Haavisto
Finland

Steve English · From: Baja, Arizona

I can work with vague......now I feel obligated to try it Laughing

Would I need the 4" wide model?

Thanks Olli !!!

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