Alumitone lookalike

[Carbion]

hello guys,

I am currently studying Lace's alumitone pickup patents and I am thrilled by that technology. Hence, I want to build my own alumitone for research purpose only. I want to document that process here, so stay tuned! I do that as a hobby and don't have so much time so I guess it is going to be a bit slow. But hey it's all about the fun while going all the way.

If you have any ideas to improve my build, don't hesitate to tell me. Right now, I am constructing the pickups in CAD and I will show pictures, as soon as there is something to show.

If you are interested, the relevant patents are:

5767431
6897369
5831196

You can look them up using googles patent search (and other tools as well).

The geometric constrains for my design are pickup cavities of 74 x 19 mm with a filet on the corners (radius = 9.5 mm)

Stay tuned!

[David Schwab]

One of the forum members, Joe Rogowski (bbsailor) has done quite a bit of experimenting with these types of pickups, and has shared a lot of insight.

You can find the threads here:

http://music-electronics-forum.com/t5447/

http://music-electronics-forum.com/t4881/

It's an interesting technology, but since it's patented, you wont find too many people here making them, except to try out the ideas.

You you want the tone and not necessarily the look of the alumitone, the first thread will show you how to make a Lace Transsensor type pickup.

[Carbion]

Thanks David, for the links - I did not know them.

I want the looks of them, I am in no way conservative as most guitarists are. I want the pickups to be visibly different. Think different.
I have a lot to read next, since I do not comprehend the principle yet 100%. But I am optimistic
Regarding the patent: Is it US only or is it worldwide? I am based in Europe, so a US patent does not apply here if I want to sell pickups in the future (which I don't but, hey... you never know. But probably I'd only sell like 2 a year or so, so no problem here!)

[bajaman]

some pictures of my builds

[Carbion]

Nice, thanks you for sharing! That guitar looks very neat. And the pickups are just perfect. Do you also have taken pictures during construction phase? How did you do the secondary coil? What are your specs? What sort of magnets did you use? The material does not look like aluminium to me. Did you choose some other metal? What is the sound like?

[bbsailor]

Thanks David, for the links - I did not know them.

I want the looks of them, I am in no way conservative as most guitarists are. I want the pickups to be visibly different. Think different.
I have a lot to read next, since I do not comprehend the principle yet 100%. But I am optimistic
Regarding the patent: Is it US only or is it worldwide? I am based in Europe, so a US patent does not apply here if I want to sell pickups in the future (which I don't but, hey... you never know. But probably I'd only sell like 2 a year or so, so no problem here!)

Carbion,

Bajaman has done a pretty clever implementation of a current transformer based pickup design. To get started, simply look at my previous posts referenced by David (above) and build one. A simple loop of AWG 10 copper wire around a flat ceramic magnet using thin copper tubing to join the wire to the transformer primary (CSE-187L or similar) or the Bajaman design where he uses the copper metal frame as the low impedance loop will work fine. Note that the output is in the range of about 10 to 20 millivolts depending on the current transformer (CT) used.

The Lace Alumitone is a patented design but the laws of physics and the application of current transformers to audio transducers cannot be patented.

Look at the wiring of the Les Paul Personal guitar with a low impedance pickup and see that the output of the CT is in the same range. Search this forum for some posts about this matter. Just put a microphone matching transformer (Shure A95U series) at the amplifier end of the guitar cord and you can build this totally passive (no preamplifier) and preserve a full frequency, wide bandwidth response.

Low impedance pickups using CTs have a few more benefits to low-volume, commercial guitar makers who want to be daring and try something new.

Post your questions and some forum members will jump in.

This is fun stuff to play with!

Joseph Rogowski

[bajaman]

Thanks Joe
Your experiments inspired me to develop my own current sensing LoZ pickups.
Carbion - sorry no further construction pictures, but the frame was made from 3mm extruded aluminium bar pieces (although i have made some with 3mm thick aluminium plate as well). The current sensing coil is a 500 turn encapsulated toroid type AS104 available from Radiospares (ENGINE ROOM).
The magnets are two layers of self adhesive hobby magnet strips easily cut with a pair of scissors - I charge them between two large neo magnets held in vice jaws - they charge up to approximately 300 gauss, so i guess you could call them a low gauss design.
I spray lacquered the frames hot rod black, then inserted the charged magnet strips (one N up and one S up), then I sprayed a clear lacquer coat over the top.
They sound wonderful to my ears - no resonant peak in the high end response gives an almost acoustivc transparency to the harmonics AND the bottom end is much tighter than a HiZ pickup. Very sweet detailed sound.
I have found that the actual pickup placement position has a far greater relevance than the pickup's own charateristics now.
The output level is a bit on the low side however, so i use a low current drain low noise discrete Jfet gain stage and Jfet buffer to bring the signal up to useable levels. I use 50k log pots for volume and tone (25k are very hard to source locally )
cheers
bajaman

[bajaman]

I have also built current sensing LoZ pickups using 3mm thick brass and copper in Humbucker and Strat sized single coil versions.
here is the preamp I use

[David Schwab]

The current sensing coil is a 500 turn encapsulated toroid type AS104 available from Radiospares (ENGINE ROOM).

For those in the USA that would be:

Nuvotem - AS-104 - Allied Electronics

Very nice work Bajaman!

[Carbion]

Guys, thanks for your input! I really appreciate it. Today, on my way to work I took the time to read the patents and I think I get the principle behind the pickups now. Maybe not with the physics and I probably cannot appreciate and comprehend all possibilities of the design, but one step at a time

Carbion - sorry no further construction pictures, but the frame was made from 3mm extruded aluminium bar pieces (although i have made some with 3mm thick aluminium plate as well). The current sensing coil is a 500 turn encapsulated toroid type AS104 available from Radiospares (ENGINE ROOM).
The magnets are two layers of self adhesive hobby magnet strips easily cut with a pair of scissors - I charge them between two large neo magnets held in vice jaws - they charge up to approximately 300 gauss, so i guess you could call them a low gauss design.

Bajaman, thanks for elaborating. With this information, the rest is pretty straightforward if i am going to use the same transformer. What diameter is the hole for the primary "winding"? I am definitely considering that option. You used the middle spacer to sense the primary "coil", right?

Bajaman has done a pretty clever implementation of a current transformer based pickup design. To get started, simply look at my previous posts referenced by David (above) and build one. A simple loop of AWG 10 copper wire around a flat ceramic magnet using thin copper tubing to join the wire to the transformer primary (CSE-187L or similar) or the Bajaman design where he uses the copper metal frame as the low impedance loop will work fine. Note that the output is in the range of about 10 to 20 millivolts depending on the current transformer (CT) used.

Jospeh, I agree that Bajaman's Version of the LoZ is nice. As are your threads posted above by David. I read them both and like your ideas. Especially using the string to pick-up itself was an idea that really blew me away. I have to try that out later! But one step at a time...

What I need to know next is how Lace does the secondary winding(s). I listened to Alumitones once and they sounded like "regular" pickups to me. Is there a trick involved? To sound "normal" you need to lose the advantage of a linear hi-fi frequency response and to introduce a resonant peak. Does Lace to that? How?
How do linear LoZ pickups sound, when they are played distorted? I am playing a lot of my songs with gain and crunch settings and while I want something new (or maybe different) I still need a good distortion sound.

[bbsailor]

Guys, thanks for your input! I really appreciate it. Today, on my way to work I took the time to read the patents and I think I get the principle behind the pickups now. Maybe not with the physics and I probably cannot appreciate and comprehend all possibilities of the design, but one step at a time



Bajaman, thanks for elaborating. With this information, the rest is pretty straightforward if i am going to use the same transformer. What diameter is the hole for the primary "winding"? I am definitely considering that option. You used the middle spacer to sense the primary "coil", right?



Jospeh, I agree that Bajaman's Version of the LoZ is nice. As are your threads posted above by David. I read them both and like your ideas. Especially using the string to pick-up itself was an idea that really blew me away. I have to try that out later! But one step at a time...

What I need to know next is how Lace does the secondary winding(s). I listened to Alumitones once and they sounded like "regular" pickups to me. Is there a trick involved? To sound "normal" you need to lose the advantage of a linear hi-fi frequency response and to introduce a resonant peak. Does Lace to that? How?
How do linear LoZ pickups sound, when they are played distorted? I am playing a lot of my songs with gain and crunch settings and while I want something new (or maybe different) I still need a good distortion sound.

Carbion,

Wow, a lot of questions!

Secondary Winding Connection. See patent number 6897369, figure 17, items232 and 234 are interlocking laminated cores to join the two coils number 230 to the primary loop number 260. Note that he mentions that these coils can be single coil or dual coil. Dual coils and be set in series or parallel for variations in sound. Typically thicker windings (lower resistance) favors lower frequencies so that controlling the primary loop gauge can provide tonal variation. You can hear the difference between a primary loop of AWG 10 versus AWG 18. To find a good balance is a matter of listening to and adjusting for what sounds good. Adjust by using different primary loop wire thicknesses and switching between series and parallel secondary loop connections offers a simple way to make a variation in tonal balance.

High Frequency Response. The general class of high impedance pickups are voltage based. More turns equals more output. But some secondary effects of more turns also means more coil turn-to-turn capacitance creates a resonant filter that is also the active part of the pickup system. That is why most high impedance pickups have a predictable coil resonance in the upper mid range where human ears are the most sensitive. One consequence of this is that the frequency response falls off at a 12db per octave rate beyond the resonant peak. Volume control loading, coax cable length and capacitance and amplifier input impedance loading on the passive high impedance pickup all influence the sound. If you want to hear the upper harmonics that you hear on an acoustic guitar but don't hear when amplified on a high impedance pickup, you need a pickup that has a higher response beyond 5 or 6 KHz.

Low impedance current based pickups depend on converting a current in the range of about 10 milliamps developed in a loop resistance of about one milliohm. The turns ratio of a typical current transformer can vary between 500 turns to over 2000 turns. The output impedance is a small fraction of what a high impedance pickup would contain. Any resonant peak is much lower and broader so the frequency response of upper harmonics, normally attenuated by high impedance pickups, is there to be added to the guitar sound pallet or attenuated or electronically boosted to return to a more electric guitar high impedance pickup response.

Using current transformers such as the Toroid-shaped AS104 used by Bajaman or the laminated E-I frames such as the CSE-187L. Instead of tying to generate more voltage by filling the bobbon wire winding window area with the maximum amount of thin AWG 42 to 43 wire, you convert that whole wire window area to a single loop of wire of equal cross section area.

This is a very low resistance loop so attaching the thick wire loops is critical The E-I frame type already has a single AWG 12 wire loop with two 0.187" stubs of the "U" shaped loop. Use soldered copper tubing to make the connections to the string loop primary. On toroid designs there are ways to use the Bajaman design where the center conducting bars can also go through the toroid center hole. He shows using ony using one toroid but he could have put another one facing the existing toroid. Then he could switch the outputs between one coil, two coils in parallel or two coils in series. For these toroid output combinations he would use the DPDT on-on-on mini toggle switch.

In my own experiments, just using a single loop of AWG 10 around three 0.75" X 1" X .187" thick magnets produces about 20 millivolts out of a 20 ohm (DC) coil. By coincidence, this 20 ohm secondary on the CSE187 seems to match the typical input impedance of a microphone matching transforrmer designed for up to 500 ohm input sources. When I put a thin ferrous metal plate under the magnet and under the loop wire, the output increases by about 30 percent because the metal plate is reflecting the underside of the unused magnet field back through the loop and string field above the magnet.

Putting a CSE187L at each end of the loop allow one to think in terms of, how thick to make the loop for maximum bass response? Then as the loop gets thinner, the treble sounds are being more emphasized. Then you can make a heavy loop of AWG 8 or 10, and another thinner loop going the other way of AWG 16 to 18 for the higher responses. Then, the two CSE187L outputs can be selected with the on-on-on switch referenced above to obtain pleasing sound combinations.

Look at the Lace Alumitone frame and see that the frame is the low impedance primary loop. Carefully look at the side and see where the two "U" shaped interlocking laminations (see reference above) are attached to the alumium pickup frame (only on one side for now). The humbucker Alumitone design is the same as the single coil Alumitone except the thickness of the loop primary conductor which shifts the tonal color of the pickup simply by manipulating the primary loop wire resistance.

If you want drive, simply play the low impedance guitar pickup through a microphone preamp module (2000 ohm actual impedance) and feed the output of the preamp into a guitar amp at what ever drive level you need. I don't think that everyone will appreciate a cleaner, extended high end, espicially when accentuated by using overdrive sounds. Low impedance pickups are, by their nature, a wider bandwidth pickup. The value of this design is in the ear of the beholder.

Did I answer all your questions?

Joseph Rogowski

[Steve Conner]

some pictures of my builds

This guitar is a beauty! I love the pickups.

Just one question: The screws that you used to hold your Lo-Z pickup together, they also carry the signal current. What metal are they made of?

[bajaman]

Hi Steve - good question
They are brass M3 slotted head machine screws.
I recently built a pair of LoZ humbuckers with 3mm thick brass plate - polished and clear lacquered - I installed them on a Squier Strat guitar. Maybe it is just my imagination but they did sound a little bit mellower than the aluminium LoZ pickups I used on the Mint Green Tele. I have also built some single coil pickups with copper plate - they are very bright sounding pickups.
Cheers
bajaman

[bbsailor]

Hi Steve - good question
They are brass M3 slotted head machine screws.
I recently built a pair of LoZ humbuckers with 3mm thick brass plate - polished and clear lacquered - I installed them on a Squier Strat guitar. Maybe it is just my imagination but they did sound a little bit mellower than the aluminium LoZ pickups I used on the Mint Green Tele. I have also built some single coil pickups with copper plate - they are very bright sounding pickups.
Cheers
bajaman

bajaman, and all CT pickup designers

You can control the voicing (tonal quality) of the current transformer-based pickup by adjusting the resistance of the current loop around the magnet that senses the strings. In my early experiments I simply made single "U" shaped loops of AWG 16, 18, 12, 10 and 6 copper wire. The thicker wire loops favored the lower (bass) frequencies.

By using various turns ratio current transformers (CT) such as 1 to 500, 1000, 1500, 2000 and higher you can also hear voicing changes while using the same gauge wire. You can even make a pickup using two overlaping "U" shaped loops facing 180 degrees from each other and each connected to a different CT. Then, like switching a humbucker between series, parallel, and single coil, this dual overlapping loop CT pickup can have two voices to select using a mini toggle switch.

When trying to maximize the output fom the CT pickup, I found that if I use a piece of thin ferrous metal under the magnet to include the width of the wire loop, I can obtain about a 30% increase in output by better concentrating the underside of the magnetic field back to the strings.

The other variable is selecting the load resistance of the CT output. Typically CTs need a load resistor burden when used in their normal power sensing application. When uses in pickups, the burden resistor will be about 10 to 25 times higher and typically be the value of the on-board volume control pot. Typically, you will start with using a volume pot values that are about 35 to 40 times the DC resistance of the CT.

In my experiments, I make my pickups such that I can suspend them above the guitar strings, mount them with double face tape and listen to the audio changes when I: (1) change the wire gauge, (2) change the CT turns ratio, (3) change the load on the CT and (4) switch the CTs between series/parallel/single CT. This is the subjective part that each CT designer needs to try for themselves. I hope those who try this share their results on this forum.

These CTs have a very low resonant hump and it is well above the normal high impedance pickup response. To restore some high impedance pickup flavor to these CT pickups, consider using a variable EQ such as the EMG-BQC control.

These CT pickups have very low noise. It is important that the low impedance loop is grounded to the final output to maintain the full low noise potential.

CT pickups can be made very quickly so all the variables mentioned above can be quickly observed with an oscilloscope or heard through an amplifier. I recommend making the volume/tone controls in a small metal box that can be guitar mounted (with double face tape) and make connecting the CT outputs with thin dual conductor shielded wire to this box. Then, all CT combinations can be switched and quickly compared.

Joseph Rogowski

[jbforrer]

Greetings,

I've been following the discussions on LoZ pickups with interest. Great stuff.
After seeing the work of Bajaman, decided to make one and see what it sounds like. Please see attached pictures and sound clip.

The sound clip was recorded straight into the LoZ input of the mixer with a flat response setting, no tone or effects editing. Plugging the pickup into a 200 Ohm to 50K mike transformer and playing into the guitar amp gives quite nice output level, however, it sounds quite different than playing through the mixer (different impedance matches I guess) .

My pickup uses a VITEC 57P184 current transformer that I had laying in my junk box. I believe it uses a 1000 turn toroid. The magnetic strips are like Bajaman described --- mine charged up to about 230 Gauss. I wired it for XLR conventions and found it extremely quiet.

Thanks for all the good work and sharing of ideas.

Regards.

JBF.