What gauge magnet wire for active pickups? Trying to find out!

[windycityblues]

Hello all, Im wondering if anybody has some insight as to what might be a suitable wire gauge to start with for experimenting with making active pickups. I dont want to sound too ignorant here, I know the math/theory here, im just looking for a good starting point for experimenting, as it would be difficult to calculate the expected area of the coil, or the magnetic permeability of the particular magnets Im using, and so on (or at least for me given my knowledge on the subject). Im thinking something like 35 awg might be a good place to start, but it would really be helpful to hear some other opinions. In addition, any info/advice from anyone who has made active pickups in the past would be greatly appreciated! Thanks -Alex

[David Schwab]

You can use any size you want depending on the tone you are going after.

Commercial active pickups like EMGs use 42 or 43 gauge wire. They do not have low impedance coils.

[Mark Hammer]

"Active pickups" are not any particular kind. They are just pickups with supporting active (rather than passive) electronics. Given that amplifiers anticipate a certain typical input signal, pickups designed in such a manner to produce a rather weak output will generally be accompanied by such suppoprting electronics. But there are also pickups with hot enough outputs that have active electronics.

The prototypic circumstance for an active pickup is a low-impedance pickup whose output level is lower than an amp expects, and whose output impedance is similarly low. That could be any sort of wire, though, really.

[bbsailor]

Hello all, Im wondering if anybody has some insight as to what might be a suitable wire gauge to start with for experimenting with making active pickups. I dont want to sound too ignorant here, I know the math/theory here, im just looking for a good starting point for experimenting, as it would be difficult to calculate the expected area of the coil, or the magnetic permeability of the particular magnets Im using, and so on (or at least for me given my knowledge on the subject). Im thinking something like 35 awg might be a good place to start, but it would really be helpful to hear some other opinions. In addition, any info/advice from anyone who has made active pickups in the past would be greatly appreciated! Thanks -Alex

windycityblues, David, Mark

Active pickups, whether using thin wire and wound like high impedance or low impedance pickups using thicker wire do one important thing: isolate the pickup from loading by the external loads and coax cable capacitance including the amplifier input impedance. They preserve and accentuate the normal self resonance of the pickup no matter whether the coax is 10 ft long or 25 ft long or if the amplifier input impedance is 1 meg ohm or 10K ohms.

In low impedance pickups that are passive, transformers are used to transform the impedance of the coil around the magnet by the square of the transformer turns ratio. If a high impedance pickup is 2.5H, then a low impedance pickup with one tenth the number of turns will be 25mH (2.5 divided by 10 squared) for a 1 to 10 turns ratio step up transformer. If the high impedance pickup has 6000 turns then the low impedance pickup will have 600 turns and the transformer will bring the low impedance coil back up to approximately the 6000 turn pickup output level, minus the transformer characteristics that might degrade the potential performance or enhance desired characteristics by purposeful mismatching from the theoritical values. Low impedance pickups have less wire, less self capacitance and typically have their resonance well up in or beyond the audio spectrum. This characteristic is preserved by adding an active circuit.

The selection of wire size gets down to fitting the right amount of wire turns in the available space to obtain the desired results. The design process starts out by calculating the theoretical values based on the available transformer (turns ratio and impedances) and then working backwards, overwind the low impedance coil with taps at 50% and 70% and listen for the desired sound. This is what is done on the Jack Casady low impedace bass with the three position selector impedance switch. Typically you want the input impedance of the transformer to be between 5 to 10 times higher than the impedance of the pickup coil to minimize loading but the ear is the ultimate test. Transformer matching is another form of tone equilization.

In low impedance active pickups circuits, the gain of the amplifier stage is set to bring the pickup output back up to the level that an amplifier wants to see for minimal noise or a little overdrive. Low impedace pickups typically pick up less noise than high impedance pickups which also make good hum antennas. Just play a high impedance pickup near a computer or monitor.

Joseph Rogowski

P.S. See this web site to build an active buffer in the guitar cable. With a little gain, you could make a pickup with less turns and put the pickup self resonance up a little higher as well as isolate the pickup from cable capacitance. http://www.till.com/articles/GuitarPreamp/

[David Schwab]

I used to use a similar JFET preamp for low impedance pickups. It worked great.

[Mark Hammer]

As always, Joe, exquisitely and wisely stated. Thanks.

[windycityblues]

Thanks for the fantastic answers guys. I've continued doing my own research on the side. I guess I'll be picking up a few different gauges between 24 awg and 35 awg (in addition to my 42 and 43). Looking forward to playing around with this stuff (now onto preamps! haha) -Alex

[bbsailor]

As always, Joe, exquisitely and wisely stated. Thanks.

Mark, windycityblues

Thanks for the kind words. I have been tinkering with pickups since the about 1960 when I built my first laptop guitar as a teenager. I had the privilege of working with a luthier in Newark, NJ, Steve Blozen and met Mike Roman the designer of the Ampeg Devil Bass. I did the pickup wiring and soldering work as Steve moved from making Yugoslovian acoustic folk instruments to making electric guitars with their exploding popularity back then. I also met Jess Oliver the VP of Ampeg and Everett Hull the president of Ampeg. One summer, soon after getting my drivers license, I worked at Ampeg in Linden NJ doing the final assembly of tube amplifiers. I guess I just remember all that guitar and amplifier stuff that I learned back then.

My career advanced in strange ways from being a faculty member in a community college and running their AV department/TV studio (while I was fresh out of college) to being a TV writer/producer for the U.S. Army at Ft Dix, and finally retiring in 2003 as a Technical Manual Writer/Editor for communication-electronic equipment where I wound up as a strategic planner for automating the DoD technical publishing system. My electronic technical knowledge and experience started with winding wire around magnets to make guitar pickups and then seeking to understand what makes them sound different and finally, in my last 20 years of work, learning how to write to make technical things understandable. I still tinker and enjoy sharing what I discover with forum members.

windycityblues, See this web link for a good explaination of the effects of pickup coil capacitance, pickup coil loading, coax capacitance loading and active buffering: http://www.blueguitar.org/new/misc/gtr_lemme.pdf . Try obtaining magnet wire with thicker insulation so you can hear the effects to lowering coil winding capacitance, placing the buffer right after the pickup/before the volume control so you can use you ear to find the pickup sound that you seek.


Joseph Rogowski