Guitar reInvention

In Uncategorized on July 25, 2011 at 8:03 pm

I’d like to share another reInvention created by myself and my buddy Are.  We imagineered this thing from scratch, built and tested it working properly on a real guitar, then of course discovered patents on the basic concept going all the way back to the 1930’s!  So it was one of the original ideas for an electric guitar pickup, but it was ahead of it’s time.

It took until the end of 2008 for us to reinvent it, and by then technology had evolved to the point that it became practical.  So practical in fact that I have the guitar in working condition sitting next to me right now as i type.  Although I say that the concept originated in the 1930’s – and also there were many other designs proposed over the decades – we put a little design twist on it that made it practical for use on modern guitars and other stringed instruments.

So enough about the origins of this reInvention, let’s talk about how it works.  It all starts when we put strong neodymium supermagnets in an alternating pattern under the strings.  I cut up a cookie tin to make thin little plates which i secured to the surface of the pick guard with double sided foam tape, right underneath the strings.  Then I stuck magnets under the strings.  See the photo below for a close-up of this arrangement.

Those are 9mm square magnets and the strings are 10mm apart, so the fit is close enough.  Note that the strips of magnets are snapped together as they run across the strings because the magnets are alternated like this:  NSNSNS.  That way the magnetic fields add up beneath each string instead of fighting with each other.  This is one of the keys to making this pickup system work.

What happens when you strum the guitar strings is that they vibrate perpendicularly to the magnetic field that they are located within.  According to physics, this creates a tiny electrical current that flows along the length of the wires.  These currents travel to the headstock where they end up at the tuning pegs and there they need a place to go so that we can collect them, boost them, and send them out to the guitar amp.  That’s where the following photo gets important.

Here I have shorted the tuning pegs together with lugs that were laboriously fastened out of tuna can lids with a Dremel tool, which tool forever and a half!  Once the lugs were created and soldered together carefully they formed a shorting block that electrically sums all six string currents together into a single combined current.

“Ah,” you say, “but how do you get that current back down the neck where it can be boosted and sent out the guitar jack?”  The simple answer is you use the truss rod inside the guitar neck as the return conductor.  That part is actually one of the main contributions to the state of the art that Are and I made.  Prior art in the patent record typically required an insulated bridge which is not standard equipment on guitars, so it is not manufacturable easily.  Our approach maintains the bridge at ground potential so no changes are necessary to the bridge.

So anyway, our tiny little electromagnetically generated currents have now gone full circle from under the strings, up the neck, down the neck, and back into the guitar body.  At this point we could just send the signal out to the guitar jack and put a gain pedal between the guitar and the amp to get our signal.  However that means super tiny currents traveling in the guitar cable which leads to noise issues.  So the solution is to boost the signal inside the guitar.

In our prototype we used a special microphone transformer with a mu-metal enclosure to accomplish the signal boosting.  The result is a signal strength about half as strong as a conventional pickup produces which is close enough for our purposes.  However we have since realized that an opamp gain circuit or similar would be the ideal choice here.

That means putting a battery in the guitar or otherwise delivering power to the guitar through the guitar cable or via solar cells with storage capacitors for playing in dark environments or other such complications.  This turns out to be worth the effort for the improvement in audio quality.

So how does it sound?  Clean, in the sense that it sounds like an acoustic guitar.  In tests with guitar players, I found that pretty much none of them like this sound, haha.  They are accustomed to the distortions created by the second order low pass filter that exists in conventional wound pickups and they don’t like the clean sound.  I tried many times to explain to them that we could introduce the characteristics that they preferred with additional circuitry and even make that adjustable without having to swap out pickups, but got zero positive response.  Not one guitar player likes this pickup system.

However, I feel that it’s great for certain styles of guitar play such as bluegrass or classical where the acoustic sound is preferred.  Also it would be useful for making an electric violin that was true to the violin sound instead of distoring it like conventional pickups.  It’s also great for any metal stringed instrument including custom instruments that people build for academic, industry, or hobby purposes.  So the guitarists do not have the final say after all.

One last thing I’ll mention is that this system should also be nice for hexaphonic guitar output where you capture all six string vibrations separately and send them out on a multiconductor cable to the amplifying equipment. That can be accomplished by not using the shorting lugs and simply sending six return wires down the neck in a separately machined channel in the neck.

So there you have it, from the 1930’s to today, about 80 years later an idea gets reinvented and made practical by the advancement of technology a a couple of hobbyist fiddling around.  Another reinvention bites the dust, so to speak.  Well, i should stay positive – perhaps some one will find this reinvention useful and actually tell me about it.  Enjoy your day.

  1. hi dear nice work

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