For a recent experiment, I decided that it would be a good idea to try to add some electric guitar distortion effects to my otherwise Classical flute playing.
In order to do this, I attached a small electret microphone to my flute, which is powered by a phantom power unit and provides an audio signal to a guitar amplifier. A rough idea of my setup is shown in the following circuit diagram:
simulate this circuit – Schematic created using CircuitLab
(I did not include component values as I don't think they are that important in this problem, but I can add them if required.)
This setup seems to work quite well, I am able to add as much distortion as I want using the amp. However, there seems to be a bit of interference (mains hum, etc.) present, as there probably would be in proper electric guitar setup. My friend, who plays electric guitar, immediately noted that I should try to implement something similar to a Humbucker pickup, which is a type of guitar pickup that cancels out most interference, but with microphones instead of pickups.
My understanding of how a Humbucker pickup works is that instead of having just a single pickup, there are two, wired in series or parallel. The pickups have opposite magnet configurations (ie. one has all magnets with the north poles pointing upwards, and the other has magnets with the south poles pointing upwards) and wire coils wound in opposite directions. Any interference induced in the coils is then cancelled out because the interference from each coil is equal and antiphase in relation to one another. The signal from the guitar string remains unaffected because the although the coils are wound in opposing directions, the magnets are also in opposite polarity.
Based on that understanding, I came to the conclusion that it isn't possible to replicate the Humbucker setup with my microphone, because there is no equivalent to "winding the coils in opposite directions" or "reversing the polarity of the magnets" in an electret microphone. Simply connecting two of my microphones in series or parallel (which I believe is what my friend was thinking) would increase the audio signal but also the amount of interference, due to the microphones (and therefore interference) being in phase with each other.
So my question is, is it possible to replicate the concept of a Humbucker pickup but with microphones instead of guitar pickups?
(And if so, will it actually make a difference? Is the perceived interference I'm getting actually from the microphones themselves, or another source such as wiring?)
Best Answer
A humbucker guitar pickup is intended to directly cancel the induced voltage caused by magnetic fields. The magnetic fields that a guitar is susceptible to will be barely a problem for a microphone because the coil is normally much smaller and shrouded by ferromagnetic material that would cause external alternating magnetic fields to bypass the coil.
A guitar pup on the other hand, has an "open" sensitive area in order to project a static magnetic field that can be "modulated" by the movement of the "iron rich" strings. It is much more susceptible to hum because of this.
If a microphone is picking up a lot of hum then, the first question to ask is if the cable feeding the microphone is balanced and is the microphone driving a balanced signal. I suspect that the answer here is no because clearly, an electret is a polarized microphone and one end needs to connect to ground whilst the other end feeds the signal to the amplifier.
I'd try using a conventional moving coil microphone and a balanced cable and balanced input module. A guitar produces an unbalanced signal and the amp is also unbalanced (because it doesn't need to be balanced).
If the magnetic field hum were picked up by the electret - you'd have to use another electret and invert its signal in order to cancel the main microphone's hum but, the problem you have here is that both microphones need to be in close vicinity to "receive" the same level of hum and this means acoustic cancellation and therefore poor levels for the signal you want to keep.