Looks like you might get the sustainer bug if you don't watch out Jaicen_solo...lol
I haven't looked at the patents for a while...there are a lot. Sustainiac uses class D to save on power. The ebow the old LM386. I'm sure there are better circuits that could be fairly easily devised. Fernandes also uses a preamp to allow the driver to work as a pickup (possibly with an auxillary coil). Although many have proposed magnetic shielding...it looks as if Fernandes has abandoned that on current models. Fernandes also used to place the driver coil/s on their side! Sustainiac also used to use dual, phase cancelling coils but now appear not, Sustainiac still do. The floyd Rose patent is more specific about how they have implimented phase compensation circuitry. It is a fact that much of what is patented has never seen production. If anything, the devices are getting simpler!
I too thought that the guitar should may as well be active, or at least the power be continuously connected while plugged in. With the idling idea you could well find that a single 3 way switch could activate the two modes (driver phase reverse) and off (driver disconnect) which would be a neat installation. In future I would not incorporate the sensitivity knob at all (replace with a trimmer) and i note that Fernandes now do the same. Many people don't want an active guitar and the power issue did seem to be of more importance. A device like this will use up batteries, it's not just a signal processor...but it's onboard status makes it impractical to power with anything else. Fernandes alway used to use two 9 volts and was difficult to build in. Presently they claim 72 hour operation BTW.
I experimented a lot with magnetic shielding with limited success. It certainly is an option though making it could be tricky. I incorporated driver coils in U shaped channels, encapsulated them in ferris epoxy...all kinds of things. Reorienting the coil and magnetic fields is another idea. Many of the hex drivers actually had cylindrical coils and balanced magnetic fields. These coils pulled the string from side to side. A dual coil system is very attractive too as it would put out equal amounts of phase reversed EMI.
Now, instead of the amplifier pushing and pulling the string by equal amounts, it can be set to pull and release the strings.
I also did some work and there has been a fair amount of discussion over the pulse width modulation. One idea was to simply cut negative waves from the signal. It worked but...no better. Theoretically, the coil being always driven into one magnetic polarity will have difficulty letting go that state between waves and will shortly magnetise in that direction. The negative waves, along with the permanent magnet, help to pull the driver's state through neutral between pulses. In short, without the opposing wave the device has trouble pulling and letting go! This is vital with higher frequencies as the driver can only respond so fast. I tried to address this with different core materials and found that a core material like ferite was excellent (used in hex drivers a lot) in terms of speed as it transmits but doesn't hold a magnetic state (as steel does for instance...hence it's use in inductors).
I'd love to see some ideas on mosfet buffers and other circuit concepts. There are a lot more modern and efficient chips than the old LM386. The driver's are still evolving. By people making there own variations the thing will evolve faster than one guy (like me) working on their own. My proposal of the "thin coil driver" has shown to be novel and a very effective, and practical solution. It's small and compacts it's energy right up close to the strings...it's size and shape also effects it's response time. As far as EMI issues it really has not been installed enough for the variations and switching problems to be fully explored.
With my working guitar it is perhaps a little more of a special case. Highly suseptable true single coils. My driver is actually built on top of the neck pickup and shares it's magnet...so it's configuration is very much like a transformer. It also has a mid pickup. All the same, other experiments do suggest that non-used close by pickups do need to be completely lifted (much to my surprise and annoiance I can assure you).
In some recent stuff on fernandes (posted on the thread recently) I see they run everything to the circuit and back out. It could be that they use electronic switching (what I would like to have done) to run everything. I think I counted at least 24 connections running in and out of their circuit to various components inside the guitar.
As other pickups are off when the device is operating anyway, I'd prefer to see a single pickup guitar, with neck driver...and if you are going to leave the thing on anyway, make it active and incorporate some nifty active filters to compensate for the loss of other pickups (if you must).
Great contributions and I hope to see you sustaining away in the near future and contributing even more to the evolution of this kind of device. For sure, the involvement in making something like this will puzzle and delight you, besides getting you a new kind of expression from the guitar...welcome aboard, all those who are coming aboard...psw