We have discussed this option in various ways...there are some major problems...you may need to run two leads to the guitar...one for the driver and the other for the signal to the amp. Mixing them could cause a lot of problems with EMI from the cables themselves. You would also likely need more power, but this would be less of an issue as it wouldn't need to run off batteries! I looked at various ways that everything could be mounted in a surface mounted box (like a tailpiece) with a very small surface mounted driver. The problem is that you would still need (except for a single pickup guitar I suppose) major rewiring and bypass switching inside the guitar.
The photo of my "sustain box" on the LP in the above post, and pictured off the guitar here...
may appear to be just what you are talking about, but it isn't really! This is a testing device...there is no bypass switching and the driver is not permanently mounted to the guitar, nor the neck HB function properly as it is lowered so much to fit the driver on, and the other coil not compensated...that it does not function too well. It is a replica though of the driver and circuit that is in my guitar and a useful device none the less...but not really for playing. There are some sounds of the thing on the sounds thread, but it did not work as well as it does on a fully installed guitar like my strat.
UPDATE: Playing my strat just now with ulta clean sounds to get the "fizz". This is not EMI. I think that this is amplification of high pitched fret buzz and loose components and such! In order to get the harmonics to ring loud and true, the amplifier needs to be set so as to reproduce such high sounds...consequently you need a lot of treble and headroom to get these kinds of sounds. You can do it quitely with some compression for instance but this brings out the background noises (like this "fizz"). It does not sound in fundamental mode on the same settings....I think...because the full bodied sound of the whole note (not just the higher artifacts) overwhelms these things and the strings vibration is more natural. More needs to be done to look into it more fully, but that is what appears to be going on. Bear in mind also, that I am talking a very sterile clean sound...nothing very attractive about it...almost painfully brittle and high fi and not something you would naormally choose to play music with in the real world. Only a slight bit of hair (would still be regarded as clean) is required to give body to these high harmonics and eradicate the "fizz" effect!!!
So...it does appear to work ok...I wish to build another, better quality sustainer guitar in the future that will shed more light on things I guess... pete
This seems like something I would be very interested in experimenting with perfecting. I was thinking about making an out of guitar sustainer system so I didn't have to route and I could switch it from guitar to guitar, and attatch it to the strap or something. And I do just have a single pickup guitar. Do you think you could send me a schematic of your sustainer in a box system? I would very, very much like to experiment with this idea.