Re: Sustain

[matthias@bahianet.com.br (Matthias Grob)]

>>However, the guitar is going (used) for $900.  No way.  I've got to build
>>me one of these....  somehow!
>
>I've never gotten around to checking out the circuit in mine, but I 
>suspect
>it is pretty simple. They just take the signal from the bridge pickup,
>filter it, and use it to drive the neck pickup in reverse. Just as strings
>moving in the pickup's magnetic field produces an ac voltage at the output
>of the coil, applying a signal voltage to the coil output will cause the
>motion of the magnetic field to move the string. NotRocketScience (tm). 
>You
>need to make sure you get the pickup placement right so that you drive the
>string in phase.

Sure I tried it, years ago. There are problems I did not have the patience
to solve:

1 To keep the correct phase for any note is not easy.

2 To drive, you need power. Either a higher tension than battery or a low
impedance pickup (DIY?). In any case, its hard to keep the strong driving
signal separate from the outgoing sound signal. If you bring the supply to
the guitar, keep the ground separate. If you bring the driver signal to the
guitar from a external amp, shield it separately.

3 The driver tends to feed back directly to the pickup. To avoid it, you
need to limit its energy, make it more effective through filtering or build
it in a specific way so it does not stray the magnetic field.

But... go ahead and find out!

Matthias