Hi all, found an old ampage thread about adding a high impedance buffer to the GE7. The author describes the mod as follows:
"I wanted to use a common Boss GE-7 pedal for a piezo preamp. It has an input impedance around 500kohms, one tenth of that which would be a good match for a bare piezo. Unfortunately, the input shunt resistor is part of the IC, so it wasn't possible to simply replace a 470k resistor with a 4.7 megohm unit. R.G., Gus, and others suggested adding an FET buffer to achieve the desired high input impedance.
Well I finally got around to doing the surgery on a GE-7 pedal. The buffer is a 10kohm source follower, using a 2N5457 with a 4.7meg gate resistor and a .02uf gate isolation cap. My prototype circuit was built on a perf board, about half the size of a postage stamp. There's just enough room to sandwich it between the input jack body and the top of the case. "[username 'Doc']
Well, AFAIK, the pedal has a standard 1M imput impedance, and I'd like it to be 5M or 10M. Main problem is, I can't quite picture the circuit described above. Can anyone give me a hand, please? The author thought it worked well. They also described it as being on as long as a jack was inserted, whether pedal was on or bypassed.
Here's the GE7 schematic for reference:http://www.hobby-hour.com/electronic...-schematic.png
Jim
"I wanted to use a common Boss GE-7 pedal for a piezo preamp. It has an input impedance around 500kohms, one tenth of that which would be a good match for a bare piezo. Unfortunately, the input shunt resistor is part of the IC, so it wasn't possible to simply replace a 470k resistor with a 4.7 megohm unit. R.G., Gus, and others suggested adding an FET buffer to achieve the desired high input impedance.
Well I finally got around to doing the surgery on a GE-7 pedal. The buffer is a 10kohm source follower, using a 2N5457 with a 4.7meg gate resistor and a .02uf gate isolation cap. My prototype circuit was built on a perf board, about half the size of a postage stamp. There's just enough room to sandwich it between the input jack body and the top of the case. "[username 'Doc']
Well, AFAIK, the pedal has a standard 1M imput impedance, and I'd like it to be 5M or 10M. Main problem is, I can't quite picture the circuit described above. Can anyone give me a hand, please? The author thought it worked well. They also described it as being on as long as a jack was inserted, whether pedal was on or bypassed.
Here's the GE7 schematic for reference:http://www.hobby-hour.com/electronic...-schematic.png
Jim
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