I have a Fishman Presys preamp. I need a schematics to repair and adjust input amplifier for a new piezo pickup. Why there is no schematics or a service manual, but there is a chinese fake of 11$?
I strongly suggest you leave your preamp alone and instead construct an additional preamp for the piezo pickup.
It will need to be a very high input impedance - more than 1 meg ohm but the sensitivity doesn't need to be high as the output of a piezo cartridge is typically 500 mv to 1100 mv, almost enough to produce a usable output from the amplifier directly into the line in...
The gain of the piezo preamp need not be great, merely enough to provide enough drive to match the line input, but it should provide RIAA correction - google will find plenty of active and passive circuits for this.
The current required for such a simple circuit is so small battery power would be a good choice for simplicity as it will simplify screening and cut hum and other interference to a minimum.
Fishman Loudbox amplifier rattle sound on bass notes
Either the speakers have loosened from the faceplate, or one or more have blown. Open the amp and tighten them down. If that doesn't fix it, remove them a take them to the nearest speaker repair shop for a checkup. If blown either have them re-coned or replace them.
Sound gets real staticy and cuts out a little
It sounds like the cord has gotten some stress at some point and damaged the wire inside. Start at one end with your fingers (while on) bending it back and forth, and work your way down the wire until you affect it, that should locate the bad spot. The only fix then, is to cut the wire, peel back the outside coating and remove the bad spot and put back together with black tape. (Or heat shrink tubing would be a better and much neater job) There should only be 2 wires inside the coating, it may have 2 inside the shielding (outside braid that goes around everything) This outside wire should be connected to ground to keep out static noise.
Crackling through amp occasionally
There are only a few things that could be responsible for your problem. Dirty volume knob on guitar or amp. Faulty ground on all affected parts; including cables. I suggest you plug into a different amp with a new chord, and see if the problem still exists. This way you can quickly eliminate compnents & focus on the actua lproblematic one. If it still exists..you can assume it'sin the pick-up.
Humbucking pickup not working
Did you solder the wires to your plug well?Did you place the pickup as in the manual?Did you connect it to the preamp?Usually the pickups for acoustic guitar need preamps to work with guitar amplifiers because the signal they produce is low.
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