I am working on an acoustic guitar with an under saddle piezo pickup running to a side-mounted active Shadow P3-Pro Preamp/EQ box. The shielded wire from the piezo is there - but the wiring that runs from the box to the output jack has gone missing.

The missing wire should connect to the preamp via a 1/4" plug. I know there are usually three wires running to the active output jack, with one disabling the battery when a plug is not in the output jack. 

Does anyone have any idea what I need here? I tried a standard stereo headphone plug and wire, but that did not seem to work. Would a mono plug work? Where does the third wire come from?  I cannot seem to find any info on this. I would appreciate any input anyone has.

Steve Wilson

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I just fixed a uke with a Shadow preamp. The undersaddle pup plugs into the preamp with a metal mini jack, the output to the endpin jack has a white and red wire and a shielding ground. The wires from the output jack attach to the preamp via a small white plastic plug. The output jack is a stereo switchcraft, white goes to the tip which on this jack is the shorter of the 2 terminals. The red goes to the longer terminal which is the ring of the stereo jack. The ring shorts to ground when you plug in a mono cord, completing the grounding circuit of the battery, and subsequently powering the preamp.

Thanks Harrison,

The preamp has a 1/4 inch jack to plug into that would connect to the endpin jack like yours. It is the plug and wire itself that are gone. I have never had to replace just the missing plug and 3-wire set. Would Radio Shack have such a 1/4" plug with three wires? I cannot seem to find any from the guitar electronics sellers.

StewMac, LMII and AllParts carry supply them via mail-order, Fry's carries them if there is one near you. Everything I get from RS breaks so I personally dont go there anymore.

I am finding lots of endpin jacks and complete active units on the sites you mention, but not just the 1/4" plug with three wires, or even a new endpin jack with wires and 1/4" plug. Maybe I will call Stew Mac or LMII tomorrow. I appreciate your help, Harrison! There is a Fry's about a half hour from here if it comes to that.

You have to wire the jack yourself

Can do!

I just realized I have been saying there was a 1/4" plug on the preamp - what I meant to say was 1/8" mini plug - and that is the plug I am looking for.

This is what I am looking for - 1/8 " plug with three wires - with or without output jack. This picture is part of a complete active preamp piezo unit I found. I cannot find this available alone.

Sorry if I misunderstood your questions, the pic makes it clear. Cheapest and quickest way to achieve your objective is to drive to Fry's, buy a 1/8 mini stereo male plug, 2 wire shielded cable if you dont already have some and the stereo 1/4 female jack and wire it up. Another slower option is to get the part ordered from a music store that deals with Shadow and buy the prewired harness. If the is room to install an all metal Switchcraft 1/4 stereo jack, that would be prefered to the plactic one in the pic.

No problem, Harrison. I wasn't very clear in what I was trying to say.

Fry's it is. Thanks for your help!!!!!

The three wires are: signal from preamp, ground for the preamp circuit and ground for the battery. The battery doesn't work until it goes to ground. The 1/4" output jack is 3 conductor or tip ring sleeve. The tip is the signal from the preamp the ring is the battery ground and the sleeve is the ground for the preamp circuit. When you use a mono 1/4" plug the ring and the sleeve are connected allowing the battery to go to ground. 

You need an 1/8" stereo plug, 1/4" stereo jack, some 2 conductor wire with shield and a bench amp. Wire the 1/8" plug with the shield on the longest leg and the other 2 wires on the remaining lugs. I have a cable with a 1/4" mono plug at one end and 2 alligator clips at the other, you should make one if you don't have one, but you can make do with little jumper cables.Find a way to run signal to your amp. The shield is the circuit ground so you only need to sort out the other 2, one of them needs to be connected to the shield to turn the battery on and the other is the output signal. You've got a 50/50 chance of getting it right the first time. If it doesn't work switch it around.

Thanks John.

You gave me a pretty clear picture of what I need to do.

I appreciate it!

I would like to revive this thread as I am also working on a Shadow P3-Pro Preamp/EQ box, and it seemed like a good idea to me to keep all of the info on this in one thread.  If anyone objects, please accept my apologies and I'll be happy to create a new thread...

My issue is that the black lead from the 9v battery snap pulled out of the box, and the plastic box containing the 1/8" (3.5mm) mini-jack crumbled and prevented this unit from operating.  I though that it would be a simple task to replace the mini-jack and battery snap.  Boy was I wrong!  First, I assumed that the mini-jack was mono, and soldered the preamp ground and battery ground to the ring of the 1/8" mini-jack, and the green lead from the board (which I correctly assumed to be the input-signal lead) to the tip connector of the new 1/8" mini-jack.  Then I cut the red battery lead coming from the circuit board (I didn't really wanna mess with the circuit board if possible) and soldered the red lead from the battery to the red lead from the board.  I learned from this thread that this was not quite right, as the battery would have then been 'on' all the time, but it still should have worked...

The problem happened when I went to re-mount the new mini-jack and re-assemble - every wire from the board broke free as I manipulated the jack and board during re-assembly!  I thought I knew where they all came from and quickly made a diagram for my reference, because I then decided to replace all of the wires with new copper ones to avoid a repeat of this problem.  Got it all back together and it didn't work!  I hope I didn't fry the circuit board by wiring it up wrong.

After I discovered this discussion - the only one on the web regarding the P3-Pro - I replaced the mono jack with a stereo one and wired it as suggested by John (above - THANKS).  So, I'm fairly certain that the jacks and battery are now properly connected, but I am very uncertain of the connections I made back to the circuit board.  There are two wires, one red and one black, leading from the to the (3/32" mono) input jack to the opposite end of the board from the phase-switch.  I would assume that reversing these wires would just cause a phase-inversion - no biggie since the phase switch isn't marked either.  At the other end of the board is the phase-switch, which has four connections available for the three wires that connect to it: one red (preamp +9v in), one black (preamp -9v in) and one green (output-signal).

Could someone, please, very CAREFULLY pull their working unit out and open it up to let me know which of my wires (if any?) are in the wrong holes?  Below are some photos of the board showing where I made my connections...

I'm pretty sure of which one of the connections to the phase whitch to leave open (no connection), just by visually looking at it - the one I left open looked as if there had never been a wire in it (the others had remnants).

Any help would be greatly appreciated!


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