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Fishman Powerbridge Buzz


Dylan
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Hi everyone,

I really, really need help.

I'm 15 and I'm building a solid body electric guitar for school. I'm almost done, but I've been frustrated at this same place for about a week. My problem is this guitar has a Fishman Powerbridge that I can't get to sound right.

The bridge piezos won't stop buzzing. When I am not touching the strings or other grounding metal, the buzz is rather loud, louder than a bad ground buzz, and no other sound is coming out of the guitar. When I touch the strings, the buzzing gets louder, like touching the tip of a guitar chord that's plugged in. Still no other sound though. When I touch the strings and the body of a volume pot in the wiring cavity (where all the grounds are tied to), the buzzing goes away slightly (still mostly present), and the actual sound of the strings can be heard how it should be, only still with a little bit of buzzing.

I have had quite a bit of experience in guitar wiring in the past two years, but I've never encountered a problem like this. I just don't understand how or why this is happening. I've redone the wiring twice myself and had my brother (who has more guitar wiring experience than I) rewire it once. IT STILL BUZZES! ARG!

What can I do? There are no liscenced guitar techs in the area and I have to have this guitar finished by the end of the semester, coming up soon. Please, have any of you ever heard of this problem or have any wisdom as to what I can do?

Thanks so much,

Dylan

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Yeah I can draw up a wiring schematic... it'll take a minute. The output is just one hot wire summed from all six saddles and a grounded shield around this hot wire. Supposedly, the shield is the common bridge ground as well, but I'm starting to think that may not be the case.

Ill draw up that schematic.

Thanks,

Dylan

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If you have a multimeter, you can easily find out if the shielding is actually the common ground. Lay one end of the multimeter(set to test continuity) on the string notch of the saddle(or just on the string itself) and the other end on the bridge ground. Once you get us a schematic, we'll be able to be of more help.

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Ok, here's the schematic... let me know if it doesn't make sense:

intrpy.gif

Unfortunately, I don't have a multimeter... I've gotta go to Radioshack soon. :D

EDIT: By the way, I only have one mag p/u and there is no volume pot for the powerbridge because I simplified the wiring to the most basic thing for testing purposes. Also, the humbucker works great.

Thanks,

Dylan

Edited by Dylan
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Here's what I see so far. First, you're using a spdt switch, but you've got stereo output. If you want to have stereo output and be able to switch between piezo/magnetic/and both, you need a dpdt switch to keep the signal isolated from one another. Also, you have the magnetic output and piezo output going to the tip and ring before the switch. They need to go to the switch, then the output. The way you have the switch wired now, you get either no signal, piezo signal, or magnetic signal. Is that what you want? Other than that, I don't see any problems. Truthfully, I can't see what would be giving you that buzz. You need to check to see if your've got a ground signal on your strings. That could reveal something. Also, you're using a stereo cable, aren't you?

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Disconnect everything but the piezos (leave the bridge ground, but disconnect the mags and volume pot completely), and temporarily hardwire them to the tip and sleeve of the jack - if the hum goes away, you've got some kind of ground problem when both the mags and the piezos are wired in. If it doesn't, your Fishman has a problem. Is that bridge designed to run passively without at least a buffer in front of it? If the Powerbridge's output impedance is too high, even a 500K volume pot may be loading them enough to seriously compromise bandwidth and signal-to-noise ratio.

Oh, and before I forget, the way you've got that volume pot wired, when you turn it down, it'll turn down the piezos also. If you don't want that, reverse the two red wires on the volume pot.

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I guess this is a very hard problem to diagnose because the wiring isn't standard for a normal electric guitar. First of all, thanks very much for your immediate help. However, this wiring diagram is exactly how Fishman says to wire it in their manual: The volume pot (which does only adjust the mag), the way the switches are connected to the jack (which, though wired oddly, does give me signals), the Powerbridge being directly connected to the jack without a buffer, even the switch being spdt. I don't think I've done anything differenly from how they told me.

If you're interested, the pdf manual is right here:

Installation Guide

Yeah, I'm using a stereo cable. One thing I just tried was, like you said, just connecting the Powerbridge to the jack alone, and I still have the problem. That means it's a problem with the bridge itself or the wiring of the piezos in the little chip underneath the bridge...

I guess I can't go very much further without a multitester anyway.

Thanks again,

Dylan

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It came with all the wiring at the bridge factory done, such as the piezo saddles being summed to one hot wire and the ground/sheild being soldered a pad. I need to figure out what that pad is actually connected to, but I can't the chip off the underside of the bridge.

How does that Schaller bridge sound? Could I have a link to the one you have?

Mine came with a 1/4" stereo jack... which seems a lot more useful than that 1/8" jack, eh?

-Dylan-

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Well, if it is, infact, wired exactly the way that fishman specifies, either you didn't shield everything well, fishman made a bad schematic(although it looks to be ok), or you've got a bad component somewhere. Once you get a multitester, you can test for resistance on the humbucker and continuity on everything else. That should turn something up.

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No, Fishman's schematic is great - I just couldn't read yours.

Haha, sorry. I'm not the best photoshop artist on short notice.

Does the humbucker buzz when it's selected?

No, the humbucker sounds great. Actually, it is almost silent as far as buzz and unwanted noise go, which was a surprise to me because it's a lot less noisey than my other electric guitar, a Gibson SG.

I'm getting a multitester tomorrow. I'll post the information that I get with that tomorrow night and hopefully you'll all be able to help me interpret it, right?

Thanks,

Dylan

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Haha, sorry. I'm not the best photoshop artist on short notice.

No worries - happens to the best of us. So, just to clarify (remember, I'm an old guy :D ), the Powerbridge buzzes even when hooked up to the tip and sleeve with nothing else connected? How about with a mono cord? I don't mean to ask the same questions over and over, I'm just trying to make sure I've got the symptoms right.

...you'll all be able to help me interpret it, right?
I hope so - we haven't lost anybody yet! :D
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Yeah, the thing still buzzes when it's just connected to the jack alone. I tried this current jack and another extra stereo jack, so it can't be the jack; it must be the bridge. A stereo or mono cord (I've tried a few) makes no difference. MUST be the bridge.

I had a ski meet today that I forgot about so I didn't get a chance to get my hands on a multitester, but I will try tomorrow. It's hard when you don't have your license. :D:D

-Dylan-

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Alright guys, I tested the continuity with the multitester today... no continuity between the strings and the common ground. That was the problem, so I just ran another standard common ground wire from the grounds in the cavity to the bridge, and it worked. I shouldn't have assumed that the shield from the piezo was the common ground. I don't think the pad it was soldered to on the bridge end was even attached to anything, but I couldn't really look under it to see.

Ah, well. It was a simpler problem than I thought it was. Thanks for all your help!

I'll post some pictures of the newly finished guitar (101 and a half hours in the making) in the In Progress and Finished Work when I get the chance.

-Dylan-

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