Acoustic under saddle pickup (piezo) grounding hum problem

[John]

I have an acoustic 12 string that has an undersaddle piezo pickup.  I didn't use the guitar for a few years, and now that I'm using it again, it has a low-ish frequency hum.  This hum goes away when I touch the input jack or the guitar cable jack.  It's not really loud, but it's enough to get on my nerves and I'm not sure I'd want to have this much hum on a gig. The preamp of the guitar has an onboard tuner, and when I engage it, the hum goes away.  The preamp has V/B/T and it's the bass control that causes the buzz to be heard. Maybe I need to turn down the bass on the guitar, and turn the bass up on the amp....but what a hassle.

I didn't have this problem when I used the guitar a few years ago.  (again, it sat in a case for a few years)  But one major difference may be that I used to use a Fishman Aura DI box, and that may have dealt with the ground hum issue. But now, I'm no longer using the Fishman DI box.  Going straight into an amp.

My internet searches are coming up dry.  One internet person said he removed his saddle, lightly scrubbed the copper pickup/ribbon and reinstalled the pickup....and that worked for him. 

I have several other guitars with pickups.  None of them make the hum...with the exact same cables and amps.  Two of these guitars have the LR Baggs Anthem pickups which have an under saddle ribbon, in addition to an internal mic.  Neither of these guitars hums, even though they have an under saddle ribbon. 

I don't know what to make of this.  I don't know if the hum is because I no longer use the DI box.  I don't know if something corroded when the guitar sat in a case for a few years.  I don't really want to spend the money taking it to a tech, because the guitar isn't worth all that much.  It's a Seagull.  Serviceable gigging guitar, but nothing special. 

Can anyone offer any advice?

[premiumplus (Dave)]

It may be that you've got some corrosion on the guitar's input jack. You might try cleaning it with DeOxit. If you are careful you could saturate a Q-tip with it and make sure that it's wrapped tight so you won't leave any cotton fibers behind...or a .22 caliber "mop brush" is the perfect size for cleaning 1/4" jacks.

If you used the DI to go straight to the mixer (via XLR output), it automatically lifts the ground. That may be it as well.

[John]

I don't have DeOxit....but I have a 22 caliber metal brush. It's not the mop brush you mentioned, but I figure I can try scraping the metal brush around inside the jack and see what happens.

And yes, the DI box went straight into the mixer.

[premiumplus (Dave)]

I'm betting on the DI box, I looked at the instruction manual for it and they say that it automatically lifts the ground for XLR output.
Please go easy with the brush, it's easy to knock plating off of a jack.

[GuitarZ]

If you caught my re-amping thread in the recording session, I ran into a similar issue. I popped on a low-to-high impedance transformer and the hum went away. So, I would also lay some money on the DI box (although my DIY re-amping had shielding issues).  I think getting some Deoxit to clean up the jack is a good idea above..  It's worth having around.

I did a little google.  I didn't think hum would be an acoustic guitar issue.  However, I did find some stuff.  The first thing that caught my eye was a YouTube video where a gent was installing a shielding plate inside the guitar under the pickup.  That sounded a bit overkill to me until I came across a discussion about Taylor installing them in one of their guitars and selling the kit.  Hmmm.

Also, in a different thread, a person reached out to Fishman (or someone like that) whose reply was that the shielding on the pickup had possibly deteriorated and that the pickup should be replaced.  Here's an article where the person did swap out the pickup and solved the problem.  There's also some good discussion below the article:  www.thegearpage.net/board/index.php?threads/fishman-prefix-plus-60-hz-ground-hum-problem.2173264/

Here's a YouTube with Taylor adding a shielding plate: 

I'm not suggesting you go the plate way.  It doesn't sound like it would be worth it for how much you use the guitar.  Just shared it to better understand the possible issues.

Seeing all that above, I'd definitely try the deoxit first to make sure that it's not simply a bad connection to ground.

[runninwiththerevil (Matthew)]

I've learned to start simple. If you didn't have this issue before I would try either switching the battery or even just take the current one out and put it back in. I know none of that is rocket science, but I have wasted a lot of time researching solutions only to find it was something really simple that fixed it all.

I also finally got some detox for like $5 at Harbor Freight.  They call it something else, but it's the same stuff.  Contact cleaner or something.  

[John]

I finally messed around with the guitar and the amp...without the DI I used to use. I think I've got it to a manageable level. It's still there, I know it's there....but it seems to be tolerable, or at least I think so. I'm wondering if I'm being over sensitive about the whole thing. I'm doing this in a quiet basement where you can become aware of even the slightest things. I wonder if anyone at a gig will even notice, much less care. We've all been in a room where a strat is buzzing away like a tornado siren when there's UV lights in the room. My situation isn't anywhere near that. Not only can you not hear it when I play, but I question if anyone (even me) would hear the buzz in between songs when I'm gigging.


So I need to go back a few times and be realistic about whether this really is worth 'fixing'. It could be additionally manageable with things like:  If I'm going to talk to the audience in between songs (or anything else that keeps me from immediately starting the next song) I could easily take my right hand and touch the input jack (to kill the hum) as I speak.  Problem solved.  (well, sort of)

["Z" Steve]

John, be thankful that you can't hear grass grow like Eric Johnson! On the other hand, if you know it's there it still might bug you, so trying to eliminate it completely may be worth the chase. You may think twice about taking that guitar to a gig.

[John]

Feb 8, 2022 9:05:58 GMT -7 "Z" Steve said:

John, be thankful that you can't hear grass grow like Eric Johnson! On the other hand, if you know it's there it still might bug you, so trying to eliminate it completely may be worth the chase. You may think twice about taking that guitar to a gig.

Thanks...just what I needed to hear!!!  ha ha

The guitar in question is my 12 string.  I only use it for a few songs each gig.  I take the last few songs....or the first few songs....of a set and play them on the 12 string.  So I'm only switching guitars ONCE a set.  I can easily play a gig without it, but I like it and I feel it lets me offer the audience something different than the same ol' 6 string all night long.  I also have a ukulele with a pickup in it...that also lets me offer something different.  You haven't lived until you've heard Beatles songs on the ukulele.

[GuitarZ]

John- I think you have the right approach.

But, Dang! Apparently your hum is contagious. I was just jamming to some tracks and all of the sudden my Maz Jr developed a substantial hum. What? I turned off a fluorescent light. Turned down the guitar and then unplugged it.

I was scratching my head. Finally turned down the reverb, and it's gone. Contagious Hum!