Piezo failure experiences ( Solution: add dedicated Ground Wires!)

Started by Elantric, October 22, 2014, 11:11:47 AM

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Elantric

Excellent advice from davidb7170 below !

All matches up with my own Variax Piezo failure experiences, Dave has documented the issues  / problems very well 

http://line6.com/support/topic/9587-low-e-string-piezo-pickup-volume-way-too-low/
Quote....Can someone explain to me just what's going on physically that creates this phenomenon of piezo saddles cutting out mid gig? Is it a bad connection?. Possible piezo damage? Wear and tear due to Whammy bar usage? It seems to be a relatively common occurance. Seems odd that it seems to occur mostly on the E string.

On my first Variax 300, I had a problem with my B-string piezo going dead on hot humid outdoor gigs. On my JTV-59 I had my A-string piezo go silent when I was playing in humid conditions in it's first year 2011 -- when I would bring it inside to air conditioned and reduced humidity, it would magically work fine.... The 59 bridge had a corrosion issue that L6 did a slight redesign and change of hardware vendor to the Korean factory -- this was one of their early QC problems they had to deal with. They sent me a replacement bridge, and it has not corroded or had a loss of signal on it's piezos, since then. My 69S bought in October 2012 has never had the issue.

My opinion is that the piezo design has a single wire lead -- the "hot" or signal lead is soldered to the little printed circuit (pc) board under the bridge. The ground return to complete the circuit is achieved with the metal case of the piezo being in contact with the grounded bridge. When my 59 bridge corroded, that ground contact became less conductive -- resistance would build up, and the signal would fade away to nothing when it was very humid...

One thing I noticed while replacing the bridge was that there are 2 solder pads per piezo element on the bridge pc board -- one for hot and on for ground. The piezo lead is soldered to the hot signal pad, and nothing to the ground pad. If I used a hand held hair dryer, I could coax the piezo back to operation by drying out the humidity from it, but it was a big hassle to do & rather embarassing to boot in the middle of a job. I actually had to do it when we had an outside gig at dusk, and dew settled in... not cool. No problems and no corrosion since replacing the bridge.

If you sweat when you play, like most people do, it could be that you might have some salts or moisture getting into and adding resistance into the contact area between the metal case of the piezo element and the bridge. That is it is on you low E string might make a certain amount of sense, as that would be the most likely side of the bridge to rest your hand for palm muting, etc. -- it is for me. I don't have an easy answer for how to get that fixed other than unsoldering it and getting any corrosion out of the bridge piece and off of the piezo. I at one time toyed with the idea of soldering a ground lead on the piezo metal case and then to the unused ground solder pad on the bridge pc board, but have not done it, as I have had 3 hot humid summers of use with my 59 since I replaced the bridge, and 2 summers with my 69S and not had it happen....

I made use of the forum when it was happening to me, and really only found 1 other guy with the same problem, so I don't believe it is a widespread issue. If you are with in warranty you should probably work with Line 6 with a trouble ticket. The fact that it works sometimes but not others indicates to me that it's a contact issue. If a piezo just fails, it would not be in and out, it would just be dead, period....

My 2 cents.
Dave

Elantric

And some advice on steps to add a dedicated Ground Wire to each Piezo saddle - to solve the "dead string" after sweating phenomena
http://line6.com/support/topic/9587-low-e-string-piezo-pickup-volume-way-too-low/

Sdhirsch wrote>
Posted 25 October 2014 - 07:39 PM
I'm pleased to say that my problem with the bottom E string was poor grounding.  This morning I removed the bridge/tremolo assembly from the JTV-69 and had a very close look.  The transducers are just breathtakingly chintzy.  They're stamped out of sheet-metal with the piezo element potted in epoxy.  There's a single wire connected to a small PCB on the lower part of the assembly and ground return is strictly through a very iffy sequence of mechanical contacts: transducer --> bridge piece casting --> adjustment screws --> plate --> lower assembly.  The good news is that you can, indeed, solder ground wires to the transducer and I'll describe the process as best I can.

The signal wire emerges from the potting compound at one end of the transducer body.  At the other, there is a small "tab" that's an artifact of the stamping process.  Trick is to take a Dremel grinder with a dental-sized grinding bit and remove a very small amount of the epoxy that lies immediately on the inside of the tab.  Surface tension causes the epoxy to climb up the tab while it's setting and this is all you want to remove - perhaps 1/32".  If done carefully you don't get anywhere near the element.  With the transducer clamped lightly in a metal-jawed hobby vise to draw off heat, put a tiny dab of flux on the inside of the tab and tin it with high-grade electronic solder.  I used a temperature-controlled solder station, but any small iron should be fine if you work quickly.  Then, strip the end of a piece of Kynar 30g wirewrap wire, tin it and carefully tack it to the inside face of the tab.  If you have removed enough epoxy, it's possible to bend it around the tab to help hold it in place while you apply heat.  After the joint cools, trim any projecting length of wire with a pair of diagonal cutters and carefully file off any solder buildup on the outside of the transducer body.  If you don't get all of it, you will have trouble getting it back into the bridge piece.  The ground wire can be dressed across the bottom of the potted area and routed out the back of the bridge piece alongside the signal lead (plenty of room).  This process is not rocket science, but it isn't a whole lot of fun either, particularly with 63-year-old eyes :-).  Definitely do NOT try this unless you have at least intermediate bench skills - this isn't a good candidate for "My first electronic repair" (I've been doing this stuff for more years than I like to think about...)  As others have observed, there are six ground pads on the PCB all ready to receive these wires.

After doing all six pickups, I reassembled the guitar and discovered to my delight that not only was the low E issue gone, but everything sounded better.  I've been thinking there was a slow, steady degradation in the sound of the modeling and that seems to have been exactly the case.

I'm glad that Line6 is saving themselves perhaps all of $5 in production costs by not using pickups with hard-wired ground return, but after this experience I can say authoritatively it was a poor decision.  Hopefully this is an area where Yamaha can help.

Another observation:  If I was responsible for the design of that bridge and tailpiece assembly, I sure as heck wouldn't put my name on it.  Let's leave it at that.


JTV-59 Bridge (Bottom View)


JTV-69 Bridge (Bottom View)



mbenigni

This is why my interest in Variax instruments waned over the years.  God bless Sdhirsch for figuring this out and documenting his work, but about halfway through reading my eyes glazed over and I got that "this is someone else's job" feeling - namely, it should have been Line 6's job.  Love their designs but - especially where a guitar is concerned - execution is equally important.

Elantric

Its important to know similar strategies as Sdhirsch describes of adding a dedicated Ground Wire will also make other types of Piezo Saddles (Godin's with RMC Piezo's) more robust.

Variax is not the only guitar with hex piezo saddles with questionable Ground signal path!

IT seems to be a universal mechanical design strategy of assuming a metal Bridge saddle will deliver consistent contact with the electrically Grounded Bridge  - but the reality is many designs have a bizzare piezo saddle Grounding method. My Variax 700 Acoustic employs an electrically conductive Graphite saddle holder at the Bridge  - which exhibits 300 ohms for all Piezo Ground connections - Making mods to the saddles and adding dedicated soldered Ground wires to each Piezo saddle improved reliability of this Guitar 1000%

HAMERMAN409

Marc - if you ever want to go down the Variax road again I could do these mods for you. Wont cost you but a few beers. :-)

mbenigni

QuoteMarc - if you ever want to go down the Variax road again I could do these mods for you. Wont cost you but a few beers. :-)

Thanks for the offer!  I still have a Variax bass and a 500 transplant in the basement - both in need of repair - but I wouldn't want to subject you to the tedium.  The beers, on the other hand, sound like a great idea.  Fatherhood has turned me into a complete homebody, but my door's open if you ever want to visit.  :)

BigJase

Thank you for this post. I am experiencing the same issue with my JTV69. Especially with humidity. Electrical contact spray resolves it for a while.

To clarify you did solder these back to the ground terminals on the PCB?

Cheers,

Jason

Elantric

Quoteo clarify you did solder these back to the ground terminals on the PCB?

Correct. Follow all details starting at the first post.

skeletonpete

Hi -

Can I expect to find a similar piezo ground layout on a Variax 600?

My "back-up" guitar was intermittently loosing volume on the low E and A strings. I was able to "revive" them with DeOxIt, but several months ago the low E string just went out. I've fiddled with the bridge and pushing down on it (hard) brings the string back, but of course that is not a solution.

Are there any similar photos of the Vax 600 internals? I haven't been around a soldering iron in ages, so I'll likely have to bring this to a luthier I know who has some VAX experience. Any graphic that explains what I'd like done I'm sure would be helpful.

Honestly I'm on the fence about a repair or looking at the Boss GP-10 as a replacement for my Variaxes and Line6 POD XTL. I've got GK3's mounted on both my VAX600's which I could transfer to other guitars in my collection and I have a Brian Moore iGuitar that I rarely use. I assume I can split the 13 pin signal and drive the GP_10 and my GR-33 from one output.

Next gig is in a couple of weeks so I'll probably mount a GK3 onto the VAX 300 I was keeping around for parts. It's the only one of my 3 VAX's that is working flawlessly at the moment. No doubt because it hasn't been played much.

Any thoughts or suggestions greatly appreciated.

Thanks,
Pete
SkeletonPete Blog
"It's Stuff We Like, You Might Too!"
http://www.skeletonpete.com

Elantric

The Variax 600 shares bulk of components with a Variax 300. See pics here:

http://web.archive.org/web/20050215134311/http://www.vettaville.com/variax-photos.htm

Also worth watching


skeletonpete

Thanks for photos and info. It's pretty clear neither I nor any of my friends have the expertise to do this fix. My first line of defense for the next gig will be to simply mount a GK3 on my Vax 300 and have it as an "oops, broke string" back-up to my main guitar, my white Vax 600 will require a visit to the shop sometime down the road.

BTW, is there any info as to whether or not the new Yamaha/Line6 "Standard" Variax design fixes this grounding issue?

Best,
Pete
SkeletonPete Blog
"It's Stuff We Like, You Might Too!"
http://www.skeletonpete.com

Elantric

QuoteBTW, is there any info as to whether or not the new Yamaha/Line6 "Standard" Variax design fixes this grounding issue?

No change in Variax Standard - Line-6 still does not consider this a problem - they suggest:

Don't play Variax with wet sweaty hands

skeletonpete

Quote from: Elantric on June 10, 2015, 09:07:39 AM
No change in Variax Standard - Line-6 still does not consider this a problem - they suggest:

Don't play Variax with wet sweaty hands

Thanks,

That certainly saves me any further research and any consideration that I'll own one.

Pete 
SkeletonPete Blog
"It's Stuff We Like, You Might Too!"
http://www.skeletonpete.com

mooncaine

I completely agree. I found this thread because of a sudden whim to maybe get a Variax, but I heard enough. None of that for me, thanks. I appreciate having a chance to learn from you experiences. Really, thank you.

Beirne

What exactly was your mod on the Acoustic700 plastic bridge?
Ive replaced various piezos 3x on mine.
Just recently, I unplugged the bridge and worked a newly dead B string peizo a bit without unsoldering it and it came back on. Assume it was just enough corrosion to cause a dropout??

Quote from: Elantric on November 03, 2014, 01:18:12 PM
Its important to know similar strategies as Sdhirsch describes of adding a dedicated Ground Wire will also make other types of Piezo Saddles (Godin's with RMC Piezo's) more robust.

Variax is not the only guitar with hex piezo saddles with questionable Ground signal path!

IT seems to be a universal mechanical design strategy of assuming a metal Bridge saddle will deliver consistent contact with the electrically Grounded Bridge  - but the reality is many designs have a bizzare piezo saddle Grounding method. My Variax 700 Acoustic employs an electrically conductive Graphite saddle holder at the Bridge  - which exhibits 300 ohms for all Piezo Ground connections - Making mods to the saddles and adding dedicated soldered Ground wires to each Piezo saddle improved reliability of this Guitar 1000%
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