Help With Piezo Sound

[Ken in Dallas]

I’m looking for some experienced opinions and help with a problem:

A customer brought in a Huss & Dalton “OM” guitar into which a Highlander IP-2 piezo transducer with pre-amp was installed aftermarket about a year ago by Gryphon in Palo Alto after which the customer moved here to Dallas, Texas. Through a fully cranked up practice amp the instrument is putting out a low-volume signal with even lower highs and a pronounced low “clack” when the lowest E is hit.

I installed a fresh battery and examined the end-pin jack, which is pristine and tight. Wiggling the inserted mono plug out to the amp gave no extra sounds or change in tone. Everything inside is cleanly and firmly installed. There’s nothing connected to the extra input jack that’s part of the unit and that the manufacturer says can stay unconnected during use.

I read the manufacturer’s website end to end for technicals and installation. They made mention of some problems that could come up if the strings are not changed two-at-a-time, so I went to look for saddle binding. I’m a mic guy and not much into piezo in the mostly nylon-strung instruments I make. I did find that the saddle didn’t lift out of the slot using my fingers but did come up when blue painter’s tape was applied to it. With fingertip pressure I found it a bit tight in the length of the slot and the saddle a dash thicker and slightly tighter at the third string.

As the guitar now lives in the humid South, which could theoretically cause the bridge wood to tighten on the saddle, I buffed the saddle ends and sides so I can remove it by fingertip, but it’s not wobbly or loose in the slot. It sits squarely on the piezo element, which looks new as they day it was bought. I have not lifted the element out of the bridge slot as it looks fine and was recently working.

 

And the sound is still bad. I feel free to tell the customer that “Piezos-R-not-Us, but I hate not finishing the job. Anyone piezo savvy and experienced? Anyone know what kind of measurements I should get on my multimeter for diagnosis?

 

Thanks in advance for any help I can get. -- Ken in Dallas.

[Paul Hostetter]

The Highlander is its own case: it's a soft flexible round cable.

[Ken in Dallas]

Well..... first ,"Thank You" for the responses. Not just for the problem at hand, but for the informed pickup information from everyone. I'm going to run some experiments mounting surplus piezo elements in series with some capacitance to knock down the noise. Blended with an omni mic element, I'm curious to hear what I get.


As to my customer's problem Highlander, after inspecting, jiggling and re-installing a few times, I noticed a minuscule-stray wire poking up from the copper braiding. Tap the saddle near it, you get a huge "bang" ( not a "thump" ) but never notes from the string.. Tap beyond it towards the trebles and you get very low volume "sounds."


The element comes up through a hole at the bass side of the saddle slot, runs the slot, and then exits via another hole on the treble side. The offending wires were in the unsupported uphill section of braid hanging free just before the bend to run along the bottom of the saddle slot. And on closer inspection this area was a visible mix of the copper braid and some silver braid that appeared to be the center of the element. So it looked like it was worn, kind of like chaffing, and appeared to be shorting out there. All other sections of the element are copper braid visible only -- no silver..


With no moving parts and a very clean looking previous installation, my guess is either it was a manufacturing defect that finally became audible or (as it was on the bass side) a fluke chaffing where the weave gently vibrated against the bridge wood when the low frequencies were played. Or it was the Ghost of Bach getting back at us for playing every song with the same three chords all the time.

I'll see the owner next week, evaluate his needs and wishes, and get him up and running. I just wanted to post what I found and thank everyone for their time and interest, especially after reading Rob Mercure's post that piezo elements "just die without reason." 

Again........ Thanks!

[Rob Mercure]

Thanks,

 

Remember that the piezo ("pee-ay-zoh" if you want the correct Italiano) is basically a capacitor and running a cap in series makes the overall capacitance much smaller and thus the impedance at audio frequencies higher (for two, and only two, cap in series add the capacitance, in farads <remember we're dealing with millionths, billionths, or trillionths of a farad usually) and then multiply the two capacitances and then divide the first sum by the second multiple - you wind up with really tiny amounts of capacitance with high impedances quickly).  A better way would be to terminate the piezo element with a 10M resistor across it - run a 1-10K resistor in series with one lead, and then put a small cap across that to "short out" the higher, "noisy" frequencies - I'd try something between 220-470 pf.  This is where, again, a buffer would really help cuz once you get a low Z output it's much less sensitive to noise pickup, less critical about lead length (sheild any RC assembly to keep your locak AM station out) and provides you with more leeway to tailor the sound and reduce noise.  I bought of the first under the saddle Fishman made Martin branded piezos on the market in the early 1980s and fought that thing like hell for years before first grasping an understanding of piezo fundamentals and secondly giving up on the tonal quality 'cept as a novelty sound.  All Electronics is an industrial surplus place that I recommend for getting all sorts of high quality components for extremely cheap and they've got "hot dot" type piezo elements (sans plastic case) for pennies.  For a few bucks you can purchase scads of "so cheap I don't care if I break 'em" piezo elements and play with wiring them in series and parallel and placing them under fret boards and, as I did once as a lark, on almost every suface of a cheap "backpacker" style guitar.  You had to handle it carefully not to accidentally make a sound but it would pick up, if you wanted, sliding your hand up and down the neck or twirling a pencil eraser on the table, etc.  If you're good with weird and inersting sounds these things can be fun. (I luckily got to meet John Hartford and hang out with him a few times in the early 1980s - really, really, nice guy - and at that time part of his contract required for the venue he was playing at to provide a 3/4" sheet of baltic birch plywood and a few pound of a certain grade of masons sand.  He'd take the plywood and attach 3-4 piezo pickups - might have been "hot dots" - and plug them into a small mixer he carried with him.  He's pour sand on 1/2 of the sheet of plywood and while playing the fiddle and singing would do rhythm parts using the plywood with the piezos - if he slid his foot across the sand he got a "swoosh-rumble" sound with snare drum like qualities while he could quickly hit it with one foot for a down beat.  Was absolutely magical seeing him perform using effectively four instruments at once - I was in mourning for 3-4 years when John passed - probably the best American musician of the 20th century!).  So have fun with the piezos but you can't make a pork belly out of a sow's ear much less a silk purse.

 

Rob