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.
I believe you've done about anything I usually do to check what's wrong. The last things you could try would be :
- unsolder the piezo from the preamp and plug it in an external preamp to check if the problem comes from the piezo or the pre-amp.
- remove the strings and tap with a nail on the saddle at every spot a string would lay on (not sure of my english on that sentence). You should here a loud and bassy "thump" in the amp each time you tap. If not, the saddle is not properly seated. It's my last chance test when something's wrong despite an OK saddle adjustment.
Well, my first comment, useless for your purposes, is that the best way to fix a piezo pickup is with a 2 pound flat faced machinist hammer <grin> . Now the clack just sounds like a piezo working correctly - our page buddy Jeff referrs to them as "quack sticks" and I haven't found a better description. Again not helpful but if you could acquire a same or similar model, remove the one in the guitar, and insert the new on with the leads coming out from the top - just enough work to test the physical assembly - that might prove helpful. Piezos sound compressed and quacky and have really high output, mostly capacitive, impedance and they need a load of at least 3 megaOhms with 10 being usual. So almost all modern ones come with either a simple buffer (amplifier with a gain of 1 or slightly less that matches impedance) or a preamp. That's what your battery powers - a basic piezo doesn't need power - and I suspect that's where you problem lays. If you can't see the preamp easily I'd suspect that it's built onto the endpin jack and you usually have to remove the entpin button and then a lock nut and then slide the preamp forward for removal through the sound hole. While most of us have done this before with the strings on the instrument it's a extremely easier to do it with them removed or very very loose. If this is a pin bridge guitar you can put a capo on the 12th fret clamping all the strings, loosen then and pull the pins, and then carefully pull the pinballs out (I usually wrap the strings with a twist tie between the capo and ball ends to keep them out of the way. Once you've got your preamp out if the leads are long enough you can restring the guitar and flex the preamp to see if it makes any diference or is there is a loose wire or one with a poor solder connection. If you determine the preamp is bad the majority of these without tone and volume controls are basically the same and your music store should be able to sell you a new one which should take care of your problem. If not it may be the piezo strip as I've seen a few that just "die" without reason. Other things to check are how clean the contacts are at each end of the guitar cord and at the female end if you pull preamp - and whether the amp being used has sufficient input impedance if a buffer isn't being used. As far as resistance checks continuity is the first as wires sometime break inside the insulation, secondly once you've located the preamp you might unsolder one of the piezo leads and then measure the resisitance at the input of the preamp. While impedance has a reactive component most piezo preamps/buffers use resistors to establish the input impedance so it should read at least 3 mOhms and up. That probably covers most of it without using an oscilloscope (although I'm sure that I've forgotten some tidbit this should work),
K&K mini, I've installed a few of those. If mounted where instructed to, sound, imho, much better than an under-saddle. They now have a integrated volume circuit version that's passive, which looks great. I've never had the chance to hear the trinity system, but I've thought that if the mic is of the same quality as their brass instrument mics (I see no reason why they wouldn't be) it should be a great system that would be ideal for most any amplification purposes.
How did you mount them?
I remember these from 1976, when I worked at St. Louis Music Supply.
I agree about the K&K Minis, I have done a few undersaddle replacements with them and wired them into the existing preamp. Worked great and the owners loved the sound.
But you still need to check whether it's the pickup or the preamp as Pierre suggested.
Also check whether the underside of the saddle is flat and whether the surface of the piezo is level. If the top dome has increased due to humidity, the bridge slot may no longer be flat. Sometimes a more flexible plastic saddle works better than the rigid bone in sitting on the piezo strip.