Piezo pickup question

[Azmjir]

Hi,

New to the forum but have been the proud owner of a ‘98 fly classic since 2014. If you don’t want to read my Parker story the question is the last paragraph. A few years ago I decided I wanted to do a few modifications for a number of reasons 1) the sound of the pups, while I didn’t hate them, didn’t give the warmth and depth I would like. So I bought some gen 2’s, and planned to disconnect mags from the preamp. 2) the controls layout is not ergonomic, especially the location of the mag selector switch. 3) I wanted to add some fun things like a kill switch. And 4) probably the main motivational reason I had a short or something somewhere that would drain the battery when not in use. One of the ribbon cables was slightly torn but I couldn’t verify if that was the culprit.

Long story short, I’m not a complete novice at soldering but this is the first guitar I’ve decided to do myself. My guitar tech clearly didn’t want to do the project and after some thought I believe my love for this guitar project will yield better results. I’m just finally getting to it now and having a blast. I’m mostly done, just waiting on 2 latching switches for coil splitting each pickup. I decided to gut the electrical cavity put a kill switch where master volume was, master volume where mag volume was, neck coil splitter where mag selector was, bridge coil splitter where mag/piezo was, and the pickup selector where piezo volume/tune was, tone stayed put, remove the preamp all together, customize a fishman end pin jack to fit, use the hole for the stereo/mono button as an IO switch for the led lights on the tesi kill switch and tesi 2 color led switches for the coil splits so I can conserve the battery even while plugged in since the guitar is completely passive other than 3 leds that are on there own circuit ( the jack still needs to be plugged in for the lights to work).

The question:
I didn’t remove the piezo pickup from the bridge, I didn’t touch anything connected to the bridge or the strings except to ground the bridge to the volume pot. Is there still a passive piezo sound in my signal? I kinda thought there could be but before I go through all that I wanted to hear how it sounded (I might discover plutonium or I might die from radiation). The guitar is playable just without the coil splits so I plugged it in and it sounds good and all but when I tap the body with my hand it comes through the speakers as though a microphone diaphragm is attached (a piezo). I grabbed my strat and while it wasn’t completely silent it was drastically quieter when hitting the body much harder in fact. So it’s either a passive piezo signal still present or the fact that the fly has just that much less mass. I’m inclined to think the piezo is still in the signal and, while I don’t hate it, I’d like to be able to either disconnect it from the signal in some way, like a switch, so I could compare the difference or in a way that I could put it back in without too much difficulty.

Thanks for any input you may have.

[mmmguitar]

If you tap the saddles and hear the thump through the amp, then your piezos are being fed into the mag circuit. If I understand your post, you removed the piezos from the circuit and rewired everything point to point, but are wondering if grounding the bridge to the vol pot housing is somehow introducing piezo signal? As you suggest, it may just be microphonic magnetic artifacts (such as you’d get plucking the springs on a strat).

[Azmjir]

Yes, I can tap the guitar anywhere and mute the strings with my other hand and hear the tapping through the amp as though the piezo signal is still present. Rolling off the volume eliminates the sound along with the mags I can also mute the strings with my strum hand at say the 20th fret and play hammer ons at say the 7th fret and those strange notes come through as well. I’m assuming by grounding the bridge and not disconnecting the saddles from the bridge I’ve kept the passive piezo circuit intact.

Don’t hate it, it’s definitely interesting but if this is what’s happening I’m wondering if there’s some way to turn it on and off or easily disconnect it and reconnect it so I could compare the sonic differences. Ideally have a switch to activate and deactivate the piezo at will but I’m struggling to fully understand how it’s in the signal at all with it just being grounded and no other wire connected for hot or is it because by grounding the bridge you also ground the strings that are then creating voltage within the magnetic field of the pickups and the piezo doesn’t require another wire for hot?

[mmmguitar]

I’m struggling to fully understand how it’s in the signal at all

Same here. If indeed what you’re hearing is the piezo signal, and you have the summed piezo leads still soldered to the bridge with the only other wire coming from the bridge being the grounding between it and the vol pot casing, then I would test if the signal is somehow shorting from the case to one of the lugs by unsoldering that bridge ground at the pot and soldering it directly to the jack ground tab (at the “end” of the signal path).

Other symptoms of the ground signal path shorting into the mag signal at some point in its signal path may include buzzing or humming from touching pot and switch shafts, as well as a marked reduction in noise from touching the strings (note that this also happens normally if you’re close to a radiation source such as fluorescent lighting, a computer monitor, or even just in a household with older wiring - So make sure any extraneous noise isn’t also from one of those sources).

[Azmjir]

So I went as far as just leaving the bridge ungrounded and I still heard the thumping of my thumb on the top horn. I also introduced buzzing as you said was a symptom of a poor ground connection (which I didn’t have before). I got out all my electric guitars and my strat was the quietest of all of them but none of them were as loud as the fly. I then plugged an acoustic in and it was quite a bit louder than the fly but the preamp could be why. I then started yelling into the pups and the results were about the same as the thumping, strat at the bottom, acoustic at the top, with the fly as the loudest electric. I then played music into the piezo of the fly and the acoustic with my phone speakers the fly didn’t seem to register the sound as long as I kept it away from the neck pup (switched to neck so bridge pup wouldn’t hear it) except very faintly when I pressed the phone to the body as though it was more so responding to the vibration the phone against it. The acoustic piezo picked up the sound with the phone a good distance away from the transducer and would feedback when the phone was about an inch away. So now I kinda think what I’m hearing is the sound of a light responsive body with some microphonic activity in play. I never paid attention when it was stock if it thumped around when in mag only mode but I know it did when it was in piezo mode for sure.

[mmmguitar]

Whether the microphonic noise is due to the body being highly resonant (which Flys are intended to be) or the pickups being somewhat microphonic, I’m curious to what extent (re)potting the pickups in wax would mitigate this. Be sure to let us know if you get any more squealing or other artifacts.

[Azmjir]

Sorry for the late response I’ve been really busy. I’ve ruled out microphonic. There’s never any squealing or artifacts in fact with everything cranked and the guitar right in front of the speaker it’s dead silent. Anyway I can’t seem to figure out what’s causing the piezo sound but I’ve decided I really like it. I can tap a beat into my looper if I want and the piezo tones are always layered under the magnetic tones at maybe 1/8th to 1/4th the volume so it gives the guitar a very subtle depth. I’m still waiting on back ordered parts to finish it up but I’m very happy with my choices on this guitar.