Again trying wiring based on a humbucker pickup. This time with results. Instead of stacking the two piezo they are side by side. One facing up the other down. Wired as shown below and directly to an output jack.
Placed between two pieces of corrugated cardboard and pressed inside a cbg. Exposed and at 12 inches from a small amp speaker. Amp set at 1/4 volume. The hum level was no different from what the amp normally has. There was no squall. Not even when strumming the guitar.
Control. The open guitar nor the amp was moved. Nor was any of the setting different.
A single piezo sandwiched in the same corrugated cardboard. Wired directly to an output jack. Placed inside the very same cbg. Squalled uncontrollably. Was not able to hear when I strummed the guitar. Squalling didn't change.
The wiring is as the gif below. One hot running to ground. The other to the hot side. The two black ground wires are soldered together and go nowhere.
Hoping other builders would try this to see what results you folks can get.
Going to try this again tomorrow ( when it's not 3:00 in the morning ) Going to try with both piezo facing the same direction. To see if there is any difference in sound or effect.
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Thanks JL. Totally dig the piezo info. So I was on to something by turning one upside down.
I really haven't stopped experimenting. Did something really stupid. Didn't realize just how dumb till I plugged it in. Wired two piezo in parallel to a volume pot. Wired a third piezo in backward, Sending it's hot to ground and black to the input. What I did was have a volume pot that was always on......: ) A piezo blend pot if you will.
Piezo crystals do have an 'orientation' (first pic). compression drives a charge one way, tension (stretching) drives the charge the other way.
by flipping a second piezo one gets compression while the other gets tension, they throw opposite charges (one gives off the red line, the other gives off the blue line. +1 and -1 at the same time result in the green line compared to ground.
It won't cure feedback, but then neither does a hummbucker.
A hummbucker kills outside RF noise that the coils pick up as though they were the UHF antennas on an old analog TV set. Because one coil is wound backwards from the other, the RF antenna effect of one is opposite the other and they cancel. the magnets don't have any effect on the coil acting as an antenna to outside RF noise.
but by flipping the magnet in the reverse wound coil, they add together when responding to the sting vibration. one sees the string coming at the N pole and generates a clockwise charge, the other one see the string coming at the S pole and generates a counterclockwise charge. so you chain the second coil backwards to the first to catch that backwards charge from the backwards side at the same time the other is getting a forwards charge, and they add up.
Yep, that all makes sense, I didn't know about the piezo orientation part though.
Taff
Great stuff CTBR .,.,love to see this experimentation.,.,piezo's and coils are definitely different animals.,.,like comparing rocks to marshmallows.,.,I have a few builds using piezo's that don't mind distortion..,most do howl if you turn it up.,.,i'll give this a try.,.,keep up the good work!!
Hi, I have just finished a cbg that will be my "Frankenstein" test bed for the testing of Piezo transducers. See, you got me started Blue Rat.
Having installed hundreds of transducers over the years, in all types of instruments, I thought it may be an educational project, as and when I find the time.
I will not be trying to eliminate feedback when using a piezo transducer pickup, as I feel the nature of the beast does not allow this, mainly due to the way it functions in a hollow chamber. Blue Rat has demonstrated how hard this can be.
What I will do is mount transducers into this cbg in areas already suggested by members on here, and some ideas of my own, and test the tone, output and feedback qualities by switching between them. I will also have a pre amp fitted to test the effects when its in or out of the loop. I will start a new thread for this.
Just a few things I'd like to comment on. B R,the backless box was for easy access, was the back replaced for testing?
Piezo size....As piezo transducers react to the tops vibrations the more sensitive the top to string vibration the smaller transducer would be used, a less responsive or laminated top may require the larger disc to get a suitable/similar output.
In my quick test in eliminating feed back the best result I got was to cover the soundhole. No feedback.
Taff
Thanks Taffy, no the box was left open. I would cover the piezo with a small piece of 1/2 ply, a chunk of foam or one or two layers of corrugated cardboard. Or leave them open and strum the strings. The CBG is in a way that allows me to have free access to the strings. This allowed me to strum them derring the testing. All with the box open and the piezo 12 inches away from the speaker. All the piezo are the same 27mm size. The idea was to create a worst case scenario for the piezo. This way the wiring setup itself would be tested. I found that it didn't matter what I covered the disks up with. Each different wiring I tried would feedback at the same volume level no matter what I covered it with, or left them uncovered. The best results are from the wiring diagram in the first post but with both black wire grounds wired to ground.
Hi, I mentioned the back of the cbg as I thought that may have been a more of a worst case scenario with the back fitted. As is normally the case the air/soundwave pressure in the box would have been added to the top vibrations [pressure] creating a more realistic situation. I think this is why I could cancel the feedback in my closed box with soundhole, by limiting air movement/pressure in the box, by covering the soundhole. Doing this I thing broke or limited the feedback loop between box and speaker.
All very interesting.
Anyway here's "Frank" waiting for the transplants.....5-6 transducers, volume pot, jack and preamp. I built this in a way that allows me to remove the neck from the closed box, or remove the neck and lid as one unit [still strung up and tuned] to allow for operations inside.
Cheers Taff
After countless tries. With three different pairs of piezo. I can't duplicate what happened with the first set. Not even with the first set. I've even tried different wiring configurations. The only good thing that's come out of this is I'm now really good at attaching wires to piezo. But that's not helping anyone. I'm not done beating this dead horse yet. Just putting it on a back burner till I find out how I can make this work. If someone can make a silent piezo underwater mic there has to be a way to make one for a CBG.
The only thing that positive that's come out of this is knowing that a dual wired piezo in this manner comes to squall at a higher volume level than a single wired piezo in the exact same position.
Could the first try result have been due to a bad solder joint on the 2nd piezo?
Another side to this is with both grounds soldered together and not going anywhere there is a lot of hum. when I touch these to the ground on the output jack the hum goes away. So i'll have to go back to soldering both grounds and one hot to ground. However because I don't have both piezo stacked I don't have the shifting phase I had with the first experiment. Even placing them where they are just about touching gives a good signal.
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