Replicate Fly piezo electronics

[JimmyFly]

Getting so close. I tried the 250k concentric pot wired as described with the 20k resistor and the volume did not behave properly and no change to tone. I swapped out the 250k pot with a 20k resistor for a 25k concentric pot. The volume works properly but there seems to be no change in tone or not perceptible by me. I tried reversing the tone pot leads and that didn't help. Any suggestions?

[mmmguitar]

Let's figure out the tone pot first:

I tried the 250k concentric pot wired as described[...]and no change to tone.

Per your post on the previous page, the project you're troubleshooting is a PDF70 with GraphTech Ghost saddles. How are the saddles being summed together, and how are you connecting the summed lead and ground wires to the Powerchip or tone pot?

If you have one of the gangs of the 250k pot wired up as in the Fishman diagram attached on the previous page (with the left and center lugs outputting to the "piezo-in" solder pad of the Powerchip), and are getting zero high-end rolloff when turning the pot down, I suggest you email Fishman with their diagram attached, and see what they have to say.

I swapped out the 250k pot[...]for a 25k concentric pot. The volume works properly but there seems to be no change in tone or not perceptible by me. I tried reversing the tone pot leads and that didn't help. Any suggestions?

A 25k pot isn't the right value for the tone control diagram Fishman provided (it specs 100-250k).

Concerning the 250k volume with 20k resistor "not behaving properly": Is it a taper issue; where the volume either doesn't roll off until the end of travel, or starts rolling off too sharply at the start?

I'm sorry to have you doing all the field work in ironing out the issues in this experiment. For the moment, I recommend you additionally ask Fishman if there's a cap value they think might work with a 25k pot in parallel with the input of the Powerchip to achieve tone pot rolloff. It would be something like this:

The hurdle we seem to be dealing with is that Fishman has spec'd a passive tone control circuit that would be quite clever, if we could actually get it to work. But even if it does, I assume you're running into the separate issue of using a resistor to change the 250k volume pot's value to 20k resulting in an undesirable taper.

In the below video, the player is demonstrating how a .0022uf value cap paired with a 1M pot sounds as a passive piezo tone control. So while that cap value may technically work with your 25k pot, the difference in pot values may cause the tone control taper to be as ugly as the modded 250k volume pot taper is.





By chance, are you able to post photos of the two different concentric pots?

[JimmyFly]

So you’ve inspired me to add jumper leads to the pot with alligator clips to try out different sized caps but from your drawing I’m not sure where the summed piezo wire goes when it enters the control cavity. I see only a connection from the center tone lug to the pcb. The pic has the 3 vol leads going back to the pcb where the original pot was removed (green, red, white). The tone pot has the white (summed piezo-in) and the red bridged wires back to the pcb piezo-in. I had the tone leads reversed where the white piezo-in was on lug 3 but I was getting the same result. Hope this helps. At least the vol works. I positioned the volume on the lower knob because I’m using a 250/500k mag pot and the 500k vol pot is on the lower knob so both mag and piezo pots will have vol on the lower knob. Not ideal.

[mmmguitar]

from your drawing I’m not sure where the summed piezo wire goes when it enters the control cavity.

The most recent drawing is a different circuit for if you want to try a 25k tone pot; in which the summed piezo lead wire is soldered to the input soldering pad on the Powerchip, and a jumper wire soldered to the same pad goes to the center lug of the tone pot. This is more in line with how a "normal" tone pot works.

Fishman's 250k passive tone diagram has the pot in series prior to the preamp input; and uses the impedance of the pot as a low-pass filter via bridging the two "output" lugs. But if a 25k concentric pot works better for you, then I'm suggesting that maybe using the tone pot in parallel with the preamp input and finding the right cap value will be a working compromise. The challenge in engineering a passive tone control for a piezo signal is that you have to find a mating of resistor and capacitor values which achieves both a usable taper and the desired amount of roll-off.

[JimmyFly]

After rewiring to the more common pot/cap config I tested several cap values and all of them seemed to cut the volume by at least a third. By the time I had cranked the tone to its highest resistance the volume disappeared too.

PDF70 with Dimarzio's, Piezo and battery pack

After all that experimentation I decided I liked the piezo sound better without the tone pot so I unsoldered the stacked pot and reinstalled the pot that came with the powerchip. The really weird thing is that the volume pot for the piezo and the magnetic pickups turn in opposite directions to increase the volume. I hadn't noticed until it was all assembled. Finally I installed a Fishman universal rechargeable power pack which fit nicely in the control cavity, and the project is done for now. I truly appreciate all the help and learning along the way.

[mmmguitar]

The really weird thing is that the volume pot for the piezo and the magnetic pickups turn in opposite directions to increase the volume. I hadn't noticed until it was all assembled.

If you swap the outside lug connections for the pot gang sweeping in reverse, it should then be wired right-handed. I wonder if you're using a "blend" pot.

Thanks for your patience in documenting trying out the components you had on-hand. i have spare Powerchips, but no Flys set up for reproducing your experiment(s) (all piezos are hexaphonic; rather than summed). For what it's worth, if I ever end up buying another Fly, I'll revisit this and determine the prescribed pot and/or cap values for achieving a dual-concentric piezo volume/tone, as well as master volume in the "refined" era circuitry. That you were having significant volume loss from the tone pot with a cap meant that a resistor would need to be placed in series with either the input lug of the pot, or the capacitor itself (depending on the pot value).

[JimmyFly]

I'll make the necessary tweak to that pot connection. Thanks. Your comments have been invaluable and I will at some point do another remod on this guitar to do the full Fly Classic update. This was a good learning project. The nice thing about these Fly models are that they are relatively cheap, easy to mod, comfortable to play and look cool. They don't have nearly the build quality of the pre-refined Parkers so be prepared to drop some setup cash. I paid $600 for this and another $200 into the neck. I've got some VintageVibe Charlie Christians I'd love to try pop in one of these days, yet another project.

[mmmguitar]

I've got some VintageVibe Charlie Christians I'd love to try pop in one of these days, yet another project.

Please let me/us know how you like them. I have a Fly bridge pickup wound by Pete, and have held off on asking him to wind a jazz neck pickup because all my current Flys have Sustainiacs. The Charlie Christian is the one I was most curious about.

[JimmyFly]

I currently have them on a Strandberg Boden 6 and love them. I play everything through a Henriksen Bud 10 amp which makes anything sound amazing so maybe I’m not the best judge.

[JimmyFly]

And of course switching the leads on the piezo pot worked perfectly.

[JimmyFly]

Crazy question. Does a "best" parts list exist of exactly which parts to get to replicate a pre-refined fly? I love my 'new' guitar but to my ear there seems to be something missing that makes my '96classic sound so robust. ( I guess I should have asked that question in my initial post).

[mmmguitar]

Crazy question. Does a "best" parts list exist of exactly which parts to get to replicate a pre-refined fly? I love my 'new' guitar but to my ear there seems to be something missing that makes my '96classic sound so robust. ( I guess I should have asked that question in my initial post).

If there is, I’d be curious to see it. I’m hoping others will chime in; because I consider it a matter of opinion, rather than anything strictly prescriptive:

I think a Fly sounds like a Fly due to the peculiarities of its construction; and that there are gaps between your PDF and Fly which component values won’t necessarily bridge. Though you can certainly experiment with different pickups and how their resonant peaks are affected by component values, I expect it’s the same uphill challenge that getting your PDF to replicate your Strandberg’s timbres would be.

If, for example, you transplanted a ‘90’s Fly’s pickups, pots, ribbon assembly, and Fishman preamp into a Les Paul or a Strat, they still wouldn’t sound like the donor Fly.