Need help with push/pull wiring on a piezo

[jmax]

I've got a couple of questions:

This has gone into a 335 style 12 string kit. It only took about six tries to get it through the f-hole without breaking a solder joint, so the fact it works means everything should be pretty solid.

Here's what I was after:

• Coil splitting on the humbuckers with the push/pulls. This works
  
• The ability to bleed in the piezo signal. This works
  
• The ability to run the piezo on its own. This does not work. The classic wiring on the humbuckers is also taking the piezo to zero when one of the humbucker volumes is taken to zero. I had thought that putting the piezo on the middle lug of the switch would solve that, but it doesn't seem to have worked that way.
  
• The push/pull on the piezo is meant to remove the piezo from the signal chain, but the piezo signal is coming through regardless of whether it's pushed or pulled. I also seem to be getting a bit of 'tone suck' from the impedance miss-match, which is why I wanted to use the push/pull as a cut out switch.

I'm a bit out of my depth here, so all help is much appreciated.

[Simon Barden]

I have no idea why the piezo doesn't cut out when you operate the switch, it certainly should do. All I can think of is that the switch may be faulty or you may have a strand of wire bridging across the contacts so it's always made. You really need to check the switch with a multimeter. And if wires have broken several times when you've put the harness in, then it could well be possible that a strand has pulled out and shorted across the switch contacts.

These days I always use heat-shrink on connections wherever I can, as it both prevents accidental shorts and provides some mechanical strength to the solder join.

For the piezo-only operation, it looks like you'll have to do the alternative volume pot connection method and swap the blue and red wire connections over on the two volume pots. That means that the taper will be modified a bit, but you'll always have 500k resistance between ground and the signal connection for a single pickup selection, and 250k between signal and ground if both pickups are selected. Both will be sufficient resistance to keep the piezo signal happy.

[jmax]

Thanks! I think you're right about a short.

I guess I was my own worst enemy on the blue/red wiring. I did it the old fashioned way because I was worried about hum when both pots were at zero, but I guess that wouldn't be a problem because the piezo will be live.

[Simon Barden]

There shouldn't be any hum. The volume pot in most Rics and jazz basses are often wired that way (pickup output to the wiper and signal out from one end of the track) and there's no extra hum.

[jmax]

In my haste to resolder the wires that broke off on one of the attempts to stuff everything through the f-hole, I had attached the out wire from the piezo pot to the third lug instead of the push/pull section, so it was simply doing what I had wired it to do - operate as a normal pot.

The output of the piezo is nice and hot, so it blends in with the humbuckers very well, and works great on it's own. I've got some acoustic guitar impulse responses, and when I apply those to the piezo-only signal, it sounds pretty close to a real acoustic.

[Simon Barden]

It's easy to do. I've certainly soldered wires to the wrong places many times.

Great to hear it's all working and sounding good.