LES PAUL PIEZO

GRAPHTECH ACOUSTI-PHONIC INSTALL

11/22/16- You don't need to know how musical instrument transducers work to use and appreciate them, but basic knowledge is useful for understanding the differences between them and where their strengths and weaknesses lie. They all convert sound/vibrational energy to electrical signals that can be processed and amplified to reproduce the original sound, but do it in different ways with different results. Piezoelectric materials convert pressure on the material to an electrical charge-- it's very different than the way that a metal guitar string cutting through a magnetic field induces an electrical signal in a coil.

Piezo pickups are used on acoustic instruments as an alternative to a microphone or magnetic pickup. While condenser microphones capture the acoustic quality most faithfully, they're prone to feedback when amplified. Magnetic pickups on an acoustic guitar tend to sound like electric guitars and can pick up hum from stray electromagnetic fields. Of course, there are upscale hybrid and multiple pickup solutions, but they tend to be pretty spendy.

Piezo pickups are frequently used in mid-level acoustic guitars because they're relatively cheap, practically invisible, and have an extended frequency response which makes them sound very different than an electric guitar with magnetic pickups. They can also be used on instruments that aren't strung with steel strings.

It's true-- piezo pickups don't make a solid body electric guitar sound exactly like an acoustic guitar, but neither does a piezo-amplified acoustic guitar. It's its own sound, and like any pickup, it samples a specific but limited perspective of what we experience when we hear an acoustic instrument in person (which is likewise influenced by our placement in the physical environment).

I see the piezo sound as simply an alternative to the electric guitar's magnetic pickup sound. I like the sound and play-feel of a piezo pickup in an electric guitar, especially the heavily compressed piezo sound that Monte Montgomery gets from his Alvarez acoustic guitar. The piezo sound is more crisp and full-range than a magnetic pickup, with a sharp attack transient that gives it a different playing "feel", especially with over-the-top compression. Guitar amplifiers (which are relatively low-fi) don't do them justice-- piezo pickups sound best through a keyboard or PA amplifier.

I think the main downside is that they readily pick up all bridge sounds, including any mechanical noises and thumping that a tremolo system makes-- these are sounds that magnetic pickups usually don't amplify.

Les Paul DIY Options: There are several do-it-yourself options besides Graphtech, notably LR Baggs and Fishman. Although I'm curious about them, I've installed Graphtech piezo pickups in a Stratocaster (with a two-point floating tremolo) and a faux Ibanez partscaster (with Floyd Rose double locking tremolo) and have been happy with the results. I thought it would be cool to have that sound in a hard-tail guitar with a shorter scale length.

Graphtech makes a Tune-o-Matic piezo bridge specifically for hard-tail guitars like Les Pauls. It's a drop-in replacement, with the minor improvements of screwdriver-adjustable bridge height posts (versus Gibson's thumbscrews) and a magnetic attachment to prevent the bridge from falling off when you remove all the strings (although you still have to deal with the stopbar falling off). The saddles are made of a "String Saver" material which is supposed to reduce string breakage. Opinions vary, but I don't feel that they affect the tone in a significant or objectionable way.

In addition to the piezo bridge, the installation would also need a preamp. Graphtech sells a full Acousti-Phonic kit with all the options, and for significantly less $$$, a basic kit with just the essentials. Graphtech sells pre-wired switches and controls separately, but they're expensive. If choosing the basic route, it's a good idea to buy a dual connector cable (or two) to get the plugs that fit the pins on the circuitboard so you can make your own plug-in switches and controls.

Reversible Installation: I like tinkering with guitars but have been skittish about desecrating Les Pauls... they're such pretty guitars! There's also the "investment/resale value" thing that hovers at the back of the brain: Any kind of tinkering makes a guitar lose resale value, no matter how cool and useful you think the modification is. Even though I don't like to think like that, I can't deny that it's there, which is why I'm very aware of the line between a "reversible mod" and one that's not. That's one of the things that convinced me to install piezo pickups in my 2007 GOTW #33 Les Paul. The Graphtech Acousti-phonic piezo pickup system can be installed in a Les Paul with no permanent, irreversible modifications to the look of the guitar.

Thanks to some Internet research, I was turned onto the idea of feeding the piezo pickup wires (in black heat-shrink tubing) through an opening drilled through the bridge pickup ring-- a cheap plastic part that's easy to replace. No need to drill through the top to the controls cavity. The mod is visible, but not very noticeable.

Once the pickup wires are connected to the summing block (hidden in the pickup cavity), the single pickup lead is routed through the hole to the controls cavity where it plugs into the Acousti-phonic preamp. From there, it's a matter of studying the wiring options and soldering the plug/leads to components. There are a lot of wiring options.

Controls layout- I've simplified the wiring of all my Les Pauls to a master volume and tone, so this leaves two unused pots/controls that could be repurposed. In this application, the obvious thing to do was use volume pot#2 for the Piezo volume. I left the tone pot as a master tone for the magnetic pickups only (no tone control for the Piezo pickups). The second unused pot position was free to be repurposed.

Passive magnetic pickup operation- The Graphtech Piezo/Acousti-Phonic preamp circuitboard is an active, battery-powered system that equalizes and amplifies the piezo pickup signal and mixes it with the magnetic pickups. Unfortunately, batteries die so I considered it desirable to have a "standard" passive magnetic pickup mode that bypassed the circuit and didn't require battery power.

Power switches- Most battery-powered onboard guitar circuits use the output jack as the switch to connect/disconnect the 9-volt battery from the circuit. If you leave the cable plugged in, the battery drains. Wherever possible, I prefer to install a separate/redundant on/off switch so I don't have to unplug the guitar. It's a very simple mod that only requires a single switch pole to make/break the negative connection of the 9-volt battery.

In this case, a double-pole double-throw switch was the obvious choice for combining the active circuit bypass function and the battery on/off function in a single switch: The active circuitry would only be used when power was switched on, so it makes sense to switch them on and off with the same switch.

I used the magnetic pickup master tone pot (push-pull pot) for this. The default (down) position turns on the active circuit. The prevents the circuit from inadvertently being turned off (by bumping the pot) while in Piezo mode. Of course this also means that if you forget to switch the power off, it could drain your battery.

Fortunately, with no battery installed, the Acousti-Phonic circuit passes the magnetic signal through to the tip contact on the output jack, regardless of the position of the push-pull pot and whether it's powered or not.

Mono versus Stereo Output- The Acousti-Phonic circuit detects whether the "ring" contact of the supplied stereo jack is connected to ground (indicating that a standard mono guitar cord is plugged in). In that case, the magnetic pickup output and piezo output are mixed and sent to the "tip" contact of the stereo jack. If a stereo guitar cord is plugged into the stereo jack, the circuit routes the magnetic signal to the tip contact, and the piezo signal to the ring contact of the jack. This means that you can send the two pickup signals to separate signal chains and amplifiers.

The main downside of doing this is that you can't use the supplied jack's ring contact to make/break the battery's negative side to ground: Ergo, no battery connect/disconnect from plugging/unplugging the guitar cord. If you forget to pull the push-pull switch pot or put the guitar in its case and the case's lid pushes the pot, the battery may drain.

Redundant Power Switch- You can get around this with a 9-lug stereo jack (available at stewmac.com) that has 2 switches that make/break when a plug is inserted. The diagram to the right makes it look like contacts# 2 and 6 make contact with the tip and ring, but they don't-- they're insulated, independent switches.

To make a redundant (series) battery cut off, I ran a wire from the push-pull switch's center lug (see diagram below; disconnected from ground) to lug #6 (or #2) on the jack and jumpered the jack's ground lug to lug #5 (or #1). This gives some additional insurance that the battery isn't draining when the guitar isn't being used.

The Acousti-Phonic circuit may have a way of detecting this as well (I didn't use the "SW" pin on the circuitboard because I didn't understand how it worked).

EQ toggle switch- The Acousti-Phonic documentation shows how to connect a dark/mid EQ switch. I've never felt the need to install one and didn't want to sacrifice switch space for one.

Quick switch- It's not absolutely necessary, but it's a genuinely useful feature that lets you quickly switch between magnetic/both/piezo pickups. Without one, you have to turn on/off the two types of pickups with their volume knobs. It also lets you preset volume levels for the two types of pickups.

Normally, you would drill/install a mini on-off-on toggle switch in the body, but that's not a reversible mod. If you replace a pot with the switch, it alters the traditional Les Paul aesthetics.

I did have a spare pot position, so I came up with a compromise "slow switch" solution to retain the Les Paul aesthetics. Instead of using an on-off-on toggle switch, I used a modified pot. I cut the carbon track of the pot at both ends with an Exacto blade, turning it into a long-throw rotary switch (like a no-load tone pot, but at both ends). In the end positions, the wiper (ground) connects to the magnetic/piezo Quickswitch pins. In between, neither are connected to ground, which tells the circuit to mix the outputs of both.

It's a "slow switch" because most of the travel is through the "both" mode, so you can't switch from piezo to magnetic as quickly as an actual toggle switch. However, it's an easy mod, and spares you the search for an actual 3-position rotary switch that has the correct shaft length and a knurled shaft end to fit your knobs. Another downside is that if you switch to bypass/power off mode with the pot in the Piezo position, you won't get any output. It's much easier to read the position of a toggle switch than a pot.

Installation Observations- The basics of guitar wiring are pretty simple, but WTF!!! The factory wiring of this Les Paul is funky and primitive. The metal plate with a riveted terminal strip has a vintage vibe like an old tube amp, but seems out-of-place in a guitar: Most manufacturers solder wires directly to controls. In this case it was easier to start with a relatively blank slate, so that meant gutting a good portion of the innards. Removing the output jack and replacing pots took longer and more effort than it should have. (Despite its vintage charm, I don't think I could bring myself to restoring the wiring to its original state.)

This diagram shows the wiring and connections to the Acousti-Phonic circuitboard (adapted from one of Graphtech's installation sheets):

The Tone pot with capacitor isn't shown since they didn't fit in the diagram (it's really a no-brainer). Instead, the diagram shows the tone pot's push-pull switch wiring.

The plugs give the board many paths to ground, so you can remove the black ground wires from the RING-TIP-SW plug as well as the unused white SW wire (use an Exacto blade to lift the retaining tab to remove the wire and connector). This reduces clutter in the controls cavity (though apparently not enough!).

Fitting it all inside- The Les Paul controls cavity has plenty of empty space, but it gets filled up quickly with all the Acousti-Phonic wires. I wasn't worried about fitting everything inside, so I didn't commit to specific placement of components and left plenty of length on the leads. The circuitboard is small with several places to fit on its side attached to the wall.

The only question was whether I'd be able to fit a battery box on the control cavity cover: I preferred one for convenience. The install kit includes a battery holder clip that attaches to the underside of the cover, but I didn't want to deal with four screws to access the battery. It looked like a shallow battery box would work; I'd just have to place tall components (like the push-pull pot) at the sides to leave enough clearance and depth for the box in the center. I used clear acetate to plan where the box would fit and to make a cutting template for the spare cover. It worked, but it was a tight fit.

Summary: Graphtech has a great line of DIY piezo pickup installation solutions. Not only is it easy to install, but it's very modular with a well thought out set of features that are flexible and let you make modifications easily. It's designed to work with their Hexaphonic circuit board for 13-pin synth/virtual guitar systems (although I believe that's an evolutionary dead-end). For me, the main thing is that they sound great and work reliably. Although there may be better sounding piezo systems out there (or not), I'm satisfied with the bang-for-the-buck so I don't have much incentive to look elsewhere.

 

Audio Samples: These awe-inspiring samples are meant to show the difference between the piezo pickups and the humbucker pickups (Gibson '57 Classic Plus and Gibson '57 Classic). I was too lazy to change any settings, so there's some reverb, chorus, and a bit of compression.

In the first sample, it's an open G chord strummed 3 times each:

  1. Piezo
  2. Piezo + Bridge
  3. Bridge
  4. Bridge + Neck
  5. Neck
  6. Piezo + Neck
  7. Piezo

The second sample is a short riff:

  1. Piezo
  2. Piezo + Bridge
  3. Bridge
  4. Bridge + Neck
  5. Neck
  6. Piezo + Neck

 

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