When we set out to build the world's best acoustic instrument preamp, we knew that we would be faced with many challenges. Particularly when attempting to jam all of the features we had in mind into a compact pedal. If it were easy, there already would be one available. The following describes the many features and why each one plays an important role in delivering your sound on stage.

Transitioning from the microphone to the piezo

Since the first PA systems began to amplify acoustic instruments, audio engineers have tried to find an alternative to a microphone that would enable them to increase audio levels to the point where the crowd could hear the instrument without constantly having to battle feedback. Early innovators such as Barcus-Berry set the path with contact pickups also known as piezo electric elements that would transmit the vibration from the instrument to the PA as sound. Finally there was hope.

The problem with piezo transducers is that unless they are treated properly, they sound awful. Plug in an acoustic guitar and you immediately notice the sound becomes peaky and squawks when you play hard. Plug in an upright bass and it seems that the low frequencies are strained and unnatural. Connect a violin - the sound is shrill and unpleasant. You ask yourself if piezos are so bad... why do folks even bother? It has to do with convenience. Unless you attach the microphone to the instrument, the sound level constantly changes making it practically impossible to amplify. And as noted before, when you turn it up, the microphone often causes feedback. Piezos are super compact and are easily attached to the instrument so we live with the less than desirable tone in order to get the job done.

Solving the piezo problem

As we started experimenting with various piezo transducers, we discovered that the problem is actually not the piezo at all, but the preamp that is being used. Most piezos do a pretty good job. The problem is that piezos need to see a very high input impedance for them to work properly. But as you elevate the input impedance, you also increase the noise. It took us about three months to work out the PZ-Pre feature set, and over a year to get rid of the noise!

Most preamps are set with a 1 meg-ohm input. This 'standard' likely came from Leo Fender's early tube amplifier designs and was adopted for piezos. The PZ-Pre has a 10 meg-ohm input impedance. This ultra high setting is engaged when the PZB booster is activated. The high input impedance acts almost like a limiter that smoothes out the peaks and edginess of the piezo and gets rid of the squawk. This also broadens the frequency response for a more natural tone. With the PZB engaged, you no longer need to use a booster preamp... you merely connect directly to the PZ-Pre and it does all the work. This means you do not have to cut a hole into your favorite vintage guitar for a pickup or screw on some type of preamp to your upright bass. You simply attach the piezo and you are set to go.

Two instrument inputs

Most performers, whether they play acoustic guitar or mandolin, tend to have two instruments on stage. The second instrument is often for backup should a string break. In some cases it may be tuned++++++++ differently, maybe it has a completely different pickup system or it may even be a completely different instrument! We thought it would be smart to equip the PZ-Pre with two inputs to address these needs and give each input a separate volume control to set the levels.

In an effort to adapt to all types of instruments, each channel is equipped with the aforementioned PZB booster circuit. This 'set & forget' circuit is turned on when using piezo transducers. When connecting instruments with magnetic pickups or built-in active electronics, you simply disengage the PZB and the PZ-Pre automatically lowers the impedance and reduces the sensitivity to adapt. Once each input is set, you merely depress the footswitch to change instruments.

Controlling feedback on stage

Anyone who has played a live show knows that when you turn the volume up, acoustic instruments are prone to howling, whistling and runaway low frequency resonance. This is usually because the on-stage monitors or PA system cause the top of the instrument to start vibrating, creating a resonant feedback loop. Acoustic instruments, whether a guitar, mandolin or contrabass, all resonate at different frequencies. To address the problem, we incorporated several controls that work in tandem to help tame the feedback beast.

  • High pass filter
    A three position high-pass filter is used to cut bass, while allowing the high frequencies to pass. A HPF is one of the most effective controls you can use to eliminate feedback. By reducing bass energy, you immediately eliminate much of the resonance that causes the problem.
  • Notch filter
    This is a narrow-band 'cut only' EQ that is used to find an offending feedback frequency and surgically remove it without affecting the instrument's natural tone. The PZ-Pre gives you a choice of two notches (narrow and extra narrow Q) and variable center frequency control to locate the problem.
  • Polarity reverse
    As you move around on stage, you can often find a position where all of a sudden everything sounds amazing! Move a few feet over and it seems like you are overwhelmed with feedback! This 'positional' effect is caused by the interaction between the PA system, monitors and instrument amp and the interaction with the room acoustics that cause artefacts known as room modes. The PZ-Pre is equipped with separate phase reverse switches for the stage amp and PA system to help eliminate hot spots by electronically moving the problem out of the way.

Getting the very best tone

Our primary goal with the PZ-Pre was to deliver a studio quality preamp in a compact pedal format. What determines 'studio quality' is the quality of the audio circuit, the headroom, the background noise, and the quality of the equalizer. The PZ-Pre begins with class-A buffers for exceptional signal transfer. The 15V, 400 milliamp power supply gives you almost three times more power than a traditional Boss style 9V supply. This increases the headroom and reduces distortion. This produces more natural dynamics and greater feel when you play. We then thought long and hard about what kind of EQ would work best. We decided that a semi-parametric would be the ideal solution as it is easy to get great tone and it will keep those that are not audio engineers out of trouble! In other words, with this type of easy to use EQ, you cannot go too far wrong.

Giving you more control on stage

With more and more musicians doing coffee house or solo gigs, we then thought about the performance aspects. How do you accentuate the instrument during a solo without a full time soundman? We decided to add a fully variable power booster that lets you boost the signal for solos. We then went a step further by incorporating an effects loop to add a reverb or delay. The effects loop can be used on it's own or you can link it to the power booster footswitch. One foot stomp and your tone can go from regular acoustic to electrifying madness by linking the loop to the boost footswitch.

Maximizing the output options

In a live situation, there are often several audio systems in use at one time. These 'zones' all have very different needs. Thus the reason the PZ-Pre is so equipped. Here's why:

The musician's zone

As a musician on stage, you may want to use your own stage amp. This is very common with upright bass players. A stage amp lets you dial in your amp's EQs and effects for the sound you want without having to worry about what it will sound like in the monitors or the PA system. To address this need, a separate stage-amp output was added. This is equipped with a 180° polarity reverse to help combat feedback.

The monitor system

Most acoustic performers rely on wedge monitors or in-ear monitors to hear themselves on stage. The PZ-Pre's amazingly smooth sounding EQ is perfectly suited to set the tone for your on-stage mix. You can also add effects like reverb or echo to give you a more comfortable sound. This is particularly important when using in-ear monitors as these can sometimes sound too dry and unnatural. The PZ-Pre has a post EQ XLR output designed specifically for this.

The house PA system

If you add reverb to make your monitors sound good, you may be causing a major problem for the front-of -house engineer, particularly when playing in an arena, gymnasium or house of worship as these types of venues usually have so much echo, your instrument will get lost in the mix. The solution: give the FOH engineer a dry mix and let him add ambiance to suit. The PZ-Pre has a pre-EQ XLR out that gives the engineer your sound without the effects or EQ.

Finally, we thought about tuning. There's nothing more embarrassing than having to tune in front of an audience. So we added a footswitch that mutes the signal going to all outputs, except for the tuner.

In the end, the PZ-Pre has more controls, more switches and more connectors than any other acoustic preamp pedal... but take heart, all of these controls are essential and actually quite easy to use. And when combined, they make the PZ-Pre a very powerful tool that you can depend on to bring your best performance to the show each and every night.