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Radial Engineering Tonebone PZ-Pre Acoustic Instrument Pre-Amp Review

By Steve DellaSala
Tonebone PZ-Pre Acoustic Instrument Pre-Amp

Tonebone PZ-Pre Acoustic Instrument Pre-Amp


  • Product Name: Tonebone PZ-Pre Acoustic Instrument Pre-Amp
  • Manufacturer: Radial Engineering
  • Review Date: June 15, 2014 21:00
  • MSRP: $299
  • First Impression: Gotta Have It!

Circuit Type: Proprietary active circuit
Standard input impedance: 6.8k Ohm at input jack ('PZB' switch out)
Input with PZB switch in Impedance: 10meg Ohm at input jack
Output Impendence: 1k Ohm
Low cut roll-off: Position 1: 75Hz; Position 2: 2:220Hz;
Notch Freq. range: 56Hz to 330Hz; Notch Q: Setting 1: -8dB; Setting 2: -15dB;
EQ : LOW Shelving +/- 12dB @ 75Hz; MID Parametric +/- 12dB @ 82Hz to 5.6kHz; HIGH Shelving +/- 12dB @ 7.5kHz
Boost level: 12dB
Effects send & receive: -10dB
FX loop impedance: Send: 1k Ohm; Receive: 15k Ohm
Polarity: 180° switch (absolute phase reversal)
Construction: 14 guage steel, baked enamel finish
Size: 8"w x 4 ¼"d x 2"h (205 x 110 x 51mm)
Weight: 2.7lbs (1.2kg)
Warranty: Radial 3-year limited warranty

Tonebone PZ PreAfter our review of the very first African Tongue Drum with built in piezo-electric pickups, my challenge was to find a way to share that instrument with my custom dual output guitars through the same single channel SWR Strawberry Blonde acoustic guitar amplifier.  However, an issue arose with the output signal between the drum and guitar which makes a simple splitter impractical.  The tongue drum uses four passive piezo-electric pressure transducers, with no pre-amp; both my Guitar Factory and modified Carvin guitars have active piezo-electric systems, which include pre-amps.  The difference in output voltages meant that I needed a two channel pre-amp that would allow for different sensitivity on the inputs while also having separate volume controls in order to balance the output signal of both instruments.  I never really expected to find such a device when typing “dual channel acoustic guitar pre-amp” into Google, but when I did, I was absolutely stunned to discover the Radial Tonebone PZ-Pre Acoustic Instrument Pre-Amp.  During my first bewildered glance, I noticed it was equipped with an arsenal of options, outputs, and features which are truly remarkable.  I also quickly recognized that this would be the exact Pre-Amp I needed, and it came neatly packaged in a foot pedal design, meaning it could easily be integrated to my pedal board.  My review of this dual channel pre-amp focuses on my favorite, and most often used features.  Tonebone’s website has a detailed 6-page write up of all the features of this very capable and well equipped pedal, for those who wish to delve further. 

First Impressions

pzpre applicationThe Tonebone PZ-Pre Acoustic Instrument Pre-Amp is not a simple plug and play device.  To get the best performance from the PZ-Pre, it’s best to understand your instrument’s output signal and how to optimize the PZ-Pre’s settings before plugging it in to play.  On very rare occasions, I read product manuals.  In this case, Tonebone’s simple guide was easy to follow and allowed me to quickly set up the Pre-Amp before ever plugging it in.  For example, each input has its own sensitivity setting that is changed via a recessed switch.  When depressed, a class-A booster increases impedance from 6.8kOhms to 10meg-Ohms, which is ideal for the passive piezo system installed in my African Tongue Drum.  I also wanted to have the option of playing both instruments (guitar and drum) without having to switch between channels.  The reason is that I loop my performances, and in order to sync instruments quickly, it’s best to not have to deal with a channel select switch prior to switching from one instrument to the next.  I was happy to learn that the PZ-Pre had a recessed switch that, when depressed, blended both channels.  I also read about the Notch Filter, 3-Band Semi-Parametric EQ, Boost, Phase, Footswitch, Low Cut Filter, and the plethora of output options found on this beast of a pre-amp pedal.  Doing the research and set up prior to plugging in proved to make my first performance with the PZ-Pre instantaneously gratifying.  With just the turn of one level dial, I was able to balance the output volumes of the African Tongue Drum and the acoustic output side of my Guitar Factory guitar.  My grin was ear to ear as I looped my first live dual instrument background tracks and then turned to the electric side for some wicked leads.  Something worth noting, after shutting down my system and turning it back on the next day to play again, there was no sound coming from my acoustic guitar amp.  It drove me bonkers as I tried to wiggle cables on my effects pedals and input jacks while also banging on the guitar amp in case there was a short.  After about two or three minutes of frustration, I noticed that the “Mute” LED on the PZ-Pre was lit to red.  Oops, silly me, my bad.  I didn’t realize the pedal’s default when turned on is “Mute.”  I didn’t see this mentioned in the manual, so be forewarned.  Admittedly, it still tricks me once in a while, especially when I haven’t played in a few days.  The pedal also automatically defaults to Line 1 at each start up too.

Fighting Feedback      

As expected, having the tongue drum on at all times created feedback.  This was mainly due to the constant resonation within the drum as influenced by the amplified guitar during play.  Feedback has many causes, some of which require numerous solutions.  Fortunately, the Tonebone PZ-Pre is well equipped with three distinct features that are more than capable of eliminating this otherwise unavoidable nuisance.                     

fighting feedback

The first weapon to fight feedback includes a high-pass filter with three settings (Bypass, 80Hz, 200Hz).  At first, I pondered why 80Hz and 200Hz were the two chosen values as it seems like trying to attack the problem with a sledgehammer.  But through a bit more reading about this feature, it began to make sense.  For larger instruments, like a big-body acoustic guitar, upright bass, or in my case, an African Tongue Drum, the 80Hz allows you to keep the desired low frequencies while eliminating below 80Hz, which in reality, most guitar amps are not designed to accurately reproduce anyway.  For smaller acoustic instruments, such as Ukuleles, Mandolins, Violins and such, low frequencies are not part of the instruments natural tone, so it makes sense to cut off anything below 200Hz.  The problem with this switch; however, is that it is not channel specific.  Setting this filter will affect both channels equally, thereby impacting the tone of both instruments.  Given the fact that the tongue drum and acoustic guitar have desirable low frequencies, I opted to use the 80Hz filter in order to preserve the bass tones.  Selecting this option cut most of the feedback from the drum, but there was just a bit more needed.  That’s where the adjustable Notch Filter came in handy.  This filter has three settings (Bypass, Normal, Deep) and once engaged, the frequency can be adjusted between 56Hz to 330Hz via a potentiometer found on the upper part of the pedal.  The adjustable frequency allows you to selectively hunt down the exact cause while minimizing the filter’s overall effects on the natural sound of the instrument.  The “Norm” position decreases that frequency selection by -8dB.  If the problem persists, the “Deep” setting provides -15dB reduction thereby terminating its effect.  The third feedback killer on the PZ-Pre is one that is most useful when performing with a guitar amp and house PA system.  The Phase switch allows you to flip the phase 180° between the unbalanced instrument output and the balanced XLR outputs which will virtually eliminate any potential feedback between your guitar amp and PA speakers.  The pedal also has a “set and forget” switch on the back that makes the phase shift permanent. 

3-Band EQ with Bass, Semi-Parametric Mid Range, and High Frequency Controls

parametric-eqI’ve never found a need to have an elaborate EQ within my system.  That’s likely because my SWR Strawberry Blonde acoustic guitar amplifier comes equipped with adequate tone controls.  However, having such a powerful EQ system on hand, as that found on the Radial Tonebone PZ-Pre, proved to be a useful and appreciated feature, especially when it came time to optimize the tone of the African Tongue Drum.  The bass and high frequency controls on this pedal are straightforward and offer +/- 12dB at 75Hz and 7.5kHz respectfully.  For all three knobs, the 12 O’clock position is neutral.  Where the EQ really shines is with its semi-parametric mid-range adjustments.  I had to read the product manual and Tonebone’s website in order to really understand this powerful feature.  The mid-range adjustments are +/- 12dB between 85Hz to 5.8kHz.  This range is right in the sweet spot of most acoustic instruments, so it encompasses the range in which some of the amplified instruments’ harsh overpowering tones would be found.  The best use for the mid-range feature is to reduce those harsh tones.  To do so, the manual suggests turning the mid-range to around the 3 O’clock position, at which point, you would sweep the band using the “Frequency” knob while listening for any excessive tones.  Once you’ve found the frequency setting that encompasses the most annoying tone, you would then turn the “Mid” knob below 12 O’clock to the desired reduction level.  This feature really improved the overall tone of the African Tongue Drum, but just like with other adjustable features on the PZ-Pre, it cannot be assigned to a specific channel, so the mid-range reduction will be heard in both channels/instruments.   

Output Galore

input-output-diagramThe Tonebone PZ-Pre Acoustic Instrument Pre-Amp is a remarkable foot pedal style controller.  When I first discovered this amazing Pre-Amp, I was shocked at how many features it contained, some of which I didn’t even think about when first searching.  For example, the PZ-Pre has a host of different outputs ranging from ¼” unbalanced instrument level for sending to a guitar amp, XLR balanced dry (without on-board effects) to send to the house PA System, XLR balanced wet (with on-board effects) to send directly to speaker monitors or powered PA speakers and an Effects Loop send and return.  It even has a separate line for plugging in a tuner, which is perfect when considering there is a “Mute” switch that can be activated during tuning.  Having this many options displays how this pedal was designed and built for on-stage, live performances of multi-instrumentalist musicians. 

boost-featurePower Boost

One of my favorite features of the PZ-Pre is the easy access power boost, conveniently located right in the middle of the pedal.  This adjustable 12dB gain is perfect for soloing right after laying down loop rhythm tracks.  The boost foot switch is also assignable via a toggle switch for selecting between activating the Effects Loop, boosting the power, or both.  The toggle switch feature is a little awkward as described in the Effects Loop section.

Effects Loop Vs Connecting Effects to the Output 

return-sender-featureThe PZ-Pre comes equipped with an Effects Loop Return/Send.  These days, it seems most high quality effects pedals claim to have “True Bypass.”  This means that when the effects pedal is not activated, the signal bypasses the pedals’ circuitry, thereby eliminating any potential noise, distortion or degradation of the sound quality.  Since the main purpose of the Effects Loop is to take the pedals out of the line when not playing, I see no real reason to use it when the True Bypass features on the added pedals effectively do the same thing.   Why I particularly think this feature is a detraction on the PZ-Pre is that in order to activate the built in loop, you must first assign the toggle switch to either “Loop,” Boost,” or “Both.”  Sharing the Footswitch toggle for Boost and/or Effect Loop activation diminishes the overall diversity of both features.  For example, if the switch is assigned to “Loop,” there will be no volume boost when activating the footswitch.  Instead, it sends the signal to the effects pedals, so it leaves no option for adding volume during solos.  Setting the feature to “Both” will then mean the volume will be automatically boosted when activating the effects pedals, which isn’t always desirable.  Some may like having the Effects Loop option; however, given the limited real-estate inside this box, I would prefer other useful features that could easily take its place, as described in the Product Improvement Suggestions section.

Product Improvement Suggestions

pzpre-top-lrgI never expect any product to be perfect, simply because every user has different requirements and reasons for selecting the product.  In this case, the Radial Tonebone PZ-Pre is a nearly perfect dual channel acoustic instrument pre-amp that effectively allows me to share two instruments on a single channel acoustic guitar amp.  Packed with a plethora of options and features, it goes beyond any dual channel and most single channel instrument pre-amps available today.  But even with that, there’s always room for improvements, some of which should be considered for the eventual replacement to this powerful product.  Since its initial introduction in 2008, guitar accessories/pedals/electronics have clearly evolved, hence my comment about the need, or lack thereof, of an Effects Loop.  Perhaps one of the most notable shortcomings to me was the fact that in order to have both instruments on simultaneously, one needs a tool/pen in order to depress a recessed switch located on the side of the pedal.  This dipswitch bypasses the Instrument 1 and Instrument 2 footswitches, thereby allowing both channels to be on at the same time, and is not easily accessible during live performances.  Perhaps a more novel approach would be to have two separate footswitches, one for Instrument 1 and the other for Instrument 2, and to allow both switches to be activated or deactivated at the same time.  This would also eliminate the necessity for the mute footswitch, which means the layout of the pedal could remain the same.

Many reviews of the PZ-Pre have pointed out that the EQ is not channel assignable.  In fact, none of the features of this pedal can be channel assigned.  This is simply due to the fact that it is currently an all analog pedal.  Aside from adding two of each option, which would drive up the size, cost and complexity, there is no method by which parameters can be assigned.  Another feature that suffers the most by the inability to assign settings is the high-pass filter.  Right now, there is no way of taking advantage of the 200Hz setting if you plan to play a small instrument, without taking away from the tone of the larger instrument on the other channel.  On that note, perhaps it’s time for Radial Engineering to consider a hybrid (digital and analog) dual channel pre-amp where features such as notch filters, EQ and high-pass filters can actually be assigned and stored to each channel/instrument.  Over the past six or seven years, numerous digital pre-amps have been introduced to the market, with warm welcoming, though none that I am aware of have two channels.
power supply
Perhaps it’s just my nit-picking habit, but if I were to make one complaint about the durability of the PZ-Pre, it wouldn’t be about the sturdy 14-gauge steel housing, the double up solder points potentiometers, the mil-spec circuit board, the extra durable toggle switches rated to 20,000 cycles or the class A circuitry.  Instead, it would be about the flimsy bright red wire used for the power supply cord.   This thinly coated wire is easy to kink and poorly protected (coated), which means noise can easily intrude; it’s certainly not up to par with other power supplies in my rack.


The Radial Tonebone PZ-Pre dual channel acoustic instrument pre-amp is now a permanent addition to my ever expanding set up.  I am truly amazed that I was able to find such a diverse pre-amp that allows me to easily connect and balance two completely different instruments to the same single channel acoustic guitar amplifier with an added bonus of an easy connection to a house PA system.  Despite some of the product’s shortcomings, such as the inability to assign features to channels, the PZ-Pre is an essential pedal that not only blends two instruments, but also enhances the tones, eliminates feedback and allows for easy connections to a house PA system without the need for microphones placed over amplifers.  To have all of this in one pedal is stellar.  But to have this with no discernible distortion or noise, as common with lesser quality pre-amps, is another reason PZ-Pre gets such high marks.  The product website shows plotted curves of the performance of the pedal.  Comparatively, the curves show that Radial Engineering did an excellent job of designing a low distortion pre-amp.  If you are a multi-instrumentalist and currently trapped in a single channel amplifier, but still want to be able to connect two instruments, than look no further, as the Tonebone PZ-Pre is the best dual channel acoustic instrument pre-amp on the market today.

Unless otherwise indicated, this is a preview article for the featured product. A formal review may or may not follow in the future.