StageBug SB-4™ Development

As odd as it may sound, ever since the very first piezo transducers were introduced by Barcus-Berry in the 1960s, there have been concerns with respect to their performance. The primary concern has to do with the tone in that musicians and engineers constantly complain that the frequency response is peaky, dynamic response inconsistent and the instrument lacks natural warmth.

Since the introduction of the Radial PZ-Pre, we have come to understand some of the challenges and discovered that the problem is not so much the transducer, but the interface between the transducer and the PA system. Piezo electric elements sound best when they are connected to a very high input impedance, but the higher the impedance, the more noise you get.

Think of it this way, as you increase the impedance (or resistance) of a buffer (or amplifier) less signal will pass through. With less signal, you have to increase the magnitude of the amplification to make up for it. As with all amplifiers, the quality differs greatly. Chip based amplifiers that are incredibly efficient tend to not sound very musical. Great sounding amplifiers such as a well designed class-A circuit sound great but are much more susceptible to noise. It is the careful balance between a class-A input buffer and the selective use of operational amplifiers (Op-Amps) that makes Radial products stand out. And this is why some of the world's most renowned artists use the PZ-Pre, PZ-Deluxe and PZ-DI for their piezo instruments.

The StageBug SB-4 Piezo is essentially a cut down version that enables the average musician to carry his own personal direct box to a gig and get the quality and performance that has made Radial the leader in instrument to pro-audio interfaces.

Comparing Radial piezo-optimized interfaces


Features SB-4™
PZ-DI™
PZ-Deluxe™
PZ-Pre™
Number of inputs 1 1 1 2
Selectable input impedance No Yes Yes Yes
Low cut filter (HPF) Yes - 1 pos variable yes - 2 pos yes - 2 pos
On board EQ No No Yes Yes
Variable notch filter No No No Yes
180° polarity reverse Yes Yes Yes Yes
Low-Z DI output Yes Yes Yes Yes (2)
Mute footswitch No No Yes Yes
Tuner out No No Yes Yes
Stage amp output Yes Yes Yes Yes
Ground lift switch Yes Yes Yes Yes
Power 48V Phantom 48V Phantom 15V/400mA
supply
15V/400mA
supply
US retail price $90 $280 $300 $400

All four of these Radial products are active devices, designed to interface with piezo pickups. When developing the SB-4, we focussed on providing the user with the most basic functionality and critical features that would enable the artist to perform with confidence. All four share the same 10 meg-ohm class-A input buffer and similar gain stages. Where they differ really comes down to functionality and application.

Critical to maximizing gain before feedback is a high-pass filter that cuts low frequency resonance that often will cause the body of the instrument to resonate and feedback. By reducing excessive bottom end, you also enjoy a cleaner, less obtrusive mix.

Another very useful but often misunderstood feature is the 180⁰ polarity reverse switch. Feedback is often caused when the sound coming from the PA system interacts with the room acoustics causing peaks and valleys at various frequencies. In studios, these are known as room modes. When two low frequencies collide in phase, their magnitude is amplified which in turn causes feedback. By reversing the polarity, we are essentially moving the problem out of the way by causing a phase cancelling valley where a peak once was. This eliminates feedback without having to resort to extensive notch filtering which can often cause the instrument to sound less natural.

Critical to the design was portability. We wanted the SB-4 Piezo to fit in a violin case. We decided to eliminate the external power supply that normally comes along and instead, use 48V phantom from the mixing console as the power source. An innovative ground lift technique was developed that helps eliminate hum and buzz caused by ground loops – yet it does so without disturbing the 48V phantom supply.

The result is a direct box that sounds great, does what is it supposed to do and gets the job done as efficiently as possible in the smallest most convenient package ever!