PZ-DI Development
PZ-DI Development
PZ-DI Development
PZ-DI Development
PZ-DI Development
PZ-DI Front Panel

PZ-DI Development

As with all innovative designs, the development stems from audio engineers, backline technicians and touring musicians that are faced with problems and are seeking solutions. In this case, we had received a number of requests for a direct box that could enable orchestral instruments to be used 'live' in the context of a large concert show. To fully understand the situation, you must first go back and look at what was used in the past and how large venues and new technology has in fact accentuated the problems we are faced with today.

The traditional approach

The traditional approach to amplifying an orchestra has always been done using spot microphones. These are usually condensers as they have more 'reach' than a dynamic and are able to better capture the sound of the instrument due to the larger pickup area or polar pattern. This of course continues to be preferred approach when amplifying an orchestra when on its own. Trouble occurs when the orchestra is brought on stage to play alongside electric guitars, bass and powerful rock drummers. This is exacerbated in a concert touring environment such as a hockey rink or football stadium. When played at normal 'rock & roll' levels, the guitars and drums bleed into the microphones making it difficult if not impossible to mix. Then, as you increase the sound level on the violins and violas to compensate, feedback has a nasty habit of creeping into the system.

The solution: the microphone is replaced by a piezo transducer. Piezo elements are devices that are 'bonded' to the instrument and convert the vibrations from the top or bridge into sound. Although they have been around for a long time, they have never gained universal acceptance due to the unnatural sound that they produce. Most engineers and musicians find the sound of a piezo to be squawky, edgy, peaky, and unbalanced resulting in a harsh tone that is difficult to mix.

The PZ-DI solution

When developing our popular Radial PZ-Pre instrument preamp, we quickly came to realize that as you increase the input impedance, the smoother, rounder and warmer the piezo will sound. You also enjoy a broader frequency response and the overall character of the tone becomes quite palatable. To this end, we gave the PZ-DI a 10 meg-ohm input impedance. OK... But if increasing the impedance is the solution, why it has not been done before?

The problem is noise. As you increase the impedance, you are essentially building up a big wall which acts like a limiter that only allows a small amount of signal to pass. This tames the piezo and smoothes out the sound but with only a small fraction of the signal left to work with, extra amplification is needed to boost the output to a manageable level. This introduces a new problem: signal-to-noise. It takes tremendous engineering skill and a lot of time to work out the kinks to get great sound and eliminate noise. In fact when developing the PZ-Pre, it took us a month to work through the feature set and over a year to make it quiet enough to be practical! To avoid the challenge, most manufacturers simply reduce the impedance to 1 meg-ohm. With a low input impedance you need less amplification and this results in less noise. You end up compromising the sound. In the past, lesser quality PA systems masked the sound, but with today's better audio systems we have become all the more aware of any audio shortcomings. In other words, we now hear the problems.

The PZ-DI was designed to solve the problem by combining the unique 48V phantom power circuit we developed in the Radial J48 with the smooth-sounding 10 meg-ohm impedance and noise prevention employed in the PZ-Pre. Like the J48, the Radial PZ-DI is powered by standard 48 volt phantom making it super convenient. Because of the unique DC to DC switching supply circuit that is built in, you can lift the audio ground to eliminate hum and buzz caused by ground loops without reverting to batteries. This amazing circuit delivers plenty of current for extra headroom, less distortion, a wider frequency response, and an exceptionally warm sounding cascade of even order harmonics. This makes the PZ-DI ideal for all instruments, big and small.

No pickup is left behind!

The downside to optimizing the circuit for a piezo transducer means degrading the quality for other pickups. To solve the problem we added a three position selector switch that lets you set the load for the type of pickup being used.

Over the years, we have come to realize that magnetic pickups can be made to sound very different depending on the load. When the load is too high, the sound can be brittle. When too low, it can sound flat and loose punch. We found that a good compromise is setting the load to 220k-ohms. This works particularly well when in the studio as it provides a warm tube-like tone that can later be used for Reamping. To address the traditionalist, we set the third position to 1 meg-ohms. This can be beneficial when using low output vintage instruments that may not always fare well when presented with a lower impedance.

To help tame high output active instruments, a gentle low-pass filter has been added that reduces excessive high end and warms up the tone. As an added precaution against overload, you can also activate a -15dB pad to reduce the input sensitivity. This will prove to be helpful when using the PZ-DI with an active 6 string bass or high output digital piano - instruments that often overload everything!

Focusing the energy

One of the most powerful tools built into the PZ-DI is the high-pass filter. This is used to eliminate unwanted low frequency resonance which can cause feedback or make an instrument difficult to mix. Adjusting the low frequency cut-off point lets you size the instrument as needed. In fact this 'Nashville trick' has been used for years when blending multiple acoustic instruments together when recording. And it works equally well in a live environment.

Different Instruments used at certain levels

Another wonderful extra built in to the PZ-DI is the 180° polarity reverse switch. This can be used to eliminate acoustic hot spots where sound waves from the stage amplifier and PA system combine at a certain frequency to cause feedback. Reversing the phase can shift the acoustic problem away without having to introduce radical equalization. This results in a more natural tone.

Keeping it simple stupid

Finally, we went back and forth several times trying to balance the right feature set and make sure that we did not incorporate functions that could cause confusion or possibly make the sound worse due to misuse. The PZ-DI has been carefully crafted to enable the audio engineer to set the sound so that it works... effortlessly.

We are confident you will enjoy it.