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PZ-DI Using & Applications

The Radial PZ-DI is designed to provide maximum flexibility while being 'plug & play' easy to use. The following page describes the primary functions. For more details, we invite you to download the full manual by clicking on the icon at left.

Like all direct boxes, the PZ-DI's primary function is to enable unbalanced high-impedance instruments to be properly interfaced with the low-impedance balanced inputs employed both in live sound touring and in the recording studio. Balancing the signal enables it to travel long distances without noise. Where the PZ-DI excels is in its ability to instantly adapt to various types of pickups, transducers or instruments to improve the frequency response, increase dynamics, and produce a warmer more natural sound.

Connections to and from the PZ-DI are straight forward: The instrument connects to the INPUT using a standard ¼" cable. If a stage amp is being used, the THRU is used to feed the amp. The XLR output is used to connect to the PA system or recording console. Powering the PZ-DI is done via 48 volt phantom power from the console. There is no power switch. As soon as you connect the XLR and turn on phantom power, it will go on and a 48V LED will illuminate. Always ensure level controls are turned down or off before making connections as this will protect more sensitive audio components like tweeters from turn-on transients that could cause damage.

Selecting the right impedance


Following the block diagram, the PZ-DI begins with a 3-position LOAD switch that lets you select the appropriate input impedance to match the source:

  • Traditional 1 meg-ohm for reduced loading
    Ever since Leo Fender built his first tube amplifiers with a 1 meg-ohm input impedance, the industry has followed suit. 1 meg-ohms delivers a good clean signal that can be used with most instruments and will not excessively load a magnetic pickup which can cause lower output instruments to sound flat.
  • Warm sounding 220k-ohm for magnetic pickups
    Solid state circuits sound very different that tube amps. In fact, after much listening, we have come to the conclusion that a 220k-ohm load on a solid-state circuit tends to sound very much like a 1 meg-ohm input on a tube amplifier circuit. This sounds warmer than 1 meg-ohm with most magnetic pickups.
  • 10 meg-ohm for piezo transducers
    Most engineers find that that piezo transducers tend to sound peaky and edgy. This is because they are usually paired with a 1 meg-ohm input impedance. The PZ-DI lets you increase the impedance to 10 meg ohms which immediately smoothes out the sound and extends the frequency response.

When using the PZ-DI with an active source, since the signal is already buffered by the instrument's built-in electronics, changing the input impedance will have little or no effect. For instruments that have exceedingly loud output signals such as active basses or digital keyboards, engaging the -15dB pad will enable the PZ-DI to be used without fear of distortion.

Using the filters


There are two audio filters on the PZ-DI. A variable high-pass filter (HPF) that cuts bass, allowing the highs to pass and a low-pass filter (LPF) that cuts highs to allow lows and mids to pass. The variable high-pass filter performs two functions: In the studio it is used to 'size the instrument' whereby low frequencies that may cause interference or modulation with other instruments can be removed to produce a cleaner signal path. It also serves double duty by helping eliminate unwanted resonance that can cause acoustic feedback on stage. Start by setting the dial completely counter-clockwise and then slowly turn clockwise as you listen.

The LPF (low-pass filter) is used to tame overly bright instruments, in particular those that employ active circuits as part of their signal path. The LPF gently rolls off the high end to produce a smoother, warmer tone.

Eliminating feedback

There are two functions built into the PZ-DI that can help reduce feedback: The first is the variable low cut filter. This is used to eliminate excessive low frequencies that can interact with the PA system to cause the instrument to resonate and then 'feed-back'. One simply dials up the HPF filter to suit.

The other is the 180ᵒ polarity reverse switch. Reversing the polarity changes the relative phase of the XLR output by toggling pins 2 and 3. This can be very helpful at eliminating feedback: When an artist is using an amp on stage, the sound from the stage amp and the sound coming from the PA may combine at certain frequencies to cause feedback. Reversing the polarity of the signal going to the PA can often move the problem out of the way. This can also have a similar effect on the room acoustics. By reversing the polarity, you are in fact causing frequency dips to occur where certain frequencies previously were amplifying each other. Best of all, you are reducing feedback without a tone-altering EQ.

Using an amplifier

If you are using an on-stage amplifier for personal monitoring, use the THRU to make this connection. This is basically a pass-through that takes the original signal and feeds it to your amp.

Side access Buffer Thru ON switch

The PZ-DI features a side access buffer ON ‘set & forget’ switch that allows the thru-put connector to be used two ways.

Buffer Off

When OFF (out position) the direct signal from the source instrument is sent thru to the amp. This setting is typically used with an active instrument such as an acoustic guitar or passive instrument such as a bass where you do not want to ‘amplify’ the signal before it reaches the stage amp. This sends the original ‘dry’ signal from the instrument without the buffer.

Buffer ON

When on (in position), the signal is buffered (or amplified) before it is sent to the thru-put connector. This is typically used when the source is a piezo transducer and the buffered signal at the thru-put will benefit the stage amp with a more appropriate output. Buffering the signal also allows longer cable runs with less noise.