Active, tube-based DI box with a four-band filter circuit.
The Palmer PDI-CTC – which stands for Palmer Direct Injection Box Classic Tube Circuit – is much more that your standard impedance matching DI boxes. This particular DI box is a step above the normal in that it also features a tube-based preamp with transformer-balanced output and a four-band filter circuit. All of this is housed in a 2-unit high, half-rack width design, complete with ventilation to allow airflow in to cool the tubes. It also allows for the warm orange glow of the tubes to shine through, which makes for an excellent visual aesthetic.
In addition to the standard parallel and balanced mic level outputs the PDI-CTC also features both a balanced line level and a ¼" unbalanced low impedance output. The wide band low, lo-mid, hi-mid, and high frequency filters are "musically" voiced. A bell-shape filter characteristic has been chosen to prevent boosting undesirable subsonic frequencies as well as those beyond the audio range.
To exactly reproduce sound settings each and every time Palmer decided on individual toggle switches to set each of the four frequency bands to 0dB, +4dB, or +8dB. Essentially, the PDI-CTC circuit design is based on the idea to realize the shortest possible signal path in order to bring out the subtle tone characteristics of a tube. For that reason the unit does not incorporate a volume control. Due to the unit's extended dynamic range no limiting occurs before signal levels exceed +30dBu at the line output.