The Palmer PDI-CTC (Palmer Direct Injection-Box - Cassic Tube Circuit) is intended for DI and preamp use. For the latter, a 4-band filter circuit has been integrated. Featuring a true tube circuit with output transformer, the PDI-CTC provides a balanced signal at the XLR output connectors that is electrically isolated. There are no semiconductors throughout the entire signal path including the filter stage. The PDI-CTC is mains powered, and the integrated power supply generates the necessary tube voltages.

In addition to the standard parallel and balanced mic level outputs the PDI-CTC also features both a balanced line level and a 1/4" 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.