The Cartec THC (Tone Harmonic Compressor) is a two-channel hybrid compressor that employs eight tubes and four discrete amplifiers to achieve a unique level of control over dynamic range, harmonic distortion content, and tonal balance.
After the transformer coupled input, audio is split into two separate parallel processing paths. The first stage is a pair of variable trans-conductance EF183 valves operating in a push-pull configuration and feeding an ECC82 with an inter-stage transformer. By varying the input and output level in different proportions, this stage can change from fast, transparent compression, to a more aggressive crushing character with added distortion.
The second stage which splits from a separate winding of the input transformer, is intended to be blended together with the compressed output to either restore some natural dynamics, or add extra character. This uncompressed or 'Dry' signal is passed though a set of passive filters which allow three different bass and three different treble shelving frequencies to be boosted, should you want to blend a higher amount of a particular uncompressed frequency range. In combination with this is a variable asymmetrical clipping threshold, which can greatly increase the second harmonic content for anything from subtle warming, to heavy distortion, and added to taste or even used as an effect on its own.
Both signal paths each have a separate output fader before the discrete mix bus and transformer coupled output amplifier. The THC can also form a passive Mid/Side encoding and decoding matrix with its input and output transformers, and features a switchable side-chain high pass filter at two frequencies.