The Gristleizer Pre-Amplifier is a new addition to the existing circuity of Roy Gwinn's "Guitar Effects Pedal" design. After Chris Carter's suggestion of a guitar pre-amplifier for use with the rest of the Gristleizer series, the TG5 came into being. Based upon Jonny Reckless' FET-based discrete amplifier circuitry, Roy Gwinn has designed a pre-amplifier with a high quality VCA back-end which allows for any external audio source to become fully integrated into a Eurorack system.

The Guitar or Line input is firstly fed through one FET stage of the pre-amplifier, and then into a super-clean THAT VCA, the direct output of which is available at the Clean output. This source is then fed through two more FET amplification stages and a tone section (featuring the typical Bass, Mid and Treble controls found on many guitar amps) to the Master output. Bite and Boost controls allow for further control over the tone of the input signal.

An RMS detector (found as part of the THAT VCA) is employed as an envelope follower, as well as a gate detector. The Sensitivity control allows the user to set how the RMS detector reacts to the incoming signal's level. Access to the THAT VCA's Gain control input allows the two Envelope outputs to be used as control sources for the pre-amplifier itself, turning the module into a dynamic compressor (Inverted Envelope) or expander (Normal Envelope).