The IVP Preamp is based on the Intersound™ Instrument Voicing Preamp (IVP), a rackmounted preamp that was first released in 1978. The IVP has a six EQ bands (four semi-parametric and two Baxandall) and two channels, clean and drive.
The drive channel, called “Tube Voice”, is of particular interest and is the main reason for its enduring reputation. It uses a combination of op-amp gain, a transistor amplifier and a transformer to get its overdrive tone—no clipping diodes in sight. All of the EQ comes before the overdrive, so it can be used as a tool to get a wide variety of drive tones and clipping characteristics.
The “Tube Voice” channel doesn’t quite nail the tube tone as it claims, but it’s such a unique sound that the IVP has built up a reputation in the four decades since its release. Steve Albini is perhaps the most well-known advocate of the IVP, using it as part of his own live rig as well as in the studio. It was also used by Bob Weir of the Grateful Dead.
The Aion FX IVP Preamp is a direct clone of the rackmounted unit in pedal format. It runs on the same voltage as the original, using a DC-DC converter to get +/-15V from a standard 9VDC input. The Clean and Tube Voice channels are footswitchable, and the other footswitch allows the whole unit to be bypassed. It does not include the two effects loops (pre-drive and post-drive) by default, although these can be added with a few trace cuts, described in the build notes.
The Isotope Amp Overdrive is another project based on the IVP, an adaptation of just the Tube Voice channel and 2-band Baxandall EQ. It’s much simpler to build, but without the parametric EQ and clean channel, it’s a very different piece of gear than the full IVP.