The Aurum Amp Overdrive is the first pedal in a series that utilizes BOSS’s “discrete op-amp” topology. This topology allows the pedal to overdrive more like an amplifier rather than using diode-clipping circuits. The Aurum Amp Overdrive is based on the BOSS OD-2 Turbo Overdrive, which introduced the “discrete op-amp” circuit topology using two JFETs and a PNP transistor. This configuration creates a variable gain stage that can be controlled like an op-amp but clips gracefully when overdriven.

The OD-2 Turbo Overdrive was released in 1985 as the successor to the OD-1. It was later replaced by the OD-2r in 1994, which featured a remote footswitch to switch between channels. The OD-2r also addressed the issue of the original unit not being able to reach unity gain at the highest volume setting.

The Aurum Amp Overdrive is specifically based on the “Turbo” mode of the OD-2r circuit, incorporating the gain recovery stage and other minor tweaks. The non-“Turbo” mode is a separate drive circuit within the pedal and is generally unremarkable compared to the Turbo mode.

The OD-2 was succeeded by the OD-3 in 1997, but the BD-2 Blues Driver can be considered an intermediate member of the same series, as it shares much of the same circuitry as both the OD-2 and OD-3. However, each of these circuits has its own distinct sound and brings different tones to the table.

The original OD-2 used the 2SK117-GR JFET, which is no longer produced in through-hole format. The SMD version, 2SK209-GR, is still in production and performs the same as the original. The JFETs in the pedal have extra pads for soldering SMD parts, but if you’re not comfortable with SMD soldering, Aion FX offers pre-soldered 2SK209-GR JFETs on adapter boards for through-hole applications.

Summary created by AI from the original source.