The Heliodor Amp Overdrive is the final installment in a series of renowned pedals that utilize BOSS’s “discrete op-amp” technology, which provides a more amplifier-like overdrive compared to traditional drive circuits. This pedal is based on the BOSS OD-3 Overdrive, which was released in 1997 as the successor to the OD-2r Turbo Overdrive.

Similar to its predecessors, the OD-2/r and BD-2 Blues Driver, the OD-3 features BOSS’s signature “discrete op-amp” topology. It utilizes two JFETs and a PNP transistor to create a variable gain stage that can be controlled like an op-amp, but gracefully clips when overdriven. However, unlike the OD-2, the OD-3 incorporates clipping diodes in this stage to achieve a more traditional soft clipping effect.

There is speculation that the OD-3 was actually designed as the successor to the Blues Driver, given its circuit similarities with the BD-2. However, BOSS may have decided not to interfere with the success of the Blues Driver and instead released the OD-3 as part of their Overdrive series.

Regardless of its origins, the OD-3 draws inspiration from both the OD-2 and BD-2 and manages to improve upon them from a design perspective. While the Blues Driver may receive more attention, the OD-3 is considered the pinnacle of BOSS’s discrete op-amp technology.

The Heliodor Amp Overdrive is essentially an exact replica of the OD-3, with the only modification being the conversion to true bypass. The original OD-3 utilizes the 2SK184-GR JFET, which is a low-cutoff type similar to the J201. However, this JFET is no longer produced in through-hole format. The 2SK209-GR is the surface-mount version that is still in production and performs identically to the original. Each JFET in the Heliodor has additional pads for soldering surface-mount components. If you are not confident in your surface-mount soldering skills, Aion FX offers pre-soldered 2SK209-GR JFETs on adapter boards that can be used in through-hole applications.

Summary created by AI from the original source.