The Apollo Preamp Drive Mk. I is an adaptation of the Catalinbread WIIO, based on the Hiwatt amplifiers used by Pete Townshend of The Who, particularly their Live at Leeds show from February 14, 1970. (The artwork for the original pedal makes it obvious that “WIIO” is intended to resemble “WHO”.)
The WIIO was originally released in 2009 as a limited run of 100. The limited availability caused a huge debacle as people from gear forums bought up all the preorders and flipped them for profit, capitalizing on Catalinbread’s favored status among gear aficionados.
Catalinbread was not happy with the way the circuit turned out, so before releasing the non-limited version, they overhauled the circuit to reduce the gain and tweak the EQ so it was more versatile as an amp platform. Most people agree that the second version is superior, but the hype surrounding the first version has given it a lasting reputation.
The WIIO was succeeded by the RAH, which is largely the same circuit but with a midrange knob added, and the circuit re-voiced for Led Zeppelin’s famous show at the Royal Albert Hall. (They even referred to the RAH as the “Royal Albert Hall Edition of the WIIO” in the manual.) The WIIO was discontinued shortly after the release of the RAH.
The Apollo Mk. I is a direct adaptation of the V2 WIIO (non-limited version). The only modification is the addition of a trimmer that makes a feedback resistor variable, allowing adjustments to the gain, tone and feel of the circuit. The RAH is also available as the Apollo Mk. II.
Important note: According to Catalinbread, the WIIO (and thus this pedal) should only be run at 9V. It should not be used with an 18V adapter or with the Aion FX 18V bypass PCB.