Since the early 1960s, Ritchie had used effects units, starting with Deep Purple, which I will, however, not enumerate here. But I would still like to mention, as this is going to be important, that Ritchie actually owned a Vox Wah-Wah, amongst other things, around 1966-67, when he was still a session musician. In 1968, he acquired a Marshall Reverb Fuzz #2021 (the Moody Blues had one as well) and also used it live, for instance, in “Mandrake Root”. The spring reverb was of a Hammond type, and the fuzz unit, equipped with germanium, was a copy of the Marshall Supa Fuzz which had actually been manufactured by the Macari brothers (=Colorsound) as OEM for Marshall or Park. On the photo from Jazz Bilzen (see above), the effect box is placed on the floor between the Marshall Stack and the VOX AC30, placed on a chair. This part was also used in the studio for the first DP records. On the first two DP LPs, in particular, the above Wah was manifestly employed. The last time the Wah appeared again after a long break was in Rainbow’s first LP in the song “Snake Charmer”, but no longer after that.
In 1969, Ritchie acquired several boxes of Arbiters in one go, an “Add-A-Sound” (also used by Frank Zappa from approx. 1973), and a “Soundette”. The Soundette was a belt-driven disc echo (similar to the friction wheel-driven Binson Echorec) featuring a total of 5 heads, incl. recording & erase head and GE transistors. The echo time was, however, quite short due to the high rotational speed of the disc. For “Mandrake Root”, Blackmore replaced the Marschall #2021 by the Soundette approximately until mid-1970 after which the device disappeared into RB’s evidence room. But Ritchie was really taken with the Add-A-Sound, in particular. This was a Fuzz that could generate an octave higher and an octave lower at the push of a button. Many tracks on the “In Rock” were recorded with this, e.g., the octave effect of Living Wreck or Flight of a Rat. The Add-A-Sound is noticeable almost throughout the entire record. At the same time, a new FuzzFace of 1969 was frequently employed (BC108C), e.g., in the intro to “Speed King”. This one was usually employed far less as an aggressive Fuzz rather than to just crunch the signal. The low gain sound of the subsequent “FireBall” was also played in with this FuzzFace, along with a Hornby Skewes as booster.
In “Machine Head”, the Fuzz was no longer employed but a/the treble booster was used in front of Ritchie’s AC30, instead.
All this was dubbed in the storied Rolling Stone Mobile Studio, a converted truck equipped with the legendary Helios mixer plug-ins whose resourcefulness was in its formal simplicity. After a three-stage Si transistor input stage, the entire sound field was passive and, well, still had real inductors & transformers inside and that not too scarcely, and even the parametric middle EQs were passive, so that this was a solid piece of discrete analogue craftsmanship! The output was equally formed by a three-stage line amplifier module. It can be clearly assumed that the Helios contributed significantly to this sought-after sound creation under Martin Birch’s fingers. Many authoritative recordings were made in the Rolling Stones’ Helios Truck in the 1970s, see also Wikipedia.
1970: Led Zeppelin III - Led Zeppelin