This version has R28 mounted on the circuit board and also switch from six op-amps to three TL062 dual op-amps. Below is a circuit board from 1979/1980 with an arrow highlighting the added feedback resistor.Ī short time later MXR introduced an updated version of the Phase 90.
This resistor– which later became known as “R28″– gives a bit of a midrange boost and adds more resonance in the circuit. In 1977 the Phase 90 transition into its Block Logo form which more or less was the same exact pedal except for one resistor. This model was released in 1974 and lasted until 1977. This likely has little to do with tone and more to do with the availability and cost of ICs at the time. The most noticeable difference between this model and the future iterations is this one has six ICs all of which are single op-amps. This is the holy grail of Phase 90s and has been in such high demand that MXR reissued the pedal made using the same circuit board as the original one seen below: Specifically we’ll be looking at the three oldest versions of the circuit boards and what the key differences are.įirst up is the Script Logo Phase 90 which gets its name from the elaborate script font used on the casing. Now I’ve seen hundreds of MXR Phase 90s over the years and by far the most common request is for info on the “Script mod.” I’m certainly not an MXR historian but what I can offer is a first hand account of repairing and modifying these pedals.
