FX20B Stereo Phasor / Stereo Phaser
FX20B Stereo "Phaser" (1987) and "Phasor" (1988)
The FX20B Stereo Phasor / Phaser succeeded the FX20 in late 1985, adding a Depth control and another output while revising the circuit to use three dual OTA chips. The FX20B featured six stages of phase shifting, while the Boss PH-2 Super Phaser (introduced in 1984) featured up to 12 stages of phase shifting. The FX20B was produced with several cosmetic variants (see below) until 1998, when it was replaced by the final-series FX20C.
- Controls: Speed, Depth, Regen
- Cosmetic variants:
- "Stereo Phasor" vs. "Stereo Phaser": The original FX20 phase-shifting effects pedal followed in the footsteps of DOD's first-issue 201, 401, and 490 Phasors, which used the Mu-Tron spelling of "phasor" (instead of "phaser", as used by Ross and Boss, among others). The first FX20Bs were labeled as a "Stereo Phasor", although the instruction manuals referred to a "Stereo Phaser". In or around early 1987, the pedals briefly switched to the "Phaser" spelling, but they switched back to "Phasor" by the end of that year. Finally, when the "second series" DOD FX pedals were introduced in early 1989, the FX20-B was called a "Stereo Phaser" and retained that spelling for the rest of its production run.
- Gray vs. gold sparkle base coat: In the early 1990s, DOD "dressed up" the appearance of a few of their older pedals, including the FX20-B and the FX25. In early 1993 (around serial number 1300k), the FX20-B's drab gray base coat was replaced by a gold sparkle base coat.
- Instruction manuals: At least three different covers/versions of the instruction manual exist: (left-right) mid 1980s, late1980s/early 1990s, mid 1990s. None of them have a copyright date, and all refer to the FX20B as the Stereo Phaser. Aside from the size and front cover they are identical, with exactly the same content (including the apparently erroneous claim that the FX20B is a 4-stage phasor, which if true would imply one of its three dual OTAs is not used).
- Technical info:
- Specifications (circa 1986): Input impedance = 500 k Ohms, Output impedance = 1 k Ohms; Maximum Input Level = 4V peak to peak; Gain = Unity; Stages of Phase = 6; Phase Shift = 1080 degrees; Signal to noise ratio = 90 dB
- Official schematic provided with pedal by DOD (circa 1986)
- Corrected official schematic (circa 1986)
While repairing his early-issue FX20B (see below), Rocl Li noted that the overview IC/transistor map had inadvertently switched the locations of U5 (should be MC 1458) and U6 (TL022). Although both chips have an identical pinout, it is unclear if they are exact replacements for each other as used in the circuit.
- Notable IC chips: three dual OTAs (NE5517s on the original schematic, LM13600Ns on every production FX20B we've seen thus far)
- Component-side circuitboard images: April 1986, stock and repaired (courtesy of Rocl Li) April 1987 June 1988 February 1991 June 1997
- FX heritage: FX20 FX20B FX20C
- External links:
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