Mackie CFX20
A compact effects mixer built around three identical four-channel slave boards - the biggest of Mackie's CFX trio, and the one that scales the same circuit up rather than reworking it. Contemporary UK retail listings from the period placed Mackie's dfx mixers starting at £279, per Sound On Sound (January 2003, p.272).
Overview
The CFX20 is the largest of Mackie's CFX-series compact effects mixers, a family that also includes the CFX•12 and CFX•16. The three aren't redesigns of each other. Each mixer is built from five circuit boards - Effects, Master, Slave, Power, and AC Power - and the Slave board is the one that adds channels. The CFX•12 carries a single Slave board, the CFX•16 carries two, and the CFX•20 carries three. Per Mackie's own service documentation, that is "the main difference between the three models." The CFX20 is the same mixer as its smaller siblings with one more four-channel block bolted on.
That layout matters if you work on one. The Master board is the main mixer circuit, and the Effects board mounts directly on its back. The service manual notes that design is identical to the one used in Mackie's PPM Professional Powered Mixer series. The Slave boards chain off the left of the Master board. The power board regulates AC into ±15 VDC, +5 VDC, and +48 VDC for phantom power. The AC power board holds the IEC connector, fuse holder, power switch, and caps. The CFX20 stacks three Slave boards where the CFX•12 uses one, so the internals are denser, but the circuit blocks are the same parts.
The input stage centers on a trim control with a ±6 to −50 dB range. It feeds a mic input rated at 3 kΩ balanced, with +48 V phantom power available. Line inputs sit at 40 kΩ balanced, and the insert, stereo line, tape, and effects-return jacks are all 10 kΩ unbalanced. On the output side, the main, insert, tape, sub, and effects-send jacks are all 150 Ω. The mic input takes a maximum of +18 dBu with the trim at +6 dB, and the line input takes +38 dBu with the trim at −15 dB. Rated output is +4 dBu, with a max rated output of +20 dBu.
Mono channels get a low-cut at 100 Hz rolling off at −18 dB per octave, plus a three-band EQ: ±15 dB at 12 kHz on top, ±15 dB at 100 Hz in the middle, and ±15 dB at 80 Hz on the bottom. Stereo channels get four bands - ±15 dB at 12 kHz, 3 kHz, 400 Hz, and 80 Hz. On top of that sits a nine-band graphic EQ with ISO octave centers at 63, 125, 250, 500, 1k, 2k, 4k, 8k, and 16k Hz, each band ±15 dB with a Q of 1.414. On a compact mixer, that graphic is the feedback-fighting tool, which makes the board a fit for small rooms and monitor gigs.
The noise numbers are respectable for the class. Equivalent input noise measures −127 dBu. Residual output noise on the main, monitor, and effects outputs with channel and master levels off is −95 dBu. Common-mode rejection is 60 dB at 1 kHz with the trim at 0 dB. Crosstalk between adjacent inputs or input-to-output is −90 dB at 1 kHz, and −80 dB at 1 kHz for the mute switch and break switch mute. Maximum voltage gain runs from 30 dB (tape input to main output, or effects return to main output) up to 76 dB (mic input to main output).
The onboard digital effects section is a 16-bit, two-channel unit with 16 presets. It's the same effects board used across the CFX line and borrowed from the PPM series. Sixteen presets is not a deep library, and nobody is going to mistake it for a dedicated outboard processor, but it saves a small rig from carrying a separate reverb box. The Effects board mounts on the back of the Master board, which keeps the internal cabling short.
One thing for anyone buying used: Mackie's service documentation lumps the entire CFX series - CFX•12, CFX•16, and CFX•20 - together with the PPM powered mixers (406M, 408M, 408S, 808M, 808S) under a single service bulletin describing a symptom to verify on any unit coming in for repair. The manual doesn't spell out the symptom in the excerpt available here. The grouping suggests these boards share service patterns across the CFX and PPM lines, so a tech familiar with one is likely familiar with the other. The service manual also includes full board layouts, a complete parts list, and a BOM that runs down to individual knobs (slide knobs, 9 mm knobs in light gray, magenta, blue/gray, and dark gray, plus a dedicated master volume knob).
Power handling varies by market. The AC input board is fused at 0.5 A slo-blo for the 100 VAC version, 1.0 A slo-blo for 120 VAC, and 1.25 A slo-blo for 230 VAC. The CFX20 ships with an IEC line cord and a 1 A slo-blo fuse on the 120 V variant. The IEC connector is standard, so a replacement cable is a hardware-store item.
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