Rev A, Rev D, Rev F and AE: which FET compressor revision for which job

The classic FET limiting amplifier stayed in production for decades, and its circuit changed several times along the way. Ask five engineers which FET compressor revision sounds best and you will get five answers, because the differences are real: the preamps, the output stages and the transformers all changed. PINCH-76 models four of those revisions in one plug-in, so you can hear the argument for yourself.

If you need a quick pick before reading on: Rev D (LN) is the clean all-rounder and the right default. Rev A adds grit, Rev F cuts through a dense mix, and AE is for compression you feel rather than hear.

Rev A: the raw original

The first version has the most character of the four. Its FET preamp runs about 5 dB hotter, it produces the most harmonics, and its release reacts strongly to the music. Push it and it growls.

Use it on: vocals with attitude, room mics, crushed parallel drums, anything that should bite.

Rev D (LN): the clean workhorse

The low-noise version is cleaner, with a full low end and smooth gain reduction. It is the one most engineers mean when they talk about this compressor on a lead vocal or a bass, and it is the PINCH-76 default.

Use it on: lead vocals, bass, acoustic sources, anything that should stay clean while it is controlled. Settings for both are in how to compress vocals and how to compress bass.

Rev F: the one nobody talks about

Rev F is rarely modelled, which is a shame. Its class A/B output stage makes it brighter and leaner in the lows, with more odd harmonics, and it holds gain reduction a little longer. The result pushes a sound forward without making it jump out.

Use it on: snare, electric guitars, vocals that have to cut through a dense arrangement.

AE: the gentle one

AE is the softest voice of the four. Its whole attack range is slower, position 1 becomes a true slow setting of about 30 ms, and its ratio keys are 2, 4, 8 and 20 instead of 4, 8, 12 and 20. That makes it the revision for buses and gentle levelling.

Use it on: the mix bus, drum and vocal buses, acoustic guitar, piano.

What the measurements show

Character is easy to claim and harder to prove, so PINCH-76 was measured on the bench. With no gain reduction, Rev A, Rev D (LN) and AE are flat from about 200 Hz up and differ only in the deep bass. Rev F is voiced differently: a broad presence lift of about 1.3 dB around 3.4 kHz and a gentler low end.

The harmonics tell the rest of the story. At 1 kHz with 8 dB of gain reduction, Rev A's second harmonic is about three times stronger than in the other revisions. That is the grit you hear.

Quick guide

You want	Load	Why
A clean, steady vocal	Rev D (LN)	Smooth, transparent, full low end
A vocal that cuts through	Rev F	Presence lift, holds gain reduction longer
Grit and aggression	Rev A	Hotter preamp, most harmonics
Exploding room mics	Rev A, all buttons	The classic smash
Tight bass	Rev D (LN)	Clean low end
Mix bus glue	AE	Soft, slow attack, 2:1 and 4:1

Switching revisions in PINCH-76

Turn the ERA switch on the right of the panel. The change crossfades, so you can switch while the music plays, and all knob positions stay where they are. Each revision has its own gain structure, so leave AUTO GAIN on or re-check OUTPUT when you compare. In Dual Unit mode, the two units can run different revisions: Rev A catching peaks into Rev D (LN) levelling is a favourite.