UnderTone Audio UnFairchild 670M mkII – Vari-Mu Compressor Plugin

The Fairchild 670 is the most mythologized compressor ever built — and one of the most awkward to use, with six preset time constants and threshold behavior assuming 1950s console levels. The unfairchild 670m compressor plugin models something different: hardware that took the Fairchild circuit and rebuilt the control set around it.

What Is the UnFairchild 670M Compressor?

UnderTone Audio, run by Eric Valentine, built the UnFairchild 670M II as an answer to the original’s limitations, not a clone. The variable-mu tube core follows Fairchild principles, but the controls were redesigned: four continuously variable time constants join the six originals, the DC Threshold became user-adjustable for modern and vintage gear, and the detector switches between feed-back and feed-forward behavior. Mid/side operation, sidechain processing and true bypass followed. The plugin, developed with MixLand, models that hardware — so it neither sounds nor behaves like a stock 670 clone.

Why Choose the UnFairchild 670M Compressor?

Separating distortion from compression is the standout trick of the unfairchild 670m compressor. On real tube hardware, harmonic content is a by-product of drive level — more color means more gain reduction. The plugin’s THD control breaks that link: heavy compression with the character pulled back, or minimal reduction with tube color pushed forward. Neither is possible on hardware.

Control depth runs deep: ten time constants plus adjustable DC Threshold span the most delicate touch to genuinely aggressive processing, with knee behavior a single-threshold design cannot reach. Feed-back detection reacts gently and musically; feed-forward responds faster and more precisely — two personalities in one unit. Mid/side operation, praised in the Tape Op review for its widening effect, makes this a mastering-grade tool.

Feature Highlights

The unfairchild 670m compressor pairs the rebuilt hardware control set with software extras:

• Variable-mu tube modeling of the 670M II hardware, built with MixLand
• 10 time constants — six presets plus four continuously variable
• Adjustable DC Threshold for modern and vintage signal levels
• Feed-back / feed-forward switchable detection
• THD control — tube color independent of gain reduction
• Mid/side, sidechain, true bypass plus makeup gain and wet/dry mix

Who Is It For?

The unfairchild 670m compressor is for mix and mastering engineers wanting Fairchild-style tube glue without 1950s ergonomics — and for anyone whose conventional 670 emulation feels too polite. Rock, pop, soul and hip-hop producers will reach for it on buses, vocals and drums where tube character is genre vocabulary.

Compatibility

Available for Mac and Windows, working in all major DAWs. Check the product page for current format details and system requirements before purchase.

Mix Tips for the UnFairchild 670M Compressor

On the mix bus, start with a variable time constant and feed-back detection for glue that breathes — then flip to feed-forward when transients need taming without dulling the mix. The adjustable DC Threshold is your friend with hot modern stems: raise it until the knee behaves instead of fighting input gain.

Use the THD control like a parallel color send: dial in the tube character you want without the extra gain reduction, or push saturation on a drum bus while M/S mode keeps the center solid. Bypass often — the difference should be felt, not assumed.

FAQ

How does it differ from other Fairchild plugins?

Most model a stock 1950s unit. The unfairchild 670m compressor models hardware that deliberately diverged — variable time constants, adjustable DC Threshold, dual detection — so it sounds and behaves differently from conventional clones.

What does the THD control do?

It adjusts harmonic coloration independently of gain reduction — tube character without extra compression, or hard compression kept clean.

Does it do mid/side?

Yes — mid/side operation plus sidechain processing and true bypass suit it to mix-bus and mastering duties.

Want the Fairchild sound with modern control instead of 1950s limitations? The unfairchild 670m compressor is that plugin — get it at Plugboutique’s deal price today.

Explore more Mix & Master Plugins at Plugboutique, or pair it with SIR Audio Tools StandardCLIP – Precision Clipper Plugin for an even bigger toolkit. Also listed on PluginsBoutique.