Colby Mod Machine 22/100 Reviewed

Mitch Colby knows a thing or two about British tube tone.
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AFTER WORKING FOR MARSHALL’S U.S. distributor for 32 years, and making several trips to the U.K. to ferret out and collect dusty vintage amps, Mitch Colby knows a thing or two about British tube tone. Colby’s new Mod Machine 22/100, which debuted at NAMM earlier this year, is the culmination of his curated tour of British lead-amp tone, in a head that aims to take us from the thick, edge-of-breakup sounds of the early ’60s, right through the high-gain tones of the ’80s, ’90s, and beyond. If this implies multiple channels and button-loaded footswitches, hang fire: This is a single-channel amp with a totally hand-wired, all-tube signal path—but one that’s packed with switches and bypassable added gain stages that enable players to “mod” the circuit for themselves, without lifting a soldering iron. As such, it’s both a nifty toy for fans of big British amps, and a powerful performance tool. The Mod Machine 22/100, as reviewed here, coaxes 100 watts from four EL34s, but is switchable down to around 22 watts—in four combinable stages—via its Fixed/Cathode Bias switch and Pentode/Triode Mode switch, both of which act directly on the output tubes (a 50-watt Mod Machine 12/50 is also available).

The core of the amp is found in the Volume, Treble, Mid, and Bass controls in the front panel’s upper row, along with the Presence and bonus Hi Trim (Cut) controls in the bottom row. Pre- Vol and Post-Vol provide, respectively, a sort of JCM800-style pre-phase-inverter master and contemporary post-phase-inverter master, in series. A Stage 2 Gain control with On/Off switch lashes on modern high-gain tones as desired. A 4-way Emphasis switch clicks you from straight-in vintage voicing to early plexi high-treble to thick and nasal to brighter and more aggressive, while a 3-way Shift switch sets the midrange voicing. Combine them as you like, and you run the gamut of blues-rock to classic-rock to proto-metal to shred tones—all from one amp. The Mod Machine’s décor is monochromatic and businesslike outside, although the view inside the box is rather more festive. All the “mods” require some considerable wiring prowess, which Colby achieves neatly, using industry-standard components hand-wired on a thick eyelet board.

Tested with a Strat and a Les Paul through a Marshall 4x12 cab (loaded with Celestion G12H speakers), and a Sourmash 2x12 with Scumback M75-65s, the Mod Machine proved itself, first and foremost, an amp that was looking to rock out. Setting up the more vintage-certified signal path issued bold, round, clean tones with the Volume around 11 o’clock (Gain 2 off), and sweet, easy blues bite when rolled up toward mid afternoon. At these settings, leaping right into more sizzling, stinging plexi territory was easy with a twist of the Emphasis and Shift controls. Full-on scorched-earth leads were then just a tweak away, with the introduction of the Stage 2 Gain and some judicious application of Pre- and Post-Volume masters to tame the maelstrom. Switching to Cathode Bias brought a slight drop in headroom along with more harmonic saturation and chime—not so much Vox as a slightly gnarly Selmer Zodiac 30—for some fun alternative-vintage grind, although I found the Triode Mode a little dark and loose, and therefore less useful. Most of all, though, the Mod Machine seems to dig screaming away in its firmer, punchier Fixed Bias and Pentode settings, pumping away like any powerful British four-holer, where the dual masters do a good job of reining in the decibels.

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In short, this amp does a lot, and the majority of its sounds are very, very good. But it definitely takes some serious exploring to make the most of the Mod Machine’s potential, and the comprehensive user’s manual helps. Some combinations of settings just sound like they’re made for each other (and, in fact, they are, according to Marshall’s own evolutionary history), while others kind of clash, sounding a little rough or strident. That said, if you’re mod-minded and willing to explore, this amp has a ton to offer. Some players will segue through lovely clean and crunch tones to the lead tone of their dreams, only to wish they had a footswitch to take them instantly back to the former. Nope, you’ve got to click your way back. But such is the nature of the Mod Machine, and unlike those mods that you’ve paid to have hardwired into your old British tube head, at least Colby’s mods are all easily reversible.

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PRICE $2,850 street; head only


CONTROLS Volume, Treble, Mid, Bass, Stage 2 Gain, Pre Vol, Presence, Hi Trim, Post Vol, 5-way Emphasis switch, 3-way Shift switch
POWER 100 watts (down to 22 watts in four stages)
TUBES Four 12AX7 preamp tubes, four EL34 output tubes
EXTRAS Impedance switch (4/8/16Ω). Dual speaker outs. Fixed/Cathode Bias switch. Pentode/Triode Mode switch. Tube buffered effects loop with send and return levels and front-panel on/off switch.
WEIGHT 46 lbs
KUDOS Like a history of big-box British tube-amp tone in one package. Excellent build quality.
CONCERNS Takes some learning to discover the best settings. Some players might yearn for foot-switchable channels.