Fargen Mini Plex

December 21, 2005

Like many boutique builders, Ben Fargen (pronounced Far-gen, as in Gen-X) does everything himself. There’s no greater motivation for quality than having your name on the front, and there’s also no payroll leaner than a one-man show. Fargen also simplifies production by using the same basic zinc-plated steel chassis for many of its models, including the Mini Plex. This sturdy and simple open-box design has no extra reinforcement folds, fancy welded corners, mounting ears, or blocks, but it’s punched to accommodate every component needed for all the applicable models. This universal-chassis approach saves Fargen (and you) money because it allows him to place orders for larger quantities, which further amortizes the sheet-metal shop’s setup fees.

While a good chassis can be costly, an amp’s transformers are typically its most expensive components. The Mini Plex uses a standard Hammond power transformer, and this transformer is used in some other Fargen models, as well. Buying off-the-shelf power transformers in large quantities helps to reduce cost, which allows Fargen to splurge on the Mini Plex’s most tone-crucial component—it’s custom-wound, interleaved and paper-layered output transformer.

Fargen Cool

From the outside, the Mini Plex may look like just another run-of-the-mill Marshall plexi repro (albeit an upside-down one), but a careful study of its circuitry reveals that it’s far from being just another copycat. For starters, the Mini Plex has a very unusual parallel single-ended output stage. While most amps with two output tubes configure them in a push/pull arrangement, the Mini Plex has two cathode-biased EL34s wired in parallel. You don’t get as much power this way, but the tone is noticeably richer in lower harmonics. The Mini Plex also has a Hi/Low power switch that reduces the amp’s output from 12 to 8 watts by disabling one of the EL34s.

The Mini Plex has only two preamp tubes. Of course, a simple design reduces parts count and, therefore, cost, and it also reduces labor time as there are less components to install and wire. And many tone gurus will also agree that a simple circuit can often provide a richer tone, as well. The two halves of the Mini Plex’s first 12AX7EH preamp tube are wired in parallel—a configuration that’s somewhat reminiscent of a vintage Marshall preamp with it inputs jumpered.

Fargen’s front-panel Decade switch provides three different preamp voicings by bypassing the first stage’s shared cathode resistor with a .68uF capacitor for the ’60s position (for enhanced upper mids and treble), and a 25uF cap for the ’80s setting (for full-range boost). The ’70s position leaves the resistor unbypassed for lower gain and more clean headroom. The Mini Plex’s Volume knob follows this first stage, which feeds the Marshall-style second gain stage—a cathode follower-driven classic 3-knob tone stack.

Immediately following the tone controls, the Master Volume control is a simple voltage divider that also feeds the output tubes. That’s right—there is no phase inverter tube like you would expect to see in a typical Marshall clone. Remember the Mini Plex has a single-ended output stage, so there’s no need for a phase inverter/splitter, and the preamp’s two gain stages are more than sufficient to drive the EL34s to maximum power. How’s that for tube-savvy economics?

Flex The Plex

So how does a Marshall-inspired preamp sound when it’s driving a parallel single-ended EL34 output stage? The Mini Plex can sound amazingly lush, rich, and warm at low volumes, and it gets gradually more aggressive and grinding as it gracefully makes the transition into overdrive. Set to Hi power mode, and at relatively moderate volume levels through the J Design Old Dog 12-12 test cab, I coaxed some absolutely luscious jazz tones from a Guild archtop. Grab a Les Paul, crank it a little more, and you’ll be steppin’ out with some authentic-sounding Beano-era Clapton snarl. The Mini Plex maintains its vintage-amp character and responsive dynamic feel when run wide open, but with only two preamp gain stages, you can’t expect modern high-gain preamp saturation. This is truly an amp for those who love classic tones, but want to get them at more manageable, and tolerable, volume levels.

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