Teac EX-20
A four-mic input expander that turned a small Tascam board into a bigger one — assuming you could find the other modules.
Overview
The EX-20 is not a mixer. It's a building block, and that distinction matters more than anything else about it. Teac's Tascam System 20 was a modular console concept, and the EX-20 was the input expander — the module you bought when the base unit's complement of microphones wasn't enough. On its own it does very little. As part of a System 20 stack, it's the difference between tracking a drum kit and tracking a singer-songwriter.
The System 20 was unveiled at the February NAMM Show in Los Angeles, and the concept behind it was unusual enough that contemporary coverage spent real column inches explaining it. The system comprised four building blocks that could be coupled together to construct a mixer as small or as large as the user needed. The heart of it was the MM-20 Master Module, which carried six inputs — a pair of transformer-isolated mic inputs and four line-level inputs — along with four main outputs, a stereo auxiliary send output, and separate monitor and headphone feeds. The EX-20 was the input expander: four transformer-isolated microphone inputs plus a stereo auxiliary send. Stack one onto an MM-20 and you had six mic channels. Stack two and you had ten. That was the whole idea.
The design rationale, according to Teac, was that the system should operate much like an electronic patch-bay. Instead of switching signals around inside a mixer or routing them to dedicated multitrack, monitor, foldback and echo send outputs, the user treated the sections as building blocks and connected them up in whatever format the session demanded. Tascam's US marketing manager at the time, Dave Oren, framed the absence of switches as the system's defining virtue — remarkable flexibility achieved by leaving routing decisions to the patch cables rather than to front-panel controls. Whether that reads as liberation or as extra work depends entirely on the temperament of the person behind the desk.
What the EX-20 bought you, concretely, was microphone inputs. The MM-20's two transformer-isolated mic inputs panned between outputs 1 and 2, while its four line inputs were connected between 3 and 4. Hooking up the EX-20 expanded the mic count substantially — contemporary write-ups noted that up to six microphones could be connected to the MM-20 once the add-on EX-20 was in place, with the mic channels usable as subgroups if the engineer wanted to combine them with the final stereo house mix via a couple of line inputs. For a four-track operation, that meant a realistic path to miking a kit properly rather than close-miking one source and DI-ing everything else.
The System 20 modules were designed to sit permanently patched to as much outboard recording hardware as possible. That's a philosophy with real consequences for how the system was used: the four multitrack inputs stayed connected to the MM-20's line inputs, available at all times for foldback and monitoring during overdubs and instantly ready for a trial mixdown. During mixdown, outputs 2 and 4 became the recording outputs feeding the mastering machine and meter bridge. The EX-20 slotted into that permanently-wired world as an always-available bank of extra mic preamps — not something you patched in for one session and pulled out for the next.
Cosmetically, the System 20 modules bore a similarity to the Model 144 Portastudio — comparable overall dimensions and weight, similar style switches (of which there were very few), knobs and faders. The comparison is instructive precisely because it breaks down: the Portastudio was a self-contained unit for making simple cassette demos, while the System 20 demanded that the user decide up front what format of mixer was wanted and then build it. The EX-20 is the purest expression of that demand, since it does nothing at all until it's patched into an MM-20 and given something to do.
Pricing at introduction put the EX-20 at £125 in the UK, against £195 for the MM-20, £119 for the PE-20 parametric equaliser module, and £85 for the MU-20 meter unit. The four units were slated for UK availability in July. A complete system — master, expander, EQ, meters — came to £524, which was serious money for a home recordist but a fraction of what a conventional four-buss console cost. The PE-20 itself was worth understanding as part of the ecosystem: four identical channels of parametric equalisation designed to be inserted between the send and receive sockets fitted to each input channel on the MM-20 and EX-20 modules, with three bands offering up to 12dB of cut or boost, the low band continuously adjustable between 60Hz and 1.5kHz, the mid between 1.5 and 8kHz, and the high fixed at 10kHz. The fact that the EX-20's input channels carried those insert points is the detail that makes it more than a passive mic preamp bank.
Contemporary coverage of Tascam's modular concept in the US trade press framed the MM-20 as the heart of a professional-quality four-track recording system available for under $400 — the advertising line ran "Start a Studio. Under $400" (Modern Recording, June 1982, p.45). The EX-20 was the first step up from that entry point. Period write-ups also noted the system's provisions for four-track monitoring and its stereo line, monitor and cue output busses, which is the architecture the EX-20's stereo auxiliary send feeds into.
What the EX-20 asks of a buyer today is patience and a complete system. A lone EX-20 module is close to useless — it needs an MM-20 to supply the master section, the outputs, and the monitoring, and it benefits enormously from the PE-20 and MU-20 completing the stack. Collectors chasing System 20 components should expect to assemble them piecemeal and should budget for the whole system rather than the expander alone. The absence of switches that made the design flexible also means there are few front-panel controls to fail, which is a small mercy; the patch sockets and the transformer-isolated mic inputs are the parts that matter, and they should be checked carefully on any example offered for sale.
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