Teac AX-300
A four-channel mixer built to sit between a TEAC reel-to-reel and the rest of the rack. In its day it was priced at less than the tape deck it was made to serve.
Overview
The AX-300 is an audio mixer with six inputs and four outputs. TEAC sold it as an optional accessory for its quarter-inch four-track machines. TEAC positioned it as a serious add-on, not a throwaway.
The AX-300's own manual is thin on what's inside it. The documentation that survives is mostly instructions for using the mixer with the A-3340S, and it treats the AX-300 as one of several tools in the TEAC ecosystem. TEAC's own literature groups it with the AX-20 Mixdown Panel and the AX-10 Sound on Sound Echo Unit as accessories "capable of the proper mixing action." The company's guidance on why you'd want one is blunt: fold a four-channel recording down to two channels without sacrificing the output level of each individual channel. That's the AX-300's job in a sentence.
The manual's copy instructions spell out the practical case. When making two-channel copies of a four-channel tape, TEAC recommended a mixdown panel or audio mixer to "establish the desired balance without losing the required output level from each channel." The AX-300 is the mixer in that pairing. The AX-20 is the simpler panel. For anyone running a 3340S today who wants to bounce a four-track master to stereo without a modern interface in the chain, the AX-300 is the period-correct answer, assuming one can be found with its accessories intact.
The accessories matter here. The AX-300's rear panel carries a remote/timer control connector that accepts either the RC-120 Remote Control Unit or the RC-320 Timer Control Adaptor. The manual is explicit that unless one of those two optional units is plugged in, a dummy plug must be inserted in that connector "to permit proper operation of the tape transport." Lose the dummy plug and you've lost basic transport function until you source a replacement or wire a substitute. That separates a working AX-300 from a shelf ornament, and it's the first thing to check on any example offered for sale.
The rest of the rear panel is what you'd expect from a period TEAC. There are line-in jacks on four-pin cord connectors (two pairs of the pin cords were included as standard accessories), mic inputs, output jacks, a ground terminal for tying the chassis to other components or earth, and an AC power inlet with a 2-amp fuse holder for overload protection. The output jacks are meant to feed either the discrete inputs of a four-channel amplifier or a pair of two-channel amps. TEAC notes that the channel designation on the outputs corresponds to the VU meters and level controls when viewed from the front, which makes patching less error-prone.
TEAC's manual is candid about the limits of simul-sync. When the record head is used for playback in that mode, the reproduced signal is of poorer quality than from the dedicated reproduce head, and the manual explicitly warns against judging tape quality from the simul-sync monitor output. The AX-300 doesn't fix that. It's a mixing tool, not a monitoring cure. What it does is let you balance four sources into a stereo pair while keeping each channel's level intact.
The classifieds that survive show people hunting for used AX-300s alongside AX-10s and AX-20s "in original boxes." Even in period, the accessory chain looks to have been harder to complete than the deck itself. The fact sheet offers no current market data, so no prices are given here. The AX-300's value is tied almost entirely to whether it comes with the dummy plug, the pin cords, and ideally the original manual.
Maintenance is similarly undocumented in the sources at hand. The 2-amp fuse is the obvious first check on a dead unit. The remote/timer connector and its dummy plug are the second. Beyond that, the AX-300 is a passive-looking accessory in a metal case with no published service data in the material available here, and anyone buying one should expect to trace signal paths by hand if something's amiss. TEAC's documentation focused on the flagship decks, and the AX-300 was a low-volume accessory.
The AX-300 is a niche tool for a niche workflow. If you're running a TEAC four-track and want to mix down in the period manner, it's the right box. Verify the dummy plug before you pay.
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