Heathkit AD-2002
Twenty-nine ninety-five bought you the Electro-Voice four-channel decoder in kit form - and roughly three hours of soldering.
Overview
The AD-2002 is a Stereo-4 decoder, Heathkit's kit-built version of the Electro-Voice EVX-4 matrix decoder, sold for $29.95. It is not a receiver, not an amplifier, and not a self-contained quadraphonic machine. It is an add-on box that sits between an existing stereo system and the extra amplifier and pair of rear speakers that four-channel playback demands. The owner has to commit to the second amp and the extra speakers first. Then the box turns two channels into four.
It decodes material encoded with the Electro-Voice matrixing system - tapes, records, and stereo FM broadcasts carrying Stereo-4 encoding. It also synthesizes a four-channel effect from plain unencoded stereo. Electronics Illustrated (November 1971) described the kit as Heath's version of the Electro-Voice EVX-4, producing four-channel stereo from any encoded source while also enhancing ordinary stereo program material. Owners didn't need a library of encoded discs to hear something coming out of the back channels.
The circuit relies on an integrated circuit supplied by Electro-Voice, so the Heathkit operates in essentially the same way as the original E-V decoder. Electronics Illustrated (May 1972, p.?) put both the Heathkit and the competing Metrotec Stereo-4 through their paces and concluded that the performance of either kit could not be distinguished from that of the original Electro-Voice unit — and that both did a good job synthesizing four channels from non-encoded two-channel sources. For a $29.95 kit, that is the verdict that matters.
What's on the front panel
The Heathkit's front panel is spare: a master gain pot with on/off control and a selector switch. Tape monitoring is handled by the decoder itself rather than by a separate control on the panel. That separates it from the Metrotec, which added front and rear decode pushbuttons and a front-to-rear balance control to the basic E-V design. The rear panel carries an extra tape input and output, plus the selector switch that lets a tape recorder be connected for recording or monitoring through the decoder.
The lean control set is a real trade-off, not just a cost saving. The Metrotec's rear-decode switch lets a listener strip a soloist out of the rear channels and leave only hall ambience back there. That helps when full decoding smears a centered voice across the wall. The Heathkit offers no such refinement. Owners who want that flexibility are looking at the other kit; owners who want the E-V circuit for half the money are looking at this one.
Building it
Heathkit's assembly manual is the reason to buy this one over its rival. Electronics Illustrated (May 1972) noted that the Heathkit manual is very well thought out, that parts location is clearly identified on the printed-circuit board, and that all parts are properly labeled and easily identifiable. The technically unsophisticated builder should have no trouble. The reviewer built the Heathkit in just under three hours. The Metrotec, by contrast, arrived with an unlabeled board, no transistor basing diagrams, no lock washers, and too little hookup wire.
The Heathkit was not flawless. The same review reported errors in both manuals. An addenda supplied with the AD-2002 to replace page 15 created a fresh problem elsewhere, and a corrected diagram on one page introduced an error on page 20, where a soldering instruction should read S-3 instead of S-2. Builders of the era learned to read the addenda before touching the iron.
The board itself is tighter than the Metrotec's, though every component location is clearly marked. Weight is listed at 5 lbs. in Heath's January 1972 catalog listing.
How it sounds and what it needs
In the encoded-decoded configuration, Electronics Illustrated (November 1971) found the E-V system's sound very closely approximated a discrete four-channel setup and rated it good to excellent on all criteria, with the listening location only slightly more critical than a discrete system's. Synthesizing four channels from an ordinary stereo record was less impressive but quite acceptable: definition excellent, spatial perspective fair, listening-position requirement fair to good. The Heathkit shares the E-V circuit, so it inherits those results.
The catch is the system around it. The AD-2002 requires an existing stereo system, another stereo amplifier, and two more speakers. That is a substantial hidden cost stacked behind a $29.95 kit, and it is why these decoders were often bought by people already halfway into quadraphonic playback rather than by curious stereo owners. Electronics Illustrated (November 1971) estimated a full discrete four-channel system at around $2,000. The encoded-decoded route with the E-V or Heathkit decoder came in at roughly a quarter of that.
Collectibility
The AD-2002 is a niche piece even by Heathkit standards. It is useless without a second amplifier and rear speakers, it decodes a matrix system that lost the quadraphonic format war, and its value as a synthesizer of fake surround from stereo is historical rather than practical. What it has going for it is price and provenance: an unbuilt or cleanly built example is an inexpensive way to own a working piece of the four-channel era, and the E-V-derived circuit means it actually performs. Buyers should expect to check the addenda-corrected assembly against the manual, verify the Electro-Voice IC is present and seated, and confirm the tape-loop jacks and selector switch are intact — those are the parts that make it useful in a modern system. Collectors note that documentation matters more here than condition; the manual's errors are part of the object's story.
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