Sansui’s late-70’s line of hi-fi equipment is fairly collectible; I’ve had several of them over the years, and they generally sell for good money. My last pair, a tuner and integrated amp, actually went to a prop stylist for a film… I wish I could remember the name of the picture. Anyhow, aside from the usual amps, preamps, tuners, and integrated amps, Sansui also made this very unusual device during the ‘first-wave’ of home-music-production: The AX-7 ‘Audio Mixer.’ A four-input HI-Z mixer, the AX-7 was designed to allow the user more easily use multiple stereo tape decks to ping-pong tracks into a layered production. It also offered global spring reverb!
There is a good-looking example on eBay right now for $99 BIN, which is a great value just for the spring reverb!
“Bob Heil (October 5, 1940) is…most well known for creating the template for modern rock sound systems. He founded the company Heil Sound in 1966,which went on to create unique touring sound systems for bands such as The Grateful Dead and The Who. He invented the Heil Talk Box in 1973, which was frequently used by musicians such as Peter Frampton, Joe Walsh and Richie Sambora, and is still in use today.”
Bob Heil is a great American inventor. I’ve written about him before on this site; click here for an example. Here’s a quick look at some of Heil’s products from the mid 1970s. If anyone out there is still using any of these pieces, drop us a line and let us know…
The Heil HM88 Stereo Mixer
The Heil HM1000 Stereo mixer with optional plug-in phaser. Wow can you image. What would the modern equivalent of this functionality be? Built-in AutoTune?
The Heil HM1200 console with +/- 22DB equalization. Good lord.
The Heil Talkbox, the first of its kind. The bio-mechanical translation of a vocoder: pitch and formant information are supplied as distinct elements and a unique hybrid results.
Download a three-page article from Electronics World “Hi Fi Annual & Audio Handbook 1960” which details the construction of a 4-channel tube mixer:
“Electronics World” Magazine published these ‘hi-fi annuals’ in the late 50s/early 60s; from what i can gather, they seem to be collections of reprints of the notable audio-content that EW published in the prior year. I picked up this 1960 edition a few years ago in the excellent Antiques Mall of Madison; some excellent vinyl LPs and rare paper dealers as well.
Anyhow. This mixer has some interesting features; nice simple circuit for calibration pot for DB meter; the best part though is the output stage: a 6AK6 tube is used into a 10k ohm load and promises a .8 watt output. I am not aware of any other hi-fi line output stages with 6AK6s; def want to try it. .8 watts output would very welcome in many of my builds… can’t get enough of that clean headroom…
Here’s the schematic (included in the download as well).