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ADC amp brings back memories of its phono titan

technofile  by al fasoldt

Columns and commentaries in a life-long dance with technology
 

Simple gray rule



ADC amp brings back memories of its phono titan 


By Al Fasoldt

Copyright © 1988, The Syracuse Newspapers

The tiny Audio Dynamics Corp. was once the darling of audiophiles. Perhaps more than any other company of its size, ADC helped pull the reluctant audio industry into the glorious ‘60s and ‘70s age of high-quality stereo phonograph playback.

When ADC introduced its Model 25 phono cartridge more than two decades ago, thousands of record lovers switched immediately from the shrill phono pickups of that day to the airy ADC. They were spurred on, no doubt, by audio-store back-room tales of feather-light disc tracking and violins that sounded so sweet you could smell the sharp smack of shellac.

But all was not sweetness and lightness. ADC's legendary cartridges turned out to be a problem for speaker designers and amplifier manufacturers, because the cartridges gasped under the weight of the massive record-player arms then in use.

Records that weren't perfectly flat caused a problem. The arm wobbled up and down to try to keep up with the hill-and-dale obstacle course thrown up by the record, and the phono cartridge mistook all this commotion for extra-low bass notes. Bass notes, it should be noted—no pun intended—are wonderful things. But not when they are impostors, and especially not when they sneak into the sound system from the sub-basement. Regular lows, the kind that bass drums and organs make, go down into the 30s and even the 20s (in hertz, or vibrations per second).

Fluttering phono cartridges, however, can create artificial bass notes that drop all the way down toward zero. An interesting thing happens when an alternating current's vibration heads toward zero. As it goes back and forth at a slower and slower rate, it shows signs of an entirely different nature. It looks more and more like DC. If AC makes the speaker cone push out when it surges in one direction and pull in when it switches the other way, you can imagine what happens when direct current shows up. The back-and-forth party is over. All those electrons grab hold of the speaker cone and tell it to start marching.

If it could, it would two-step right out of the wooden enclosure and trot all the way to San Jose. But it can't, of course. So that's when it sits down and does the world's best imitation of a paper-and-plastic meltdown. And what you end up with is shredded speaker and fried nerves. It happened to me a half-dozen times in the five or six years that I pledged my allegiance to ADC's astonishing phono pickup, which would track Big Bill Broonzy's wildest piano bangings at one-fourth of the force needed by competing pickups from Shure and Stanton.

But any time the disc wasn't perfectly flat, this ballerina phono cartridge didn't dance well with my record player's King Kong arm, and so I sent it off to that retirement home for tired parts that I keep in the bottom of my closet.

And I forgot all about it until a few weeks ago. I was going through a product-release bulletin when I noticed that ADC was introducing an unusual amplifier, the CA-2000E. Built into the amp is a special circuit that was designed for just one purpose—to shut the door on those false-bass boomlets that sneak in when the phono cartridge can't keep up with record warps. The circuit works like the bass control on your amplifier or receiver, except for a big difference: The bass control trims the signal or boosts it a bit, but the circuit in the new ADC amp turns a raging torrent of low-frequency rumbling into a trickle.

When the music itself grumbles and groans, the ADC circuit lets it all come through. But if those record-warp woofer-bashers come along, the circuit deflects the foreign signals instantly. In technical terms, the circuit leaves a 20-Hz sound—about as low as you can hear—just about unscathed. But it cuts the level of a 4-Hz sound by 30 dB. What the technospeak means is that the circuit cuts out unwanted low frequencies 100 times more effectively than the familiar Dolby B circuit cuts out unwanted high frequencies.

Another unusual aspect of the CA-2000E is its remote control, which operates not only the amp itself but a matching ADC tuner and CD player. Unlike any other remote I've seen, the ADC model has three sending units— including one light-emitting diode that fires straight up so you can bounce the control signal off the ceiling instead of worrying about aiming the remote.


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