JAPAN RARE VINTAGE HI-FI ENGINE HARMAN/KARDON HK 6900 INTEGRATED

JAPAN RARE VINTAGE HI-FI ENGINE HARMAN/KARDON HK 6900 INTEGRATED AMPLIFIER IN MINT & 10/10 WORKING The HK6900, rated at 170 watts per channel into 8-ohm loads from 20 to 20,000 Hz with less than 0.08 percent harmonic or intermodulation distortion, is Harman Kardon’s most powerful integrated amplifier. Among its design and circuit features are the use of discrete (as opposed to integrated) electronic components throughout, low overall negative feedback (only 12 dB), and a wide bandwidth, extending far beyond the audio range. It is also designed to deliver high instantaneous peak currents into low-impedance loads. According to the manufacturer, the HK6900 can supply as much as 90 amperes of instantaneous output.

The HK6900 is a large, heavy amplifier, measuring 17-3/8 inches wide, 16 inches deep, and 6-1/4 inches high and weighing 37-1/2 pounds. Its full-size control knobs operate with a strikingly smooth and positive feel, and their functions are clearly labeled in gold characters on a black panel. Bar knobs select the speaker outputs for one or two pairs of speakers, monitor the playback from either of two audio or video tape recorders, and connect the amplifier to any of five input sources: phono, CD, tuner, a/v, and auxiliary. The tuner input can be switched to either set of tape outputs independently of the listening selection, and the two decks can be connected for dubbing in either direction.

At the bottom of the panel are two small pushbutton switches. One turns off the amplifier’s video-preamplifier circuits (the manual says, without elaboration, that this is “for purest possible sound quality”), and the other selects between the moving-magnet (mm) and moving-coil (mc) phono-preamplifier inputs (there are separate rear-panel jacks for the two types of cartridges).

There are four flat, rectangular switches at the lower left of the control panel for power, tone-control bypass, loudness compensation, and the subsonic (infrasonic) filter. Another switch, main direct, bypasses the preamplifier stages, routing the selected signal directly (but through the volume control) to the power-amplifier input. All of the front-panel controls use high-quality electronic switches.

According to Harman Kardon, the HK6900’s loudness-compensation circuit has been designed to correct for the midrange phase errors normally associated with low-frequency equalization. It is said to be free of the coloration or stereo-imaging degradation said to occur with conventional loudness-compensation circuits.

In addition to the various signal input and output phono jacks, the rear apron of the HK6900 has video input/output jacks for the two tape loops, which are designed to switch VCR’s as well as audio tape decks.

There are also monitor outputs as well as audio and video inputs for use with a laserdisc player. The speaker terminals are large, heavy-duty binding posts; unfortunately, they are spaced too widely to accept dual banana-plug connectors.

A somewhat unusual feature is a pair of jacks labeled “pre-out”— without the usual accompanying main-amp-in jacks. After some investigation, we determined that these jacks simply provide a separate line-level feed from the preamp section. They could be used to drive an external amplifier, although with no provision for disconnecting the HK6900’s own power amplifier that would be a waste. A more likely use for these jacks is to feed a signal to a surround device, a tape deck, or a mixing board.

A rear-panel pushbutton labeled SPEAKER OPERATING MODE adjusts the power-supply voltage on the output transistors for safe operation with either 4- or 8-ohm speakers. The instructions suggest normal use of the 4-ohm setting, which insures the coolest and safest operation of the amplifier. If only a single pair of 8-ohm speakers is used, however, the 8-ohm setting provides the maximum possible power output. Two of the three AC outlets are switched. Price: $1,299