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Harman/Kardon hk670 receiver amplifier (Stereo Review, Apr 1979)

RickSanchez

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#1
I was inspired to do some research after reading Amir's review of the Yamaha A1 vintage amplifier. Anyhoo, this thread is offered more as a nod to the website AmericanRadioHistory.com (https://www.americanradiohistory.com/index.htm) which has a fantastic catalog of Stereo Review magazine back issues:

A brief history of Stereo Review:
Stereo Review was an American magazine first published in 1958 by Ziff-Davis with the title HiFi and Music Review. It was one of a small group of magazines then available for the individual interested in high fidelity (the other major ones being Audio and High Fidelity). It featured a blend of record and equipment reviews, articles on music and musicians, and articles on technical issues and advice. The name changed to HiFi Review in 1959. It became HiFi/Stereo Review in 1961 to reflect the growing use of stereophonic technology in recordings and broadcasts. In 1968 it became Stereo Review, reflecting the broad shift to stereophonic reproduction and simplifying the title. In the late 1980s, the magazine was acquired by CBS Magazines and in 1989 it absorbed High Fidelity magazine. The magazine became Sound and Vision in 2000, changing its focus to home theatre.
Always nice to find objective reviews in places beyond ASR ...



Harman/Kardon hk670
(Full disclosure: I own one of these and use it for vinyl, FM, and some digital music listening when I'm not using headphones.)

From ToneAudio: "The HK670 twin powered integrated receiver was Harman/Kardon’s top of the line model from about 1979 to 1981 and was its last with an analog tuner." The original retail price was $569. This retail price was for the standard metal case; there was an optional walnut case that cost extra.

hk670_frontpanel_cropped.jpg





Basic Specs
(pulled from the hk670 owner's manual)
  • Power output: 60 watts per channel into 8Ω (stereo)
  • Frequency response: below 3Hz to 140kHz (-3.0 dB)
  • Total harmonic distortion: 0.03% 1kHz at rated output
  • Intermodulation distortion: 0.05% at rated output
  • Damping factor: >30 at 8Ω
  • Input sensitivity: 2.2mV (MM), 130mV (line)
  • Signal to noise ratio: 90dB (MM), 102dB (line)
  • Speaker load impedance: 8Ω to 16Ω
  • Dimensions: 18.5 (W) x 6.25 (H) x 14.0 (D) | 476mm (W) x 159mm (H) x 360mm (D)
  • Weight: 26 lbs | 12kg
  • Years: 1979-1981

hk670_specs.png





Measurements
Some highlights taken from the April 1979 edition (pages 47-50) of Stereo Review magazine. *Please note*: I cannot speak to the equipment that was used for these tests, nor how it compares with Amir's test equipment.
  • "The receiver's outputs clipped at 74.4 watts per channel into 8 ohms (IHF clipping headroom = 0..94 dB). The output into 4 and 16 ohms at clipping was 112.4 and 43 watts, respectively. The IHF dynamic headroom was 1.05 dB, corresponding to a short-term output of 76.5 watts into 8 ohms. The closeness of the clipping- and dynamic- headroom ratings indicates the use of well regulated power supplies in the hk670."
  • "The harmonic distortion of the hk670 at 1,000 Hz was extraordinarily low at most usable power levels. From less than 0.002 per cent at 0.1 watt, it increased smoothly to 0.003 per cent at 1 watt, 0.01 per cent at 20 watts, and 0.028 per cent at the rated 60 watts. The intermodulation distortion was about 0.028 per cent at power outputs from 1 to 10 watts. It increased at lower and higher outputs, to 0.08 per cent at 0.1 watt and 0.095 per cent at 60 watts."
  • "At rated power, harmonic distortion was under 0.03 per cent through the mid frequencies, rising to 0.04 per cent at 20 Hz and 0.05 per cent at 20,000 Hz. At reduced power, the distortion was consistently lower than at full power, with typical readings between 0.006 and 0.01 per cent over the entire audio band at normal listening levels."
  • "The hk670 evidently has a very effective system [in the FM tuner section] for removing the 19 -kHz pilot carrier from its audio circuits (no schematic was supplied, so we do not know if it uses a filter or a canceling circuit). The frequency response was almost ruler-flat-within +0.1, -0.2 dB from 30 to 10,000 Hz, rising to +0.4 dB at15,000 Hz. In spite of the fully maintained high -frequency response, the 19 -kHz leakage into the audio was a very low -69 dB. The tuner hum was an inaudible -71 dB."

hk670_measurements.png





Conclusion
Some highlights taken from the April 1979 edition (pages 47-50) of Stereo Review magazine.
  • "Our measurements of the hk670 showed it to be an absolutely first-rate receiver, with audio and FM distortion levels that until recently were found only in the most expensive and esoteric components. Its other performance characteristics were of comparable excellence."
  • "Harman Kardon appears to have done almost everything exactly 'right' in the design and execution of the hk670. Any criticisms we might care to make would be rather minor. There is no question that the hk670 is a fine receiver and a fine value in its price range."
 
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restorer-john

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Mar 1, 2018
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#5
I love the mini components from the start of the 80s. I have a heap of them. Lots of little Aiwa integrateds and some gorgeous Akai units. Fun.
 
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