Harman/Kardon hk770

Harman/Kardon M770

1 9 8 0 1980
1 9 8 3 1983

Harman/Kardon 700s : super-high bandwidth, swift slew-rates, discrete components only, DC design and minimal use of NFB.
More of the same since the early 1970s at H/K but, this time... different. For two reasons.

As sternly touted by Dr Matti Otala himself in Japan over dozens of ads and articles, T.I.M. and I.I.M. were the real enemies and nothing else.
T.I.M. stands for Transient Intermodulation Distortion, a nasty one that stems out of excessive use of negative feedback and results from increased I.I.M. (Interface Intermodulation Distortion) - all from the excessive use of NFB to reduce said distortion !

According to H/K, TIM is ten times more audible than THD and can be detected at leveles as low as 0,03% - read the TECH 1 explanation for the details about all those nasty distortions few ever... suspected :)

The 700s weren't made in the USA, just like said Citation series. They were made by the Shin Shirasuna Corporation, a company also known for products bearing the SILVER name.

The hk770 was an M770 in Japan and a Silver SA5050.

The hk770 is a dual-mono symmetrical DC circuit design with dual quad differential cascode, two toroidal transformers, discrete components only (no ICs), protection circuit which remain out of the signal path and 250Khz of frequency response.
It makes for two hk775 in one enclosure... with a loss in weight : both weigh 10,1kg.

Like the Citation XX, it has one subsonic filter and one ultrasonic filter, the slopes and cutoff frequencies of which I haven't been able to find...
Unlike the Citation XX, you need two hk775 to delve into the pleasure of powerful, tight and dynamic stereo.

Harman/Kardon hk770, image 1 Harman/Kardon hk770, image 2 Harman/Kardon hk770, image 3
Harman/Kardon hk770 specifications
Title Value
Power : 2x 65W (RMS / 8 Ohm / 20Hz...20Khz / 0,03% THD)
2x 90W (DIN, 8 Ohm)
Power bandwidth : 8Hz...100Khz (32,5W /channel / 0,03% THD)
THD : 0,006% (1Khz ; rated output)
IMD : < 0,02% at rated output
Frequency response : 1Hz...250Khz (-3dB)
Damping factor : > 50
Slew rate : 150V / us (8 Ohm, rated output)
Square-wave rise time : 1,5us (20Khz ; 8 Ohm ; rated output)
Square-wave tilt : < 2% at 20Khz
Total TIM distortion : < 0,007% at rated output
Total Interface IM distortion : < 0,007%
Power supply crosstalk : 100dB (20Hz...20Khz, inputs shorted)
S/N ratio : 123dB (IHF-A)
Input impedance : 1,2V for rated output
Input sensitivity : 35kOhm
Dimensions : 38,5 x 7,25 x 32cm
Weight : 10,1kg.
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page online since : 2006
page updated : march 2010
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