Introduction to Harman Kardon HK 990 Stereo Integrated Amplifier with Digital Room Correction and Dual Subwoofer Bass Management – Part III

Circuit design and the tape recorder section are the focus of the final section of my HK 990 review. The topics are addressed to different groups. Those interested in the tape recorder section will find information on Page 9. The tape recorder interface section outlines matters of connectivity and usage. Usability issues are discussed. The tape recorder interface section is at the level of the prior two parts and assumes no knowledge of circuit-level electronics.

The circuit-design section enters the land of high-end design, mostly guided by the design principles of Matti Otala. My intent here is two-fold: to identify anything that might make the unit sound better subjectively, and to objectively quantify whether any aspects of the design have inadvertently degraded performance.

This circuit design section assumes the reader has knowledge of analog design equivalent to a 1980’s Audio magazine. I started reviewing in the 1980s. I took my cues at what level to write from Audio and never let go. Some of the technical terms bubbled to the surface in the HK 990 literature as the marketing folks tried to capture the unique aspects of the unit. You get only words without graphs or block diagrams. Usually, only when engineers write the literature does it all jell. Accuphase is an example of this practice operating to perfection. The literature Harman produced in the 80s and early 90s included circuits, novel measurements and even Bode plots. Sansui and Kenwood were producing similar material. Sansui was a big loss from the creative circuit view when it went out of business.

Here are links to Part I and Part II of this series.