Integrated Amplifiers

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


Analog Input Signal Flow of the HK 990

The electronics represented on the block diagram (Figure 10 above) are located on the left-most daughter board as dictated by the placement of the analog inputs on the rear panel.

Relays, not silicon switches common to most AVRs, drive the function selector for the analog inputs. As can be seen, the signals from the phono board are also routed to the relay bank. Each relay is a fraction of an inch from the analog input jacks on the back. The MMI at the front of the unit activates a relay based on the user's selections. In the direct mode, the output of the relay is connected to the digital volume control. Some posters in the AVS forums have been complaining about the clicking sound of relays in higher-end equipment. They should stop and think: does one just want the signal to be transmitted across a metal strip or would they rather the signal was transmit across a MOSFET transistor with significantly higher resistance that varies with the incoming voltage. Relays and the associated drivers are more costly than a silicon switch. Reliability of a relay and the associated driver circuitry is the only downside.

For DSP functionality to be enabled, the analog inputs must be converted to digital by an Analog-to-Digital Converter (ADC). In the HK 990, the ADC is a Cirrus CS5361, one notch down from top of the line Cirrus ADC. The bit-equivalent signal-to-noise ratio (SNR) is 17.5 bits worst case (A-Weighted). The bit-equivalent distortion is 16.5 bits worst case at 1kHz with an input signal 1dB below full-scale.

Even on expensive AVRs, the ADC is often a low-grade single-ended part, a kludge by AVR designers who assume the only analog signals entering emanate from cassette decks and VCRs. They completely forget about converting a phono signal, which needs a high-quality converter to prevent sonic degradation.

The tape output path has its own function selector and ADC. This supports the option of listening to one input and recording another. I elaborate upon the tape output path in Part 3.