Harman Kardon HK 990 Stereo Integrated Amplifier with Digital Room Correction and Dual Subwoofer Bass Management – Part III
- Written by Dr. David A. Rich
- Published on 03 November 2011
- Harman Kardon HK 990 Stereo Integrated Amplifier with Digital Room Correction and Dual Subwoofer Bass Management – Part III
- Page 2: Construction of the Analog Blocks
- Page 3: Volume Control
- Page 4: Power Amplifier
- Page 5: Phono Stage
- Page 6: Headphone Stage
- Page 7: Analog Circuitry Connected to the DACs
- Page 8: Conclusions About the HK 990 Circuit Design
- Page 9: Tape Recorder Outputs and Tape Monitor Details
- Page 10: Proper Connection
- Page 11: Conclusions About HK990 Tape Recorder Functionality
- Page 12: Overall Conclusions
- All Pages
Proper Connection of the HK 990 Tape I/Os to a Digital Tape Recorder to Avoid Self-Oscillation
When connecting the HK990 to a tape recorder, I advise one of two methods to prevent self- oscillation:
1) Use only analog cables for the input and output connections.
Given the quality of the ADC in the HK 990 (AK4683) little is lost since the ADC in your CDR is likely to be as good as the one in the HK 990, especially if the ADR a semi-professional unit. Coming out of the CD-R analog to the HK 990 does degrade the signal since it travels through the DAC in the CD-R and the ADC (AK4683) in the HK 990. This is a redundant DAC – ADC path.
2) Use only the digital cables for the input and output connections.
Self-oscillation is avoided by coming into the HK 990 from a recorder's digital output (in the all-digital hookup) because both digital inputs mute when record selector is set to CD-R or Tape. In this manner, the oscillation is broken on the input connection for the digital inputs and the output connection (discussed above) for the analog connection. This is what makes mixing analog and digital connection so dangerous.
By simultaneously muting both CD-R and Tape digital inputs, tape-to-tape copying from CD-R digital in) to Tape is enabled. This is probably related to the Digital Millennium Copyright Act, whereby Tape-to-Tape copying is allowed with only analog interconnections.
At first glance, an all-digital connection of the CD-R appears preferable. The all-digital path eliminates the DAC – ADC redundancy on the recorder output side. However, conversion quality is crimped because the AK4683 ADC replaces the ADC in your CD-R.
With only one digital output, I do not understand why it is not marked digital output for CD-R and made to mute when CD-R is selected as the analog CD-R does. This should be a straight-forward software fix to allow mixed analog and digital connections.
The digital output is limited to a 16 bit depth and 48kHz sampling rate. Consumer digital recorders would mute if high resolution SPDIF data was allowed to appear at the output.