SECRETS Blu-ray Player HDMI Benchmark
The Secrets Blu-ray Player HDMI Benchmark - Part 2
- Written by Secrets Senior Editors
- Published on 02 August 2011
- The Secrets Blu-ray Player HDMI Benchmark - Part 2
- Page 2: The Tests
- Page 3: Test 1 Summary and Results
- Page 4: Test 2 Summary and Results
- Page 5: Conclusion
- 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
HK 990 Headphone Stage
The high performance Texas Instrument TP6120 obviates DC coupling or blocking capacitors in this stage. The TP6120 has very low distortion and noise. It has a current feedback topology and 1300V/us slew rate. I have no idea why it is designed with a slew rate 100 times larger than what is required. Without circuit details, I cannot conclude if Otala would approve, but with a THD under full load approaching 0.0002% at 1 kHz, I doubt this design has low return-loop gain.
One issue I identified involves the calibration microphone connected using the headphone output. If nothing is done, the microphone could potentially be damaged when plugged in while a large level signal is at the headphone jack. The headphone amps are disconnected when the HK 990 is put in calibration mode, but it is unclear if they are disconnected automatically when the microphone is inserted and the unit is not set to calibrate. I suspect all HK units with room calibration have the same issue but they use a small IC to drive high efficiency headphones. The TP6120 can deliver much more current and only a 20 ohm resistor is between it output and the headphone jack. The instruction book does not caution about these circumstances.
