The Secrets Blu-ray Player HDMI Benchmark - Part 2


HK 990 Dual-Domain Tape Recorder Outputs and Tape Monitor Details

Having been involved with tape recorders since reel-to-reel was the state of the art. I invested considerable effort in testing the dual-domain tape recorder interface function. Conceptually, a dual-domain tape output path should be a must-have for those seriously rooted in recording. With a dual-domain configuration, both analog and digital inputs appear at the analog tape output jack (to recorder in) for the two tape recorders (Harman calls these CD-R and Tape). Analog and digital inputs also appear on the single record digital output (to digital-in on the CD-R or MiniDisc player). The rear panel section with the tape outputs is shown below.

Harman allows the tape outputs to record a source (analog or digital) independently of what is heard on the speaker. This feature is relatively common in analog integrated amplifiers and preamplifiers replacing the single tape monitor button.

Listening to one input and taping another provides a tape monitor function. For example, one might tape the Tuner with the cassette deck connected to Tape using this sequence of operations:

  1. Select Tuner using the record-out selector.
  2. Select Tuner on the remote control to listen to the source through the speakers.
  3. Press Tape on the remote to hear the recording off the cassette deck.

Even with a CD-R, monitoring is important. I cannot tell you how many times I thought I hit the record button, but inadvertently hit Play instead. With the meters moving, everything looks OK, but it's not. Another example where monitoring could save the day is when the Tuner is selected as record-out and not Phono that you wanted to record; again, the meters are moving but you are recording the wrong thing.

Source selection for the tape recorders is only available on the front panel, making the selection more than a nuisance when all the buttons on the front panel are similarly-sized with low-contrast lettering.

To select a recorder, the Record Output button is first selected, then the two Source Select buttons are toggled, and finally Record Output is re-pressed to return the source selector to its normal function so the speakers are operative. From the remote, toggling the source select for the output to the speakers is unnecessary. Each input is assigned a button.

Closely-spaced buttons may cause an adjacent button to be depressed. Put your finger a little to the right of source select and you press the input assignment setup button. Cancelling that is no fun.

Many AVRs offer one or two tape outputs (with composite video outputs also supplied for at least one). These outputs are analog and transmit only analog inputs. No monitor function is available.

You can try to mimic the Harman's functionality using the Room 2 analog outputs on the AVR, but care is required as there is no protection for self loops under this setup: say goodbye to your tweeters were both Tape for Room 2 and source selected at the same time with the recorder activated. The oscillations are typically a square wave at the maximum swing of the tape recorder.

You may be able to work around this using the AVRs Room 2 input assignment GUI. One might try to assign Room 2 Tape In to an unused analog input. I make no guarantees you can perform a setup with an AVR Room 2 that will insure a disaster will not occur. I play it safe and live without the monitor function with an AVR. I use headphones connected to the recorder to do the monitoring function.

Almost all AVRs provide only analog inputs (single domain) at the Room 2 outputs.

Tape I/O signal flows at the block diagram level

This diagram is similar to the block diagram of the digital input selector presented in Part 2, but the circuitry to support tape recorders has been included. The yellow box highlights the added circuits. The Texas Instrument SRC4392 multi-function chip has two digital input selectors. As can be seen one selector is used for the tape output path and one for the main path. In the tape output path the selector only routes SPDIF signals (green) and does not recover the PCM data as it does for the main path. A second set of input selectors are required for the tape recorder output path because the digital input selected is different from what is being sent to the speakers.

An extra DAC is required in a dual-domain tape system to convert the digital inputs to analog. This is highlighted in the yellow box. The DAC for the analog record outputs is part of a multifunction AKM 4683. The performance of the AKM DAC is lackluster, with a worst-case dynamic range equivalent to 15.5bits and distortion of 13 equivalent bits. The AKM 4683 also houses the requisite SPDIF receiver.

Older cassette and reel-to-reel machines need the analog output. The quality of the conversion of the digital inputs to analog is not that important since all CD-Rs and MiniDisc recorders have digital inputs; however, a problem with this assumption in the case of the HK 990 will be identified below.

A designate the diagram above BLOCK DG.

The analog selector block is shown in this diagram, with the circuitry to support tape recorder in yellow. Like the digital path (BLOCK DG), the analog input selector has second set of switch selectors that aggregates the analog inputs for the tape recorder outputs. Everything in this tape output channel (in the yellow box) is only AVR grade: the switches, for example, are MOSFETS, not relays.

The selected analog input must be converted to digital to provide a digital tape output. The ADC should be of high quality because it replaces the ADC in the digital tape recorder. Unfortunately, the HK 990 disappoints. The ADC is also in the AK4683 (with an ADC and DAC, it is called a CODEC). The ADC has a worst-case dynamic range equivalent to 15.5 bits and distortion of 13 equivalent bits.

You may ask why the output of the high-quality Cirrus CS5361 ADC in the main path (in the upper right of the diagram) is not used instead of adding an ADC just for the tape recorder outputs. The principle justification is the bifurcation of the input to be recorded from what is played on the speakers.

A designate the diagram above BLOCK AN.

This block diagram illustrates the conclusion of the recorder output's journey as it makes its way to the rear panel RCA jacks. This diagram clarifies the dual-domain aspect of the tape recorder path. Both digital and analog outputs are shown at the right. Depending on the component that the user has selected to record, a signal from the analog block (AB) or digital block (DG) is sent to the output (signals entering at right).

Note the switch prior to the two analog outputs CDR-Out and Tape-Out. The switch prevents self-oscillation. When listening and recording from CDR, the switch mutes CDR-Out, preventing a self-oscillation through the CDR recorder. Tape-Out is muted under similar conditions.

The digital Coaxial Out lacks the switch. The single digital output is live when you select to record from the CD-R or the Tape input. In contrast, the analog output for CD-R (Tape) mutes when to-record CD-R (Tape) is selected. Mixing analog and digital connections in a recorder can cause a self-loop and high-level oscillation that may damage your speakers.