Marantz DP870 Processor

Although primarily intended as an outboard companion piece to add Dolby Digital (AC-3) decoding capability to the Marantz SR-96 receiver, the Marantz DP-870 has facilities that enable it to be used with other Marantz components - and even, if you are really clever in setting it up, components from other manufacturers as well.

You can connect the DP-870 to an existing A/V system in two ways, which we'll call "upstream" and "downstream." The more desirable upstream connection utilizes only the DP-870's six line-level RCA analog outputs (left/right front and surround, center, and subwoofer), feeding the decoded AC-3 signals into the system at a point "upstream" of the main volume control, presumably in an A/V amplifier of some kind. Any A/V component with six-channel line-level inputs, such as Marantz's SR-96 and the nearly identical Harman Kardon AVR-80 receiver, is suitable.

Ironically, the less desirable "downstream" connection option is more versatile, since it inserts the DP-870 after the main system volume control but before the system power amplifiers, a more accessible connection point in many systems. In this case, the DP-870's set of six rear-panel line-level inputs are connected to the main system's six line-level outputs (five main channels and subwoofer). When the main system is being used for, say, Dolby Pro Logic or stereo playback (the DP-870 does not have a Pro Logic mode), you press the DP-870's front-panel bypass button, which connects its six-channel inputs directly to its six-channel outputs.

Downstream connection suits separate-component home-theater systems (with an A/V preamp and separate power amps) as well as the few integrated A/V amplifiers with six-channel pre-out/main-in connections. If you have any doubt as to which connection best suits your system, check before you buy.

In addition to deciding between upstream and downstream hookup, you must also decide on the settings of the DP-870's rear-panel "speaker-type" slide switches: front large/small, surround large/none/small, center large/none/small, and subwoofer on/off. Marantz recommends that the "large" positions be used when the speakers concerned are "capable of handling sounds below 100 Hz." The "small" switch positions will redirect sounds below that frequency away from the chosen speaker(s) either to the front left/right speakers, if they are "large," or to the subwoofer, provided the subwoofer switch is on.

The manual doesn't mention that changes in the speaker-type switch settings do not take effect while the unit is on. You have to switch it off and then on again for changes to take effect. The manual also doesn't tell you that for the best chance of getting an accurate bass response, you have to set the subwoofer's own internal crossover as high as it will go or switch it out altogether. Otherwise you'll probably get a double dose of crossover filtering, one from the DP-870 and another from the subwoofer's crossover, that is likely to degrade bass performance. Also not covered in the manual are possible problems in bass response - which, in the two worst cases, will leave you either with far too much bass or with none at all - caused by interactions among the connection method, any pre-existing system bass redirection and crossover filtering, the DP-870's speaker-type settings, and various playback modes (Dolby Digital from the DP-870 and Dolby Pro Logic, stereo, and others from the main system). You'd probably need a textbook on complexity theory to figure this out anyway.

If you have a typical six-speaker home-theater system (including three fronts, a center, two surrounds, and a subwoofer), the simplest recommendation we can make to avoid hookup problems is to start with the front, center, and surround speaker switches all set to "small" and the subwoofer turned on for both your main system (if possible) and the DP-870.

The manual also doesn't tell you that the DP-870 has just enough versatility to operate as a basic system preamplifier all by itself - provided all your signal sources have digital (S/PDIF) outputs. On its rear panel the DP-870 has three Dolby Digital inputs: an RCA jack for an RF AC-3 bitstream from an appropriately equipped laserdisc player, another RCA jack for a coaxial s/pdif digital audio signal, and a Toslink optical connector for an optical s/pdif signal. Front-panel pushbuttons select among these inputs. Receipt of a Dolby Digital signal at any of them will automatically switch the DP-870's AC-3 decoder circuitry on. Receipt of a plain stereo s/pdif signal at the coaxial or optical connectors, however, will turn the DP-870 into the functional equivalent of an outboard stereo digital-to-analog converter (DAC) with volume control. So while Marantz intends the DP-870's optical and coaxial digital audio connections for future Dolby Digital sources like a DVD player or a cable/satellite decoder, in the meantime you can use it as an outboard DAC.

Although the manual specifically warns against connecting "standard audio outputs" to the digital input jacks, we encountered no problems with standard digital s/pdif signals. In fact, the DP-870 behaved quite well as an outboard DAC: Its performance was equivalent to that of a better-than-average CD player.

Use of the stereo-DAC mode also enabled us to accurately determine the characteristics of the filters activated by the speaker-type switches. All of them turned out to have a -3-dB crossover point at 100 Hz, with the subwoofer low-pass filter rolling off at 24 dB per octave above that frequency and the main-channel high-pass filters (activated with "small" speaker settings) rolling off at 12 dB per octave below that point. These filter traits make the DP-870 suitable for use with higher-quality home-theater speaker systems. But since the decoder was intended for use with the SR-96, which contains bass-management filtering at the standard THX crossover point of 80 Hz, Marantz should have given the DP-870 the same crossover frequency.

Our Dolby Digital measurements also came out very well, particularly in the noise and distortion tests. The high end of the frequency-response measurements was limited by the interaction of our test equipment with the test disc's signals and does not accurately reflect the DP-870's multichannel frequency responses, which probably extend right up to 20 kHz.

The lack of suitable signals on the Dolby Labs test disc prevented us from determining what precisely the DP-870's front-panel Delay Time button does. We had good results when we listened with DP-870 settings of 0 and 5 milliseconds while our main system's Dolby Pro Logic delay was set at 15 to 20 milliseconds.

The channel-balance tracking figures in the table indicate the DP-870's ability to maintain inter-speaker balances as the overall level was changed using its large volume control knob. It did very well in this regard, and we heard no anomalies due to shifting channel balances. We actually never heard any anomalies with the DP-870. Although it is not marketed as one, the DP-870 does as well as many outboard DAC's costing far more. Dolby Digital playback was as spectacular as always, showing that the DP-870 is fully capable of decoding anything an AC-3 soundtrack can dish out.

Our principal complaints about the DP-870 concern its facilities for hookup and setup. The most important technical deficiency is that the speaker-balancing test tone does not include the subwoofer output. Instead, we are given only the sage advice to "adjust the subwoofer output to the appropriate level." Unfortunately, if you use the DP-870 in its "downstream" mode, you have no other subwoofer-balancing options.

But the "upstream" mode provides a way out. If you are using the DP-870 with any receiver or amplifier that has a six-channel direct input and its own speaker-balancing facilities, and if those facilities are located in the signal-flow sequence after the six-channel input, you are in luck. Simply set the DP-870's six level-balancing knobs to their 12 o'clock detents, completely ignore the decoder's test tone and balancing procedure, and set speaker balances, including the subwoofer, using the facilities in the system receiver or amplifier.

Since the SR-96 receiver memorizes channel balance settings for its six-channel inputs separately from those for other modes, set the channel balances with the receiver in Dolby Pro Logic mode; then transfer the settings to the six-channel direct-input mode. With other receivers or amps that allow upstream connection, set channel balances using the system's Dolby Pro Logic mode, a test disc (such as Delos DE-3179, which includes subwoofer-setup tones), and a sound meter.

So, despite all my cavils at the manual, if you are able to connect the DP-870 to your system in the upstream configuration it will prove to be an easy way of obtaining state-of-the-art Dolby Digital performance. It is an ideal companion to the SR-96 - really. But get out those books on complexity theory if you need to use the downstream connection!

Marantz DP870 Processor photo