PT-7000 PreProcessor Setup and Listening Tests

I am sure everyone remembers the "Attack of the Clone Processors" article we wrote nearly a year ago, where I showed multiple hardware vendors selling a common processor platform and slapping their own logos and cosmetics on it. In fact, it was this very article on this processor that generated interest from Sherbourn for Audioholics.com to evaluate along with their new seven channel power amp. Ron Fone was very forthcoming, more so than Peter Tribeman from AtlanticTechnology / Outlaw, about the differences with the Sherbourn PT-7000 version of this East Tech Processor.

The one key advantage to the latest version of the Sherbourn PT-7000 processor is its improved analog section from its successor version, resulting in a reduced noise floor and more audiophile sound characteristic (more on this later). Ron also claims the price difference between this unit and the cheaper Outlaw unit has to do with the associated increased costs of the nicer cosmetics, upgraded video circuitry for extended bandwidth, and the different marketing model followed by the two companies (IE. Sherbourn-dealer based, Outlaw-internet based), as well as the fact that the Sherbourn unit comes already equipped with audio and video cables. I have to chastise Ron on his last point regarding the Sherbourn "cables". I would rather see the retail price of the Sherbourn PT-7000 drop by $100 than for Sherbourn to supply the so called "cables" that they do. Don't get me wrong, I am the last person to promote exotic cables and the lunatic theories that buttress many of them, but one has to draw the line between the "exotic" and the bare essential. The Sherbourn supplied cables are typical throw away patch cords that come standard with commercially purchased CD/DVD players. The supplied video cable is no different than the audio cables, other than the yellow color of the RCA connector. None of these cables meet our recommended Cable Budget Guidelines for serious audiophile set-ups. My advice, is to go out and buy or build your own audio and video cables to achieve maximum performance of your home theater systems. The PT-7000 is supplied with a more primitive version of the Home Theater Masters SL-8000 in that is doesn't have an LCD display window at the top of the remote to let the user know what device the remote is operating at any given time. I personally like that feature and wish the processor clone manufacturers would have unanimously decided for it. In any event, if it bothers you as much as it did me, you can remedy the situation by purchasing one of the excellent all-in-one remotes from Home Theater Masters or Phillips, etc starting at about $100 or so.

The Set-Up of the Sherbourn PT-7000 Pre-processor
Making all of the connections was quite simple with the PT-7000. The backpanel was well laid out and the connectors had adequate spacing between them to accommodate all of my "exotic" (gasp) interconnects with ease.

When setting up the PT-7000, its bass management limitations became apparent to me quite quickly. This processor does not allow subwoofer output in two channel if the front main speakers are set to large. I almost assumed by now that hardware vendors have overcome this oversight, but I suppose that's arrogant presumption on my part.

In comparison, my almost four year old dated Aragon Soundstage allowed subwoofer output in 2CH analog bypass with the main speakers set to large, as did the Yamaha RX-Z1, and even the vintage by today's standards, DSPA-3090 and successor DSP-A1 for that matter.

Based on this shortcoming, I had to configure my speaker system as follows:

• Front: Small; fc = 60Hz
• Center: Small; fc = 60Hz
• Surr: Small; fc = 60Hz
• Surr Rear: Off
• Subwoofer: On

I commend the effort the designers on the PT-7000 have made on incorporating bass management for the 6CH Channel Direct Mode. This is one of the first processors we have reviewed with full bass management for applications of DVD-A / SACD. The 6CH Direct Mode's bass management scheme is independent from all other modes of operation, and is an analog implementation with a fixed defeatable 80Hz 2 nd order HPF for the five main channels and a non defeatable 4 th order LPF for the subwoofer channel. I was pleased to see that the HPF's were defeatable while still retaining bass management for the subwoofer channel. However, I did note in my set-up that the subwoofer output in this mode seemed to be phase reversed by 180 degrees. If this becomes an audible problem with your set up, you may find yourself having to reverse the phase on your subwoofer every time you engage this mode.

Unfortunately the channel trims on the PT-7000 were only adjustable in 1 dB increments, which at times proved challenging to get all channels at equal loudness from my listening position. I would have liked to see 0.5dB trims which are very common in A/V receivers in this price range. What really irked me more than the 1dB trim accuracy was the fact that there was only one global setting for channel trims and crossover settings. This became most bothersome when switching between digital inputs decoding DD/DTS and 6CH analog input for listening to DVD-A / SACD due to the inherent level differences of the formats.

Each time I listened to the latter, I had to readjust the subwoofer output to achieve proper levels to compensate for the lower subwoofer level of DVD Audio inherent in many of today's DVD-A players. A separate channel trim configuration for this mode would have been nice, especially since the PT-7000 had two registers for channel level settings, but for some reason they were dependent on each other. This can be seen in the set-up / configuration menus. There is a speaker level setting named "Channel Calibrations" in the main set-up menu where you can adjust all of your levels via test tones, then for some illogical reason, there is a separate setting called "Channel Trim" which you can also adjust speaker levels on the fly, but when you change the levels in this mode, it also changes them in the prior set-up mode. Why?

Editor's Note: Workarounds for Bass Management Issues

• Enable the 6CH Bass Management Analog HPF. This will crossover every speaker
  at 80Hz, sum the bass and combine it to the sub. This should raise the subwoofer level output enough to not require any tweaking when switching between DD/DTS and DVD-A/SACD.

• Set the subwoofer level control of the DVD-A/SACD player to maximum. However, do this with care as many of these players may clip their analog outputs, resulting in audible distortion, when their channel trims are maxed out.

• Readjust the PT-7000 channel trim each time when switching between DD/DTS and DVD-A/SACD to compensate.

The PT-7000 allowed for digital delay compensation for all channels via its digital inputs by entering distances relative to the primary listening position in feet or meters. I Would have liked to seen a setting for the subwoofer as well to compensate for any potential phasing issues that often arise when mating large front speakers with a subwoofer. For more on this topic, please review the article titled "The Marriage Between The Subwoofer and Tower Speakers".

Despite these configuration glitches, I still managed to set up the PT-7000 to achieve superb performance in all modes of operation. Despite the fact that I had to cross over my large main towers at 60Hz, my sub was more than capable to handle bass frequencies below that and I really didn't feel like I was missing anything.

I was particularly enamored with the Prologic II music mode when listening to normal CD's and the Prologic II and DTS Neo Movie modes when watching old VHS tapes or stereo TV. The PT-7000 seemed to handle all surround modes quite well. The five channel stereo feature was a nice option to use when hosting parties or when you prefer to rock your entire house with a room full of sound, but I preferred the more natural and balanced sound of DTS Neo and Prologic II. I actually preferred the Prologic II modes over the DTS Neo counterparts when using this processor. They just sounded more lively and realistic to me. This was quite surprising to me since I preferred the DTS Neo modes over the Prologic II ones when I reviewed the Yamaha RX-Z1. I suppose this may be subjective on my part, thus I recommend making this determination for yourself when comparing the two different processing modes

I found Mike Oldfields's Tubular Bells 2 CD sounded quite enveloping in Prologic II on the PT-7000. It added a sense of realism and depth to an already well recorded CD. There were times that I swore I was listening to a discrete recording when listening to this CD in Prologic II mode on the Sherbourn PT-7000 Processor. Since this CD was mastered with higher than normal dynamic range, free from compression artifacts, typically found in today's pop recordings, I had to crank the volume up quite high on the PT-7000 to compensate. This never presented excessive noise problems demonstrating that the PT-7000 had both a clean and quite analog preamp.

I spent a good deal of time listening to DVD movies with the Sherbourn combo. I can't tell you how many times exactly that I viewed my two year old daughter's favorites such Stuart Little 1 & 2, Disney's Beauty and the Beast, and Eric Clapton's "One More Car One More Rider".

While any sane person would grow tired of watching these videos over an over again, I didn't. Partly because I am not sane, after all, I am a father :-) Or, perhaps I really enjoyed the sound that the Sherbourn combo provided in my reference system.

Eric Clapton's concert DVD sounded absolutely stellar in DTS mode on the PT-7000. Track #2 "Reptile" contained such chillingly deep bass and flamboyant guitar textures that were all clearly conveyed on the PT-7000. In fact, I didn't really mind my large tower speakers being crossed over at 60Hz, due to the previously mentioned bass management limitations of the PT-7000, since my subwoofer was doing a bang up job filling the gap, and the system was properly phased to make any bass nulls between channels mostly undetectable to my ears and my handy SPL meter and Avia test set-up disc. All in all, the PT-7000 delivered all of the latest surround tricks quite admirably.

One pleasant surprise of the Sherbourn PT-7000 pre-pro was its superb analog preamplifier for serious two-channel or multi-channel high resolution listening. The PT-7000 contains a true analog bypass that keeps all analog signals in the analog domain with no digital processing when engaged in this mode. When listening to my favorite SACD's and DVD Audio discs, I didn't hear any excessive noise or glare that is typical of many mass market receivers in this price range. I was curious about Sherbourn's latest hardware revisions implemented to this processor, and they were kind enough to provide me many of the technical details. For your convenience I have summarized the most important differences in the table below.

As we can see, the channel separation, output drive levels, and signal to noise ratios have all been improved with the latest hardware revision of the PT-7000.

The frequency response via the analog direct inputs is nearly ruler flat within the audio band and threshold of human hearing sensitivity. These characteristics seemed quite apparent to me when I was using the PT-7000 to play my latest SACD and DVD Audio recordings. The PT-7000 never sounded harsh or fatiguing, in fact I would characterize its sonic signature as "warm". It didn't have that typical mass market electronic signature which is something I was pleased to live without.

So what does this all translate to? The PT-7000 will not only serve well as a home theater processor, able to decode most of today's surround formats, but it appears to cater to the audiophile for those who demand uncompromised performance for their critical listening needs.

What surprised me about the PT-7000 was that it literally grew on me. I won't try to convince you on the wonders of "break in" like many exotic cable vendors attempt to do. Bottom line, cables do NOT break in. However, there is something to be said about electronics "break in" over time. Usually it is subtle, if at all audible. I suspect I experienced a combination of "break in" as well as endless successful tweaking to get the system to sound just right. Whatever it was, I found it somewhat difficult to box the PT-7000 for shipment back to Sherbourn at the end of my three month evaluation. It is a worthy contender for modest separates installs and for those who desire an alternative to the mega receivers.