Q&A # 106 - March 9, 1999

Staff

Q I have a receiver which has pre-outs for the front left and right, center, and subwoofer. I took your advice to add outboard power amps (monoblocks) rated at 125w/ch to the three front channels for more "steam". My subwoofer is powered by an external amp. I have my surrounds directly attached to the surround speaker outputs of my receiver (65w). (1) Would this be OK for a DD setup, or should an equal amount of power be distributed among all five channels? (2) What would be the advantage of having monoblocks vs. a one-chassis five-channel amp (aside from modularization and upgrade paths) from an electronics standpoint (crosstalk, power sharing, etc)?

A For DD and DTS, it would be advantageous to have the 125 watts for each of the rear channels just like in the front. However, by not using the front power amplifiers in your receiver, the rear channels will perform better, so the 65 watts may be a bit conservative in this case. They should be sufficient for now, but eventually you probably should upgrade to have the same power all the way around. Since so many five-channel power amplifiers these days are modular, with complete power supplies on each module, the only real difference is that you just have to turn one component on rather than five. However, the modular amplifiers generally are around 125 watts per channel, while the non-modular ones, which share the power supply, can be anywhere up to about 400 watts per channel. Crosstalk is not a problem I have ever encountered with any of the multi-channel power amplifiers, modular or non-modular, so it is really just a matter of how much power you want. If you like the idea of 750 watts per channel, then monoblocks are the only choice. Otherwise, multi-channel power amplfiers are the best way to go.

Q You mentioned that phase-shift can be a problem in audio. As long as the phase is shifted equally in all the channels, wouldn't it be inaudible?

A The problem with phase-shift stems from harmonics rather than just any single frequency. Musical instruments, and all other natural sounds, have multiple frequencies consisting of the fundamental and their harmonics. It's the harmonics that allow us to distinguish which instrument is playing. If instruments only produced a single fundamental frequency, a bassoon would sound the same as a trombone. The harmonics produced from these instruments are aligned in time with the fundamental. Let's say that an instrument produces the fundamental and one harmonic. The diagram on the right shows how the natural harmonic (shown in red) would line up with the fundamental (shown in blue). When phase-shift occurs with the harmonic, which might be the case when a narrow bandwidth amplifier is used, the position of the harmonic in relation to the fundamental is shifted to a different location (shown in green). (The harmonics occur all the way along the fundamental, not just at the peaks. The red and green bars are just to illustrate the relative positions of the natural and phase-shifted harmonics.) If the harmonic is not in the right position, the instrument will not "sound right". Of course, this is an extreme example, but the idea is that the most accurate sound reproduction requires the least amount of phase shift. No amplifier would be designed having lots of phase shift. It would sound terrible. But, in our search for high fidelity, we look to reduce any type of distortion, and phase-shift is one of them. In specification sheets, you might see the phase-shift listed, which will be in degrees.

Q I was in a bookstore looking at various hi-fi publications, and I noticed one that had an article about internet audio magazines. There were a number of websites that I had never heard of before, but Secrets, which I have been reading for years, was not mentioned. Are these people just plain stupid or are there politics involved?

A The mediocre printed magazines stand a great deal to lose by the success of on-line publishing, so you won't see the e-zines that are a threat to them listed there. The high quality printed magazines may not welcome the competition, but they don't seem afraid of it. You are more likely to see a complete list of e-zines in the best printed magazines, at least the ones that are not paranoid. The beauty is that it does not matter which on-line magazines are or are not listed by any particular printed magazine. People who use the internet and enjoy audio/video know the magazines there. Newcomers to the web can type in just about any audio keyword in the major search engines, and all the on-line audio magazines will pop up in the search results. It won't be all that long before the printed magazines worry about whether or not we mention them.

Q After reading your review on the 2095, it was hard to tell where the limitations of sound on this unit lie: only with the power amps or also with the preamp section. Here's my concern: I own a 2095 and will be getting a Sunfire Stereo Power Amp for my old Magneplanars (always needs plenty of power!).

How will the 2095 hold up as a preamp when I'm playing stereo and want to get a great musical sound (I'm already happy with the home theater part)? Does the preamp stage, including its internal DAC, compare well to separates, or will the sound be inferior for stereo music? My setup is that I'll play CDs on my Toshiba 3108 DVD player and pass a digital signal in to the Yamaha, relying on the Yamaha's own DAC. Then the Yamaha will pass the signal on to the Sunfire.

A The 2095 and DSP-A1 preamplifier sections are really quite good. I use the DSP-A1 for music regularly. However, the limitation in your system will be the DVD player, since they don't perform all that well when playing CDs. It's in the nature of the laser pickup rather than in the DAC, so simply routing the digital out from the DVD player into the Yamaha for decoding won't necessarily make it sound better. Even an inexpensive dedicated CD player will improve your system sound for CD stereo. Get one with a digital output jack so you can use the DAC in the Yamaha in case it's better than the one in the player. Be sure to use a 75 Ohm coax interconnect or a Toslink optical cable if the player has a Toslink output.

Q I am planning to wire my new construction house for audio/video distribution. Are there any benefits to using 12 gauge speaker wire compared to 14 or 16 gauge wire?

A If you keep the length from amplifier to speaker at less than 20 feet, 14 gauge should be fine. If you are planning to have really long connections to rooms at the other end of the house, then use 12 gauge.

Q I can't find any information about the use of Data-Grade Projectors for home theater. What's the difference in quality between LCD and DLP projectors (Sony VPL-X600U vs. InFocus 735)? Is XGA (1024 x 768) the correct resolution to prepare for HDTV? How will DVD/DSS sources look on these square grid formats?

A Both LCD (Liquid Crystal Display) and DLP (Digital Light Processor) projectors give excellent images now. LCD may have a slight advantage in brightness, but the pixels with DLP are pretty much invisible. After examining the two, I prefer DLP. With LCD, the light shines through the chip, while with DLP, it reflects from the surface (DLP chips, made by Texas Instruments, use tiny mirrors for the pixels, and this is really incredible technology). Some projectors have individual chips for red, green, and blue, while others use a single chip that has all three colors alternating. CRT projectors are extremely bright (for use with very large screens), but the red, green, and blue CRTs deteriorate, while LCD and DLP chips do not, with only the projection bulb needing replacement now and then (and it's a lot cheaper than replacing CRTs). The XGA spec of 1024 x 768 will not handle HDTV's highest resolution of 1080 x 1920, but some of the projectors may handle 720 x 1280. Obviously, the XGA projectors will all handle 480 x 704. Widescreen 16:9 looks great on these projectors using the 480p format, with line-doubling, and DVD sources. We are heading into a transition phase right now, with HDTV rear projection TVs that have line-doubling for use with NTSC signals (like DVD, and DSS), and will handle HDTV signals too, although some will downconvert 1080i to 720p. You can get one (rear projection HDTV) with a very large screen and LCD technology for about $7,000, whereas front projectors with LCD or DLP technology are not quite at the HDTV resolution stage yet, but they will be soon. The question is how much they will cost. There is a new gadget coming now that will line double from S-Video inputs and output RGB for front projectors, and it is only $700. You connect it between your DVD player or DSS, and output the signal to the projector. If this turns out to be a good product, then it becomes attractive to get a lower cost LCD projector (SVGA - 800 x 600) that will do 480p, and use it with the $700 line doubler. Total cost for high quality front projection, with line-doubling, becomes affordable (say, around $3,000).

Q I enjoyed your review of the DWIN Transcanner. I have had a DWIN CRT projector now for more than two years, and the Transcanner since last May, but a completely new unit under warrantly for about four months now. I'd like to offer a few comments and questions in consideration of my hands-on experience with these products and your review. Let's keep in mind that I have a 4:3 aspect ratio 100" diagonal screen just like you, but apparently yours is perforated with a 2.0 gain, and mine is non-perforated with a 1.3 gain. My room is fully darkened with flat black and dark gray colors throughout.

1. Doesn't your 2.0 gain screen give you some color shift, and therefore, isn't a 1.3 gain screen the way to go if you don't have any speakers behind the screen?

2. Edward at DWIN advised, and I confirmed, that the DWIN CRT will not shrink the picture down all the way to 2.35:1. Following his advice, for the Transcanner 2.35 setting, I shrank the picture to 1.85, and then blanked the picture from the 1.85 border to the 2.35 border. Isn't this what you did?

3. I have a Sony DSS. Very rarely do jagged edges or artifacts intrude on my viewing pleasure. I did have a lot of them with the DWIN Line Doublers. Initially with the Transcanner, I still had some of them. After I got a replacement Transcanner about 4 months ago, I learned how to adjust the focus at the lenses, and I also added a Bybee Quantum Power Filter to the Wood Block already attached to the power for both the CRT and Transcanner, and Power Wedge Ultras with balanced AC power (I found these items improved the color and contrast). Could these items improve the picture to significantly reduce artifacts and jagged edges?

4. When I received the replacement Transcanner 4 months ago, I remeasured the screen to determine the number of lines to run the Transcanner, just like you did. I came out at a number about 840 to 850, the same as you did (852). However, I set up line settings of 750, 775, 800, 825 and 850 to compare the picture. My findings were the same regardless of the source material. 775 or 800 lines looks best. 775 lines is sharper, but not as smooth or filmlike as 800 lines, and I still use either setting depending on the source material. For Component DVD, I use 800; and for DSS I use 800 if the picture is well defined and clear (like "Sliders" on Sci-Fi Channel or "Stargate" on Showtime), or I use 775 if the picture is softer. I have found that using the 825 or higher settings blurs and softens, but does not improve the picture. If you still have the Transcanner, try these other line settings and tell us what you find.

A 1. Absolutely! A 1.3 gain screen is the way to go. The screen and the projector in the room belong to an associate and 2.0 is the screen he chose. A 1.3 gain screen will give you better color fidelity at a slight loss in light output. It's well worth it though.

2. In the last few months, the DWIN projector has been updated and can now shrink down to 2.35:1. I don't believe they can fix existing models, so it is just something they added.

3. DWIN did send a second unit, and it exhibited the same results. This artifact was only present on the news and talk shows. DVD movies being played on the Transcanner did not have the same effect. It seems to be an artifact of DWIN film logic detection.

4. Getting the best setting is a very subjective part and often time consuming because you have to re-converge. I agree that you must play around to find the best settings. Because of the lack of scan lines, the screen material is present. This requires me to sit a little further back from the screen.

I think the DWIN Transcanner is a great product. I just hope that they can bring the costs down so people who purchase HDTV sets can use one of these instead of the internal line doublers that are inferior.

Q I wish to connect a Toshiba SD-2108 DVD player, a RCA DS5451 DSS with AC-3, a Toshiba M754 VCR with S-Video, and a CD player to my Yamaha RV-1103 receiver and Toshiba CX36H60 TV. I would like to use the connections that will provide the best quality audio and video. The receiver does not have enough "digital" connections for this purpose. Are any remote controlled S-Video and/or optical or coax switchers available at a reasonable cost? Are there any other solutions (perhaps something a simple as "Y" connectors?)

A The Entech will do the trick but it's not inexpensive. For switching the video you can find a passive S-Video switcher made by Elite Video http://www.elitevideo.com. There are some other very affordable S-Video switchers (less than $200) available at http://www.smarthome.com/8288S.html and http://www.smarthome.com/8278SR2.html.

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