Q&A # 46 - January 13, 1998

Staff

Q I am in the process of putting together an audio system which will be used primarily for music but also for home theater. I have selected most of my components, but am confused with regard to a choice of preamps. There appear to be several kinds of amps: tube, minimal electronic processing (i.e., McCormack line drive preamps) and digital preamps like the Meridian. I understand that tube amps have a certain sound that many people prefer, but I do not understand the difference between the other two. Doesn't a digital preamp alter the signal in some fashion? Wouldn't you have more accurate sound by using a McCormack and relying on the sound source to accurately reproduce the sound? After all, isn't that why people buy CD transports and DACs?

A In general, the purist philosophy is that the less there is in the signal path, the better. A single wire with gain, as some would say. Unfortunately, a single wire doesn't produce gain, so we have to deal with reality, and that means things in the signal path, such as transistors, capacitors, inductors, and many wires. Every one of these items alters the signal, so the designer tries to figure out how to achieve gain with minimal distortion (distortion being defined as deviation from the original waveform). Tubes and solid state have different sound characteristics, as you noted. Lots of arguments abound on which is "better", but it is really just a matter of the sound that one prefers. At the CES in Las Vegas last week, about half the amplifiers in the high end section were tubed. Tubes are enjoying a renaissance. They have a musical, easy-on-the-ears quality that is hard to resist. Perhaps they are less accurate than solid state amplifiers, but . . . if it feels good . . . do it.

Meridian has been making digital preamplifiers for some time. NAD has a relatively new digital preamp. In the case of the Meridian, the input is digital too (CD) and the preamp does its thing on the signal in the digital domain, and then converts it to analog via a digital to analog converter (D/A or DAC), for amplification. The NAD can input an analog signal, such as the analog outputs from a CD player (which has the transport and DAC in one box), or from a DAC, and converts the analog signal to digital, via an analog-to-digital converter (A/D), does its thing in the digital domain, then converts the signal back to analog with a DAC. Handling the signal in the digital domain allows many things to be done to it without adding distortion and noise (hiss), and in the case of the Meridian, since the signal is digital to begin with (digital output from the CD transport), preamplification can occur with minimum distortion. However, good A/D and D/A circuits are critical. Eventually, we might have digital sources (CD, DVD, etc.), digital preamplifiers, and digital amplifiers which could very well be more accurate than any current analog components. In any case, though, the bottom line is in the listening. Theory isn't nearly as enjoyable as reality, so purchase with your ears, not a textbook.

Q I've just bought a centre channel speaker (B&W CC6) and installed it. I placed it on top of the TV and found that noise is coming out from the tweeter. When I turn off the TV or move the speaker away from the TV, the noise stops. The noise remains when I turn off the amplifier if the speaker is connected. What is the possible reason for this and how can I solve it?

A What you have discovered is the reverse problem of a speaker magnet interfering with the TV. That buzzing noise in the center channel speaker is caused by induction from the high voltages in the TV. These alternating current voltages in the TV produce magnetic fields that induce currents in the voice coil of the center channel speaker, and this makes the cone of the speaker move, just as if the currents were coming from the amplifier. You will find that the noises will occur even if there is no speaker cable connected to the center channel speaker. You can reduce this phenomenon by placing the center channel speaker farther above the TV rather than directly on top of it. The magnetic shielding of the center channel speaker does not seem to prevent the reverse induction from occurring.

Q I have one question for you regarding the use of an external power amplifier with the Denon AVR-3200 DD receiver. For some reason (and I can't figure out why), Denon decided to only provide pre-outs for the L/R Fronts, Center and SW channels , but not for the L/R surround channels. My question is: if I add a good quality, say 100W, 3 channel Power Amplifier for the Fronts and Center, will more power out of the AVR-3200 be available for driving the L/R rears when in surround mode? Do you feel the sound for HT movies would be improved with this configuration?

A Since the AVR-3200 has DD built-in, and there are several digital inputs for this, plus a set of 5.1 inputs for an outboard processor, I suspect it was just a matter of space on the rear panel that caused Denon to eliminate the pre-outs for the rear. But, I agree that pre-outs should have been there for all channels. I think that performance of the rear will indeed be improved by using an outboard amplifier for the front left/center/right, since the power supply of the Denon can then concentrate on the rear. You will not only get better rear sound, but the outboard amplifier is likely to be better than the inboard amplifiers anyway, so you will get improved sound quality all the way around.

Q Will current DVD players be able to play DTS encoded movies????????

A As of this date, it appears the answer is no. There were some DTS DVDs at the CES in Las Vegas this year (January, 1998), but they appear to be PCM encoded, which may not be the final method for DTS DVDs, so what really scares me is the possibility that the DTS processors we already have may not decode the DTS tracks on later DVDs. This would mean getting a new DVD player to handle the DTS DVDs, AND a new DTS processor to decode the data. It's really too bad that all of this is happening, because I think DTS is potentially a fine product. On a slightly different note, I heard the first 24 bit, 96 kHz audio disc at the CES. It was on a DVD, and I think they will call it DAD for Digital Audio Disc. Instead of 16 bit words, such as are on current CDs, they use 24 bit words, so the word (which codes for a voltage value on the music waveform) can have 24² values instead of 16² values. That's a huge difference. While current CDs have 44,100 samples every second, the new disc has 96,000. These discs WILL play on current DVD players, and the disc I heard was demonstrated on a mass market DVD player. It sounded better than the CD version played on a $10,000 CD transport and DAC. The mass market DVD player only resolves 20 bits, and even though the remaining 4 bits were lost, it STILL sounded better than the CD on the expensive transport and DAC. New DVD players will resolve all 24 bits. Current CD players will not play these DADs, but I am sure eventually we will have players that handle everything.

Q I am currently using BP2000 speakers, a CinemaGrand amplifier and an old Pioneer receiver pre-out. I just bought a Marantz CD-67se CD player and found that it has a volume control for its analog outputs. I hooked the CD directly to the CinemaGrand and got a sound so sweet, so full, that it gave me goose-bumps. The soundstage is huge with very well definded image and 3D definition. Am I at the best of this system? Do shorter path and less circuitry between source and speaker means better sounding? If so, what's the point of spending $4-5K for a good pre-amp? How about using the money for a good AC-3 decoder with vol control pair with the CinimaGrand and connect the CD player to the LtRt inputs of the amp using "y" connectors?

A Actually, you are going through a preamplifer when using the volume controlled analog outputs of the CD player. Usually, the signal passes through an operational amplifier (op amp) for this purpose, and usually they are very inexpensive chips. You are lucky that you like the sound this way, because often it is not very good. Using y connectors to connect two sources with one amplifier is different than splitting the output of one source for connection to two amplifiers. If you have both sources on at the same time, you might cause some damage. I would suggest using one of the source switchers such as can be found at Radio Shack instead. This way, only one source will be connected to the amplifier at any one time. This is really one of the functions of a preamplifier (source switching) anyway, so you might want to consider a dedicated preamplifier at some point. There are many good ones out there at much less than $4,000.

Q I am interested in buying a LCD projector but I cannot decide which one to buy. I want to decide between these: The Mitsubishi Big Easy G1A; The Vidikron Crystal III; and The Sharpvision XV-H37VU. I do not have a big budget. I am going to use it mostly for movies, but it would be nice to surf the internet too. I am going to install it at home, so mobility is not an issue. I want to get the best for the money. Can you give me any advice?

A If you plan to surf the net, you will either need to get a data grade LCD, one that can scan at your computer rate ($$$), use a PC to TV converter, or invest in Web TV. Vidikron is known for making high quality projectors, but your best bet is to stick with a Rear Projection TV (RPTV). LCD projectors still do not look as good as a properly set up RP.  Sony, Toshiba, and Pioneer produce some of the best looking RPs on the market.

Q I have browsed your site with interest, and it's great that a non-affiliated group offers support where the manufacturers fail ! I've searched the site but cannot find any guidance on a problem I have with subtitles.

I recently bought a Sony DVP-S7000 here in Hong Kong, from a reputable chain store rather than a one day hack shop. My problem is with the display of subtitles on screen. When on, the subtitles are on, they are intermittently perfect, compressed and illegible, half on top, half on the bottom of the screen. The discs I have are T2 (region 1), Space Jam (region 3) and Turbulence (region all). My TV is a 25" Sony multi system (Kirara Basso I think). If I use T2 as the best example, it plays in letterbox, and I'm unable to select any other mode. My TV is fixed in 4:3, and the same problem affects all languages. I seem to recall reading that the picture may require fine tuning, but just don't know.

I would love to dispense with subtitles altogether, but my wife prefers them on, as it helps her to follow the movie. Obviously we're not going to have separate sittings!

A I tried the various titles you listed on the Sony 7000. My titles were all region ID 1. The subtitles all appeared across the bottom of the picture, and they were visible the entire time.

You might not have your TV image properly centered, and the bottom of the screen could actually be appearing across the top. This also could be an effect of the multi-system TV, but I have not seen any occurrence of your problem before.

T2 DVD only contains the Letterboxed version of the film. Even though you have your DVD player set for 4:3 and Pan & Scan, your player can only play what is available on the disc.

� Copyright 1998 Secrets of Home Theater & High Fidelity
Return to Q&A Index.