Q&A # 219 - February 17, 2001

Staff

Q I recently purchased a HSU 1220 sub from a friend, and I was considering using a NAD 2200 amp that I have. The sub is rated at 4 ohms. Should I bridge the 2200, which seems like too much power, or just use one channel, which may not be enough power?

A When you bridge an amplifier, you double the minimum impedance that it will drive. In other words, if it is designed to handle 4 Ohms unbridged, it will only handle 8 Ohms when bridged. Since the HSU is 4 Ohms, the NAD would have to be rated into 2 Ohms unbridged. There is no such thing as having too much power in the amplifier available to drive the speakers. Ten watts are ten watts, whether it is from a 50 watt amplifier or a 500 watt amplifier. However, during the transients, lots of power is demanded. This is especially so with subwoofers. If your NAD has separate power supplies for each channel, you might be able to bridge it and drive the HSU without problems. But, if there is just one power supply for both channels, I would suggest using just one channel and not bridging the amplifier.

Q Why are the DVD players with the built in DD/DTS decoders still there in the market (with new models appearing every month or so) whereas at the same time there are a lot of receivers with DD/DTS decoders built-in? I suppose for those who want to start from scratch should buy a DVD player without DD/DTS decoders. Is this correct?

A Manufacturers use templates that have holes in certain places. It is less expensive to just leave the 5.1 analog output jacks there for now than to make new templates with no holes. Secondly, many people still have receivers with 5.1 analog input jacks and no DD or DTS decoders. Third, with DVD-A coming out now, the 5.1 analog output jacks will be required again on the players. So, all the way around, the 5.1 jacks on the rear player panels will become a permanent fixture.

Q I'm building a system around a Denon 4800, B&W DS6s for surround speakers, and my old B&W P5s as front speakers. What do you recommend for the center, surround back, sub(s), extra amp? As I'm sure you know, the 4800 has 7.1 channel preamp outputs, amplified channels, 5 are amplified @ 125W max. The B&W DS6s are rated at 100W max. My thinking was to put a 100W amp on the extra channels for the DS6s - given what I already have, would that be the best configuration? I have the opportunity to purchase two B&W PCS8s from a friend - do you think that would be overkill in a 20 x 16 room, 12 ft ceilings, one side open to staircase, entry hall, etc.? If not, do I need a THX-rated amp for them? What power level would be optimal?

A Having 100 watts per channel in a two-channel power amp for the extra two channels would be about right, given that the 4800 has 125 per channel built-in. I would suggest another pair of DS6s for those two channels. With the new receivers that handle THX EX and DTS-ES, there will be two channels in the rear and two on the rear-side. When in 5.1 mode, the rear speakers could be used as the two channels of surround, and when in EX mode, the rear will be mono in the two speakers, with the surround sent to the two sides. So, it would be best to have all of those four speakers in the sides and rear the same model. The subwoofer has its own amplifier and special driver, and does not have a particular timbre, so get whichever one suits your tastes.

Q Here is my system:

Yamaha DSP-A1
B&W HTM2 Center
B&W DM 604 Fronts
Boston Acoustics CR8 Rears
Polk Audio PSW100
Toshiba TP55H95
Toshiba 3109 DVD Player
Room 12.5 Ft Wide (Front), 28 Ft Long (Listening area in first 18 Ft), 8 Ft ceiling.

I have been building my Home Theater system in a stepwise fashion. My question is this. What would be the best next single step in improving my system? A more powerful subwoofer, or a five channel amp? My budget is about $2500. My second question is this. For my existing subwoofer (or an upgrade), is Front Left and Right speaker output to the sub, Left and Right pre-out to the sub or, subwoofer output the best to use for my system, given that I listen to 70% Home Theater, 30% Music?

A I think a nice big subwoofer is your best upgrade choice. The DSP-A1 has good amplifiers already. A Velodyne HGS-15 or HGS-18 would be great. The Sunfire Signature Subwoofer (12") is also a fine product. Use the mono-sub-out jack on the DSP-A1 to the subwoofer line-level in jack.

Q I'm thinking of buying a professional amp for my home theater application. My question is will this be a good choice for my main (front) speakers? I  currently have the Yamaha E-1000 processor for the center and rear speakers.  My current main amp is the M-80 which puts out 250w @ 8ohms per side but it's broken, and I have a C-40 preamp. I'm running with B&W 602s for the mains, CC6 for  the center, D6 for the rears and a Velodyne 12" sub for the lows. I'm  thinking about buying the Mackie M-1400i professional power amp which puts out 250w @ 8ohms. Other than the fan noise, is this amp good for a home theater system?


A The Pro Market is primarily for musicians who use the products on stage when giving performances. They are optimized for high power rather than for high fidelity, and are usually rated into 2 Ohms. They tend to operate in class D, which means digital switching power supplies for efficiency. They also usually have 1/4" phone jacks for inputs, rather than RCA, which means you need adapters for connecting cables from your preamp to the power amp. Having to go through an adapter reduces the fidelity a bit. The fan noise is not a big objection to me, because I run my own pro amp (Carvin) at high level, to drive a ButtKicker. However, the ButtKicker is not a speaker, and it only uses the very low frequencies, something even an inexpensively engineered digital switching supply can handle. To be a great switching supply, the switching frequency needs to be high, probably up around 200 kHz or more. The pro amps don't need to do that because they are playing at deafening levels, and the people in the auditorium are screaming. So, what I am saying is that the pro amp has its uses in a home theater, but top notch high fidelity they are not. Fix your M-80. It is a better product.

Q While my new home is being built, I am wiring the AC to the area where my AV system will live. I use a Denon AVR 5700 receiver, and would like to know the advantage of using 120v/ 30amp outlets, and/ or heavier gauge AC wire, dedicated circuits and whatever else I should be doing regarding AC wiring to "future-proof" this home for the next 10-15 years .How about a 220v/ 40 amp line for future "monster" amps?

A A dedicated 120 volt - 30 amp line to the wall where your equipment rack is located would be excellent. Have it feed three AC sockets spread out along the base of the wall. If you plan on eventually getting several thousand watts of amplification, then 220 volt line should be included, with just one socket somewhere along the middle of the wall at the base. However, a dedicated line will not protect you from noise in the wiring. It will just let you have lots of big amplifiers going, regardless of whatever else is drawing electricity in the room. Be sure to include a socket along the equipment wall that is part of the regular room wiring, for a lamp or other appliance that you might find necessary. For removing line noise, you will need an AC line conditioner that plugs into the wall, and your equipment into the conditioner.

Q A lot of companies seem to use Burr Brown DAC chips. Are they all the same?

A No, there are several levels of quality. For example, the PCM1704U-ND is a 24/96 DAC that has a rating of 0.0030% THD, while the PCM1704U-K-ND is rated at 0.0015% THD. The latter DAC costs about $25 each in lots of 100, while the former is about $14 each. They also have a PCM1728E-ND, which is just listed as a 24/96 stereo DAC. It is only $4. Their new PCM1737E-ND DAC is 24/192, priced at a little more than $4 each, and a 24/96 six-channel DAC is about $8. The PCM1744U-ND is listed as a "low cost stereo D/A converter", at about $2.50. So, you can expect the low-end DACs in the low priced mass market players and receivers, but even the most expensive chips are not really all that expensive. What makes a high-performance DAC is the rest of the parts being precision items, such as 1% laser trimmed resistors, and of course, a large power supply.

Q Do you happen to know of any DVD players that contain a built in Dolby Digital (and/or DTS) decoder that can be used by the player as well as another source (i.e., a DSS receiver that outputs a DD signal)?

A There are a few high-performance CD players that have a digital input jack for use with other digital sources, but they are standard two-channel PCM stereo. I have not seen this in mass market CD players or DVD players, and no player that will do it for DD and DTS. But, once players settle down to being able to play all discs, including video and audio (DVD-V, DVD-A, and maybe even SACD), I would imagine the high-performance players, with their digital input for outside sources, will be able to do what you are asking about. If someone knows of a player that already does this, let us know and we will post it (them).

� Copyright 2001 Secrets of Home Theater & High Fidelity
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