Q&A # 193 - August 3, 2000

Staff

Q I have a JVC 888VBK digital receiver which, I guess would be considered "mass market". I am in the process of upgrading my speakers one channel at a time to the B&W CDM SE series. I have two questions. One, would I get appreciably better sound by adding an outboard power amplifier, and two, since there are no pre-outs on this receiver is there any way to hook up an amp? Since I have only had this receiver for less than a year I would hate to have to buy a new one so soon.

A Yes, outboard power amplifiers really make a difference when used with mass market receivers. At $550 MSRP, the 888VBK is right on the edge of the price range where the products begin to have pre-outs. You really need the pre-outs to connect an outboard amp. Even if a third party company could add the pre-outs to your receiver, it would cost almost as much as the receiver itself. If you are determined to use outboard amplifiers, try selling the 888 on newsgroups or auction sites. If it is a year old, then a price of about 60% - 70% of what you paid for it would be fair.

Q Why does the volume of dialogue on DVDs seem so much lower? I have a Denon AVR-2800 receiver, and Boston Acoustic front, rears, and center (no sub as of yet). Is this the way movies are recorded? Is the only solution turning the volume up on my center speaker?

A The positioning of the center could affect its perceived loudness with respect to the other speakers, since the center is on the top of your TV (assuming it is), and the others are at ear height when you are seated in the listening position. If you have not already done so, use the test signal generator in your receiver to balance the loudness in all channels at your listening position, or if no signal generator, use one of the setup and test DVDs that we have reviewed. Other than that, yes, simply increase the volume in your center channel. Personal preferences and room setups are why each channel is individually adjustable.

Q I use a pair JBL L-7s for my Home Theater front channel. They are bi-wireable and have very large inboard facing 12 inch woofers. My decoder is an Acurus ACT III. Would I be able to successfully use a separate amplifier to power only the low end of the JBLs using one of the sub-out RCA terminals on my decoder? I have an Energy ES 12 subwoofer.

A Yes, you could do this. However, the crossovers in your JBLs are expecting full range signals coming in, and the low-pass to the woofers is probably higher than might be coming from your sub-out. Let's say it is 200 Hz in your JBLs. This means that the high-pass to the mid-range drivers is 200 Hz (approximately) and above. Therefore, if the sub-out on your ACT III is a low-pass set to 80 Hz, you will be missing the signal between 80 Hz and 200 Hz in your JBLs.

Q I am trying to build a stereo system that will also play home theater. I will receive a pair of Magneplanar 1.6s and a Maggie center channel speaker in a few months. In the meantime, I purchased a Musical Fidelity (MF) A300 integrated amp. I will also receive a pair of Triangle Titus speakers for surround sound next week. My source components are all inexpensive: one DVD player and one cassette deck. My initial thought was that I would connect the amp through a Yamaha DSP-A1 when I purchased one. I called the dealer to find out if I could connect the MF amp to the DSP-A1. Their response was negative. The A300 does not have a main-in, so it cannot be used as a power amplifier (it does have a tape monitor loop though). I have the option of returning the A300 and getting a power amp (MF A3 CR) at the same price. That will allow me to hook up the A3 CR power amp to the DSP-A1 (and using the A-1�s built-in amps for the other three channels). However, I feel that this configuration might defeat the sonic benefits of a fine power amplifier. I would have to connect the A3 CR power amp to the  preamp on the DSP-A1. I could buy a tube preamp, such as Audio Electronic Supply AE-3 (or perhaps the MF A3 CR preamp) to feed the A3 CR power amp. However, in order to switch from stereo to surround I would have to unplug all the source components from the stereo preamp and hook them to the DSP-A1 because I could not probably use both the stereo preamp and DSP-A1�s preamp section at the same time. How do I handle this problem? Is there any way to use a tube preamp and the surround receiver with the MF power amp at the same time? Alternatively, could I use the following configuration?: source --> AES AE-3 --> DSP-A1 --> MF A3 CR --> Magenepan Main speakers. The DSP-A1 will also drive the center and surround speakers.

Another consideration is that the input impedance for the A3 CR power amp is 31 kOhms, and the output impedance of the AE-3 is 560 Ohms. Will this create any matching problems? I cannot have two different systems � home theater and stereo. If the above setup is not possible, what option do I have that will give me excellent stereo performance and good home theater sound? By the way, I do not want to break the bank, and I can at best spend $3,000 for the DSP-A1 and preamp.

A I would suggest connecting your DVD player two-channel analog out to the tube preamp inputs, and the outputs to the DVD two channel analog input on the DSP-A1. Then, when you are playing two-channel CDs, use the direct through on the DSP-A1 to your power amplifier (with the DSP-A1's front left/right pre-outs). This bypasses the DSP-A1's preamplifier circuit. When you are playing DVDs, use a digital cable connection from the DVD player to the DSP-A1. This will require that you use a different input on the DSP-A1, such as CD. Otherwise, the DSP-A1 will default to the digital input all the time, as both the analog outs and digital out from the DVD player will always be connected to the DSP-A1, and there will be signal flowing in those cables each time you are playing CDs or DVDs.

The impedances you describe are fine. It is only when you get down to around a 10 kOhm input impedance that things are tricky. The irony is that some designers feel that a high output impedance on the preamplifier and low input impedance on the power amplifier gives better sound through low distortion. This is a situation where the input of the power amplifier is driven based on the current rather than the voltage. The problem with this approach is that it requires a hefty power supply in the preamplifier, and that makes it expensive.

Q I will soon be in the market for my version of a home theater system (i.e., a big screen TV and surround sound audio system). However, I am totally clueless as to what components would suit me best and what is the difference between HDTV and digital TV? I am not looking to upgrade soon if I don't have to. Any help on where I can research this or any tips you have would be much appreciated.

A All HDTVs are digital, but not all digital TVs are HDTV. You just have to ask that question when you are looking at specific models. There are some 4:3 TVs (the standard shape we have now) that are HDTV compatible, but they have to letterbox when watching HDTV broadcasts, so I would suggest getting the 16:9 shape HDTV. If you want big screen (rear projection), then check to see if it has the ability to do 1080i in its native format and full resolution (1080 pixels by 1920 pixels). This requires 9" CRTs in the projector. Some, but not all, will handle 720p in the native format rather than upconverting it to 1080i. There are a number of them coming out this fall in the < $5,000 range. As to receivers and speakers, this is an entire world of an issue, impossible to cover in the Q&A. Our primer (Volume 1, # 1, 1994) has been updated and will contain most of the info you want. But, I would suggest a receiver that has pre-outs for all channels, an outboard power amplifier of at least 100 watts per channel, and a subwoofer in the $800 range or above, if you like powerful room shaking bass. We will be updating our recommended systems pages soon.

Q I have heard more and more that with DD and DTS, the optimum home theater and multi-channel music setup is to have full-range, monopole speakers all around. In a recent Q&A about the center channel, it was said that an option would be to have a subwoofer in line with the center channel to make up for the limited size and range of a typical center channel to match the fronts and rears. I plan to have Paradigm Reference Studio 100s for the front and rears, and the CC-450 for the center channel. I would also like to add a Servo-15 subwoofer to my system and possibly have it in line with the center channel to enhance the power and depth of that all important channel. My question is that if I purchase a Servo-15, is it possible to have it in line with the center channel and also be able to use it for the mains? The Servo-15 is relatively large and somewhat expensive, so I would like to be able to use it in line with the center and also take advantage of it for the mains and for general two-channel music playback. Is it possible to split the signal somehow without degrading it, or would I have to purchase two subs, one for the center and one for general use? It is a large sub with lots of power, so I hope I could use it in as many ways as possible due to size and expense. Secondly, for a multi-channel amplifier, what is considered better--a transformer for every channel, or a larger transformer shared by all the channels, considering multi-channel music and DTS, etc? Which feature tells more about performance: Output devices per channel, transformers, power capacitors (mF), balanced from input to output, etc?

A Yes, you can use the subwoofer for the center, the mains, and all the other channels at the same time. It is a matter of selecting those channels in the bass management menu of your receiver. However, in my opinion, it is best to use the "Large" speaker setting and the full range pre-outs from the receiver to the subwoofer so that you can use the low-pass crossover setting on your sub to match the low frequency limitations of your center channel. For a reasonably sized center channel speaker, the low end would reach about 50 Hz - 70 Hz. Setting the receiver to "Small" will undoubtedly send everything below about 80 Hz or 90 Hz to the subwoofer, and the frequencies above 50 Hz are directional, which would change your soundstage. If you are using an outboard power amplifier, then you will need a Y adapter in between the preamp and the power amp, so that you can connect the preamp output to the power amplifier and subwoofer at the same time.

Q I have a question similar to the second question in # 176. My Boston Acoustics PV800 thumps every time I change sources, but it doesn't thump when nothing is connected. It only thumps while connected and a change of source. I am running a cable from my Denon 5700's line-out to the subwoofer's line-in. I previously owned a BA VR500 and that didn't thump at all. Any suggestions? BTW: What is the "DC" that you referred to in the previous question?

A Some products have a thump and others don't. This does not reflect on their quality. Even high-performance products occasionally do it. It is produced by transient voltages during switching. The switching transients can be controlled simply by turning the volume down when changing sources. Power-on or power-off thumps are common, but they are often not altered by turning down the volume control. As to DC (Direct Current), you can get it in a constant state at the output in some products, called DC Offset. If it is at a power amplifier output, It "offsets" the speakers from their natural resting position. Sometimes the DC is transient, such as during switching.

Q I am building a home theater system. I would like to have my Klipsch klf 30's lay horizontal under the screen. What is your opinion of this?

A While LCR speakers are identical units that are for front left/right and center, with the center laying on its side, the KLF-30s are horn speakers designed for upright placement to have proper dispersion. I assume you want to do this so that you will have a full range speaker for the center, and most likely, you have KLF-30s as front left and right speakers. It won't destroy the sound quality, but it will certainly alter it by doing this. If you try it, you should experiment with the height.

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