Q&A # 217 - February 3, 2001

Staff

Q I've got a PC with an ASUS GeForce2 MX video card that can be set to any of the ATSC (DTV) formats including 1080i, 740p, and 480p. I want to connect it to my Toshiba 50HX70 RPTV that has component video inputs. I figured that I could use the Audio Authority 9A60 or the RCA/Thomson VHDC300 for the conversion from RGB to component. So far, the Toshiba doesn't like the output from the VHDC300. All of the advice on the web refers to S-Video (low res) connections. Do you know a good way to connect PC to HDTV using a hi-res mode?

A I found a couple of solutions for you that might do the job from Key Digital.  I'll start with Key Digital's KD-VTC-1, which shows a price of $129. The product page is here: http://www.keydigital.com/cgi-bin/detail.cfm?action=detail&ProductID=90.
Another option is their KD-TCDA2, which also includes two audio channels with the converter, but it is much more expensive than the first item. It takes a single RGB input + L/R analog audio and outputs two Component Video signals with L/R analog audio. It looks like this item isn't on the market yet, but will run $349. The KD-TCDA2 product page is here: http://www.keydigital.com/cgi-bin/detail.cfm?action=detail&ProductID=5. (John Kotches is our new PC-Home Theater Editor.)

Q The question of connecting two receivers together has been answered several times in the Secrets Q&A. The answer seems to be yes, using the pre-outs of one to either the CD or aux input of the other. My concern, though, is whether a straight RCA plug connection to either the CD or aux inputs is appropriate. I thought, since both receivers already have a preamp section, that the signal would have to be somehow downgraded before it could be fed directly to another receiver (unlike connecting a preamp directly to a power amp). I want to try to accomplish the ES rear surround effect with a center speaker by using the front and center channels of a Pro Logic receiver connected to a digital receiver's pre-outs. Straighten me out and put my mind at ease?

A With any input to a preamplifier, the volume control varies the voltage sent to the power amplifier or the pre-outs within a range that is below the original input voltage (when the volume control is near 0), to a voltage above the original (when the volume control is set to its maximum). The exception to this is with passive preamps that vary the output voltage from 0 up to the original input voltage. So, when you connect the preamp output of one unit to an input of a second preamp, you just use the volume control on the second preamp to control the level of what is going through. Let's say that a setting of 10 o'clock on the second preamp volume control produces an output voltage that is the same as the input voltage. At 10 o'clock then, the voltage at the pre-outs of the second preamp would be the same as the voltage at the pre-outs of the first preamp. There would be some noise and other artifacts produced by the addition of more cables, jacks, and second preamp circuitry in the signal path, but that is a different story. So, just use the second preamp volume control judiciously, and you will be fine.

Q I have Infinity Kappa 8.2 series II in front and four matching Infinity Kappa Video series II as center, L/R Surround, and Back Surround (EX). I really want DTS-ES and THX Surround EX, but I have problems finding an amp or A/V Receiver suitable for both the front and the other speakers. I have been considering the Onkyo TX-DS989 with or without two old NAD THX 2700 for each front, but I am not sure. Can you help me with suggestions based on a $4,000 budget? Perhaps you have a better idea for a setup matching my speakers? I also wonder if it would be better to run two Kappa Video as center to better match the front speakers, and perhaps also a sub to avoid blowing away my surround speakers.

A The Kappa 8.2 speakers have an 89 dB sensitivity and a 6 Ohm nominal impedance. You might have trouble driving them with the power amplifiers in receivers, including the Onkyo 989. However, many receivers do have excellent processing capabilities, so I would suggest getting an outboard five-channel power amplifier to go with the pre-outs on the receiver. In order to stay within your budget, wait a couple of months until some of the lower cost receivers begin including EX/ES. Then, get one in the $1,500 range, plus an outboard five-channel amp like a Rotel RMB-1075 (THX certified, 120 watts x 5 into 8 Ohms - $1,199 USA), and a good subwoofer in the $1,200 range. As to running two speakers for the center, that will be OK, but wire them in series rather than parallel, so you don't overload your amplifier, whether it is the built-in one or the outboard one. You can use the receiver's built-in amplifiers to drive the EX/ES channel.

Q I am torn between the Bryston 4BST and Adcom GF8502 power amplifiers.  Can you give me some pros and cons on the amps and which one would you recommend?

A These are both nice products. The difference, other than the 4B being rated at 250 watts per channel and the 8502 being rated at 300 watts per channel, is that the Bryston uses bipolar transistors in the output stage while the Adcom has MOSFETs. This will result in the Adcom having slightly less sharp edge to the sound. If I were going to use the amplifier mostly for music, I would probably get the Adcom, but it it were mostly for cranked up home theater movies, probably the Bryston.

Q I'm planning on buying Definitive Technology BP-2006 speakers with a matching C/L/R 2300 center channel for home theater. Unfortunately, for the moment I only have a 27" TV. Because of my room configuration, I have many restrictions: the TV can only be placed in front of a window, my equipment rack can only be placed under the TV, leaving with no other chance than to place the center channel speaker right on top the TV (putting it on the wall is out of the question because of the window). Unfortunately, the top of the TV is not big enough to hold it. Is there any stand (or other solution) that I could use to put the C/L/R 2300 on top of the TV, taking into consideration that it is an 8 5/16"H x 25"W x 16"D active speaker?

A For this particular situation, I would suggest contacting a cabinet maker and having a shelf custom made to fit on top of your TV that will hold the speaker. This should not be very expensive if you ask for something plain. It could be out of ordinary pine that you finish with stain and polyurethane yourself.

Q I'm a car audio enthusiast who's just getting into home audio. I just  recently bought an Onkyo TX-DS484 receiver from Circuit City (with a gift certificate I got for Christmas), and I read on Onkyo's web site that its rated down to 140 watts dynamic power at 3 ohms (it's 55w rms at 8 ohms).  But I've read that there is usually a switch on the back of the receiver to change impedance. My receiver doesn't have this. Most car audio amps that are stable at lower impedances don't have this either. So is it  possible to run 4 ohm speakers to increase power output without frying my receiver's amp?
A I have never seen a receiver that does well at 4 Ohms. The switch, when present, just limits the voltage that goes to the output stage compared to the voltage when using 8 Ohm speakers. This keeps the current demands from getting too high. I would not recommend using 4 Ohm speakers with your receiver, but it is more for your speakers' protection than the receiver. If the receiver gets too hot, it should shut down temporarily, but an overdriven amplifier produces lots of harmonic distortion, which can damage your speakers.

Q I have a Hitachi rear projection TV. I would like to know if there is any kind of line doubler that would work on my unit? It has 1000 lines capability, but I can only get 480 lines resolution, even with a progressive scan DVD. The TV is analog.

A The 1000 lines refer to vertical lines on the screen, even though this is called "Horizontal Resolution". Secondly, your TV must have the capability of doing 31.5 kHz scanning in order to perform line-doubling, or showing a progressive scan output from your DVD player. If your TV does handle 31.5 kHz, it may have a line-doubler built-in. Also, your progressive scan DVD player will do the line-doubling for you.

Q I just purchased my home and found that after I moved in there was less room in my living room that I anticipated. I am planning on having a living room window taken out and a stereo cabinet built into the space. I would like the entire unit to be flush with the wall and preserve as much floor space as possible. I really don't know what I don't know other than it sounds like a good idea. What should I be aware of? Are there any plans ready made for such a project?

A Make sure you have plenty of ventilation but no loose panels. Speakers would be better off out of the cabinet, but if you put them in, fill the area that they occupy, or rather the volume they don't, with damping material, such as polyester fiberfill, or fiberglass. Otherwise, the air inside the internal volume of the cabinet surrounding the speaker will resonate and make the sound extremely chesty.

� Copyright 2001 Secrets of Home Theater & High Fidelity
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