Q&A # 141 - September 29, 1999

Staff

Q A few years ago, I purchased a Carver HR-895 Pro Logic receiver. I've just recently picked up a pair of Polk RT800 speakers for the front mains to go with a CS200 center and RT3 surrounds. It's taken me quite a while to get all my components together, and now Pro Logic is nigh obsolete. So, I'd like to purchase a DVD player with a built-in DD 5.1 decoder because the Carver is still in beautiful shape. However, it is not "DD5.1 ready" -- but it does have pre-ins and pre-outs for all five channels. If I buy a DVD player with a built-in DD 5.1 decoder, I could connect the DVD player's five analog outs to the Carver's five pre-ins (not worrying about LFE yet). However, this makes the preamp portion of the Carver totally useless until I disconnect the cables and replace the pre-in/pre-out shorting plugs. Every time I'd want to switch between DVD or CD and radio or TV, I'd have to fiddle around with wires in the back. Do you see any way around this, without adding significant investment?

A From your description, your pre-ins are actually power amplifier ins. The plugs you mention connect the output of the preamplifier section to the inputs of the power amplifiers. When you remove the plugs, the pre-outs could be used to drive some other set of power amplifiers, and/or you could connect a line-level source to the power amplifier ins on the receiver. You would need to have volume control somewhere in the lines if you connect your DVD player this way, since the volume controls are in the preamplfier section. DVD players with 5.1 analog outputs usually have some amount of level manipulation, but not an overall volume control. You could put multi-ganged potentiometers, say around 10 kOhm each, in series with each line output from the DVD player, but this would be a lot of work, and you would need to use a shielded box to mount the pots in. You could use toggle switches (double pole, double throw, to isolate the ground from each source) to output either the pre-outs from your receiver or the outputs of your DVD player to the amplifier inputs of your receiver. If you decide to go ahead with this, just get one potentiometer, one toggle switch, and one set of RCA jacks, along with a shielded chassis to mount them in, before you invest in the whole thing. Run one set of wires from one input jack to one set of poles on the toggle, then to the pot and then to the output jack, with the hot wire (the center connector on the jack) through the pot. Run another set of wires from a second input jack through the other poles of the toggle directly to the output jack, and not through the pot. If it works satisfactorily, then all you would have to do is throw the toggles when you use the DVD player vs. the receiver preamplifier. You could end up spending quite a bit of money on this. I would prefer to just get a new receiver that has DD and DTS built-in.

Q I recently purchased a professional CD recorder. It has any combination of inputs/outputs you can imagine. Currently, I use RCA line inputs to record analog sources. I run all of my analog equipment (turntables and older CD players) into a Numark DJ mixer (was their top of the line several years ago). I have noticed an audible hum when monitoring the input signal through the RCA line-in on my CD recorder. It is really only noticeable when no signal is present, or probably during silent segments of a song. It is not turntable hum since the buzzing is present when their pots are all the way down. I have determined that the hum is also present with the RCA line connection to the amp. The mixer has RCA record outs and a regular RCA line out that plugs into my CD RCA input on my amp. Since both RCA terminals transmit the hum to both the CD burner and the A1, it is obviously that the mixer is introducing the hum. I am hoping it can be remedied by using XLR connections. Do you think this is likely? Both the mixer and the burner have XLR connections, but I noticed the HHb CD-R 850 has two inputs for XLR, one at +4dBu and one at, -8dBu. What is the difference between these two XLRs? How can I determine which to use? (I have no manual for the mixer!)  I don't think I should run the turntable directly into the line input on the back of the CD recorder, so I have to run it to some preamp that has the proper RCA jack for phono first. I am really new to XLR, so any information will be greatly appreciated.

A XLR connections will probably reduce the hum, and I suspect this is a case of ground loop hum if you are not using long cables. The 4 dB vs. the 8 dB inputs probably refer to whether you are using a high level or low level signal. Just try them both and see which works the best. One may not be loud enough or one might be overloaded by your signal.

Q I was wondering if you guys could tell me how to use the line-out connection on the back of my Velodyne CT-100 subwoofer. I currently have Monster THX cable running from the processor line-out to the sub. Also, can the sub turn into a passive one with an outboard amp plugged into the output or input?

A First, let's make sure we are talking about the same thing. On the back of the subwoofer are line-ins and line-outs. The line-ins on the subwoofer are for connecting to the line-outs from a receiver or processor. The line-outs on the subwoofer are for connecting to a power amplifier that drives satellite speakers. The line-outs are high-passed such that only frequencies above a certain value (say 100 Hz) go to those power amplifiers. You should never connect any power amplifier to the line-ins on the subwoofer. The line-outs of the subwoofer are for that purpose. Only preamplifier ("sub-out") or processor outputs should be connected to the line-ins on the sub. A powered subwoofer is never passive unless you went inside the enclosure and disconnected the power amplifier from the driver. If you have a receiver with pre-outs and main-ins, you can run the pre-outs for the front left/right channels to the line-ins on the subwoofer, and the line-outs from the subwoofer back to the main-ins on the receiver. For this method to work, your receiver should have a set of jumpers that connect the pre-outs to the main-ins for the front left/right channels. Some receivers have them, and others don't.

Q I am new to all this home theater stuff, but my plan is to start building slowly. I have a decent 27" Zenith TV, and I am planning to upgrade to DVD and a 5.1 surround speaker setup. My problem is that my Family room is not the greatest for this. It is rectangular (21x16, with cathedral ceilings), with a fireplace and windows on one side (the long side), and windows and a sliding glass door in the center of the short sides, and a large opening to the kitchen opposite the fireplace. The only reasonable place for my entertainment center is in the corner to the left of the fireplace. I have no idea how to set up the surround speakers to get decent sound if the TV is in the corner of the room. I can't find any examples of this, or suggestions. Can you give me some pointers, or at least head me in the right direction?

A For a situation like this, I would recommend putting the rear surround speakers near the sides of your listening position (couch). This will limit listening to those sitting on the couch, but it will work fine. Putting rear speakers on the wall will open up the listening to a larger audience, but it is not necessary for a small audience (all sitting on the couch or in front of the couch). Aim the speakers towards a point near midway between you and the TV rather than directly at you where you are sitting.

Q I have a very old Toshiba SA-775 Receiver that has been having some intermittent problems lately. Is it worth my while to have it fixed or should I scrap it for newer technology?

A It all depends on what is wrong, and how much it will cost to have it fixed. Labor is very expensive, much more so than the parts. If the estimate for repair is more than about 25% of the original cost of the receiver, I would suggest getting a new receiver.

Q I have a Yamaha AVR-V503, Cambridge Soundworks center speaker, Bose SE-5 main speakers, Bose 100 surrounds, and a Sony SLV 740 HI-FI VCR. The performance is poor. I have noticed the newer AVRs have the same wattage across all five channels (mine has 70 watts main and only 20 watts for surround. I'm considering buying a power amp. Or should I upgrade to a newer AVR? In $500 - $600 range.

A If your receiver has pre-outs, then you might look around for a used five-channel power amplifier. On the other hand, you should be thinking Dolby Digital, so a new receiver might be in order.

Q Can you compare Nordost Blue Heaven and Blue Angel cables? Is it justifiable to spend the extra 50 dollars for the Blue Heaven?

A The differences between Blue Angel and Blue Heaven are very subtle, but I don't think Blue Angel is in Nordost's product line anymore. Don't get in a panic attack over whether or not to spend an extra $50. Just decide what your budget is and stick to it. Don't listen to any cables outside of your budget.

Q What do you think is the average current (ampere) output capability of a mass market receiver?

A If the receiver is rated at 72 watts per channel into 8 Ohms, and assuming about a 24 volt rail, it will output 75/24 = 3 amperes from each channel when 72 watts are being delivered. A $20,000 power amplifier rated at 72 watts per channel will also output 3 amperes, but it will do so for a longer period of time.

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