Q&A # 127 - July 20, 1999

Staff

Q I want to get into the DJ / Traveling audio-for-hire business. I want to drive my speakers with an amplifier called the Carver M-400, also known as the Carver Cube. I have a reprint of a review extolling the benefits of this little amplifier. It weighs 9 pounds yet delivers a gargantuan 500 rms watts into 8 Ohms. I have never heard this amplifier play, but to someone who has lifted other amplifiers with that power rating (Hafler, BGW, Hill, QSC, Peavey), it sounds too good to be true. Maybe it is. I know they stopped making them about 1985, and I hear that they don't deliver much sub bass and they are unreliable. The report says that they are specifically not for industrial use, but I cannot ignore an amp with such a high power-to-weight ratio. However, I want verification from professionals . . . starting with do they actually have the power that everybody's raving about? I also see a lot of people on the Net wanting to obtain a power transformer for their cube. Is this a weak point ? I hope I'm not ranting, but I want to tell you a little about my intended application. I want to get into the P.A. business, but don't want to have to lug around an amplifier rack that weighs over seven hundred pounds. Since each cube weighs 9 pounds I would mount these amplifiers in each enclosure (four sub bins, three bass bins, two low mid enclosures with four cone type drivers, one horn enclosure with two horn type drivers, and a high frequency enclosure with four bullet type tweeters). Each enclosure would be a Fane type design modified to JBL specs as I want to use all JBL drivers, and they would be made from aluminum. Four cubes for the subs, three for the bass, two for the low mid, one for the high mid, one for the high frequency enclosure adds up to 11 amplifiers. The kicker is, I don't want to run shielded cable from each leg of the crossover, and I don't want to run speaker cable either, so I want to use a quality wireless mike system to take the full audio range and mount individual FM receivers in the boxes as well (a receiver for each leg of the crossover.) Well basically you now know my story, so do you think all this can be done?

A Carver's designs use several rail voltages, and this is the reason they are so powerful. It is a result of power supply efficiency. They don't get hot either. As long as you make sure your speaker loads are 8 Ohms or above, it should work. I assume you are considering the Cube because you can get these amps for a good price somewhere. There are plenty of other Class H amplifiers out there as well, and they are all pretty efficient and powerful for their weight. Actually, Class H is an excellent idea for using in DJ applications because of the weight and heat issues. You do need to be careful of the repair problem though, since the Cubes are no longer made, and they all are more than 10 years old. I would suggest getting a couple of them and putting them through some tough paces to see if they hold up. If you can use some drivers in series, to give a 16 Ohm load, this will probably make life easier on the amplifiers.

Q I have a strange problem. Some DVDs sound real bad in DD 5.1 mode, which, I am told, should sound excellent. For example, the "Alien Legacy" box is supposed to be very good in both video and audio. Certainly, the video is superb, but the sound is a complete disaster. The background noise/hiss is very loud, and nothing I do helps. Fiddling with different controls on the receiver and DVD player does no good. Some discs simply sound bad, but they should not according to other users. The hardware, PAL Harman/Kardon AVR-65 and PAL codefree Pioneer DV-505, has been tested separately in lab by technicians and is found problem free (although technicians have not tested the stuff together yet because the place of purchase of the items is different). In my home, the receiver and player are connected with inexpensive coaxial digital cable (will be replaced soon), and speaker cables are Supra and Monster. Cables do not seem to be the problem, as I tried different types of coaxial and optical cables with the same results. So, I suspect that the culprit is the DVD player somehow. Any suggestions on how to proceed with a case like this, besides sending away both the receiver and player to be looked at by technicians? I never heard of compatibility problems between receivers and DVD players.

A Since only some of your DVDs have this problem, I think it is the DVDs and not your player or receiver. The industry is still perfecting DVD production, and some of them just don't come up to standards. Noise and hiss could be in the master, and if they are not removed, they will be in the final product. Noise and hiss could also be introduced in preamplifiers and other electronic equipment during the process of mixing, if it is not done digitally. There are all sorts of ways to get noise, hum, and hiss into a product that is listened to by digital means at the end. As to why you might notice the noise when others said the discs are good, well, that may be just that you are tuned into the noise, while some others are not.

Q I just bought a new Pioneer VSX-D608 receiver to replace my old Sony STR-D711, but I think the sound was better through my Sony. I have a 6 head VCR and RCA DVD/DIVX player. The DVD is connected with S-Video jacks and fiber optics cable. But when I play the DIVX movies, the sound doesn't seem as good as before. I haven't played a non-DIVX DVD yet. And, the VCR seems to sound better though. I am confused. Is the Pioneer a better unit than the Sony? I know there are more features on the Pioneer, and it puts out more power. Maybe it's just me. I also have a powered sub hooked up. Can you tell me anything about the VSX-D608? My friend has the same Pioneer, and his sounds great. My speakers are Bose 201s, a JBL center, and Bose 100s for the rear.

A There are several issues to consider. One is that not all DD decoders are equal. Just like not all CD DACs are equal. If they were, no one would be interested in paying a few thousand dollars for an outboard DAC. So, it could be that the DD DAC in the Sony is better than the one in your Pioneer. However, this is complicated by the fact that your friend's identical model Pioneer sounds fine. In that case, it may be that the Sony is a better match for your speakers than is the Pioneer. This is assuming that your friend is not using exactly the same speakers. You might try using two channels of the Sony's power amplifiers for two of the channels in the Pioneer (pre-outs of Pioneer to pre-ins on the Sony). This will ease the stress on the Pioneer's power supply.

Q I have two 8 Ohm passive subwoofers that I want to connect to one channel on my 200w/channel amp. Please explain to me what kind of results I would get when I connect them either in parallel or in series. What would also be the result if a third woofer (which is 4 Ohms) is added.

A When the subs are connected in series, the load will be 16 Ohms, which will be less of a drain on your amplifier's power supply than when they are connected in parallel (this would give a load of 4 Ohms). If you put the third one in series, the impedance would be 20 Ohms. You might try connecting the two 8 Ohm subs in parallel, and then put them in series with the 4 Ohm sub. This would give an impedance of 8 Ohms to the amplifier. In any case, be careful when you turn on your amplifier to any of these experimental setups. Set the volume control low to start.

Q I have an EOSONE Satellite Speaker system # RSS 705 with a Yamaha R-V1105. The problem is that I have a lot of hum in the surround speakers and subwoofer, even in DD or DTS mode. I have upgraded to shielded Monster cable for the line input and a shielded y connector into the sub. I just don't know what to do. This only happens when I am hooked up to the sub. Please help.

A You are getting a ground loop somewhere. Ground loops are caused when current travels along a route that it is not supposed to, such as interconnects. It results when one component is plugged into an AC source that is at a different ground potential than one or more of the other sources. Sometimes, it can be reduced if you use a three prong adapter for one or more of the components that have grounded plugs. In other words, you use the adapter to eliminate the ground prong. These plugs can be purchased at any electrical supply store, Home Depot, etc. You have to be careful though. The ground plug is for safety purposes, so you won't get electrocuted in certain situations. Also, there is the occasional product that REQUIRES a ground prong to function properly. Look at your instruction manual to see.

Q Regarding recent questions about two channel analog stereo coming out of DVD players, here is some further info. All DVD players have the capability of playing Dolby Digital Soundtracks from their analog outputs. When presented with a discrete 6 channel mix, the player "on-the-fly" creates a 4 channel matrixed soundtrack (the four tracks are folded down to two stereo tracks) and outputs the sound as Dolby Stereo (for Pro Logic decoding). With me so far? Here's where it gets interesting. II was fooling around with "Video Essentials" last night, which as you probably know has both a 6 channel mix (soundtrack "1") and 2 channel Dolby Stereo mix (soundtrack "2"). In the audio portion of the disc, using analog outputs and the 6 channel soundtrack, the sound level test for each channel works perfectly, with tests tones where and when they are called for, except for the subwoofer. During this test, a deep bass test tone playing from the .1 LFE channel is used to set the sub level. There is no sound whatsoever from the analog outputs during this test tone. If you switch to the second soundtrack (2 channel Dolby Stereo), you can indeed hear the low bass test tone (rumble). From this I simply have to derive that when my Toshiba 2108 "creates" the Dolby stereo output from a 5.1 mix, it is leaving out the .1 channel. If a DVD has just the one sound track (as many do) and IF the sound team put sounds in the LFE track which are not duplicated in any of the main channels, then it could be said that something is definitely missing (or at least being left out). If any of you have VE-DVD handy, why not try unhooking the digital cable and see if the same holds true on your player. - Brian Florian -

A Thanks Brian.

Q I have been searching on the Web for the correct way to hook-up my Toshiba SD3108 DVD player to my RX-V795 receiver and my Mitsubishi 35" (CS35701) TV with PIP. I am a novice Home Theater enthusiast but am Yamaha mechanically inclined. Can you direct me to a Web page where there are diagrams or can you tell me the best way for me to do the connections? I would like to be able to have the TV be the control of sound. In other words, when I switching between inputs PIP, "A" to "B" or Ext 1,2,3, the receiver stays on one audio source, but by switching inputs, the sound changes with the video. Is it possible to do this?

A I assume your TV has several sets of inputs, and at least one set of outputs, called Monitor. Connect the audio and video analog outputs of your VCR, and DSS or cable to these inputs on your TV. Then, connect the audio outputs to a set of analog inputs on your receiver. When switching inputs on your TV, the appropriate audio signal will go with the video. In the case of DVD, you should use the digital out from your DVD player to the 795 so you can make use of the 5.1 digital surround. Otherwise, if you went through the TV like the other sources, you would be limited to Pro Logic.

Q I am starting a slow upgrade of my system toward a decent HT setup. I'd like to buy a quality DD/DTS receiver with 5 or 6 channel pre-outs but a small to medium power output (say 50 to 85 watts/channel) to save dollars. My plan would be to use the receiver alone to power my speakers until such time as I buy or build an amplifier section of 100 - 150 "high quality" watts per channel, then use the receiver as a high quality preamp, bypassing its mass market amplifier section. My question is this. What receivers would you recommend in the $500 - 1,000 range ($750 - 1,500 Canadian) that provide a high quality signal to the pre-outs? I'm looking for a signal that would eventually do my amp upgrade and speaker upgrades justice. If necessary, I'll spend a bit more.

A Probably something like the Yamaha RX-V795 or 995. Most new receivers have DD and DTS decoding in your price range, but not all of them have pre-outs, so you need to look carefully at the ones you are considering.

� Copyright 1999 Secrets of Home Theater & High Fidelity
Return to Q&A Index.