Q&A # 173 - April 13, 2000

Staff

Q Do I need any special device in order to playback the DD music recorded on a CD? I have a CD which as a Dolby Digital logo on it and the seller said it has DD music recorded. But my Pioneer DVL-909 only recognizes it as an ordinary CD and outputs stereo music.

A You are probably using the analog outputs of the CD player. You have to use the digital output from the CD player to your processor or receiver. Also, your processor or receiver must have DD decoding, which I assume yours does. So, just connect the player to your processor/receiver with a digital coax or Toslink optical cable.

Q My question is about amplifier design. I am in the market for a high-end multi-channel amplifier and am interested in the many different designs that are present. One feature of many amplifiers today is balanced design. I have found that just because an amplifier has balanced outputs does not mean that it is fully balanced in operation. In many cases only a stage may be balanced such as a voltage gain/output stage, but the rest is unbalanced. Some companies tote balanced operation from input to output, but do not offer any specifics as to how this is accomplished. Mark Levinson No. 33s and No. 33Hs are the only ones who go into detail as to how this design is accomplished. They describe it as each channel having basically two symmetrical mono-amps that are bridged at output to create the fully balanced from input  to output, which the lower 300 series amps do not have. The new Krell Master Reference series also claims balanced input to output. My question is how substantial is a balanced circuit from input to output toward performance? And can it be done without using the two mono-amps bridged per channel as in the ML No. 33 series? Is the ML No. 33s considered the top amplifier design approach at this time with the two bridged amps for balanced from input to output? What other key factors of amplifier design should be considered as far as the quality of the amplifier and its sound?

A A fully balanced design is essentially two mono amplifiers bridged. This eliminates the ground from the signal path. The mono amps are usually in one chassis and the inputs are XLR jacks (outputs too if it is a preamplifier). This is compared to a stereo amplifier with a bridging switch. The inputs are RCA jacks. There are some other differences too, but basically, that is what's happening with a fully balanced design. Some will argue that, unless the fully balanced amplifier has an output transformer, so the + and - outputs can be referenced to the center tap on the transformer, the fully balanced amplifier is not truly balanced. Others would counter argue that, with the transformer, any improvement due to true balance would be lost due to a transformer being in the signal path. The non-transformer designs are sometimes called "direct coupled". In any case, fully balanced designs provide for a sound with complete silence in the background. No hum or other noise that would otherwise have been introduced by cables. I use a fully balanced preamplifier and power amplifier in our lab, and I really love them. There are a number of companies that make fully balanced products, but they do not necessarily sound the same any more than unbalanced products from different manufacturers. Amplifier design is very complicated. All kinds of things have an effect on the sound: the quality of the parts, how many gain stages are used, amount of negative feedback employed, balanced or unbalanced, solid state or tubes, MOSFET or bipolar, single ended or push pull, class A, AB, Digital Switching, Multi-Rail, size of the power supply. There is no single determining factor on which to base judgment.

Q I am trying to set up an ersatz Surround EX (6.1 Channels). I was able to achieve my goal by doing the following: connect the Left Surround (LS) and the Right Surround (RS) lines out of my Marantz Dolby Digital Processor (DP870) to the Laserdisc line input on my Pioneer VSX D2S receiver. I connected my LS and RS speakers to the Front Left and Front Right speaker terminals. Fortunately the D2S receiver has two center channel speaker terminals, so I was able to connect my two Surround Center (or Center Surrounds?) speakers. I set the D2S in "three-channel logic" mode. As the Surround EX extra rear center channel is matrixed from the LS and RS, the Dolby Pro Logic Processing of my D2S serves me well to extract the extra channel in the surrounds. Before, my setup ran like this: L, C, R, LS, RS, and Subwoofer pre-outs of the D2S receiver went to the six channel ins of the DP870, then to B&K AV500 and the powered sub. If the source is not Dolby Digital, I just press the bypass button in the DP870 and I can listen to Pro Logic soundtracks. My question is, if I use this same setup and connect the LS and RS output of the DP870 to the laserdisc input of the D2S, would it cause any harmful effects (like feedback, loops)?

A This is difficult for me to determine without actually seeing your setup. However, all you have to do is make sure you don't have any output going back to its own input. Depending on how your processor and receiver's input selectors are set, it might cause some feedback. Even if it does however, the way to test it out is to have all the volume controls turned down completely before you turn the components on. Then, turn the processor on, and adjust the volume up a bit to see if you hear any feedback squeal. If not, then turn the volume control of the processor down, and turn on the receiver. Turn the receiver volume up slowly. If no squeal, then, leaving the volume of the receiver up a bit, turn the processor volume up slowly. If no squeal, you are in good shape. Otherwise, if you hear the feedback squeal, you need to run some of the cables using a different route.

Q I am a bit confused about all the talk and specifications around 24/96 audio. In a recent review of a processor in a printed magazine, the writer stated that the processor would not decode 24/96 audio, but that did not matter because so few sources are available at this time. Do not most DVD players today provide 24/96 outputs? What advantage is there in 24 bit DACs if most CDs are recorded in 16 bit formats?

A The review did its readers a disservice because DVD-Audio is here. True, the recordings are few right now, but they will come. However, there is the saving fact that the DVD-Audio DAC in the players can do all the 24/96 decoding. So, a 24/96 DAC in the processor is not necessary. In fact, some would argue that using an outboard DAC risks introducing artifacts like jitter because of the necessary jacks, cables, and plugs that are between the transport and the DAC. Most DVD players now will decode 24/96, but they don't have 24/96 bitstreams at the digital output. They downconvert 24/96 to 16/48. A few players will pass the 24/96 digitally, but most do not. On the other hand, you can get just about any DVD player converted to pass the 24/96. The advantage of having a 24/96 DAC when you are playing 16/44.1 CDs is that the DAC's resolution is so high, it does a much better job of decoding the lower sampling rate than the old DACs that were 18 bit resolution where 16 bit samples were getting near the limits of the DAC.

Q I am using an Acurus ACT3 pre/proc for my home theater system. I would like to use an Adcom GPF-750 preamp for my audio-only sessions since the Adcom preamp has a pass-thru switch. Is this possible? If so, please guide me through. My amplifier is rated at 120wpc, and I am using a pair of B&W N805s with a sensitivity of 85.5db. Whenever I raise the volume to 50 (0 to 70), the protection circuit of the amp cuts off the sound until I lower the volume. Should I buy another 120wpc amp and bi-amp the speakers or buy a 200wpc amp?

A Here is the procedure: Connect the analog stereo outputs of your CD player to the analog CD input on the Adcom. Connect the digital output of the DVD/CD player to a digital input on the Acurus. Connect the stereo outputs of the Adcom to the front left/right power amplifiers. Connect the front left/right pre-outs of the Acurus to a different set of inputs on the Adcom (such as Aux). Now, when playing CDs for two-channel stereo listening, select the CD input on the Adcom. You don't need to even turn on the Acurus. When you are playing CDs in surround sound or DVD movies, turn on the Acurus and Adcom (if the Adcom has to be turned on when using the pass through), and select the digital input on the Acurus and the Aux input on the Adcom, with the Adcom set to Pass Through. This will send the DVD/CD digitally to the Acurus which will decode it and send the surround sound front left/right to the pass through on the Adcom, and the other channels to their amplifiers. The pass through on the Adcom will send the front left/right surround sound to the front left/right amplifiers. Set the Adcom to Aux and Pass Through before turning on the system. The B&W specify 88 dB sensitivity and are 8 Ohms. Getting another 120 watt amplifier and bi-amping would be the most efficient use of your existing equipment.

Q I have an integrated amplifier (NAD 314: 35W per channel) with PREAMP OUTPUT and MAIN IN jacks. They are connected together with factory-installed U-shaped metal jumpers. I wonder if I can connect my Quad 405-2 power amp to my integrated amplifier after I remove the metal jumpers? Then I want to connect speaker cables to the Quad 405-2 and use only the preamp component of the integrated amplifier (to play CD player and Video-related audio signal; video cassette). Is it possible to do so, and if it is, is there anything that I need to be careful about the connection?

A Yes, you have the correct procedure in mind. Remove the jumper pins, but be sure to put them in a safe place in case you want to reconnect them. Then, connect the pre-outs of the integrated amplifier to the inputs of your Quad. If your speakers are bi-ampable (meaning the tweeter and woofer have a jumper bar connecting them at the speaker terminals), you could use a Y splitter in place of the jumpers on the NAD, connecting one plug of the Y splitter to the pre-out of the NAD, one plug of the Y to the main-in of the NAD, and the third plug of the Y to the input of the Quad, and then connect the speaker outputs of your NAD and the speaker outputs of your Quad to your speakers. If you do this, the jumper bar on your speakers MUST be removed first. Otherwise, you could harm both power amplifiers. You should NEVER connect two amplifier outputs to the same speaker posts on a speaker.

Q I'd like your opinion in using a tone bypass switch on a receiver. My receiver (Yamaha) documentation states that by using the switch, you receive a pure, flat signal. Is this a preferred choice? Or, do you recommend adjusting the bass and treble controls?

A When using the tone bypass, the signal is routed around the tone control potentiometers. However, switches are still in the circuit, and the signal still will suffer the loss that switches cause. However, using the 0 setting ("Flat") on the tone controls will accomplish pretty much the same thing. Using the bypass just makes sure that the 0 setting is achieved, resulting in no phase shift.

Q I just spent the last 2 hours adjusting my Mitsubishi 27" TV to the Video Essentials (VE) disc, and I have to say that I am not impressed with the results. The picture now after all of the adjustments looks flat and completely lifeless. Do you receive other messages from your readers with similar complaints?

A That is why there are brightness, contrast, tint, and color intensity adjustment controls on the TVs. Everyone has their own preferences. Also, that is why TV stores turn up the brightness and contrast in their displays. It is more impressive. The VE recommended settings are just for a standardized starting point. After that, adjust things to suit your tastes.

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