Q&A # 228 - April 30, 2001

Staff

Q The input impedance of my power amp is 47 k Ohm, so if I add a 50 k Ohm potentiometer or attenuator just outside of the input RCA of my power amp, will this potentiometer control the loudness (I mean will it get louder than before adding the potentiometer)?

A The 47 k Ohm input impedance is not just DC resistance. It includes capacitance and inductance. The 50 k Ohm potentiometer represents DC resistance. It should be able to control loudness, but it will not make it louder than without the potentiometer. Only the same loudness and lower.

Q I recently received an Alphasonik amplifier from my friend along with a pair  of alpine 6x9's. I was wondering if this amp was any good because I never heard of this brand before, and I'm having trouble finding information on it.  The amps model number is A-225.

A Sometimes, large companies with well known brand names will manufacture a line of products with similar quality, but with a different brand name that is not famous at all. This gives them the opportunity to sell good products at a lower price, without the fancy brand name and markup price that goes with it. It may be that Alphasonik is one of these, and marketed by Clearwater. Here is a link     http://www.realbig.com/miata/miata/1996-10/2183.html.

Q I was just wondering if there is any substantial difference in sound if I use my DVD player as a transport when compared with something like a Proceed Transport or a Wadia?  Isn't all the transport's job is to pass data to an external DAC? Can you clarify any other responsibilities that a CD transport will perform?

A The job of the transport is to get the bits off the disc and pass them to the DAC. A high performance transport will have better vibration isolation, higher quality internal wiring, and (hopefully) the proper 75 Ohm impedance output jack. In my experience however, a mass market CD player makes a very good transport, as long as you use the Toslink optical output jack. The RCA output jacks on these players are likely to be 50 Ohms and maybe even lower. Toslink does not have impedance issues. In the case of DVD players, you have another problem, which is the size of the laser beam. It is different with CDs vs. DVDs. Most DVD players have only one laser beam size, which is optimized for DVDs. Some players have two lasers, one for CD and one for DVD. These players (Sony for example) will likely make the better transport for use with CDs and an outboard DAC.

Q I have a Sony STR-333ES receiver that is used as a preamp. I was planning on using the 5.1 input of the 333ES as a SACD/DVD-Audio input because it bypasses the internal AD/DA converters. My dealer told me that the 5.1 input is not really an analog bypass and I should purchase an analog preamp. My question is will the 5.1 input suffice with SACD/DVD-audio?

A Yes, in fact, the 5.1 analog inputs are exactly what you should use with multi-channel SACD and DVD-A (two-channel SACD can be used with a conventional two-channel analog input set). At present, only analog out is available with these players, so digital inputs on receivers are not applicable.

Q I have noticed with DVD movies, at least a number of them, that about 2/3 of the way through the movie the picture and sound stop for a few seconds and then continue. The picture remains clear and undistorted, but the sound just stops completely. Is this normal, or is the DVD player misbehaving?

A DVD technology is still far from working perfectly. One of the main problems is that DVD (the discs) manufacturers don't adhere to all of the standards. The result is discs that players have problems with. Not all players have problems with the same discs. It is sort of like certain software or peripherals will work with some computers but not all. We fix these issues occasionally by flashing the ROM BIOS on the computer, or an update of the operating system version. We need to be able to do the same thing with digital consumer electronics, and I think that eventually products will have this capability. In your case, it may just be the layer change happening. It should not take a few seconds though. More like a half second or so. Again, updates in the player BIOS would fix it.

Q I know you've recently addressed the topic of HT speaker matching in a general sense but I'm hoping you might revisit it to provide some additional detail. I just purchased a Dolby Digital receiver (Marantz SR 685) and am in the process of upgrading from a two- to to a five-channel system. Currently my main speakers are Cambridge SoundWorks Model 6 (crossover between 8" woofer and 1 3/4" tweeter at 2,000 Hz). My question is this: I'm shopping for a center channel in the $300 range and want to know if you would recommend staying with the Cambridge SoundWorks brand. I know there are better speakers out there but since I've committed myself to the CSW Model 6 as my mains, conventional wisdom tells me that I'm "locked in" to their line of center channel speakers. Am I right?

A You are not locked into anything. You can use any center channel speaker that pleases you. You are most likely to find a tonal balance by using the same brand, but for the center channel, it is critical to find something that is neutral in sound. Voices will be very annoying if they sound boomy, chesty, nasal, or overly sibilant. $300 actually should get you something pretty nice. Often, you can find last year's models on closeout sale, and they might not be any different from this year's model, except for a model number. A nick or a scratch will reduce the price considerably, and you can touch them up with wood tone felt tip markers available at any art supply store.

Q Seems like you folks have the best Q&A I have seen. Here is my question:

I currently have the following system:
-32 in Sony Trinitron tv
-Pioneer VSX-305 Pro-Logic receiver
-DirecTV system that is DD 5.1
-Fronts JBL HLS 610s
-Center and Rears JBL Flix 1
-Sub JBL PSW1000 powered sub

My goal in about 8-12 months is to purchase a Pioneer Elite Pro-710 or 610 or 510 HD (what ever is the best HDTV on the market at the time between $5k-7k) to finally set up "real" home theater. I would like to upgrade sound wise (not speakers yet) and get a DVD player now. What models of receivers and DVD players should I be looking for? I know I would need to probably be looking at Progressive Scan DVD players in order to take advantage of the capabilities of my "future" HDTV. With ES/EX and 6.1 (not sure exactly what these mean) being the next generation in sound should I just wait till prices go down? Should I just upgrade my receiver now with a system that will be ready to accept the new sound technology formats and just buy an inexpensive DVD player at this time? If so, which models should I be looking for in regards to receivers? Also, another question is should the "decoding" element be preferably located in the receiver as opposed to the DVD player?

A One feature that appears to be potentially important in HDTVs is the inclusion of an IEEE 1394 (Firewire) port, or at least the possibility to add it later. Progressive scan DVD is the way to go if you get an HDTV, so there is no point in your wasting money on something less. Just get the products that you really want, one at a time, and don't worry if you can't use all the features right now. You will be able to use them later. All modern receivers have DD and DTS decoding built-in. The higher priced DVD players seem to have 5.1 analog output jacks as well as the other more important features, such as component video and progressive scan. Looking for a player that has progressive scan but no 5.1 analog out would limit your choices, so ignore the inclusion of 5.1 analog out. It is a very inexpensive part of the design.

Q Thank you for your advice in Q&A # 226 concerning using a preamp as a  possible improvement over the built-in preamp in mass market receivers for two-channel CD listening from a CD/DVD player. I researched this, and I came across a recommendation in Q&A # 55 on how to do this. However, I am  confused! In Q&A # 55, you explain to route the pre-out on the receiver to processor loop input on the preamp and the processor loop output on the preamp to auxiliary inputs on the receiver. What are the auxliary inputs?  May be I am expecting too much but is there a way to insert the preamp into a system for CD and route to the external amp the other sources connected to  the receiver, i.e., tape, VCR, phono, and tuner, which uses the receiver's built-in preamp to do the switching and DSP modes? I use the coax digital input for DVD. 


A The auxiliary inputs on a preamp or receiver is a set that is not labeled CD, DVD, TV, Tuner, etc. It is for anything you want to connect to it. It is usually labeled "Aux", but is more often found on older products. It's a line-level input like CD and Tuner. The idea for using a high performance preamp with CDs, integrated with a surround sound receiver, is to keep as much of the receiver out of the signal path when playing CDs with the preamp. So, the circuit would go CD player to preamp, preamp to power amp, power amp to speakers. The use of tape loops keeps the volume control of that unit out of the circuit. Connecting the pre-outs of the front left/right from the receiver to an input set on the preamp lets you have CD playing and surround sound movies without having to disconnect and reconnect anything. This will not interfere with your receiver's DSP or other sources, since the front left/right is just going through the high performance preamp on its way to the front left/right speakers. What you want to be very careful of when experimenting with the connections is not to connect an output back into the input that serves it. That would produce some terrible oscillation (screeching sound). So, when trying to configure the setup, keep the volume control all the way down. Then turn it up very slowly. If you hear oscillation, something is plugged in to where it should not be. Turn the volume back down and the power off. Then disconnect the last cable that you had plugged in and try again.

� Copyright 2001 Secrets of Home Theater & High Fidelity
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