Q&A # 40 - December 2, 1997
Staff
Q I listen mainly to classical, acoustic jazz, acoustic folk, and acoustic international music, much of it performed by soloists. Hence, I'm
looking for the warmest, most natural sound I can generate from my system.
I understand that warmth and CDs are somewhat mutually exclusive, but, I'd
like to enhance my chances, nonetheless. I use KEF Q-90s right now with a
Denon CD player and an HK receiver. Would you please advise me on how I
might upgrade? Thanks.
A There are a number of things you can do to increase the warmth of the sound (usually meaning a more full bodied mid-range and slightly laid back highs). One is to put a tube preamplifier between the CD player and the HK. This could be in the form of an actual preamplifier, such as the Audio Electronic AE-1 (we reviewed this unit some time ago), or something (tube interface) that serves to warm up the sound, but is not a preamplifier per se. A review of the Z-Man Audio Signal Enhancer (a $198 tube interface for placing between the CD player and preamplifier) will be published next week. Other than that, you could use interconnects and/or speaker cables that have laid back highs, but such an approach is more in the vein of filters. For your purposes and set of equipment, I would suggest going with a tube interface. They are inexpensive and quite effective. Note Stacey Spears' caveat, however, that the tube interface works well with CD players that are a bit harsh to begin with (generally the mass market players), but not necessarily with high performance CD players that are detailed, but not harsh, to begin with.
Q The new Polk Audio RT 1000B (90dB/w/m) speaker model seems to me like an interesting one. In the tech specs, I read the following:
"Recommended power of amplifier: 30-250 W"
If I connect these speakers to my amp (its power
is less then 100W) what sound would I get in comparison
with any other solid state amp which is 200w/ch?
I asked this question to the "specialist" who works in a
near salon that sells almost all types of speakers, and
he answered me that this 'factor' is not important and
the only difference between 60w/ch and 150 w/ch amps
connected to these speakers is..... LOUDNESS.
??????? Is that true??????? What about the detail level, sound pressure, etc?
And the last question: what do you think of these particular
speakers? I plan to use it for music more then for movies.
A The sound would not necessarily be different (better) with a 200 watt amp, and in fact, it might be worse, depending on the quality of the 200 watt amp. Assuming both amplifiers were of equal quality, the 200 watt amp would drive the speakers to a level 3 dB louder than the 100 watt amplifier. If you played both amplifiers at about 10 watts average, they would probably sound the same. If you played them at about 50 watts average, then during transient peaks, the 200 watt amplifier would perform better. Detail would be the same. Polk speakers are very nice for general purposes, and they do well with mass market receiver amplifiers because they are 8 Ohms nominal impedance and relatively high sensitivity. We have not tested the RT1000s, but a review of the RT800s is being published this week. The referee, Karl Suager, thought highly of them.
Q I guess I have one of those questions where you read tons of tests and comparisons and at the end you would like someone who knows the stuff to
comment on the choices.
I currently have the following system:
Denon Receiver AV-2500
Klipsch FC-3 (main), Klipsch 1200 (Sub) and Klipsch Center and Surrounds
Mitsubishi 35 inch TV
I would like to get into Dolby Digital and go "Separates" with the
following two possible packages:
1) B&K AVP 3090 Processor/Preamp and ATI- AT1505 Five channel Amp. What I
like about this package is the DTS addition and the capability for future
upgrades.
2) Parasound: P/SP-1500 AV Processor/Preamp; P/DD-1500 DD Surround
Processor and HCA-1206 six-channel Amp. I have heard good things about
Parasound and would save $1,000 on the package as it stands right now.
Missing DTS and 3 separate components (limited rack space) are downsides.
I would like to add a Sony DVP-S7000 as a DVD/DTS player to either of the
packages.
What are your words of wisdom? Is any of the two packages a better deal
(quality, sound, value) - am I missing something in this price range that is
a no brainer? Is it worth the investment, or should I stick with a receiver
(Denon AV 5600 or the new Marantz)? Would I be able to notice improvements
over my existing system or are my Klipsch now becoming the weak link in the
system? If (as the very last question) you could also recommend a source to
buy the equipment (St. Louis is not necessarily audiophile heaven), I'd have
an early Christmas this year.
A I think it all depends on how important DTS is to you. In either case, the B&K or the Parasound would give you better results than just about any mass market receiver. The Parasound could be used with a DTS decoder if you pass the analog out from the preamp through the DTS decoder to the power amplifier. Not the best way to do things, but it would work. That would add a fourth component to your rack, and from your concerns about space, I suspect that the B&K with the ATI would be the right choice for you. That will give you both DD and DTS, with excellent power amplification, and all in just two components. However, you need to be careful about DVD players and DTS. Right now, it is unclear as to whether current DVD players will handle DTS-encoded DVDs. But, the Sony DVP-S7000 is a superb player, and will certainly play DD DVDs with aplomb.
Q Does a receiver send an AC or DC current to speakers? I have heard from reliable sources that it is DC. I just want to make sure. Also, how
do tubes work? I am not a complete moron so don't worry about getting too
tecnical for me. I already read your page on amplifiers. Could you please
go more in depth?
A The AC power from the wall socket is first converted to DC by the amplifier power supply. That DC is converted to AC which varies in frequency according to the music signal, and it is this AC that is sent to the speakers. The DC you heard about may be what is called "DC offset" which is caused by a slight DC voltage that is permanently across the amplifier's speaker outputs, sort of like a small battery were there. This DC offset causes the speakers to be moved a little bit away from resting position, even when there is no music, and this increases speaker distortion. As to tubes, I will explain this in depth in the updated primer (Volume 1 Number 1) section on amplifiers soon.
Q I have noticed that you recommend receivers to people a lot and your reasoning goes against what I've found in the audio world. My simple
60w/ch Rotel Integrated flat outperforms any reciever I've auditioned and believe me (or ask my wife), I've listed to a lot of them including models you recommend. I'm unwilling to take a step backwards in sound quality so I can add home theater. It's been my experience so far that good stereo beats so-so surround anyday. *getting off my soapbox* - Anyway, I would love to see some articles focused on the next plane of sound quality, stepping above the receiver market into the often
ignored (IMO) but still affordable, separates home theater systems. More of companies like Adcom, Rotel, NAD, Parasound, B&K, etc and less of the mid-fi, mass market world.
A Indeed, two channel stereo from a CD does sound somewhat better than surround sound, because with Pro Logic, the decoding process induces some artifacts, and with DD and DTS, the decoding is compounded by lossy compression. We have reviewed some of the separate processors, such as Lexicon, Meridian, Parasound and Rotel, and we plan to review other such units in the near future. The recommendations are based on reader's specific needs and budgets. When money is no object, of course one would always go with the ultra-high performance processors. Unfortunately, money is usually a concern. Receivers combined with multi-channel power amplifiers make a very cost effective choice, in part because the receiver does almost as well as the high performance processors, but also because they have a tremendous array of features that you only get with mass market receivers. We have a policy of never recommending anything that we would not be comfortable with having in our own homes. So, we are pretty careful what we say to the readership. Stacey Spears has Meridian processors and Dan Long has Lexicon. Those are both high performance units. I use mass market receivers because I am very comfortable with them, there are lots of features, they have complete flexibility for me to connect outboard decoders for review, and it is much more fair to the readership for at least one of us to have a mass market surround sound product. This gives a balanced surround sound viewpoint for everyone. On the other hand, my stereo (two channel) reference audio systems are top of the line, very high performance reference components, while the rest of the staff has more down to earth components. Again, it provides balance of reference to the readership. At least, we hope so. I know it may be a little unusual, but then, this magazine believes in setting standards, not following them.
Q I have just upgraded my sub to a Velodyne FSR-12, and have a question about some switches which my previous sub didn't have, in particular, the
Crossover switch. My system consists of a Marantz SR880 receiver, B&W 602
front, CC6 center, and 601 rear. The sub is hooked up via line level
connection to the pre-out sub on the Marantz. My dealer doesn't seem to be familiar with the Crossover switch and recommended setting it to the "in" position. However, I get more signal by
setting it to the "out" position. Can you suggest the best setting for
this, considering my setup? Any other suggestions on other settings would
also be very helpful.
A The "In" position places the low pass crossover of the Velodyne into the signal path, sending low frequencies filtered by the crossover, to the subwoofer's built-in amplifier. With the "Out" position, the crossover is removed from the signal path, so if you connected a regular pre-out jack from the receiver to the line-in of the sub, the sub amplifier would be sending full spectrum frequencies to the speaker driver. Since you are using the subwoofer output on the receiver, you already have a low pass signal in the line to the subwoofer. Therefore, if it sounds best to you in the "Out" position, use it. However, subwoofers can sound boomy if they are handling frequencies at about 90 Hz and above, so you should temper your desire for high output with the sound quality. B&W 602s have pretty good bass, and too much signal in the 90 Hz region can be fatiguing. If it sounds boomy, set the crossover switch to the "In" position, and set the crossover frequency to about 50 Hz.
Q I'm curious as to whether the laser lenses of CD/LD/DVD players really get "dirty" enough to affect performance or not? If so, are lens
"cleaners" effective or not? I noticed they have little brushes on one side
for cleaning. If these brushes do the cleaning, then how does one clean the
"dual focus" laser lense of CD/DVD players? Are the "dual pick-up" lenses of
the Sony DVP-S7000 better, since the cleaners can clean the lenses directly
as opposed to the "dual focus" system? Thank you again, as I have been to several internet audio sites and none (including discussion groups) has been more helpful to me than Secrets.
A I have a personal policy of not touching the lens surface with anything if I don't have to. I make sure that my CDs are clean and that the CD drawer is clean as well. That way, the lens is not likely to get dirty. It's not like a tape head where the tape is constantly rubbing against the head and depositing iron particles. The laser lens never touches the CD. Any dust that settles there would likely be blown away when the CD is spinning. If your CD player is in a room with a fireplace, then perhaps, once a year, it might be necessary to clean it. But I would not use a brush. Rather, I would use CD cleaning liquid and a cotton swab (Q-Tip), dabbing a little on the lens, then gently wiping it away with three successive clean dry cotton swabs.
Q What actually causes an amplifier to "clip"? Does this happen as you approach maximum current capacity or rail voltage? We all know that as
you pump up the volume, voltage goes up and so does current draw, but I
am asking this question with respect to mismatching amplifier and
speaker impedances. Based on a Q&A #34 item (Oct. 21, 1997) it would
seem clipping occurs due to current draw and not voltage output. Also,
does the music signal determine if the amp will clip or not? What I mean is
given a situation of near clipping level, will loud music clip the amp while
soft music won't?
A From an electrical engineering standpoint, it is a voltage problem. Even with a large power supply, the rail voltage is a finite value, let's say 40 Volts. Once you reach that value, it does not matter how much current the power supply can deliver. The 40 Volts is a brick wall, and at that point, clipping will occur. An amplifier is usually designed to place 40 Volts across an 8 Ohm load and deliver the appropriate current (5 Amperes) continuously. With a 4 Ohm load, if the power supply is adequate, the amp will still clip at the 40 Volt value, but if the power supply is not strong enough to deliver the current (10 Amperes), the VOLTAGE DROPS to a lower value, and clipping will occur at this lower voltage. Basically, yes, loud music may clip the amplifier, while soft music won't. If the power supply capacitors are small and few, they won't be able to deliver high current, and the voltage drop occurs. The power supply is the most expensive part of an amplifier. If you look inside one of the high performance amplifiers, most of the chassis is occupied by the power supply. Transient peaks (the front edge of a gunshot, for example) demand about 20 times the average power that is being used, so if you were listening at 20 watts, and along comes the gunshot, about 400 watts are demanded for a very short time. A BIG power supply makes all the difference in the world.
� Copyright 1997
Secrets of Home Theater & High Fidelity
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