Q&A # 61 - April 28, 1998
Staff
Q
I'm looking for a good Dolby Digital
preamp and 5 channel power amp that would cost $5000 or less. I recently purchased the
****** Series components and they were defective! I'm now considering the Citation
components for a high end combo or the Marantz preamp with some $1000 power amp for a
lower end combo. Music quality is more important to me than home theater, and I hate hum
and hiss! What do you recommend?
A New chips have just been
introduced that decode HCDC, DD, and DTS. Having all the decoding done by one small
circuit will help to eliminate both hum and hiss . Also, you might consider an outboard
amplifier that has either a DB-25 input connection or balanced input connections. Of
course, the preamp will need the corresponding output connections. There are several
models that have these features, but since the "decode everything" chips will be
incorporated into products late this year (hopefully), I would suggest waiting until then.
My own system has outboard decoders for DD and DTS, with enough interconnects that I could
hang my laundry on, so I am ready for a preamp that does it all.
Q
I'm trying to find the best blank video
tape for my money. Have you ever tested the wide variety of video tapes on the market to
find the best? Currently, I use Maxell HGX Gold exclusively, and I have a Toshiba 6 head
VCR (M752), but is there a better quality tape on the market, or does it just depend on
the VCR?
A The high gain (HG) tapes, such
as the one you use, are generally the best. The differences between the various brands in
this category are subtle. The bargain tapes have not only less video quality, but the
metal particles flake off and result in "dropouts". The circuits for analog
recording are about as good as they are going to get, so even the low priced VCRs have
pretty good image quality. But, the high performance VCRs, such as the one you have, will
last longer, record better at the slow speed, have better sound due to flying audio heads,
have no color bands at the beginning of recorded scenes due to flying erase heads, and
have better freeze frame. Be sure and take it in for professional cleaning once a year,
especially if you rent videos, or do it yourself with our recently published DIY.
Q
I was reading your latest amp review, a
$2500 amp with 35 watts of power. In other places, you have stated that we should buy as
much power as we can afford. Well for $2500, I can get a Sunfire amp, for example, with
300 watts of power which would deal with musical peaks much better than a 35 watts amp.
Why would anyone choose the low powered amp? If you've addressed this question before,
just tell me where.
A I haven't addressed this
particular aspect of power amp choice before, so I'm glad you brought it up. The Alternate
Audio CA-35 Power Amplifier is Class A and single ended, which results in extraordinary
detail in the sound. That is why it's expensive. The power supply will let it produce 75
watts per channel with short term transients. Class AB amplifiers will clip just above
their rated output. Of course, 300 watts per channel will stilll produce more punch than
the small Class A amplifier, but it won't have quite the detail in the sound. For Class A
though, you need a first rate CD player, preamp, and speakers. Otherwise, the Class A will
get buried. Lastly, some people do not like Class A. It sounds "dry" to them. I
like Class A sound, and I don't generally listen to music really loud, so it works fine
for me even with low power. On the other hand, in our laboratory, we crank things up now
and then, and there is nothing like a high performance, large, powerful Class AB amplifier
to do this. If I were able to have only one amplifier, it would be high power Class AB
rather than low power Class A. Even if it has less detail, I would rather have the massive
raw power for when I turn things up. Of course, there is the option of 300 watts per
channel in Class A, but they are $20,000.
There are lots of terms to look for when purchasing an amplifier.
The class of operation (A, AB, D, H - see amplifier section of Volume 1, Number 1) is just
one. "High Current" is another term, and it means that the amplifier will handle
low impedance loads, such as 4 Ohm speakers. Whether the term is used with the product or
not, though, you should look to see how low an impedance the amplifier is rated into. If
it is rated into 2 Ohms, this means it will deliver high current, and that the power
supply is big. Some are even rated into 1 Ohm. "Differential" or
"Balanced" refer to having the ground separate from the + and - section of
the signal. However, balanced inputs or outputs do not necessarily mean that the amplifier
is balanced all the way through the internal circuitry, and occasionally, a balanced input
on an unbalanced amplifier can sound worse than just using the unbalanced input, since the
balanced input adds an additional circuit to the signal path. There is an old platitude
that says you can judge a power amplifier by lifting it, and this is generally still true.
A heavy amplifier means it has a big power supply, and the power supply is critical to
good sound. When I listen to amplifiers in shops or at shows, I always look through the
chassis slots on top to see the power supply transformer and the power supply capacitors.
A BIG transformer is good. BIG capacitors are good, or lots and lots of small ones.
Q
When I was out shopping for some equipment, one of
the dealers made a point of telling me about gold plated jacks. Does this make a
difference in the sound?
A It all boils down to the
choice of metals for conductors. They should have low resistance, be ductile (malleable),
have low oxidation, and be inexpensive. No metal has all these properties. Copper has low
resistance, is ductile, and inexpensive, but it oxidizes. Silver is a better conductor
than copper, is ductile, but it is expensive and it oxidizes. Gold is not as good a
conductor as copper, but it does not oxidize. Oxidation on the surface of plugs and jacks
can impede signal flow, so manufacturers put a very thin coating of gold on the plugs and
jacks. Over time, this could make a difference. The alternative is to use a liquid contact
cleaner now and then.
Q
I have an older model Yamaha M-40 power
amp that I am using to power a sub that I built using the NHT 1259 speaker. At the present
time I am just using one side of the amp to power the sub. I was wondering if it is
possible to bridge this amp to put out watts and use both channels in the amp. I have
heard that you could invert the input phase on one channel and use the positive speaker
ouputs from each channel but not sure exactly how to do this or if it is possible with
this amp.
A Amplifiers that have the
bridging switch connect the input to both channels, and invert the signal before it goes
into one of the channels. Then, you use the + terminals of the speaker connectors. The
process should work on any stereo amplifier, but I don't know of anyone who makes a
product with a single line level input jack, and two line level output jacks with one side
inverted. If one of our readers knows of such a product, let us know and we will post it.
Otherwise, it sounds like a neat product to build. It could probably be done with a couple
of op amps and a battery or wall wart DC supply to eliminate any hum. Maybe a DIY is in
order here. There are undoubtedly a lot of people out there who have a stereo amp sitting
around that could power a subwoofer. You just have to make sure the speaker is 8 Ohms
since bridging an amplifier doubles the minimum impedance it can handle.
Q
I recently found out that a couple of hifi
companies I buy from are in financial trouble. How can that be with the economy doing so
well?
A It's a result of the
Asian financial crisis. A number of audio manufacturers in the US were selling a large
percentage of their product to the Asian market. Since the crisis occurred over there, the
sales to that area dropped off, and they are having trouble. Companies whose market was
mainly domestic did not suffer from this, but unfortunately, the effects of foreign money
problems will eventually get here to affect everyone. That's the ripple effect. Let's say
there are one kajillion dollars in the world. We all spend more than we have, on credit,
so there are two kajillion dollars being spent. When there is a crisis somewhere, people
in that country spend less on credit and put some money in savings. Even though there are
still the original one kajillion dollars around, 1.8 kajillion are being spent. Global
markets are eventually all affected by this, even if their own local economy is good.
Sooner or later, the countries where that 0.2 kajillion dollars used to be spent will cut
back their spending because they aren't making the income they did before. World economy
is really a matter of consumer confidence. Once that confidence is broken in one place, it
is a chain reaction across the planet.
� Copyright 1998 Secrets of Home Theater & High
Fidelity
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