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Q Can you suggest the minimum Tube Amp Power that I need, to drive the NHT SuperZeros, which has an 86dB sensitivity (not-so-sensitive)? Subject to your confirmation, I conjectured it would be about 30 to 35 watts no less. Does this mean that Single Ended Triode (SET) amps (5 to 15 watts only) would already be out of the question? Will SET tube amp clipping cause damage to my speakers?
Kindly differentiate the sound characteristics of push-pull and SET tube amps. This will help me decide which of the two to get.
A A
SET amplifier will drive the low sensitivity speakers, but it
would be more suited for listening to chamber music rather than
thunderdous symphonic music. However, if you are going to invest
in an SET amplifier, you should also consider upgrading your speakers
to something that will have greater sensitivity (about 92 dB or
so). SET amplifiers have no crossover distortion, while push-pull
amplifiers do. Crossover distortion occurs when the signal is
crossing over from the + portion of the waveform to the - portion,
since different output devices handle the + and - portions. An
additional stage is also required to split the phase into the
two portions (the + and - portions). Triodes can be used in single-ended
configuration and push-pull too. The differentiation is therefore
not only between whether it is push-pull but whether it is a triode,
tetrode, or pentode tube. Triodes have the "sweetest"
sound, followed by pentodes, and then tetrodes. Single-ended is
smoother than push-pull in sound quality. If you really like the
tube sound, then get a SET with higher sensitivity speakers. SET
amplifiers usually have very little or no negative feedback, and
therefore, only second ordered harmonic distortion. Any distortion
is bad for speakers, but I have cranked up a 7 watt SET amplifier
far into its distortion region and it did not bother my ears in
the slightest. The waveform of a pure second ordered harmonically
distorted signal is rounded on the edges, so it is not irritating.
I would imagine it is less stressful on the speakers too.
Q I've
been seeing of lot of movie reviews lately with the terms "matte"
and "open matte" used when referring to the aspect ratio
of the film. Can you explain what this means?
A A
"matted" film is one that has been shot with spherical
lenses (not anamorphic), and the top and bottom of the film frame
are masked (matted) so that they do not appear on the projection
screen. This produces a more rectangular image, which is the "widescreen"
image. If it is hard matted, the masking is done in the camera
so the top and bottom are permanently missing. If it is soft matted,
the top and bottom are there in the camera negative and release
print, but the masking is done by metal plates in the movie theater
projector. Super 35 is a soft matting technique used so that the
theater image will be widescreen, and the home TV image can be
full screen, usually with a little more image at the top and bottom
and a little less at the sides than the image seen at the theater.
Matting is not the same as "Pan & Scan" where an
anamorphic film (CinemaScope or Panavision) is shown with the
right and left sides masked off to make the viewed image fill
a 4:3 NTSC TV screen.
Q I
have a Denon AVR3200 which I am planning to use as a preamp to
drive a Parasound 1203A power amp. The pre-outs of the Denon are
specified as 10,000 Ohms impedance. This seems very high to me,
compared to other preamp output impedances I have seen listed
in specifications. Is this unusually high? The Parasound specifies
its input impedance as 47,000 ohms. Will there be any incompatability
problems with these two? If so, what would be the likely symptoms?
A I
suspect the 10 kOhm output impedance is a typing error, and the
more likely impedance is 1,000 Ohms (1 kOhm). If the output impedance
were 10 kOhm, you would probably hear a loss in frequency response,
depending on the impedance of the interconnect.
Q I have a question for you concerning the types and choices of a power amplifiers and speakers for music vs. home theater (HT). I realize a lot of listening preferences are subjective and specific to each listener, but I was wondering if you had any opinion regarding the choice of a HT amplifier and speakers that are VERY good with music and HT.
I am looking at Proceed's new Amp 5, five-channel
power amplifier, and the reviews on this amp are very positive.
My question really has to do with combining a system selection
for music as well as HT. Can a five-channel amplifier that has
been designed for HT be the best for music listening as well?
In your opinion is there a certain amplifer brand, or type (Bipolar
vs FET vs Tube) that is best for both worlds? Also, is there a
HT speaker system that is best choice for HT and music? Or do
you need separate systems for music and HT as some have suggested?
A One
system can certainly work for both music and home theater, but
it is likely that you will need much more power than if you were
going to use it only for music, since movies tend to have intense
sound tracks, especially with DD and DTS. Tubed amplifiers that
have lots of power are very expensive, so if you are combining
music and home theater, get a solid state five channel power amplifier
of at least 100 watts per channel. MOSFET tends to be a bit more
musical and bipolar tends to have an edge. Both sound great, and
the choice should be based on your sonic preferences. For speakers
in a combined system, you should probably stay away from those
specifically designed for home theater, since they have a different
dispersion pattern than regular speakers.
Q Are
foam surrounds acoustically superior to rubber ones or are they
just cheaper to manufacture speakers with? I ask this because
although rubber surrounds last (to my knowledge) more than double
the lifetime of foam surrounds, some speakers still use foam ones.
A Rubber
(butyl) lasts longer, and contributes more to the damping of not
only the suspension, but also of the diaphragm, all other things
being equal (not the case if the foam is really thick). I like
the longevity of rubber and/or butyl, but you can't really say
that a driver is superior or
inferior based simply on the surround, nor is replacing one with
the other a good idea, as it changes the driver characteristics
which affect the
low-end rolloff as it changes the interaction between the driver
and the enclosure.
Q I
own a Harman-Kardon receiver that has separate left and right
subwoofer-outs. The manual says that to use these outputs with
a subwoofer that only has a mono-line level input, as in my case,
one can use a Y-adaptor. I went into the store and saw several
Y-adaptors, and all of them mentioned that they are ideal for
splitting a signal. I asked the store rep and he said that the
Y-adaptor can be used either as a splitter or as a combiner. I
need a combiner. Then he showed me a THX certified monster cable
to be used with subwoofers that came with a Y-adaptor. Now the
box says that this adaptor is a really good splitter, and balh,
blah . . . . My question to you is whether or not I can use this
adaptor as a combiner? In general, can a Y-adaptor be used as
a splitter and as a combiner? If so, why is only splitting mentioned
on the boxes?
A I
think it is possible to use a Y adaptor to combine the pre-outs
in your receiver because they have a common ground (the same ground,
i.e., the same chassis), and they have low output voltages that
are the same or very close to it, and especially if your instruction
manual says you can do so. You should not use the Y connector
to combine the pre-outs of two preamplifier outputs that are on
separate chassis or with different volume levels, and certainly
not with higher voltages. You can use a Y connector to send the
output from one preamplifier channel to the inputs of two power
amplifiers, even if they are on separate chassis, although you
might run into ground loops doing this. Combining outputs of preamplifier
channels is a tricky situation. We have tried this with recorder
line out jacks, and it worked, although the signal was decreased
due to the voltages fighting each other. If your receiver has
a mono subwoofer setting or a mono subwoofer output jack, use
that instead of the Y connector. Otherwise, give the Y connector
a try as per your instruction manual.
Q I
am having a problem with bass peaks. I am using a pair of PBS
Stratus Golds and an M&K MX-5000 sub. There was an improvement
when I switched the polarity on the sub from positive to negative.
One thing I have noticed is that the sub volume must be increased
quite a bit to achieve the same output volume in conjunction with
the main speakers. I believe this is because the sound waves are
additive and are canceling each other out with the negative polarity
selected. Are there other consequences of switching the sub polarity
on sound reproduction, i.e., does it affect the quality of the
sound reproduced? Why do the manufacturers put polarity switches
on subs, i.e., what is the function of the different polarity
settings on the sub?
A The
polarity setting alters the phase of the sound coming out of the
subwoofer. Some subwoofers, like the M&K MX-5000 have a two-position
switch, with one setting being 00 and the other being
1800. The 00 setting leaves the phase of
the incoming signal alone, while the 1800 setting inverts
it (making the output 1800 out of phase with respect
to the input). Some subwoofers, such as the Sunfire, have a continuously
adjustable phase between 00 and 1800. Since
subwoofers are at different locations than the other speakers,
the music from the subwoofer arrives at your ears at a different
time than the sound from the other speakers. By adjusting the
phase of the subwoofer output, you can get the sound from the
subwoofer to be more in sync with the sound from the other speakers.
There are also additive-subtractive effects as you mentioned,
with speakers that have outputs in the same region. If you are
having bass peaks, you should lower the crossover frequency of
the subwoofer so that there is not so much of the same low frequencies
coming out of the subwoofer along with the other speakers. You
might also want to try moving the subwoofer to other locations.
Q I
have a Velodyne VA series subwoofer that has an Auto On/Off feature.
There are occasions when it is necessary to play music at a lower
and quiet volume. The subwoofer would initially produce bass fine,
but would suddenly shut itself off right in the middle of the
song without any adjustment to the volume control on the receiver.
Is this considered a defect in the Auto feature, or did the Auto
signal sensor decide to quit
picking up the weak signal from the sub pre-out?
A This
is a peculiarity of several brands of subwoofers. When the signal
is very low, the auto-on/off feature turns the subwoofer off.
It is factory set at something above zero volts because there
is often a little bit of voltage in the connections even when
the receiver is off. One way around this is to turn the volume
control of the subwoofer up a little when you turn the receiver
volume control down.