Product Review -
Niles SI-250 Stereo Power Amplifier - January, 1997
By J.D. Moretti
Click to see larger photo |
Niles SI-250 Amplifier; Two channel
amplifier; Rated output 125 watts/ch rms into 8 Ohms, 185
watts/ch rms into 4 Ohms, 250 watts/ch rms into 2 Ohms, both
channels driven; Bridgeable to 395 watts rms into 8 Ohms;
Frequency response 20 Hz - 20 kHz ± 0.1 dB; THD<0.1%; Turn on
modes: audio sense, constant, trigger; Two grounded AC outlets,
one switched, one un-switched, 750 watts total; Two RCA jack
unbalanced inputs; Two RCA jack cascade outputs (for daisy
chaining to other amplifiers); 12 volt trigger output; 30 volt
trigger input; Ground lift switch; Two pairs of 3-way binding
posts; Size 5"H x 17"W x 15"D; Weight 25 pounds;
black aluminum sheet metal chassis; $729; Niles Audio
Corporation; P.O. Box 160818, Miami, Florida 33116-0818; Phone
305-238-4373; Fax 305-238-0185.
When my wife and I purchased a new condo last year, she asked me
if I could arrange the stereo system in a way that we could
listen to it in different rooms. And, she didn't want to go
around turning all the individual preamplifiers and amplifiers on
and off. She wanted something more convenient and less
conspicuous now that we are home owners (actuallly, the bank owns
80% of it, and it is REALLY a cool condo). Although, I am pretty
handy with carpentry, I thought I might contact a professional
installer to help us out here.
Niles Audio makes what are called Systems Integration Amplifiers,
which are used mostly by professional installers for home
audio/home theater applications. Niles makes the SI-1200 which
has 12 channels at 25 watts rms/ch into 8 Ohms, and which can be
used for multi-room audio systems. We decided to take a look at
the SI-250 because it is a relatively inexpensive two channel
power amplifier, delivering a respectable 125 watts into 8 Ohms
(sufficient for digital surround sound), and it is also rated
into 4 Ohms as well as 2 Ohms in case you want to have more than
one set of speakers playing at the same time (VERY few amps in
this price range are rated into 2 Ohms).
Part of the reason this amp is not very expensive is the fact
that it is mounted in a very simple sheet metal chassis. The amp
is designed to be hidden rather than showcased, so there is no
reason to put dollars into chrome plate, heavy front panels, or
any other flashy looks. However, the amp does have a very large
number of features. The front panel has an on/off rocker switch,
but there are extensive sockets on the back for remote control
on/off by several means, including 30 volt trigger and auto
sensing of audio signals. An "Active/Protect" LED
indicates power on or that the protection circuitry has come on
(short circuit). Left/right Clipping LEDs and L/R Rail Fuse LEDs
(indicates blown fuse - each channel separate) are situated to
the right of the on/off toggle. There are also two small holes
into which a screwdriver can be inserted for adjusting the
maximum output of each channel (if you have teenagers, this would
be a nice feature for preventing them from playing the system too
loud when you are away from home!)
The back of the unit has two pairs of 3-way binding posts, for
use with banana plugs, spade lugs, or bare wire wrap. Besides the
two RCA input jacks, there are also two RCA output jacks for use
in daisy chaining of multiple amplifiers. Input and output jacks
for triggers by remote control are also on the back. A ground
lift slider switch is there in case of ground loop hum problems
(likely with multi-room setups). The amp can be bridged, and
there are two grounded AC outlets (one switched and one
un-switched) for powering associated equipment; 750 watts are
allowed here. The AC power cord is permanently attached.
The electronics include a heavy duty toroidal transformer with
two secondary windings each rated at 0.3 kVA, two 22,000 µF
capacitors (63 volt), and eight bipolar output devices (four per
channel). [Click
here for photo of inside of amplifier.] The power supply will store 73.9 Joules, based
upon 58 Volts DC on the capacitors. The heat sink fins are inside
the chassis. When we tested the unit for maximum output at
clipping, the unit became warm but not hot. It is truly designed
for heavy use, and is well protected against abuse.
We listened to the SI-250 using our McCormack Audio CD system,
McCormack preamp, Nordost Flatline cables, and the Anthony Moore
Ribbon hybrid speakers. Ribbons can be a tough load for an
amplifier, but they also can sound terrific when properly driven.
One of our favorite albums is The Classical Film Music of Bernard
Hermann (Silva Screen Records America; SSD1051). It puts extreme
demands on the entire system. The opening track contains
instruments, such as trumpet and kettle drum, that produce sounds
throughout the entire audio spectrum . Brass was crisp but not
harsh, and the deep rolls of the drum were tight. We were really
quite surprised at the performance for this price level.
Sibilants were natural (the "s" in the human voice).
When we cranked the volume until the clipping lights just started
to blink, the bass was still tight, mid-range full but not mushy.
Overall, really a nice performer.
Instead of the usual output testing with sine wave pulses into a
computer system, we decided to test this amp into the speaker
load itself, and inserting the oscilloscope and rms volt-ammeter
into the circuit. At the edge of clipping, using pink noise into
both channels (all frequencies in the audio spectrum
simultaneously, each at equal energy), the amp produced 19.3
volts rms and 3.97 amps of current into the Anthony Moore speaker
load, measuring the left channel, and both channels driven. This
represents about 80 watts rms per channel. Although the amp is
rated at 125 watts rms per channel, that is a rating using
individual sine waves, one at a time, and into a testing device.
Our methods use an actual speaker load - one that is not easy to
drive - and many frequencies simultaneously. This is an
unconventional means of measurement, because there are other
variables at large, such as the back EMF, but we feel that a
"real world" approach to performance is more
informative. At the edge of clipping, with both channels driven,
we measured 98.7 dB of SPL eight feet away from the speakers (the
Anthony Moores have an 86dB/w/m sensitivity). This represents
plenty of volume.
If you are planning to have someone install a multi-room audio or
home theater system, we suggest you speak to them about using the
Niles. In my case, I am going to let my wife take care of this,
because she knows exactly where she wants everything to go.
Although, in our opinion, 25 watts/ch (the output of the SI-1200)
is not enough for anything more than background music playing,
the SI-250 is another animal entirely, and should do the job for
most applications. It is well constructed, sounds excellent, has
good flexibility, and the price is right.
J.D. Moretti
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Secrets of Home Theater & High Fidelity
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