With each
generation, Spectron amplifiers receive rave reviews
in professional hi-fi journals and more
importantly from new Spectron owners, who
frequently report, ?It?s the most musical amp I
have ever heard.? Moreover, such acclaimed
speaker designers as Albert von Schweikert,
Anthony Gallo, John Dunlavy and others have used
Spectron amplifiers in the development of their
speakers. Why is that?
Here?s
why: Spectron does not buy its class D
modules from a third party! Our designs are our
own, on the cutting edge of the technology.
Because we have complete control over our
designs, we are constantly improving them.
Moreover, Spectron's president and chief
designer, John Ulrick, introduced the first
commercially available class D amplifier into
the audio world, while he was the president of
Infinity Systems, at CES 1974. John has devoted
the last 25 years to extending a "control
system" approach to class D amplifiers, and the
Musician III Mk2 is his and the Spectron design
team's latest achievement.
Below is its
description:
Feedback: A
power amplifier is a voltage amplifier that has
a fixed voltage gain of (usually) 20. The
objective then is that the output voltage is 20
times the input voltage. This voltage must
remain 20 times the input, no matter how much
current the speaker draws. By definition, this
is a voltage control system. Control systems are
implemented with feedback loops. This feedback
loop controls the output voltage for all load
conditions. The speaker is the load. Feedback
means that a fraction of the output is fed back
and compared to the input. This difference is a
correction signal. Spectron's amplifiers are
implemented with digital logic and power
switches, the opposite of the circuitry used in
a linear amp. This digital logic corrects for
errors in the output about ten times faster than
the linear circuits (transistors or tubes) in
conventional linear amplifiers. Spectron's
amplifiers include the modulator, power section
and output filter all in the feedback loop. Some
class-D amplifiers use modules supplied by an
outside vendor where the output section and
filter are not included in the feedback loop.
Thus there is no correction for errors caused by
the speaker load. This results in the amplifier
sounding different with various speakers.
Group Delay:
It is important that all of the frequency
components of the original recording retain
their time alignment. These are the position
cues to the listener. Group delay is a
measurement of time alignment. If a drum strike
is being reproduced and the low frequency has
one position in time and the high frequency has
another, the spatial position of the drum will
be confusing to the listener. Spectron's fast
feedback loop, however, retains accurate group
delay and preserves each instrument's position
in space.
Distortion:
The published measurements of many class D
amplifiers reveal that while their THD is
primarily second-harmonic in nature, there are
also some higher -order harmonics present. This
pattern of distortion is very similar to the
pattern of distortion in poorly designed tube
amplifiers. Thus, sonically, this euphonic
coloration is confused by some with the warmth
of tube amplifiers. In reality this deviation
acts as both an annoyance and murky veil. In
exchange for euphonic, overly rich harmonic
texture (of absolutely artificial origin) the
listener gets no transparency and a lower level
of true detail. Additionally, the level of this
distortion (as well as output impedance)
increases with frequency, making the amplifier
sound bright. Consequently, with increases in
output impedance and the level of distortion,
some class D amplifiers cannot control difficult
impedance speakers at all. The distortion at
high frequencies of the Signature Edition
Musician III is exceptionally low, resulting in
an amplifier that is not only not bright or
muted, but also has a three-dimensional,
transparent, and natural musical sound.
Stability:
The Musician III is stable to loads down to .1Ω.
It will actually deliver 300 watts into .1Ω.
This means it will easily drive ribbon,
electrostatic or any complex impedance speakers.
No matter what type of speaker, the Spectron
will yield a nearly identical sonic signature.
Bandwidth:
Wider bandwidth translates into faster
transients and greater detail, better preserving
phase information. This results in a bigger
soundstage, sharper image and more holographic
representation. The potential drawback in wide
bandwidth amplification is an increased level of
distortion if the output filter is less than
perfect. Spection avoids this by a sophisticated
design of the output filter and feedback loop,
which are mathematically optimized for maximum
phase margin. Spectron's bandwidth is an
exceptional100 kHz, resulting in optimum square
wave response.
Headroom:
Spectron's Musicain III has a huge amount of
headroom. This means that when the music hits
loud passages, the Spectron will deliver
undistorted power to the speaker. It is common
in high quality recordings to see voltages near
100V peak, with medium efficiency speakers.
However, most amplifiers use power supply
voltages on the order of plus and minus 65V. The
Musician III's peak is 120 volts! In regard of
the currecnt delivery, there are many well
recognized regarded speakers whose impedance
dips down, some even lower than 1 ohm. When a
musical note is played at these frequencies
where the impedance dips, the current demands
skyrocket. When this happens with amplifiers
that do not have large output current
capability, they "current clip". These
transients will be both attenuated and quite
distorted. Spectron amplifiers can deliver peak
currents of 65 amps, with a peak power of 3500
watts per channel, for about 500msec, which
allows the amplifier to deliver the full
transient (burst of music) without "current
clipping" and/or "voltage clipping" as was
mentioned above. On the other hand, most other
amplifiers only deliver their rated peak current
for sometimes a fraction of this time. This
means that the Musician III Signature can drive
everything from conventional speakers to complex
loads such as ribbon speakers or electrostatics
and represent effortlessly the fury of a
symphonic crescendo, unlike any other amplifier!
As one of the reviewers wrote:
"I am hearing (and enjoying)
some of my classical CDs for the first time. Now
I get the FULL dynamics and powerful crescendos
without the offending harshness and
compression/congestion. With my normal system I
never enjoy the music at loud volume... The
Spectron seems to love it. I am playing louder
than I normally do because it sounds so good."
Energy Storage
Capacitors: In the original Musician
III amplifiers and Premiere amplifiers there
were two 20,000uf energy storage capacitors, one
for the +125V rail and a second one for the
-125V rail. In the Musician III Mk2, the two
large electrolytics have been replaced by one
hundred 330uf capacitors. This lowers the power
supply impedance by a factor of more than 10.
The capacitors are arranged such that the left
and right channels are now completely
independent of each other. The result, along
with other Musician III Mk2 improvements is much
improved midrange and high frequency fidelity
and improved soundstage.
Isolated low level
power supplies: Some purist designers
have used batteries to power the low level
circuits. It's a good way to go, but the
batteries must be replaced every few years.
Spectron accomplishes an equivalent result by
powering the low level circuits using a high
frequency isolation transformer. This gives
about 500 times more isolation than deriving the
low level power from the conventional line
transformer. This virtually eliminates the
effect of noise and transients from the AC power
line on the low level circuitry. In addition,
the Musician III Mk2 has two of these isolated
supplies, one for the right channel and a second
for the left channel. Having isolated supplies
minimizes interaction between the two channels,
as well as cross talk. Few other stereo
amplifiers have isolated low level power
supplies. These two +15V power supplies have
input noise rejection filters and 2% regulators.
Hum and signal:
Hum is usually measured with no signal, and it's
related to the AC line. In all amplifiers, the
hum increases with loudness. You can't hear this
hum over the music, but when reduced, the music
sounds cleaner. Spectron's high efficiency
amplifier and sophisticated feedback minimizes
this hum, resulting in cleaner sound quality.
Balanced Design:
Musician III Mk2 is capable to operate both in
stereo and mono (fully
balanced) modes. While not
necessarily an advantage in every speaker,
Spectron monoblocks configuration triples the
power and doubles the head room. The major
advantage of this mode of operation, however, is
noticeable improvement is dynamics and
resolution of details in the music.
Quantizer:
Nyquist's rule tells us that we must sample a
signal at twice the highest signal frequency.
Since our hearing goes to approximately 20 kHz,
the minimum for music reproduction is 40,000
samples per second. Conventional CDs are sampled
at 44 kHz, and the most advanced recording
systems record at up to 192 kHz. Spectron's
Class D amplifiers sample at 500 kHz samples per
second, about 11 times oversampled. This highly
oversampled signal minimizes aliased distortion.
Phase invert:
Phase reversals in original recordings sometimes
leave the signal to the amplifier out of phase.
Spectron's phase invert switch on the rear panel
allows the user to correct this error. There are
two phase invert switches on the rear panel that
control the phase of the left and right channels
individually. For example, if a kick drum is
recorded with a mic in front of it, the speaker
should move out in response to pressure pulse
from the drum. If out of phase, the speaker will
suck in - some of the transient power will be
lost. Inverting the phase will restore the
transient, making the drum sound real.
Inrush bypass:
Virtually all amplifiers have a special resistor
in series with the AC line to limit the inrush
current at turn on caused by charging the energy
storage capacitors. Spectron does too, but after
the capacitors are charged, a relay
automatically shorts out this resistor,
eliminating the voltage drop across this
resistor during loud bass passages. The result -
more and tighter bass.
PROTECTION CIRCUITRY
Current limits:
The Musician III has a full fold back current
limit. This means that when the output is
shorted or draws more than 50 amps, the current
limiter reduces the maximum current to 12 amps.
When the short is removed, the amplifier resumes
normal operation automatically. Spectron
provides modules to professional amplifier
manufacturers where the amplifiers must be
especially bullet proof. The Musician III meets
this requirement.
Speaker protection:
To protect your speakers, the Musician III has
Spectron's protection circuitry that detects
excessive DC or high frequency signals not
associated with normal music. If excessive DC or
a high frequency signal is detected at the
output of either channel (which could damage
your speakers), the protection circuit will
latch the amplifier off. This protects the
speaker from damage. The power is simply latched
off and a red LED is illuminated on the rear
panel. The reset button is also on the rear
panel. If the reset button is pushed and the
fault still exists, it will just reset again
until the fault is removed. Spectron knows of no
other amplifier with this protection.
SPECTRON REMOTE SENSE
CABLES
Optional Remote Sense
Cables: The Musician III has rear panel
connectors and the required circuitry to accept
Spectron's optional Remote Sense Speaker Cables.
The Remote Sense Cables put the speaker cable in
the feedback loop of the amplifier, thus using
the amplifier to correct for distortion of the
cables. This means that the amplifier controls
the voltage at the speaker, not at the output of
the amplifier. It's the signal at the speaker
that is important, not at the amplifier's
output. So the Remote Sense Cables dramatically
reduce the distortion inherent in the cables.
The output at any amplifier
is distortion free, but due to the distortion
from the cable there will be some distortion at
the speaker end. With measuring equipment it can
be demonstrated that the distortion at the
speaker end is significantly less with the
Remote Sense Cables.
SUMMARY:
In the above, Spectron has
mentioned some of its many important design
considerations and features,. For an audiophile
amplifier to achieve the highest quality music
reproduction, each and every one of these
components plays a very important role, and we
believe must all be there.
| Features |
| |
|
| · |
Digital pulse width modulation switching
amplifier. |
| · |
Feedback loop 10 times faster than
typical conventional amplifiers. |
| · |
Staggering headroom of 3500 volt-amps
over 500 msec. |
| · |
No
crossover distortion. |
| · |
Drives the most difficult speakers,
stable to .1 Ohms. |
| · |
Foldback current limit. Automatic
overload recovery. |
| · |
Professional quality balanced line
input. |
| · |
Phase invert. Rear panel selectable. |
| · |
Accepts either XLR or RCA input: True
balanced line. |
| · |
In-rush resistor bypass. More and
tighter bass. |
| · |
Isolated low level power supplies.
Eliminates noise from AC line in low
level circuits. |
| · |
Speaker protection. Turns amp off for
excessive DC or high frequency. |
| · |
High
efficiency for minimal power
consumption. |
| · |
Small size. |
| |
|
Technical Specifications |
|
|
|
|
| · |
Power |
Watts per
channel, both channels driven
600 Watts at 8 Ohms
800 Watts at 4 Ohms
1400 Watts at 2 Ohms |
| · |
THD |
<.03% from 1W
to 600W @ 8Ω ( in the listening range)
<.06% from 1W to 600W @ 8Ω ( > 22 kHz) |
| · |
Noise |
<180 µV (22 Hz
to 22 kHz)
-83 dB below one Watt (A measure of hiss) |
| · |
SNR |
115 dB |
| · |
Frequency response |
±.1 dB 20 Hz to
20 kHz at 8 Ohms
|
| · |
Bandwidth |
100 kHz |
| |
Power Supply
Voltage |
+ 120 VDC |
| · |
Input impedance |
RCA: 50 kOhms,
XLR: 50 kOhms |
| · |
Output impedance |
@ 1kHz .018
Ohms |
| · |
Output impedance |
@ 20kHz .095
Ohms |
| · |
Damping ratio |
500:1 |
| |
Gain |
26db (20v/v) |
| · |
Efficiency |
>92% (Amp
module) |
| · |
Line voltage |
100, 120 or
240 VAC 50/60 Hz Switch selectable |
| · |
Power draw, no signal |
40 Watts |
| · |
Weight |
52 lbs, Shipping: 64 lbs or
28 kg |
| · |
Size |
431 mm wide x 133 mm high x
368 mm deep
(17"W x 5¼"H x 14"D) |
| · |
Price |
US $3,995 MSRP |
| · |
Warranty |
3 years |
| · |
Faceplate |
Silver or Black (Anodized) |
