rockford fosgate pbr300x1 mono amplifier as seen in issue 13.02

ROCKFORD FOSGATE PBR300X1 MONO AMPLIFIER AS SEEN IN ISSUE 13.02

ROCKFORD FOSGATE
PBR300X1
As it turns out, the topology used inside the
PBR300X1 isn’t actually a whole new topology
as Rockford Fosgate’s “Class BR” marketing
materials would lead one to believe. What it
really is, is a very clever adaptation of a circuit
sometimes referred to as a “charge pump”.
While still technically a Class A/B amplifier, the
design allows higher than normally possible rail
voltages without resorting to a typical switching
power supply. This approach provides several
benefits. First, the design is inherently efficient
and the removal of power supply devices,
toroids, and so forth means the amplifier’s size
can be dramatically reduced. Second, because
the amp is not switching huge currents at high
speeds, the amount of radiated noise and radio
interference can be virtually eliminated. And
finally, through the use of high current capable
MOSFET output devices, the design can easily
drive 1 ohm loads with no problem. Rockford’s
design takes a typical charge pump idea
several giant steps forward however, in that
the design allows the rail voltage to be dictated
by the load and the output level. This further
enhances power efficiency, and less power is
lost to heat.
The PCB is typical Rockford Fosgate, with
a densely populated double-sided, plated
through, glass epoxy 4-layer board covered in
zero-tolerance surface mount-type devices,
and there are three very large 15,000µF
capacitors that are used to “charge” the rails
to a higher voltage. The devices used to charge
the capacitors and for the audio output are
TO-220 case MOSFETs. A hand adjusted bias
pot ensures proper output transistor biasing,
and low distortion.
LISTENING
As I mentioned, the first thing I did with
this amp was listen to it. Connected into
my reference system and driving a 12-inch
2-Ohm woofer, I was very impressed not only
with the amount of authority the diminutive
amplifier had, but also with the general quality
of the sound. Bass notes were well defined,
and there was no evidence of any rolloff in
the lowest registers. Several tracks with sub
30Hz notes came through loud and clear. This
thing is the real deal. Bass definition was quite
good, complex pipe organ passages sounded
natural and plucked strings on acoustic bass,
as well as tympani drums were reproduced
with the natural resonance and overtones
they produce. Only when I pushed the amplifier
really hard did I start to notice a bit less
control and loss of definition, but to be fair,
that happened at volumes my ears would
never sustain anyway.
MANUFACTURERS
RATED POWER
Signal to Noise Ratio referenced to 2V output.
(CEA-2006A) (1Watt @ 4 ohms)
Signal to Noise Ratio referenced to full 4-Ohm output.
-83.5dBA
-103.4dBA
THD+N at rated power 0.11%
CEA-2006A rated 4 ohm Power (minimum power per channel
developed over the entire intended audio bandwidth)
92 watts
Maximum Efficiency at full 2-Ohm power per ch. 77.7%
Idle Current 0.4A
Input Sensitivity 165mV- 12.0V
Maximum Current @ full power, lowest rated impedance 28.9A
Frequency Response (-3dB)
Low Pass Crossover
Bass EQ boost
Actual Measured Power
@ 1.0% THD+N
@ 12.6V Battery
Actual Measured Power
@ 1.0% THD+N
@ 14.4V Battery
75 x 1 @ 4 74 x 1 @ 4 97 x 1 @ 4
150 x 1 @ 2 137 x 1 @ 2 179 x 1 @ 2
300 x 1 @ 1 230 x 1 @ 1 300 x 1 @ 1
PERFORMANCE/ BENCH MEASUREMENTS

T
E
S
T
R E P O R T
ROCKFORD FOSGATE
PBR300X1
TEXT
AND MEASUREMENTS BY GARRY SPRINGGAY
MONO AMPLIFIER
ust when it seemed like everyone had a handle on the various types of amplifiers available for our rides the engineering
J
gurus at Rockford Fosgate have thrown us a curve. For the last 30 years or so, the vast majority of amplifiers used in car
audio have been basically one of two or three common topologies. Back in the 90s, almost all amplifiers were typical Class
A/B designs, albeit with variations on the theme. Then along came Class D, which began with amplifiers designed for bass only, but
as technology marches forward, Class D is now fast becoming the standard topology for any type of car audio amplifier. There were
a few Class T, G, H, and GH designs sprinkled in the mix, but Class A/B and Class D have always had the lion’s share of the market.

Well, now Rockford Fosgate has introduced a new,
miniature-sized amplifier design that they are calling
Class BR. A mono model is available now, and by the time
you read this, a 4-channel model will also be available.
The concept behind these amplifiers is simple, small
chassis, high efficiency, and good sound. For this review,
Rockford Fosgate sent me a sample of the $239.99
PBR300X1, which at only 1.5x4.25x6.75-inches is a tiny
little amp, but it is rated at 300Watts into 1-Ohm. I had
heard some pretty amazing stories about this amplifier
from acquaintances at Rockford, so as soon as it arrived I
couldn’t wait to put it through the paces.
FEATURES
As I mentioned, the PBR300X1 is a very small amplifier,
and at first glance it reminds me of an average size passive
crossover in terms of how much space it takes up. It
is finished in basic black brushed aluminum with red end
panels along with a chrome-colored Rockford Fosgate
logo on the top. Mounting is accomplished via mounting
tabs that are incorporated into the trim panels on each
end. Because it is so small, the controls and connections
are somewhat different from what one would expect from
a Punch amplifier. The power, ground and remote leads
are connected via a heavy duty 3-position Molex plug that
will accept 10-gauge wire. The wires are secured very
well, and the plug has a positive feeling connection when
mated with the female connector on the amp. The pair of
12-gauge speaker output wires are also connected via a
Molex type, four-position plug. There are a pair of positive
output wires, and a matching pair of negative leads.
On my sample, the respective wire pairs were spliced
together and soldered, but if you wanted to connect
them individually to multiple woofers, the harness is long
enough to allow you to cut off the spliced segment. Signal
input is also handled via a 4-position Molex type plug,
which is terminated with RCA-style connections, but if
you want to connect speaker level inputs, you simply snip
off the RCA’s and wire your high level outputs directly to
the remaining wires.
With very limited space for controls and adjustments,
the PBR300X1 still manages a gain pot,
a variable frequency crossover pot, a high/low level
switch, and a pot for adjusting the sensitivity of the automatic
DC signal sensing turn-on circuit. The amp also
incorporates protection circuitry for under voltage, short
circuit, and thermal overload conditions. An RJ-45 style
jack allows connection to an optional Punch EQ remote.
FEATURES AND TECH
Of course, the first thing I did with the tiny Punch amp
was listen to it, and after being thoroughly impressed with
what it could do, the next thing I did was take it apart to
find out what made it tick, or in this case, boom!
CHECK
THE SPECS
The PBR3001X1 features
Dynamic Thermal
Management design to
maximize efficiency of the
heatsink for increased
reliability and efficiency.