Rockford Fosgate 250 sERIES Installation & Operation Manual page 8

Balanced Line Inputs (250x
Using the 250x with the BLT (Balanced Line Transmitter)
2
provides the last word in achievable rejection of noise
induced in the cable between the source and the amplifier.
The differential input circuitry (Figure 2) used in the bal-
anced input system rejects whatever signals are common
to both of the shielded, twisted-pair conductors. Balanced
line is universal in concert installations where the stage and
mixing consoles are hundreds of feet apart. Long signal
cables and electrically-noisy environments make signal
integrity and noise rejection an extremely difficult challenge.
THE RESULT: Quiet transmission of audio from source to amplifier.
NOMAD
(NOn-Multiplying Advanced Decision)
The Power amplifiers use an analog computer process to absolutely maximize safe output power under all
operating conditions. The innovative NOMAD (NOn-Multiplying Advanced Decision) system is the most
sophisticated version of this technique ever used, bringing previously unavailable levels of accuracy, stability,
temperature immunity and reliability to this critical process. NOMAD makes advanced decisions based on
device voltages to precisely control the awesome levels of current available in the output MOSFETs to safe values
– but only when absolutely needed.
THE RESULT: Extremely fast protection system that always protects the amplifier and never degrades the sound.
MOSFET Devices
Rockford Fosgate is one of the few manufacturers in any of the sound communities to utilize MOSFET devices
in both the power supply and the output stages . MOSFET (Metal Oxide Semiconductor Field Effect Transistor)
devices offer several important inherent advantages over the 30 year old technology of bi-polar design. These
advantages include: thermal stability, switching speed, ultra low output impedance and wider bandwidth
linearity. In addition, MOSFET and vacuum tubes share many important operating characteristics. However, the
MOSFET device is much faster, wider in bandwidth, measurably lower in distortion and far more linear than
vacuum tubes.
THE RESULT: Operational characteristics of vacuum tubes without the performance limitations of tube design.
ITS
(Increased Thermal Stability)
The ITS (Increased Thermal Stability) Power Supply design is new in Rockford Fosgate amplifiers. A major
problem associated with any amplifier design is how to get rid of the heat generated by its circuitry. Clearly, it
is highly desirable to minimize the amount of heat generated in the first place. The "250 series" Power amplifiers
employ a new toroidal power transformer design in which the high current input leads are carried directly to the
switching power MOSFETs. This both minimizes PC board heating and takes advantage of natural air cooling of
these leads.
THE RESULT: Maximizes power supply efficiency by eliminating unnecessary heat generation.
)
2
(Metal Oxide Semiconductor Field Effect Transistor)
– 4 –
Figure 2
RCA Input
Center
Conductor
Outer
Shield
Differential inputs only amplify the difference between two con-
ductors. Note: the noise spikes appear on both the center conduc-
tor and the outer shield and therefore are not amplified.
Differential
Input