Rockford Fosgate 250.2 Operation & Installation page 7

Balanced Line Inputs (250.
Using the Balanced Line Inputs provides the last word in achiev-
able rejection of noise induced in the cable between the source
and the amplifier. The differential input circuitry (Figure 2) used
in the balanced input system rejects whatever signals are
common to both of the shielded, twisted-pair conductors. Bal-
anced 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 conductors.
Note: the noise spikes appear on both the center conductor and the outer
shield and therefore are not amplified.
Differential
Input