Ashly MOS-FET POWER AMPLIFIERS CFT-SERIES - Manual (Page 3)

DESIGN THEORY
Ashly FIX series amplifier circuits are totally discrete using high-voltage,
wide bandwidth electronics. The input section is a complimentary Darlington
differential amplifier stage for high common-mode rejection, low noise and low
distortion. All voltage gain stages in the ampl ifier operate class A for low distortion.
The quasi-compHmentary MOSFET output stage has almost infinite current gain,
therefore the output driver stages are nearly lossless. Ail circuitry within the
feedback loop is discrete which allows the amplifier to recover instantly and cleanly
without any spikes or glitches from a dipped condition. This overall design
approach inherently assures low noise, low distortion, and excellent transient and
overload response.
Inputs are bridging and active balanced, and all input connections can operate
as balanced or unbalanced. Tum-on delay relays are not needed because of the
symmetry of the totally discrete complementary electronics.
The MOSFET output devices do not require short-circuit protection and V.L
limiting circuitry, thus enabling a simpler, more reliable electronic design. Rear
panel accessible speaker fuses are provided to protect the amplifier from prolonged
output shorts. These fuses are wired within the feedback loop of the amplifiers to
ensure that they do not alter the audio fidelity. All electronic components are
mounted to rugged glass-epoxy circuit boards. Large computer-grade electrolytic
capacitors assure tong service.
The FTX series amplifiers are packaged in a rugged 16-gauge .steel chasses.
The power transformer is located at the frontcenter of the chassis to minimize front
panel torsion. Each channel’s electronics and heat sink are identical yet completely
independent and modular, each with a single plug-in connector for ease of servicing.
Large custom black-anodized extruded aluminum heat sinks with fan cooling
provide plenty of thermal headroom.
The CFT-1800 utilizes quiet convection cooling for studio control rooms,
home hi-fi, and other applications where low ambient noise is essential. Like the
FTX series, theCFT-lSOOis a modular design for ease of servicing. Because of the
passive cooling in the CFT-1800, thermal headroom is somewhat reduced from that
of forced air cooling, thus making it inadvisable to drive 4 ohm loads at continuous
high power with this amplifier. It is also important to allow for free air circulation
above the amplifier to achieve optimum cooling action.
Ashh FTX/CFT Owners Manual
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Page 10
Figure }: FTX-2000 Rear Panel With Standard input
1. mpuTS
The standard input panel of the FTX series amps is equipped with balanced
1/4" tip-ring-sleeve (TRS) phone jacks, balanced XLR jacks, and balanced screw-
terminal inputs. The three types of connectors are internally wired in parallel and
may be used with balanced or unbalanced connections. The inputs are configured
for pin 2 hot, meaning that a positive voltage applied to pin 2 will result in a positive
output voltage across the speaker terminals. Pin 2 of the XLR jack is equivalent to
the tip of the 1/4" TRS jack as shown in figure I, An optional plug-in input
transformer is available on all FTX amplifiers.
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¡Figure 2: Input Connectors
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It is recommended that balanced input connections be used when possible to
reduce ground-loop and environment-induced hum and noise. If an unbalanced
input connection is used, then the (-) connection (XLR pin 3) should be connected
to Input ground (XLR pin 1). if the 1/4" input jack is used unbalanced, the use of
a mono (tip-sleeve) plug will automatically tie the (~) connection to input ground.
Ashlv FTX/CFT Owners Manual
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