Ashly P70 Owners Manual
Ashly P70 Owners Manual
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Page
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DESIGN THEORY
Ashly P70 series amplifiers use a direct-coupled output stage with totally
discrete high-voltage, wide bandwidth electronics. A modulated power supply
improves output device efficiency, allowing more power with less heat dissipation.
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 amplifier operate class A for low distortion. The complimentary MOSFET
output stage has almost infinite current gain, therefore the output driver stages are
nearly lossless. All circuitry within the feedback loop is discrete which allows the
amplifier to recover instantly and cleanly without any spikes or glitches from a
clipped 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.
Turn-on delay relays are not needed because of the symmetry of the totally discrete
complementary electronics.
The P70 amplifiers incorporate output VI limiting to protect against exces-
sive current at the speaker terminals. If current becomes too high, the amplifier
instantaneously reduces output voltage to a safe level. This protects against low
impedance loads, a short across the outputs, as well as DC. Additionally, an internal
fuse follows the output signal of each channel. Under normal operating conditions
however, the VI limiter handles any fault condition at the output. A blown fuse will
only occur in the rare event of amplifier failure. All electronic components are
mounted to rugged glass-epoxy circuit boards. Large computer-grade electrolytic
capacitors assure long service.
The P70 series amplifiers are packaged in a rugged 16-gauge steel chassis. The
power transformer is located at the front center 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.
10
3
Figure 1: P70-400 Rear Panel With Standard Input
1. INPUTS
The
standard input
panel of the P70 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 1. An optional plug-in input transformer is
available on all P70 amplifiers.
Figure 2: Input Connectors
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. The CHASSIS
GROUND terminal is internally connected to the chassis, the AC earth ground, and the
p ower amplifier’s signal ground. The INPUT GROUND terminal is tied to the XLR
pin 1 and the 1/4" jack sleeve.
