E-PAC, Hardware manual (1.0E) Page 9 of 24
2.2. E-PAC power amplifier
The single channel power amplifier of the E-PAC maintains high
linearity throughout it’s operational range even into adverse loads.
With fast response to, and recovery from overload conditions,
stability and accurate performance is guaranteed. A two stage
power supply keeps the losses through heat emission low. To
maintain sound quality, a limiter circuit prevents the amplifier from
continously reaching its maximum output voltage, known as
clipping.
The E-PAC can deliver 200 W continuous sine wave output power
into a 16 ohm load or 300 W into an 8 ohm load. Selecting low
impedance mode enables the E-PAC to deliver an output power of
150 W into 4 ohms. These values apply to continuous operation for
a minimum of 30 minutes at a maximum ambient temperature of
24 C (75 F).
An E-PAC will normally be operated with speech or music
programme, complex signals where the average power
requirement is below peak power. The E-PAC will continue to
operate indefinitely even where the signal has a very low peak to
RMS ratio (Crest factor, see section 2.13. on page 41), provided
the device is installed to enable the heat generated to be
adequately dissipated.
2.3. Power supply
The switched mode mains power supply permits worldwide
application without the need for mains voltage switching or
conversion. Special regulation of the power supply unit additionally
guarantees constant output power with fluctuating mains voltage,
leading to a substantially higher dynamic stability than a
conventional power supply unit of the same performance. This
benefits the reproduction of music or speech with a wide dynamic
range.
Active Power Factor Correction (PFC) is characterised by the
current drawn being represented by an almost sinusoidal
waveform, resulting in lower loss, in contrast to the pulse shaped
current characteristic of power supplies without PFC. This is an
advantage where long mains power supply cables are used.
The mains voltage and power consumption are recorded by the
power supply and can be viewed on the LC display.
2.4. Protective circuits
The E-PAC contains many integrated protective functions:
If over temperature occurs, the device switches to mute. After it has
cooled down, the output stage resets automatically.
The output current limiter (SOA watchdog) prevents damage to the
output stage that could occur from a short-circuit or incorrect
cabling, while passing the short current peaks drawn by a complex
load like a loudspeaker.
The mains power connection is protected by a fuse.
A mains inrush current limiter provides a 'soft start' and enables
several E-PACs to be powered up at the same time without over-
loading the mains power supply.
