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Reference Manual
Reference Manual
CE 4000
The amp with an Attitude!
CE 4000
The amp with an Attitude!
Principles of Operation
Audio Signal Path
For the sake of simplicity, only channel one of the audio signal
path is described.
Signal is presented to the CE 4000 through one of three con-
nectors when using the standard input module. Each channel
is outfitted with a balanced XLR / phone jack, and a barrier
strip. These connectors are wired in parallel, which allows
daisy chaining when needed. The signal is then converted
from balanced to unbalanced in the Balanced Input Stage
where it also receives RFI protection. Signal then flows into the
Variable Gain Stage where the front panel level controls are
allowed to affect the gain.
Following this stage, the signal goes through a gain stage that
allows for the various positions of the sensitivity switch. The
signal is then put under the control of a full-time compressor
circuit comprised of a symmetrical window detector, a buffer
amplifier, and the gating op amp which uses several small
components to set the compressor’s attack and decay char-
acteristics. The actual compressing is accomplished by an
opto-isolator that affects the gain in the signal path.
The signal then is passed through a series of switchable filters
that allow the signal to be low-pass and high-pass filtered at
various frequencies. The switches are located at the back
panel. The low-pass filter is a fourth-order Linkwitz-Riley type
(24-dB/octave rolloff) and the high-pass filter is a third-order
Butterworth type (18-dB/octave rolloff).
Following the switchable filters, the signal enters a 32 kHz 7
th
Order Gaussian Low-Pass Filter. This filter prevents the modu-
lator stage and the output filter (both described below) from
receiving signals that are too high. Without the 32 kHz filter,
the modulator would be unable to process signals that are too
high and the output filter would not yield the proper frequency
response behavior. The Gaussian filter type is unique in that it
has minimal ringing and excellent phase response so even a
high-order filter such as this one does not adversely affect the
sonic excellence of the product.
The signal next enters the main amplifier error amp where it is
mixed with a small portion of the output voltage and current in
such a way as to control the amplifier’s overall output perfor-
mance.
Warning:
Details of closed loop amplifier design are
beyond the scope of this description and if discussed, would
surely put most readers to sleep!
Following the error amp is the modulator stage where the au-
dio signal is compared to an extremely accurate 250 kHz tri-
angle waveform. Comparators output a Pulse Width Modulated
(PWM) string of pulses at 250 kHz that vary in width depend-
ing on the level of the input signal. These strings of pulses, one
for the positive side and one for the negative side, are con-
nected to the output stage via optocouplers.
The signals from the optos are then passed to gate drivers that
amplify the pulses to the level required to drive output devices.
The driven ou
tput devices are now able to produce PWM pulses that have
an output voltage from the negative high-voltage rail (-Vcc) to
the positive high-voltage rail (+Vcc). This output voltage is
always the same (2 * Vcc) but the width of the pulses is still
dependent on the level of the input signal. The positive and
negative output PWM pulses then pass through inductors and
are summed together. Summing the output signals through
inductors reconstructs the audio signal, amplified to the de-
sired level. There is a small amount of ripple on the output that
is at double the switching frequency (500 kHz).
The amplified audio signal is then passed through an output
filter that removes the residual ripple voltage. The power is
delivered to the load cables through the output connector
panel which consists of one of several options.
Protection for the output devices is performed by a very pre-
cise pulse-by-pulse current limiter circuit that operates each
time the output devices switch. The current limiting is “flat”
meaning that, regardless of the output voltage, the output cur-
rent always limits at a certain value.
The turn-on delay circuitry functions to keep the modulators
turned off (which keeps the outputs from switching) until all
supplies are up and stable.
Thermal probes monitor Heatsink temperatures and power
transformer temperature. As the temperatures rise, the probes
send a proportional voltage to the fan control circuit and the
Thermal Limit Control (TLC) circuit. The fan normally runs at
very low speed when the amplifier is idling or when it is being
