HELIX C Four Manual page 18

Initial start-up and functions
LED switch
15
This switch is used to turn on and off the extended
LED illumination of the amplifier. It has no effect on
the LEDs below the fan, which are used as ultra
low-noise current sources in the output driver stag-
es. The functionality of the Power & Protect LED
remains unaffected as well.
Note: The number of illuminated LEDs depends on
the settings made on the amplifier – e.g. 2-CH or
4-CH mode.
X-Over switch
16
These switches allows to set the internal crossover
to highpass, fullrange or bandpass mode.
If the X-Over switch of a channel pair is set to
HIGHPASS the crossover frequency for the high-
pass can be adjusted with control 9 (HPF) of the
respective channel pair.
At switch position FULLRANGE the crossover is
bypassed.
At switch position BANDPASS a bandpass is cre-
ated in any case. This means that the highpass is
always active. By adjusting the highpass (control 9 /
HPF) and lowpass (control 8 / LPF) filter any band-
pass between 15 Hz and 4,000 Hz can be realized.
Unique Features of the HELIX C FOUR
Start-Stop capability
The switched power supply of the HELIX C FOUR
assures operation even if the battery's voltage
drops down to 6 Volts during engine crank.
18
Caution: To avoid a loss of gain make sure that the
crossover frequencies of the high- and lowpass fil-
ters do have an interval of at least two octaves
when generating a bandpass.
That means if the lowpass signal is adjusted to
320 Hz the highpass should be adjusted to 80 Hz
or less (one octave = doubled frequency or halved
frequency). If a subwoofer is connected we recom-
mend to use the highpass control (control 9 / HPF)
as variable subsonic / low-frequency highpass filter
or turn it counterclockwise to 15 Hz to get a sub-
sonic filter.
HDM slot
17
The HDM slot is used to mount the optionally avail-
able HELIX Digital Input Module HDM 2.
The module extends the amplifier with two opti-
cal digital inputs in SPDIF format including SPDIF
Direct In switches.
Thanks to the SPDIF Direct In switches the input
stages of the C FOUR can be bypassed and allow
to directly route the signals of the digital inputs from
the integrated DA converter to the internal power
stage. Further information about the module can be
found on page 22.
High-Resolution audio
The extremely broadband audio bandwidth of the
amplifier ensures a lossless audio reproduction of
High-Resolution audio content to provide the best
possible sound in studio quality.