Helix Amplifiers: Helix amplifiers, made in Germany by Audiotec
Fischer, feature high quality components and construction to deliver a superb
audio experience. The A4 raises the bar in sound quality and performance to
bring you a competition-grade amplifier.
Four-channel Amplifier: The Helix A4 is a Class A 4-channel
amplifier built with high grade components with 1% tolerances for the absolute
best sound quality. The amp features an extremely stable output stage with
select MOSFET transistors, a regulated power supply, 24 carat gold-plated set
screw power terminals, and a temperature-optimized aluminum heatsink for
efficient heat dissipation.
Configuration Options: The A4 can be operated in 4-channel,
3-channel, or 2-channel modes. To operate in 3-channel mode, Channels C and D
must be bridged, because Channels A and B can only be bridged in 2-channel mode.
In 2-channel mode, Channels A and B are bridged and Channels C and D are
Power Output: The amplifier delivers a solid 85 watts RMS
per channel at 4 ohms and 150 watts x 4 at 2 ohms. When the amp is bridged, it
can deliver 270 watts RMS x 2 at 4 ohms, or 395 watts x 2 at 2 ohms bridged.
Color Protection System: The A4 has a top panel made of
translucent Plexiglas which allows you to view the internal components and the
amp's LED indicators. Three colored LEDs on the circuit board show the operation
mode of the amplifier:
- Green: The green LED glows to indicate the amplifier is
in good operating condition.
- Yellow: The yellow LED glows to indicate a malfunction
of the amplifier, over- or under-voltage, or a short circuit at the
- Red: The red LED glows to indicate the amplifier has
shut down due to overheating.
Input Level: The Helix A4 amplifier features four RCA input
connectors, each with a rotary input level control. The potentiometers are
mounted on the circuit board, and require a small screwdriver (not included) to
adjust the input levels through the Plexiglas top panel. The input sensitivity range is
500mV to 8
Built-in Crossovers: The A4 has built-in crossovers that can
be set to High-Pass, Full-Range, or Low-Pass. One crossover affects Channels A
and B, and the other is for Channels C and D. The Mode and Frequency Range
Switches are located on the circuit board and require a screwdriver to make the
adjustments through the Plexiglas top panel. You can set the crossover frequency
range to 15-90Hz, 90-800Hz, or 600-7000Hz via the 3-way switches. The cutoff
frequency is adjusted within the selected range via the rotary controls on the
right side of the amplifier (Frequency Adjust A/B and Frequency Adjust C/D).
Bass Boost: The bass boost is continuously variable from 0 dB to +9 dB.
You can also adjust the center frequency of the bass boost between 30Hz and
120Hz. Both controls are located on the right side of the amplifier.
Input Signal Switch (for Channels C & D): If you only have a
mono input signal in bridged mode on Channels C and D, you can drive both
channels without using a Y-adapter by switching the Input Signal Switch to the
#2 position. If there are separate input signals for Channels C and D, the
switch should remain in the #1 position.
Full Active Operating Mode: When the A4 is set to Full
Active Operating Mode (via a switch on the right side of the amp), the signals
from inputs A and B are full range, or high-passed based on the selected cutoff
frequency on Channels A and B, and low-passed on Channels C and D. When
operating in Full Active Mode, you can adjust the output of Channels C and D,
relative to Channels A and B via two top-mounted potentiometers. The range of
adjustment is from -6dB to +6dB.
Power: The A4 is equipped with 24 carat gold-plated
set-screw terminals for power and ground. These terminals will accept up to
4-gauge wire, and are tightened/loosened with the supplied 4mm Allen wrench.
Fuse: The amp is protected by three 25-amp ATM mini
fuses, installed under the Plexiglas top panel. It is recommended that a 75-amp fuse be installed on the power wire, 12"
or less from the battery. If you use a pre-packaged amp wiring kit with a fuse
that has a different value than 75 amps, you should replace the fuse with a
Remote: The amp's remote turn-on features a set-screw terminal that
will accept up to 12-gauge wire, and is tightened/loosened with the supplied
1.5mm Allen wrench.
Speaker Outputs: The amp has four pairs of 24 carat
terminal speaker outputs which accept spade lugs up to 0.3" wide. To bridge the
amplifier, the speaker wires should be connected to the B+ and A- terminals and
the D+ and C- terminals, as indicated on the amplifier.