Features
Controls
Connections

Features

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 bridged.

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 loudspeaker output.
• Red: The red LED glows to indicate the amplifier has shut down due to overheating.

Controls

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 volts.

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.

Connections

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 75-amp fuse.

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 gold-plated screw 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.