Helix C Four 4-Channel Class AB High-End Amplifier 150W Hi-Res

Helix C Four 4-Channel Class AB High-End Amplifier with MOSFET Output Stage and Hi-Res Audio

A 4-channel Class AB high-end amplifier from Helix, the C Four delivers 4 x 150W RMS at 4Ω (up to 220W at 2Ω, 440W bridged at 4Ω), with 32 hand-selected MOSFET power transistors, Class A driver stage, damping factor above 1000, 112dB SNR, frequency response to 80kHz, active crossover with highpass/lowpass/bandpass (15Hz-4000Hz), Input Mode switch, HDM 2 optional digital input module slot for 2 x optical SPDIF, BurrBrown 32-bit D/A converters (via HDM 2), regulated switching power supply with Start-Stop capability, temperature-dependent fan control, and 24-carat gold-plated terminals.

Product Overview

The Helix C Four is the flagship 4-channel amplifier from the Helix C Series, designed down to the last detail for ultimate audio quality. At the heart of the C Four is an ultra low-noise, low-distortion Class A driver stage feeding 32 hand-selected MOSFET power transistors (8 per channel), producing a damping factor above 1000 at 4Ω for relentless speaker control and the tightest possible bass reproduction. The frequency response of 10Hz to 80kHz covers the full bandwidth of high-resolution audio content well beyond the standard 20kHz upper limit, and the SNR of 112dB (A-weighted) and THD below 0.007% represent state-of-the-art analog amplifier performance.

The C Four delivers 4 x 150W RMS at 4Ω and 4 x 220W RMS at 2Ω, with 2 x 440W RMS bridged at 4Ω and maximum output of up to 250W per channel at 2Ω. The regulated DC/DC switching power supply provides stable voltage to the output stages independent of battery voltage fluctuations, ensuring consistent output power across all operating conditions, with Start-Stop capability to 6V. The microprocessor-based amplifier monitoring system includes temperature-dependent fan control for thermal management during sustained high-power operation.

The integrated active crossover provides independently adjustable highpass, lowpass, and bandpass filters from 15Hz to 4000Hz at 12dB/Oct for comprehensive system configuration from a single unit. The Input Mode switch enables flexible routing of the input signals for different system configurations. The optional HELIX HDM 2 Digital Input Module (sold separately) occupies the HDM slot and adds two optical SPDIF inputs (28-96kHz) with BurrBrown 32-bit D/A converters, enabling lossless digital signal input from DSP processors and digital source units. Massive 24-carat gold-plated power and speaker terminals, quad-layer PCB with 70μm copper traces, and SMD manufacturing provide the highest standards of construction and signal path integrity. Dimensions are 37 x 430 x 240mm.

Features & Benefits

32 Hand-Selected MOSFET Transistors - 8 Per Channel: Each of the 4 amplifier channels is driven by 8 individually hand-selected MOSFET power transistors, providing an extraordinarily controlled and linear output stage with exceptional bandwidth and minimal crossover distortion for audiophile-grade audio reproduction.

Class A Driver Stage - Ultra Low-Noise and Ultra Low-Distortion: The Audiotec Fischer proprietary Class A driver stage provides the input signal amplification with vanishingly low noise and distortion before it reaches the MOSFET output stage, establishing the foundation for the C Four's exceptional SNR and THD specifications.

Damping Factor Above 1000 at 4Ω - Relentless Speaker Control: The damping factor above 1000 represents exceptional output impedance control that prevents the speaker's back-EMF from modulating the amplifier output, resulting in the tightest, most accurate, and most detailed bass reproduction possible from any speaker system connected to the C Four.

Frequency Response to 80kHz - Full High-Resolution Audio Bandwidth: The 10Hz to 80kHz frequency response covers the complete bandwidth of high-resolution audio content, ensuring lossless reproduction of music recorded and mastered at high sampling rates without bandwidth limiting at the amplifier stage.

112dB SNR and THD Below 0.007% - State-of-the-Art Analog Performance: The 112dB SNR (A-weighted) and THD below 0.007% represent world-class analog amplifier performance, ensuring the noise floor and distortion contribution of the amplifier are inaudible in even the most demanding audiophile listening environments.

Regulated Power Supply - Consistent Output Independent of Battery Voltage: The regulated DC/DC switching power supply maintains stable conditions for the MOSFET output stages regardless of battery voltage fluctuations during normal vehicle operation, ensuring consistently rated output power from 9V to 16V.

Active Crossover - Highpass, Lowpass, and Bandpass 15Hz-4000Hz: The integrated active crossover provides independently adjustable highpass, lowpass, and bandpass filters from 15Hz to 4000Hz at 12dB/Oct, enabling the C Four to drive 2-way active front systems, 3-way active systems, combined front and rear systems, and subwoofer configurations from a single amplifier unit.

HDM 2 Slot - Optional Optical SPDIF Digital Input Module: The HDM slot accepts the optional HELIX HDM 2 Digital Input Module (sold separately), adding two optical SPDIF inputs with 28-96kHz sampling rate support and BurrBrown 32-bit D/A converters for lossless digital signal input from DSP processors, digital source units, and high-resolution audio players.

24-Carat Gold-Plated Power and Speaker Terminals: Massive 24-carat gold-plated power and speaker terminals provide corrosion-resistant, low-resistance connections for maximum signal transfer and long-term connection reliability at all current and voltage levels.

Quad-Layer PCB with 70μm Copper Traces and SMD Manufacturing: The quad-layer PCB with extra-solid 70μm copper traces (more than twice the standard 35μm) minimises resistive losses in the signal and power paths. SMD manufacturing provides maximum component density, reliability, and signal path symmetry.

Microprocessor-Based Monitoring with Temperature-Dependent Fan Control: The microprocessor-based monitoring system continuously monitors the amplifier's thermal status and activates temperature-dependent fan control to manage heat dissipation during sustained high-power operation, protecting the output stage without requiring thermal throttling.

Start-Stop Capable - 9-16V Operating Range: The regulated switching power supply maintains stable operation during voltage drops to 6V for up to 5 seconds during engine cranking in Start-Stop vehicles, ensuring uninterrupted audio output.

What's in the Box

• Helix C Four High-End Amplifier
• 2 x Allen Key
• Mounting Material
• Instruction Manual

Technical Specs

Compatible With

The C Four is compatible with 9-16V vehicle electrical systems. RCA inputs accept 1-8V from aftermarket head units and DSP processors. The C Four has no high-level inputs and no RCA preout. The optional HELIX HDM 2 Digital Input Module is sold separately and adds two optical SPDIF inputs with BurrBrown 32-bit D/A converters. All crossover and signal processing is performed onboard by the integrated active crossover. The C Four is compatible with the Helix P Six DSP Ultimate optical SPDIF output via the optional HDM 2 module for a fully digital signal chain.

Frequently Asked Questions

What makes the C Four different from Class D amplifiers such as the Amplify 204?

The C Four uses a Class AB amplifier topology with a Class A driver stage and 32 hand-selected MOSFET transistors, prioritising the highest possible audio quality, damping factor (above 1000), and frequency response (to 80kHz). Class D amplifiers prioritise efficiency and compact form factor. The C Four is specifically engineered for audiophile installations where ultimate sound quality is the primary objective, regardless of form factor or power consumption. THD below 0.007%, 112dB SNR, and a 10Hz-80kHz bandwidth place the C Four in a different performance tier from Class D amplifiers of equivalent channel count.

What is the HELIX HDM 2 module and does the C Four come with it?

The HELIX HDM 2 (Helix Digital Module) is an optional expansion module that plugs into the HDM slot on the C Four, adding two optical SPDIF inputs (28-96kHz) with BurrBrown 32-bit D/A converters for lossless digital signal input. The HDM 2 module is not included with the C Four and must be purchased separately.

Why does the C Four have a damping factor above 1000?

A damping factor above 1000 means the amplifier's output impedance is more than 1000 times lower than the nominal speaker impedance at 4Ω, effectively preventing the speaker's back-EMF from modulating the amplifier output. In practice, this results in the tightest possible bass reproduction, exceptional midrange clarity, and precise control of the speaker cone at all frequencies and power levels.

Does the C Four support Start-Stop vehicles?

Yes. The regulated DC/DC switching power supply maintains stable internal supply voltage during voltage drops to 6V for up to 5 seconds during engine cranking in Start-Stop equipped vehicles.

What active crossover configurations does the C Four support?

The integrated active crossover supports highpass, lowpass, and bandpass filter configurations from 15Hz to 4000Hz at 12dB/Oct. Combined with the Input Mode switch, this enables 2-way active front systems with separate tweeter and woofer channels, full active 3-way systems, passive front and rear channel operation, and subwoofer configurations all from a single 4-channel amplifier unit.