Van den Hul The Flexicon B4 Jack/RCA 1.5m

In 1990, South Africa’s BOP Studios commissioned Van den Hul to equip their three 96‑channel SSL, Neve and Focusrite consoles, among the largest ever built. The Dutch manufacturer then developed the Flexicon B4, a balanced cable capable of ensuring reliable interconnections over 75 kilometers of runs. Since then, this model has become available to the general public and is notably offered in a 3.5 mm mini‑jack to RCA version.

Origins in the world of professional studios

The original specifications for the Flexicon B4 were anything but ordinary: it was intended to fully wire one of the largest recording complexes in the world. BOP Studios, located in Mahikeng in the former Bophuthatswana, housed three control rooms fitted with legendary consoles: an SSL 4000G+, a Neve VRP96 and one of the ten Focusrite Studio Consoles ever made. Within these walls, artists such as Ladysmith Black Mambazo, Miriam Makeba and even Disney’s The Lion King original soundtrack were recorded.

Van den Hul had to design a cable that met multiple, sometimes conflicting requirements: flawless transmission quality, low inter‑conductor capacitance to preserve signal clarity, effective shielding against environmental interference, and above all sufficient flexibility to make dense wiring of 96‑channel consoles easier. The result convinced three of the biggest names in the professional audio industry at the time.

Silver‑plated OFC conductors with crystalline structure

The two conductors of the Flexicon B4 are 24 AWG, each made up of 12 strands with a diameter of 0.15 mm. The chosen material is large‑crystal oxygen‑free copper (OFC), covered with a dense silver plating. This enlarged crystalline structure reduces the number of joints between metal grains, micro‑discontinuities that can disturb the electrical flow. Silver, whose electrical conductivity exceeds that of copper, optimizes signal transmission along the surface of the conductor—where high frequencies naturally travel due to the skin effect.

The resistance of the central conductors is 8.45 Ω per 100 meters, i.e. less than 0.085 Ω per meter. This value, combined with the small overall diameter of 0.52 mm per conductor, allows for compact wiring without compromising transmission. The red and black color code of the two cores makes identification easier during assembly or troubleshooting.

Double shielding and controlled capacitance

The inter‑conductor capacitance of the Flexicon B4 is limited to 47 pF per meter, a moderate value that preserves the dynamics and definition of the signal over long distances. This performance is the result of the polypropylene insulation surrounding each conductor: this material has a low dielectric constant and maintains excellent mechanical flexibility.

The shielding uses a two‑layer architecture. The first layer consists of a tight helical spiral of 48 strands of 0.12 mm, providing dense coverage and good flexibility. The second, a reinforced aluminum foil that has undergone a specific treatment, completes the protection against electromagnetic and radio‑frequency interference. The resistance of this shielding is 2.85 Ω per 100 meters, low enough to effectively drain off any captured stray currents.

Hulliflex jacket and long‑term durability

The white outer jacket of the Flexicon B4 is made of Hulliflex, a polymer developed by Van den Hul as an alternative to conventional materials such as PVC. Since 1990, the Dutch manufacturer has gradually phased out halogen‑based insulators in its production, a move driven by environmental considerations—halogenated materials release harmful compounds such as hydrochloric acid or dioxins when burned or disposed of.

According to Van den Hul, Hulliflex offers three times the mechanical stability of PVC, while retaining great flexibility. It is resistant to chemical attack, temperature variations and natural aging. As a result, the cable retains its mechanical and electrical properties for many years, even in demanding environments such as automotive or permanent installations. The 3.7 mm outer diameter makes it easy to route through tight spaces.

Gold‑plated Van den Hul connectors

This Jack/RCA version of the Flexicon B4 comes pre‑fitted with Van den Hul connectors. The 3.5 mm stereo mini‑jack plug and the two male RCA plugs feature gold plating, a treatment that prevents contact oxidation and ensures a stable connection over time. These in‑house connectors allow users to benefit from the qualities of the cable without requiring any assembly or special tools.

The mini‑jack to dual RCA configuration meets a common need: connecting a portable source, a computer, a tablet or any device equipped with a headphone output to a hi‑fi amplifier, a pair of active speakers or a car audio system. The available length allows flexible installation without excessive strain on the connectors.

Everyday use cases

The mini‑jack to RCA format is suitable for many home setups. A smartphone or digital audio player can feed an integrated amplifier, a network player with an auxiliary analog input, or a pair of powered speakers. Owners of turntables with a built‑in phono preamp and mini‑jack output will also appreciate this link to their main system.

In car audio, the cable’s low capacitance and effective shielding come into their own: the electrical environment of a vehicle generates numerous disturbances likely to introduce hiss or interference into the audio signal. The Flexicon B4 isolates the music from these nuisances. Its flexibility makes it easier to route through trim panels and the narrow conduits found in passenger cabins.

Technical specifications

Conductor construction

• Two 24 AWG conductors
  • 12 strands of 0.15 mm each
  • Total conductor diameter: 0.52 mm
• Material: large-crystal oxygen-free copper (OFC)
• Surface treatment: silver plating for optimal conductivity

Insulation and shielding

• Insulation: polypropylene ensuring maximum flexibility and minimal capacitance
• High-performance double shielding
  • Dense helical spiral: 48 strands of 0.12 mm
  • Reinforced treated aluminum foil
• Outer jacket: white Hulliflex ensuring long service life, resistance to aging, and flexibility

Electrical characteristics

• Capacitance: 47 pF/m between conductors for a pure signal
• Conductor resistance: 8.45 Ω/100 m (0.0845 Ω/m)
• Shield resistance: 2.85 Ω/100 m (0.0285 Ω/m)

Dimensions and finish

• Outer diameter: 3.7 mm, ideal for compact internal wiring
• Jacket color: white

Available versions and connectors

• Cable type: balanced analog interconnect

Recommended applications

• Internal interconnects: preamplifiers, mixing consoles
• Audio installations / car hi-fi
• General-purpose interconnect wiring

Key features

• High-fidelity audio transmission thanks to silver-plated OFC conductors
• Very low capacitance ensuring clear, precise signals
• High flexibility for easy installation
• Exceptional durability provided by the Hulliflex jacket
• Double shielding offering excellent protection against interference