Van Den Hul The MC-Digi-coupler 75 Ohm Coaxial Digital Cable

The van den Hul Digi-Coupler has been specially designed bearing the highest possible transmission quality of 75 Ohm impedance level SPDIF consumer format digital audio in mind, and is aimed at the critical audiophile as well as the professional. Its special design covers all aspects required for a flawless and reliable transmission of SPDIF digital audio at short range as well as across large studio distances and allows for notable improvements in your audio quality.

The Digi-Coupler features a very constant and precise 75 Ohm impedance: 75 Ohm ± 0.5 Ohm up to 3 GHz. This is important, since otherwise the signal will be reflected up and down the cable (i.e. standing waves). Such signal reflections deteriorate signal integrity by causing the digital audio signal as seen at the receiving end to be overlapped with time delayed replicas of itself (i.e. signal reflection induced inter-symbol interference). On the receiving side this negatively influences the D-to-A converter clock retrieval circuitry’s (PLL’s) ability to maintain a stable sample rate (i.e. fluctuations in the timing interval between the audio signal’s samples occur). The resulting distortion of the audio signal is officially called “jitter distortion” and is particularly perceivable as reduced resolution and imaging.

Note: To maintain a precise 75 Ohm impedance and avoid signal reflections, the advised minimum value of bending radius for The Digi-Coupler is 8.0 cm.

Very High Frequency Bandwidth: The Digi-Coupler features a very high frequency bandwidth. As an example: The -3 dB bandwidth of a 10 m. run is 770 MHz. A high bandwidth is important: An SPDIF digital audio signal contains frequencies that extend far beyond the usually specified minimum required bandwidth (~6 MHz). Even though this minimum bandwidth provides useable transmission, accurate data transmission and recovery of low-jitter clocks in real-world noisy environments will benefit from greatly increased bandwidth:

The digital audio signal consists of elementary data units (bits) in the form of zeros and ones. These are square waves (merlon shaped elements) where the vertical edges serve as a demarcation for the signal receiving circuitry (e.g. D-to-A converter) to be able to retrieve the signal clock and to recognise the contained bit values. Cable bandwidth decreases with cable length used. Lower bandwidths increasingly cause the digital audio signal’s square wave edges to get rounded off and become smeared over time (inter-symbol interference). This impairs the receiving circuitry’s ability to correctly determine the individual bit values and their timing. The so-called “jitter distortion” and “bit error rate” increase and the audio quality decreases.

A Case For Coaxial Over Optical Cables

A short note regarding optical fiber cables for digital audio and bandwidth. Although these exhibit a very high bandwidth and near perfect noise immunity by themselves, the bandwidth of the unavoidably extra involved optical transmitter and receiver parts (especially those used in common consumer devices) is one of the most important performance limiting factors. Others are (1) The optical power available, (2) so-called modal dispersion and (3) attenuation and connector transition losses. So, in most cases, coaxial SPDIF transfer is preferable to optical if low jitter distortion replay is aimed at, provided a good cable like the Digi-Coupler is used.

Very Low Signal Attenuation: The Digi-Coupler features very low signal attenuation per unit length. As an example: At 100 MHz the attenuation is a mere 0.11 dB/m. (For more data see HF Performance Graphs in the sidebar on the van den Hul website). Low signal attenuation (i.e. low signal loss) is especially important when long cable runs are used (e.g. in professional / studio applications).To maintain optimum signal quality, a maximum signal to noise ratio at the signal receiving side is required. The signal therefore needs to undergo as little as possible attenuation during transport. This of course equally applies to digital audio as to video and HF signals.A low signal attenuation also positively adds to immunity against external noise, though latter starts with a good shielding:

Super Screened Low Transfer Impedance Cable: The Digi-Coupler is a “Superscreened” or “Low Transfer Impedance type” cable. To maximize performance in keeping the signal in and noise (RFI and EMI) out, the highest possible shielding factor is required. Without making compromises, The Digi-Coupler’s design therefore features a “triaxial construction” which makes use of multiple highest quality shields. (Triaxial construction: essentially a coaxial cable surrounded by an extra separately insulated shield).

In The Digi-Coupler not less than 3 dense braided shields, 3 foil shields and a Linear Structured Carbon (LSC) saturated outer layer are used, which combined shielding factor results into an ultra high screening attenuation and an ultra low transfer impedance; This allowing the cable to carry the designation “Superscreened”. The Digicoupler’s supreme immunity against radio frequency and electromagnetic interference allows trouble-free use over large lengths. Multiple lengths can be run in parallel without risk of mutual interference, even with other cabling (e.g. in cable conduits).

Signal cables are denominated “Superscreened” or “Low Transfer Impedance type” when their Transfer Impedance is as low as or lies below 50 µOhm/m. The Transfer Impedance is a measure for the quality of the shielding and is defined as the relation of the voltage along the screen of the disturbed system to the current of the disturbing system. The lower the Transfer Impedance of a cable the less susceptible its transferred signal is to external interference, but equally the other way around: the less noise the cable itself radiates. The latter is also expressed in the so-called screening attenuation figure, which indicates the ratio between the power radiated from the cable and the signal level it transports. The Super Screened Digicoupler cable’s screening attenuation and transfer impedance show excellent figures up to our measurement limit of 3 GigaHertz.

High Purity Dense Silver Coated Stranded Shields: The Digi-Coupler features high purity dense silver coated stranded shields as well as a rugged and hard-wearing jacket made of our HULLIFLEX polymer insulation material. All providing an optimal protection against chemical (corrosive) attack from the outside world and ensuring a very long lifespan.

Summary

Bearing professional, broadcast and high resolution applications in mind, The Digi-Coupler’s design has all the technology on board for exceptional performance without compromise. The Digicoupler provides the cleanest possible signal transport in all 75 Ohm impedance level applications and is the ultimate choice for the critical audiophile, videophile and professional.

Specifications

Design Principle: Triaxial, Superscreened

Conductor Material Core: High purity Matched Crystal OFC

Intermediate Conductor and Screen: High purity dense Silver coated high purity matched Crystal OFC

Eff Conductor Core: 0.283 mm² / Core:

Wire Size/AWG: 22.6

External Diameter: 8.2 mm

Jacket Colour: Gold tone

Characteristic impedance: 75 Ohm

Insulation Core: PE foam;

Intermediate conductor: PE;

Jacket: HULLIFLEX / 300 Vrms min

Jacket Colour: Gold tone

Available Lengths: 1 Metre & 1.5 Metres

Manufacturer's Warranty: 12 Months Warranty