Bryston on cables lengthy post

[plissken]

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I wrote this a number of years ago:


GETTING WIRED

There is not a day that goes by where I do not get asked what cable Bryston recommends with our amplifiers. Hopefully the following will assist you in weeding through some of these complex issues.

Part of the problem is that there is an awful lot of marketing going on and not much science in some cases. The ‘elaborate packaging’ of these interconnects and speaker cables may make you feel warm and fussy but the electrical characteristics are still the primary issue of concern. Simply stated the geometry (where the plus is relative to the minus) of a cable determines the inter-relationship between the measured performance of a specific cable. These measured performance criteria are called the ‘Primary Constants’. They are R–resistance, L–inductance, C–shunt capacitance and G–shunt conductance. You can play around with all types of exotic packaging and add-on appendages you like but ultimately the measured performance (primary constants) tell the tale.

Bryston does not think cables should be 'voiced' to sound a specific way. The best cable is NO cable at all so we contend that the best cable is the cable that changes the signal the least.

COAX INTERCONNECT CABLES:
An analogue Preamp/Amplifier connection is a ‘high impedance interface’ therefore; you are looking for low measured Capacitance. An interconnect cable acts like a capacitor in the signal path so the better that capacitor the better the interconnect. We use an interconnect wire with (very low capacitance) and the RCA connectors are made for us in Switzerland. The RCA cables ‘make and break ground’ first and last when connecting and disconnecting. This prevents ugly pops and bangs from going through your system with the possible negative results.

XLR INTERCONNECT CABLES:
The XLR cables we use are also very low in capacitance. Actually the XLR cable we are currently using is in fact low noise balanced microphone cable with 100% shield coverage against RF. The advantage of Balanced XLR cables is that they have a noise canceling effect known as ‘common mode noise reduction’. This helps prevent noise and hum from affecting your system. With today’s complexity of audio and video surround systems this is a big plus, so if you ‘got em-use em’.

DIGITAL CABLES:
With ‘Digital’ interconnects things are a lot different. The wavelengths of digital signals are ‘very short’ (same for FM) so the lengths and terminations are much more critical than with the analogue signals previously discussed. When the wavelength of the signal the cable is used for approaches 1/30th of the length of the cable then transmission line effects start to appear and much more attention has to be paid to the connection and termination. If not then reflections and cancellation of data is a real possibility. For instance the AES/EBU digital connection on the back of the Bryston SP3 and SP4 should be used with a cable having an impedance of 110 ohms.

VIDEO CABLES:
Video cables also operate at very high frequencies – typically 5-6 MHz for Composite and S-Video and 8-30 MHz for Component Video depending on the scan rate and resolution. So again understanding the wavelengths of the signals and interfaces involved is important.

SPEAKER CABLES:
The Amplifier/Speaker interface is a ‘low impedance’ connection. Therefore, in a speaker cable you are looking for low ‘self inductance’ (because inductance rolls off the top end) as opposed to ‘low capacitance’ required in the RCA or XLR analogue interconnect. For speaker cables we use a stranded 9 gauge linear crystal copper with ‘Heavily Gold plated’ Spade lugs or Expandable Banana plugs specially made for Bryston.

A/C POWER CABLES:
When you plug your power cord into the wall outlet you are in 'SERIES' with all the wire on the other side of the wall all the way back to the power source. The small length of power cord from the wall to the amp is insignificant compared to the miles of wire it is connected to. As long as the power cord can deliver the current and voltage required to drive the amplifier to full power it is as good as it can get.

There are 4 basic things to remember about these issues:

1. The connection should be of similar metals (preferably gold) and be airtight. If not airtight it will break down molecularly over time and begin to rectify or produce a diode effect on the signal.

2. With all the RF floating around today the better the ‘Shield’ on the interconnect the less intrusive the RF will be.

3. The connection between your analogue Source components (Preamplifier, CD Player, Tuner, DVD Player etc.) is a ‘High Impedance’ connection and the interface between your power amplifier and your speakers is a ‘Low Impedance’ connection. So, the requirements are totally different for optimizing these interfaces.

4. Digital and Video cables are much more susceptible to reflection/phase/cancellation problems because of their short wavelengths relative to cable length.

As you can see from the above, no surprise that people hear differences in cables when connected to the variety of equipment in the market today. Given the differences in input and output impedance’s between transistor and tube gear, the lack of understanding of the high impedance and low impedance interfaces, the world of RF, and the digital/video connection issues no wonder we have these differences of opinion.

 RECOMMENDATIONS:
I highly recommend keeping the speaker wires as short as possible and utilizing XLR balanced lines if available. Given the choice of long interconnects and short speaker leads or short interconnects and long speaker leads – choose long interconnects (preferably Balanced) and short speaker leads. With digital and video cables finding out the sending and termination requirements is very important due to the very short wavelengths relative to cable lengths involved.

The cables Bryston recommends represent a scientific approach to these issues and are the cables we use in all our professional studio installations. All of these cables are available through Bryston’s Website (www.bryston.com) or our dealers if you wish.

ADDENDUM:
The line cords we supply for the 14B and 28B are 12 ga. That's more than large enough to draw 15 Amps out of the wall. 12A is the largest breaker we are allowed to put in any of our products, which is 80% of the plug rating. 12 Amps X 120V = 1440W., which is about what the amp will draw from the wall plug when delivering its rated 1000W.

An important thing to note is that the transformers used in the largest Bryston Amplifiers. (7B, 14B, 28B), are special 'energy storing' transformers. That means they don't need to draw large, narrow 'spikes' of current when charging the filter caps. Instead, the incoming current is largely sinusoidal, with a small peak-to-average ratio. The energy-storing transformers act almost like a large battery, delivering large current pulses from the secondary while the primary is charged by lower peak current from the wall.

We do offer a BIT (Bryston Isolation Transformer) power product but it is designed to ‘isolate your system’ from the rest of the equipment on the power line. It’s like having your own miniature power grid. It is not going to alter any of the issues discussed above.

James Tanner
Bryston

 

[fas42]

10 minutes ago, plissken said:

 

There are 4 basic things to remember about these issues:

1. The connection should be of similar metals (preferably gold) and be airtight. If not airtight it will break down molecularly over time and begin to rectify or produce a diode effect on the signal.

2. With all the RF floating around today the better the ‘Shield’ on the interconnect the less intrusive the RF will be.
 

 

 

And these factors are what I worry about ... take the care that ensures that these distortion factors don't happen, and the SQ that can be achieved will be the reward ...