4. Correct Earthing Procedures for Neve Modules and Consoles

Technical Earthing: For optimum noise performance Neve recording consoles should be used in an environment that includes a clean "technical earth" system. This is usually a connection to a ground that is separate from the "earth" that is available from the a.c. power outlets. The reasons for this are threefold:-

• The "mains earth" can carry noisy earth currents from other devices in the building, or even externally, all the way back to the transformer sub-station. The currents can emanate from air conditioning units, Thyristor based lamp dimmers, adjacent heavy machinery, indeed many unlikely but very troublesome noise sources are available to creep into the audio paths!

• It is essential for all the equipment in the studio environment to be a close together in terms of ground paths and impedances. The inclusion of any significant resistance to these paths will produce a proportionally sized potential difference (voltage) which can, again, find its way into the audio paths.

• This requirement is especially important in terms of unbalanced equipment where the ground forms the return path for the signal. Connecting together two unbalanced items of equipment that are, in turn, connected to two grounds of minutely different earth potential, is a recipe for hum problems!

Fortunately, a little careful design of the studio wiring can reduce the likelihood of these problems arising to an absolute minimum. The studio earthing arrangement should first be checked to see if a technical earth is available. For the moment I’ll assume one isn’t and describe the best means of retro achieving one:-

If access to an outside wall is good and there is soil nearby, earth rods (typically about 4 to 8 feet long and 1/2" diameter) can be hammered into the soil as near to the control room as practical (to keep the length of the cables to a minimum). It is better to use at least three rods, spaced about six feet apart and joined by heavy (10mm section) earth cable, and the earth to the control room taken from the centre rod.

If there is no soil and the outside is all concrete or paving, the concrete can be drilled through with a hammer action masonry drill but it is VITAL to establish that no gas, water, or electric cables are under the ground. Metal gas and water pipes (and to a certain extent electric cables) can be detected by use of a metal detector (as used for searching for buried treasure!). Electric cables can also be detected using a search coil of a reel of wire attached to an oscilloscope and noting the points of maximum signal detection. Water pipes can be detected with a couple of bent coat hangers… for tips about “water divining” in this fashion feel free to email me… It’s used every day by water company engineers!

If there is no possible way to connect the studio to this isolated technical ground it may be possible to connect to a water pipe in the building provided that it doesn’t connect to a section of plastic pipe on its route to ground or the a.c. power earth is connected to the same point. The efficiency of a ground can be tested by measuring the impedance (resistance) between the mains and technical earth (should be less than 10 ohms).

The earth should be brought to the console via 10mm section green cable and strapped securely to the earth stud on the centre cheek of the console. A further cable could "star ground" from this point to the metalwork of any 19" racks and tape machines. The fuse box / circuit breaker unit feeding the control room could also use this ground instead of the a.c. ground. The consequences of all this heavy bonding is to get every item of equipment in the control room to a similar "clean" ground potential. If the potential between any two items of equipment is the same then no earth current can flow and no hum will be induced into the connecting cables.

NB. The console power supply earth should not be connected to the console frame.

Never remove the "power ground" connection from a piece of equipment that appears to be causing a ground hum. This might cause a dangerous fault current should a power component in the device fail and create a risk of electric shock.

Always check the cable shield wiring first! This especially applies to unbalanced equipment.

e.g. Connecting unbalanced equipment to a Neve Console:

All audio connections to the Neve are balanced. When connecting an unbalanced signal to the Neve it is important not to use the shield of the cable as a conductor. The full voltage must be developed across the balanced input in order for the circuit to work at maximum efficiency.
For example, the following describes the connections of a 1/4" mono jack to a TT or TRS balanced jack. . . as might be used to link an item of unbalanced equipment to a console patch bay.

Function	_" Mono Jack Plug	_" TRS or TT Jack Plug
Hot (+)	Tip	Tip
Cold (-)	Sleeve	Ring
Shield	(no connection)	Sleeve

As can be seen, the cable’s shield gets its ground from the console but is NOT connected to the 1/4" jack sleeve (body). This prevents the likelihood of an earth loop and treats the unbalanced signal as "quasi-balanced" which helps to minimise interference. The same technique would be used with unbalanced RCA/Phono plugs, and any unbalanced equipment using XLR connectors. The shield is NOT used as a conductor, it merely screens the audio cables and is connected at ONE END ONLY. (i.e. The console end)

Connecting balanced equipment to a Neve Console:

As stated above, all connections to Neve consoles are balanced and floating.
The policy of Neve concerning grounding is that the console will provide grounds for the shields of cables emanating from the console, and this should be used in preference to the outboard gear to keep the concept of the star earthing.
Also, with one notable exception, there is no need to connect the shield of the interconnecting screened cable at both ends because this further reduces any likelihood of earth loops in the studio wiring. (e.g. Neve to Tape M/C earths at the Neve end only)
The exception to this rule being the microphone inputs which must connect back to the console ground for the 48v phantom power to work.

Earthing of Outboard Racks:

The wiring of Outboard Equipment racks for Neve modules follow the basic rules of the console connections albeit some leeway is required on portable racks as to where they derive their earth connection from!

The power supply should always be connected to a.c. ground by means of a 3 core cable and a.c. plug. This is for safety’s sake in the event of a fault occurring in the power supply. The last thing anyone should want to chance (however remote the likelihood) are a.c. voltages flying up the microphone cables! Give the circuit breakers a chance to trip by providing a path to a.c. ground.

A nice touch with power supply cases is to provide external insulated binding posts to allow for connection to a studio’s technical earth, if available. In any event, the Neve modules must be earthed and a connector pin (invariably the last pin on the module connector) is the means by which the module case and transformer screens get this earth to enable optimum shielding. Back at the power supply, a single connection between the PSU 0v and ground should be made, and the insulated binding posts previously mentioned could permit easy connection to either a.c. or technical earth without disturbing the internal wiring.

BACK • NEXT