Several things associated with electrical current can change the musicality of your system. Obviously this includes erroneous signals or parasitics different from the original 50 Hz frequency, but you also need to make sure that the various components are well adapted to the current with a view to ensure the perfect transmission of signals between them.
An audio signal presents itself in the form of a difference in voltage between two points: plus and minus. This is a dipolar transmission. The mass potential is your reference and almost more important than the minus point because it's more vulnerable. As opposed to minus (active), the transmission inside an amplifier is passive and should position itself to the same potential at all points at the same time, despite the current flow. Having said that, this is basically a utopian concept but it gives us some indication of what faces manufacturers when designing components
Transformers; their role and problems
Electronic devices are fed by current through a transformer which has two principal functions: to adapt the voltage to the required usage and to isolate the circuit of the mains potential. It is this second function that we will keep in mind for this purpose. EDF - the French electricity company- sends 220 Volts (in reality it's more like 231 volts) to the home via two conductors in two different ways depending on the region: 2 inverted potentials in phase of 110V each or one alternative potential of 220 volts and one 'neutral'.
The potential average of 110/110 and the neutral potential should be near your reference for "ground" or "Earth" (radiator, water supply). This is not always the case and explains why you sometimes will be able to feel the "current" if you put your hand on the chassis of a component. In fact, the isolation of a transformer between primary and secondary windings depends on the quality of its construction. At the same token current can leak between primary and secondary windings and create a potential of "natural" mass, indexed between the two mains potentials. As we saw before, this is not necessarily secured to the potential of your local earth.
Normally
a third conductor ("ground") is charged with positioning the
circuit to the potential of local mass at the cost of a small signal.
These "ground" signals, furnished by EDF, are generally surcharged
by the strong currents generated by home appliances. They cannot be used
for sensitive components such as audio and video equipment. Furthermore,
all the components are not always grounded. So, depending on their construction,
the transformers can release more or less current at either side of the
primary winding of the transformer.
According to the type of mains (110/110 or 220/neutral), turning the plug
could have various implications:
- at 110/110: change of phase in the potential of released current in
equal quantities.
- at 220/neutral: change of phase and level of potential, except if the
leakage current is balanced at the center of
the primary winding (double balanced windings).
On certain
components one finds balanced transformers which use two double windings.
This makes it possible to balance the potential of leakage current in
the center of each winding. In this manner the components are insensitive
to the inversion of the plug. On the other hand, the potential of leakage
current remains significant and cannot be lowered as in a simple transformer.
The change in phase of leakage current potential in one of the components
(by inversion of the polarity in the plug) will affect a change in frequency
of the dissipated current in the 50 to 100 Hz band and vice versa.
Noise or parasitics in the signal
The mains that supplies current to your audio-video components is not
as good as it may seem. Parasitic frequencies at very weak levels change
the quality of the sinewave up to 50 Hz. These signals have different
origins: remote signals, household appliances and radio frequencies. In
theory, filtering of the power supply with its huge condensators is fairly
easy to accomplish and the parasitic signals are easy to eliminate.
This is also the case for those areas where the power supply delivers
perfect voltage. But, surprise surprise, these distortions in the signal
also affect the mass of the internal circuits in each of the components
in the audio chain. They manifest themselves by modulating the balanced
power one finds between the different power supplies, in addition to the
signal, in the 'cold' driver of the connecting cable.
One can say that the filtering of the internal power supply of each component
in the audio chain generates an almost perfect 'relative' voltage, but
that this one can be influenced by alternative 'absolute' variations that
add and distort the transmission of signals between components. We will
try to understand this phenomenon a little better in order to find out
how to minimize its effect.
How do these distortions manifest themselves?
The frequencies containing parasitics in the mains are generally situated
outside the audible spectrum. They transmit themselves between primary
and secondary winding by capacitive effect and can be detected by one
of the numerous junctions (diode, transistor) and so find their way back
into the audible spectrum.
In all cases the distortions that attain the mass show themselves in the
form of parasitic currents circulating between components through the
interconnects; more exactly in the 'cold' driver. According to the impedance
of this interconnect, these parasitics cause a difference of mass potential
between devices that alter the signal and thus create a distortion. One
understands now why the 'sound' of a cable is largely due to its mass
conductor.
How to reduce these effects?
With regard to parasitic frequencies using a mains filter will prove an
essential utility. Made of coils and condensators in very much the same
way as a loudspeaker it will eliminate the higher frequencies up to 50
Hz without giving any resistance to the flow of current. It is key to
filter the mains for all the devices to prevent the filtered components
from affecting the non-filtered components via the interconnects. To diminish
the effect of balanced power coming from the mains, several measures can
be taken: eliminate the currents from switched off components and determine
the directionality of each plug.
Eliminate the influence from switched off components
As you were able to deduct, it is the 'cold' conductor (or mass) of your
interconnect that is the most important. This determines the 'sound' of
the cable. You can test this yourself by taking a source with two outputs,
connect them to a preamplifier with two very different cables on two inputs
which you can change rapidly and then pass them immediately from one to
the other. You won't hear a difference. The explanation is that your preamp
connects the 'hot' points in turn whereas the mass conductors between
components remain connected in parallel.
In any audio chain, the 'cold' conductor of the cables connects all the
components permanently, even when they are turned off, and consequently
transmits the local variations of mass potential.
The solution is to place a bipolar switch at the beginning of the cords in order to make the components turn off completely passive. An independent electronic control panel is also a refinement to be considered.
How to find the right directionality in your plug?
If you apply the preceding concepts by filtering the mains and inserting ferrite filters to protect the amplifiers from the high frequencies collected by the speaker cables (these are also excellent antennas), one can proceed as follows.
First acquire a voltmeter with the biggest input impedance. Since the voltages which we will measure are voltages of current with a very high impedance, the voltmeter must also have a very high input impedance. 1 Megohms per Volt is a good value. Below you would be likely to measure nothing. The purists will be able to have recourse to an oscilloscope Bi-curve used in differential measurements (the 'uninitiated' need not try this).
When
you interrupt the bipolar mains, only connect the components in the order
starting with the most sensitive component: CD - preamp - amplifier -
speakers (whether active or electrostats).
The heart of the chain, which can be viewed as the "zero-potential"
broker, is the preamplifier (or the amplifier in case of an integrated
amp). All the masses are connected via the cables leading to and from
the pre-amp. It is thus necessary to find its right mains directionality.
This directionality will be arbitrary so it will be sufficient to reverse
all the plugs to have more or less the same result. Thus we can seek the
direction which induces less current leakage compared to the local absolute
potential. A benefit of this is that we avoid large surges during handling.
Power on the preamp only, disconnected from any other active element and
connection. Place the voltmeter in position "alternative Volts "
around 100 volts. Put one of the two measurement probes in contact with
the mass of one of the cinch/RCA connectors at the back of the preamp.
Take the other probe in your hand. To note the value find the right measurement
scale so that the needle moves at least in the middle of the dial. Do
this again after having reversed the mains plug and choose the position
where the value is lowest. The position of the mains plug of the preamp
will not have to be modified any more and will be the reference of zero-potential
on which we will adjust the other components.
