Figure of 8

morris_minor wrote: Am I right in thinking that there's no logical (ie electronic) explanation for this?

 

Should the power be plugged to the PSU1 "contra-phase" - i.e. the plug turned round - then the AC waveform would be t'other way up.

However, the rectification to DC is full-wave - done by a bridge rectifier - so the ripple voltage seen at the capacitor filter will be identical either way.

The only difference is that the right hand diode is doing what the left hand diode is doing on the other PSU1(s).

I accept that there will be some capacitive coupling but this will be at much greater frequencies than the frequency the power "comes from". These will be interference frequencies and as such will differ with location (you all being at different ones).

(edit: I should not make mention of interference frequencies as it gets some people worried and rather edgy leading them to blame me for all their problems. Such people should realise that there are interference frequencies in everything!)

However, the interference frequencies might be mains harmonics (distortion) which might be asymmetrical, and might be a common factor if all the grid's alternators are made to exactly the same specification.

If then this "ripples through" to be so many parts per million on the supply rail of a product, then it will become part of the signal. But remember there is power supply rejection in each amplification stage. The amount of power supply artefact - should it exist - is so small that the difference is not measurable with the audio analysers at our disposal. This is not to suggest you cannot hear it - we cannot or should not assume we have discovered everything there is to discover.

Therefore it might be a good idea to make the phases the same for all PSU1's in a system.

We tend to use the same supplier of mains cords year after year, and recently there was a change to a different manufacturer.

I tested both types and found that if you orientate the Fo8 plug so that the wording 2.5A 250V~ is the same, then all the phases will be the same.

For users of the UK plug that will suffice, but for reversible mains plugs such as in Europe and the US etc, that could cause another difficulty. However, there is text moulded into these also, and if aligned the same way, that should also sort the phases same way up.

morris_minor wrote: Would swapping + and - speaker leads around negate the effect, or at least reverse it?

Sorry, wrong type of phase

The iron core of a transformer isn't a permanent magnet.