Toroid Hum Thoughts

Toroid Hum and Sound enjoyment.

I guess like many people I suffer from poor mains and consequently get mechanical hum from one or more of the Toroids in my Naim equipment. I have been thinking about this for a while and have following random thoughts/observations.

1)Dogma rhetoric: In lieu of any official statement the accepted dogma seems to be that use of mains conditioners (words chosen carefully) are to be avoided as they destroy the ‘essential dynamic’ of the sound.

2)The Hum does not affect the sound because it is purely mechanical and isolated from the signal path. (True enough for the sensitive Pre-Amp)

Taking these two statements as a whole I conclude that the mechanical hum has no ‘direct’ effect on the music, and yes this mechanical hum does not of itself feed through to the speakers. That is it does not get onto the signal as an additonal sound. However the first statement does imply that pre-toroid additions do affect the sound. For example better mains cables, etc. It also appears there is little scientific evidence of how such additions benefit or degrade the sound. All we have is anecdotal evidence and hearsay. On this forum several people have made an observation that the sound of the system changes through the day and put this down as an effect of the poor mains. (But read point 2 above, the poor mains, causing the transformer to hum, and this statements seem at odds!)

My own experience is that the sound does appear to change in quality and approach as the mains quality varies.

Mains Cleaning methods;
There seems to be a range of mains cleaning techniques that are designed to deliver the holy grail of clean, stable mains to the Power Supplies.

In no particular order;

1)Replacement Mains cables: Ranging from the Hydra, to the Power-Igel and through to just using special ‘fuses’ and uprated cables. Yes these do seem to have some benefit to the sound, at least that is the consensus, and I myself use a Hydra. But these have, in general, no effect on the poor quality mains being fed in and are thus not likely to improve, reduce the mechanical vibrations in the Toroid. (Some comment that they can improve this but I am not convinced as the mains Harmonics and possible DC offset still get transferred.)

2)Mains Suppressors/surge protectors and filtering (RFI) products. In general these are unlikely to improve matters. Though there may be some improvements if the AC transfer is capacitively coupled and this fortuitously cuts out the DC offset. The filtering in these products is more aimed at the typical ‘spark’ generated wideband interference (Thermostats/switches etc.) and does not extend down much below a 1Khz or so. Hence unlikey to stop and Harmonic distortion on the mains.

3)Power Conditioners: These seem to be souped up surge protectors with enhanced filtering. (I may be wrong as I haven’t ‘studied’ these in depth) and seem to be the widest variation of approaches. For this reason they are difficult to categorise or recommend as each will have strengths and weakenesses. It is impossible to draw any general conclusions. Many on the forum sanction strongly against these but few seem to do so from a position of experience or testing.

4)Power Regenerators: These, to me, seem to offer most hope. It these the general process seems to be take the dirty mains from the supplier and put it through a precision AC-AC converter. The end result should be a clean, consistent power supply with stable frequency and Voltage ouptut free of any dc Offset. Such a signal fed to the PSU’s should ensure a quiet transformer and the possibility of consistent sound quality over the full diurnal period. Again some have reported using these on the forum and their response is generally positive but there seems to be no official line on this type of product.

There is another range of conclusions to draw from this. Most fundamentally is the sheer lack of independent verifiable cause and effect science in all this. If changing mains cables/adding power conditioners etc. does affect the sound then it must somehow be affecting some attributes in the signal path. Whether that be Noise Floor, SFDR, Harmonic distortion, Device relaxation, Hysterisis etc. etc. and as such it is not beyond the wit of man to perform measurements to check for these effects. (I am careful here because changing device hysterisis may have an measurable impact on the signal but to a person listening the ‘resulting’ effect on the sound may be perceived and interpreted differently.)

I personally would be interested to see how Naim test these effects to make the recommendations they do. In my view I would utilise the Power regeneration units in reverse so to speak. That is use a bank of say five each set to a clean signal harmonically related to 50Hz and the vary the relative amplitude of the various harmonics to make a ‘clean’ controllable dirty mains signal. Such a Test bench would be a great evaluation tool for Toroid experimentation. (Testing such things as clamping technologies, Potting ideas etc.)
I would also like to know that Naim have done tests with some of the main Power Regenerators out there and could offer some insight into their potential benefits or drawbacks (Note I did not say mains conditioners!) I would love to see results of measurable signal analysis on these products within a system context as well blind (and open) A/B listening tests.

Some experimenters in Holland have also played with the idea of not using a regenerator to feed 240V/50Hz but to use it to select the volatge and frequency that ‘enhances’ the sound! (I think they ended up with 220V/76Hz). Now I have not seen any investigation into the potential this offers but I think it is a significant step.

An additional consideration is to consider (heresy I know) swapping out the SuperCap for a battery (or batteries) to feed the pre-amp and try and identify what if any sonic improvements accrue. I’m not sure if anyone has done this test or one similar. (Now if I can just get a battery bank with a Burnby attached!)

Sorry it’s a long post just some random jottings on this topic. I know this topic has been covered in a variety of ways and from a variety of directions before but hope people find this an interesting summary. By the way I shan’t spoil your google pleasure for the various products, it’s a whole bundle of fun looking.

(My old Audiolab also used to hum, but it isn’t as loud as the Naim toroids. Oh and by the way the Hum does affect the music, I hate having to lsiten to it during the quiet bits!!)