Bad Mains Day?

Posted by: Christopher on 01 August 2002

Why is it that some days my stereo sounds like the dog's *esticles, then others it sounds pants?... I find relief in this being a (seemingly) a common problem... people say that Naim is very sensitive to mains quality.

However, just to throw a spanner in the works, when my stereo sounds crap so does my (acoustic) guitar...


If music is about emotion, and emotions change from day to day, then our enjoyment will surely also vary accordingly... feck all to do with mains quality!

This morning I Can't Quit You Babe (Led Zep 1) blew my (and probably my neighbour's) mind! I love it when music does that for me... but when it doesn't I just turn it off and do something else until I'm ready to listen & feel the music. Equally, this morning my car feels so smooth, powerful, agile... other days it feels like a 20yr old VW Polo.... (I know, I had one)

The point I'm trying to make is that just because you love something doesn't mean you have to do it every day, and if you do you will undoubtedly be very tuned into subtle differences, and just like driving a car, snowboarding, playing tennis or even going for a beer, ultimatley your satisfaction will depend upon how YOU feel... the car is the same, the snow is the same, the racket is the same... etc, but none of these things brings the same satisfaction every day.

I used to get so bogged down when the music wasn't doing it for me, I blamed my new system (surely when you've paid this much it should ALWAYS sound good?!!!)... I spent a few weeks listening for the fault, what was to blame... it was me! I was no longer listening to the music but the system... and I realised this by hearing Martin Taylor's Georgia rendition on my Mum's Denon lifestyle system and it did it for me. Why? Because it conveys music better than the naim? Feck no! because I had no expectations, just sat back and enjoyed the music without critically appraising the equipment's performance.

Enjoy the MUSIC!
smile
Posted on: 01 August 2002 by Thorsten
right.
Posted on: 01 August 2002 by Christopher
Delivery Failure Report
Your document: testing testing 123
was not delivered to: brucet88_no_spam@aol.com
because: 550 MAILBOX NOT FOUND
Posted on: 01 August 2002 by Christopher
ah ha! trying again... roll eyes
Posted on: 01 August 2002 by Jez Quigley
I think we put down to 'bad mains' a drop in performance that we can't explain otherwise (ie no change to set-up etc). I noticed this week that during the hot and humid weather the system sounded a bit 'ordinary', but now after the thunderstorms and the bucketing down rain it sounds absolutely magical. I dunno if its a change in the mains, humidity, temperature, earthing (ground is soaked), or what, but it is REAL and not my readyness to listen etc.

"All systems are perfectly designed to get the results they get."
Posted on: 03 August 2002 by Bosh
Mine sounds much better after the wet weather too. I was told to keep my dedicated mains rod watered (although rarely do)so this will definitely contribute to the improvement
Posted on: 03 August 2002 by Jez Quigley
I do, I give the rods a drink whenever I water the pots, but I cant hope to soak the ground like the last couple of days rain - a months average rainfall in one day! At least I'm on the edge of the pennines, the poor sods in the Vale of York are under water.

"All systems are perfectly designed to get the results they get."
Posted on: 05 August 2002 by Martin Clark
Having an agreeable amount of 'nothing' to do over the weekend, I finally got around to taking a look at the mains supply at home.

The perliminary observations are here, spelling mistooks and all; if and/or when I can 'see' a change next time things really sound 'off' I'll return here and let you all know.
Posted on: 05 August 2002 by Andrew L. Weekes
I've been meaning to do this for some time, how did you interface with analyser - transformer, loose coupling, or combination?

May have to do this myself now...

A.
Posted on: 05 August 2002 by Martin Clark
Andy - click the wave image for a quick schematic on the 'how-to'; isolation was guaranteed by using a laptop (on battery power..) as the monitoring equipment.

Next idea is some Applescript to take snapshots say every 1/2hr for a few days - might make for an 'interesting' Quicktime clip.

quote:
Did you get the chance to run the scope on the general mains compared to a dedicated spur ? Although you did mention that you effectively turned your whole house off so would a difference be there ? I suspect not.


Alan - I intend to trial this at my brother's house, not that he knows this yet wink. No, the scary bit was how little difference was made by turning off all the 'nasty' stuff in the house....

The testing of mains filters is a bit beyond the scope of my equipment. Few mains filters have any effect below c 150Khz since there's no requirement to do so under the various EU EMC regs - for domestic use anyway. I did have a large filter designed to act down to 10Khz, unfortunately using it had a similar effect to playing 45s at 33-1/3...something else to investigate...

M.
Posted on: 05 August 2002 by Jez Quigley
Hey Martin, more more more!

"All systems are perfectly designed to get the results they get."
Posted on: 05 August 2002 by Martin Clark
...so here is a quick lashed-together movie (346KB, Quicktime format) showing the mains spectrum hereabouts whilst I brewed coffee after dinner.

Funnily enough, the time lapse looks exactly like what you see in real time(!) Correlating this mess to 'the sound' might be difficult, but I defy anyone to say this kind of mess doesn't have an effect.

M.
Posted on: 05 August 2002 by Paul Ranson
This kind of mess doesn't have an effect.

Paul
Posted on: 05 August 2002 by Andrew L. Weekes
I've found a suitable toroidal transformer, ripped from the yet-to-be-rebuilt AndyCAP and will endeavour to connect this to my flying calf A-D, for some long term monitoring.

Toroidals are better for this sort of thing, since they have wider bandwidth that somes from the high inter-winding capacitance of the construction (which might make them less useful for audio PSU's since the junk on the mains gets through...)

Can your analyser do waterfall or spectograms Martin? That could also be a useful means of showing the same info, with some in-built history.

A.
Posted on: 06 August 2002 by Martin Clark
Andy - yes toroidals are better, but since the bandwidth bottleneck will really be the soundcard, I'm not too bothered at the mo. I do have a variety of big ferrite cores sitting here, so I might wind a coupling transformer to check out the upper end of the spectrum.

No waterfall or spectrograms at present, hence the quicktime experiment. However, I forwarded everything to a mate at UKAS who has an interest in this kind of thing (DC-RF metrology), which may lead to helpful suggestions on methodology and/or equipment, esp. with regards to parasitic effects.

Paul - well, we'll see wink

M.
Posted on: 06 August 2002 by Martin Payne
Martin,

I can't play the video - seems I need another codec (well, a dec, anyway). What did you use?

cheers, Martin
Posted on: 06 August 2002 by Martin Payne
Martin,

it strikes me that neither if the waveforms is anywhere near a sinewave, more of a sawtooth. I guess it's the contribution of the odd harmonics.

I am especially concerned for the loss of the peaks of the waveform, as these are what re-charge the smoothing caps on each cycle.

RMS voltage (which should be 230V) would be calculated as root 0.5 (0.7071) of the peak voltage for a sinewave (which this plainly ain't).

Can you calculate what the true RMS (integrated over a cycle) is of your supply? How does this compare to 0.7071*peak voltage?

I'd expect that a waveform like that would make your kit hum quite badly. Does it?

cheers, Martin
Posted on: 06 August 2002 by Martin Clark
quote:
it strikes me that neither if the waveforms is anywhere near a sinewave, more of a sawtooth. I guess it's the contribution of the odd harmonics.
I am especially concerned for the loss of the peaks of the waveform, as these are what re-charge the smoothing caps on each cycle.


Well that's the basic problem - most rectifiers will only turn on near peak voltage, and then the current draw is collectively tremendous, hence the flat-topped peaks. Switchmode supplies are some of the principal suspects here. High, peaky current draw conspires with the impedance of the mains and harmonics are the result. BTW, this is a residential area, and I live about 100m from the substation - where the transformer is only a year old; the old one went bang in a spectacular way when members of the local Bass Disposal Squad set fire to an Astra next door. So, you see, we've gone so far as to have had the substation serviced...

quote:
RMS voltage (which should be 230V) would be calculated as root 0.5 (0.7071) of the peak voltage for a sinewave (which this plainly ain't).
Can you calculate what the true RMS (integrated over a cycle) is of your supply? How does this compare to 0.7071*peak voltage?


This is a good point; my cheapo DVM tells me that right now *reaches for kit* the mains is at 251VAC, which is high...usually 236-240ish hereabouts. But it's not a 'true-RMS' meter, so the altered crest factor is probably messing with the reading. At a guess, the mains is showing something like 5-7% THD, but that will vary constantly. I now have located some software to turn the measurements into spectrograms, will have play and see what further I can find out.

quote:
I'd expect that a waveform like that would make your kit hum quite badly. Does it?

Actually, no, but it contains no toroidal transformers (which tend to be more sensitive to harmonics - smaller airgaps= more easily saturated) and draws little power, being CD->power amp->headphones (no hum via the cans, either). That, and the fact I'd wager my pics are about 'normal' these days frown In the last 3 years I can recall only one 'hum' night.

M.

PS. the movie was saved with Quicktime using the Sorenson codec - plays on my office WinBox OK under QT5.
Posted on: 06 August 2002 by Andrew L. Weekes
But I can't resist poking around!

Found an old US Robotics modem wall-wart, AC only tonight. A quick hack later, and a suitable attenuator added and we have mains into the analyser.

Initial results were a bit scary, shed-loads (that's engineer tech-speak) of harmonic content, mainly odd-order.

Turn on the THD analysis and I have about 4.5%THD on the mains, with the same flat-topped waveform Martin has.

I'd suggest switch mode PSU's, some of which have power factor correction, would be a nicer load ignoring noise issues than the massive bank of toroidal PSU's that are all switching on about the same point every cycle and drawing 10's of amps each on the secondary side!

To confirm accuracy, I've measured the o/p of a cheap high o/p impedance AF signal generator I have which measures about 0.04% THD.

I've then injected this into the primary of the wall-wart and double checked it's o/p (rises a bit to 0.13% THD).

Finally a quick check of the o/p of the wall-wart to check it's distortion, which is a low-enough 0.4% THD.

On that basis it looks as if the mains at 9 o'clock has about 4% THD.

A check at 11 and it's dropped to 3.9%, which with corrections amounts to approx 3.5% THD.

It's about this time the system starts to sound better, so I'll monitor a bit more and post some pics when I get a mo...

Andy.
Posted on: 06 August 2002 by Andrew L. Weekes
The mains at 9...



[This message was edited by Andrew L. Weekes on TUESDAY 06 August 2002 at 23:14.]
Posted on: 06 August 2002 by Andrew L. Weekes
Heres what the mains ideally should look like (this is my sig-gen set to 50Hz)



[This message was edited by Andrew L. Weekes on TUESDAY 06 August 2002 at 23:27.]
Posted on: 06 August 2002 by Andrew L. Weekes
You may get a midnight post, if I can stay awake!



The top-right number is the total harmonic distortion figure. It still looks rubbish though!

I've not measred the supply at the system yet, this is just at a spare socket with most of the house still 'working'. I'll try some serious switching off soon and report back.

[This message was edited by Andrew L. Weekes on TUESDAY 06 August 2002 at 23:41.]

[This message was edited by Andrew L. Weekes on TUESDAY 06 August 2002 at 23:47.]
Posted on: 06 August 2002 by Andrew L. Weekes
Martin,

I think your variation in the 'phase noise' in the skirts of the 50Hz signal may just be lack of spectral resolution / the windowing function your analyser is using.

I'm not sure if you have options, but a Blackman or Hanning smoothing window may help - see attached.

Mine looks solid and stable at present.

A.
Posted on: 06 August 2002 by Andrew L. Weekes
But at 00.07 the THD is down to <3.5%, but still loads of extended crap everywhere.

Gotta go to bed now...
Posted on: 07 August 2002 by Martin Clark
Andy - I'm aware of the smoothing-window issue, it is the source of the LF confusion - but this was only intended to be a 'quick peek' wink

Better software will sort that out; I tried some spectrograms last night - next to useless due to not enough resolution in time domain. More toys required...

quote:
I'd suggest switch mode PSU's, some of which have power factor correction, would be a nicer load ignoring noise issues than the massive bank of toroidal PSU's that are all switching on about the same point every cycle and drawing 10's of amps each on the secondary side!
I'd agree, but I'm not sure of the degree to which PF corection deals with the 5th and 7th harmonic which direct rectification gives rise to. One of those things which is improving rapidly I expect. Surely a simpler solution would be, say, a 300V DC mains to supply SMPS-everything. No harmonic distortion problems, and bypass caps could be added liberally without the AC leakage problem - potentially rather dangerous though!

Next stage here is removing the compact flourescents and having a play with my stash of mains filters and X1 caps, using the current test setup, to see if any gross,er, differences are to be had...

M.
Posted on: 07 August 2002 by Martin Payne
quote:
Originally posted by Martin Clark:
PS. the movie was saved with Quicktime using the Sorenson codec - plays on my office WinBox OK under QT5.



Ah, that'll be my problem then - no QT.

cheers, Martin