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Old 6th October 2002, 10:23 PM   #1
ALW is offline ALW  United Kingdom
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Default Late night listening (aka your mains supply)

Stirred into action by the 'How big do the capacitors have to be thread', I mentioned the phenomenon of HiFi sounding better late at night.

It's something I've noticed for years, and there are obviously several possibilities as to why.

Generally ambient noise levels are lower, so quieter sounds and more detail can be heard. There's something more fundamental than this though, that affects the system beyond simple resolution improvements.

The noise levels present on the incoming mains supply are a candidate, and with this in mind, spurred on by another correspondant I made some interesting measurements using the spectrum analyser.

The measurement system is a simple wall-wart transformer (AC out), and an attenuator on it's output to reduce the mains fundamental to suitable levels. A quick check with a signal generator to ensure it's bandwidth is suitable and off I went.

Initial plots were eye-opening, you may think your mains supply is a nice 50 or 60Hz sine wave (even mine looks good on a 'scope) but there was an extended sea of odd-order harmonics extending right across the audio band.

Could these be part of the reason for the improvements late at night?

I left the PC recording the audio data from the mains overnight, and started to examine a few gigs of data the next evening.

The following FFT plots show what I found, of particular note is that whilst THD does drop later at night / early morning, the harmonic extension reduces considerably, levels at where the ear is most sensitive all but disappear in the early hours of the morning.

With my system, despite almost everything being fed from regulated PSU's with low noise levels and ultra high line rejection there still appears to be a mechanism by which this noise affects sonic performance.

I've also noticed at times during the day, when the system sounds better I can usually correlate this with an improvement in the mains noise levels.

What can be done about this is something I need to apply a lot more thought to, since the easy solution of applying line filters to the mains inlets of the HiFi is a sonically degrading solution that kills the music.

Thought it might be of some interest - thoughts and ideas welcome!
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Old 6th October 2002, 10:25 PM   #2
ALW is offline ALW  United Kingdom
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Default A bit later on...

Later that night...
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Old 6th October 2002, 10:26 PM   #3
ALW is offline ALW  United Kingdom
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Default Into the wee hours...

When most are in bed...
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Old 6th October 2002, 10:29 PM   #4
ALW is offline ALW  United Kingdom
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Default Finally

All three for comparison...
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Old 7th October 2002, 01:21 AM   #5
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Filtering and an isolation transformer does not kill the sound IMO - improves everything IME.
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Old 7th October 2002, 01:36 AM   #6
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Quote:
Generally ambient noise levels are lower, so quieter sounds and more detail can be heard. There's something more fundamental than this though, that affects the system beyond simple resolution improvements.
Totaly agree with these points, and power pollution too. I suspect another source of pollution is seismic. Low level vibration affects EVERY component in your system. Could be from traffic or industry depending on where you live, which is reduced late in the night. If you haven't tried isolating components from vibration you might get a surprise, even if your components are not in the listening room.

Music Machine
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Old 7th October 2002, 02:12 AM   #7
fcel is offline fcel  United States
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Default late night ... or early morning ... electrically & envirnomentally?

In commercial cases or even homes, computers , printers, copiers, etc introduces a lot of harmonics to the power lines and that could be one of the reason you see so much noise on your scope. There are lots of ways to remedy that but generally it gets expensives the "cleaner" you want the power line to be.

For me, the best time (or to get the best "high') to do critical listening is first thing in the very early morning ... right after I get up and during my first cup of coffee. I find that in the early morning, my mind is "fresh" from the previous night sleep, my ears has not been bombared with noise pollution and typically the environoment is quietier. As you can tell, it's not an easy thing to do since everybody in the house is sleeping ... not to mention the neighbors!
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Old 7th October 2002, 03:54 AM   #8
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Thanks for the spectra ALW. I'd seen similar done before when I was apprenticing to an engineer and we were trying to trace a noise problem in a system, so we put the specan across the mains and looked, and saw something similar to what you posted. We were in an industrial area with some businesses that ran 24/7, but there was still a reduction at night. There was also a difference between individual phases on the mains with A phase being the worst and C the best. I would expect this to be even more pronounced in a residential area where a majority of homes are wired across the A phase, especially in areas with overhead wires, simply because it's easier to reach the A phase.

The solution to the problem at the time was to use a huge surplus 5kVA isolation transformer and a grid of earth stakes. The bandwidth of the iso trans was only a few hundred Hz, so EVERYTHING above that was attenuated drastically.

Nowadays, I won't build gear with torroidal transformers for the exact same reason: too much bandwidth lets too much junk into the system which is a real hassle to try to filter out. I like first order solutions. Even a huge mains torroid I got recently with an electrostatic strap isn't very effictive at isolation.

BTW, if any Aussies in the BrisVegas area know where I can score a large surplus iso trans I'd be grateful for the tip.

Toodles
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Old 7th October 2002, 08:22 AM   #9
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ALW

I've done similar measurements in South Africa and came up with very similar results. Didn't show that clear a correlation between day and night though. My feelings towards mains filltering is very similar to yours, or maybe i've just been unlucky. As with everything else you get a huge spread in opinion about this issue, mostly i suspect due to individual sound preferences. It's similar to the preference for sound absorbtion/dispersion in a room. If you prefer high absorbtion you're likely to prefer mains filtering, paper-in-oil caps in amps, lots of chokes in valve power supplies, damping in arms. All of the above calmes the sound but of course at a price.
May i suggest that we start a new group project dedicated to power regeneration? My modest attempts have shown that 0.5%thd sounds a lot better than 5% albeit on the small scale of my experiments (<50W).

peter
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Old 7th October 2002, 12:19 PM   #10
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Quote:
Originally posted by analog_sa

May i suggest that we start a new group project dedicated to power regeneration? My modest attempts have shown that 0.5%thd sounds a lot better than 5% albeit on the small scale of my experiments (<50W).

peter

A thread like this already appeared. It just needs more input.
I'm very interested in the project as well.

AC Power Regeneration anybody?
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