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Old 7th May 2003, 09:50 AM   #21
dhaen is offline dhaen  Europe
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Quote:
So seperate isolation transformers for each component is preferable?
Bas,

Possibly.... It's a grey area.
Let's wait for some other opinions

Cheers,
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Old 7th May 2003, 10:56 AM   #22
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Quote:
Originally posted by Bas Horneman
So seperate isolation transformers for each component is preferable?
That would probably be the ideal, with each well sized for the device it's powering. But I'd just try one for your digital stuff, and one for analogue, as big as you can get or afford. A great place for iso transformers is a metal recycler, where large units can be picked up cheap. If I had a basement where I could put them, I'd have no problem having a multi-kVA trans for each component, because the ones I've sourced from recyclers in the past have been very modest in outlay, but physically large and ugly industrial items. I also bought a 2.4kVA toroid off ebay that was surplus from a manufacturer of medical gear. It came with multiple 240V secondaries, dual primaries and an ES sheild for about $US20. He'd thrown others away before this because he couldn't sell them!. Hunt around, you might be able to find something cheap.

Years back we measured some large EI core iso trans for frequency response (noise) on a specan because of a noise problem we couldn't quite get rid of in an industrial area with VERY dirty mains, and the ones we bought dropped off quite steeply above 1kHz or so.
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Old 7th May 2003, 10:56 AM   #23
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I've noticed things sound better at night, too. But I don't think it's RF noise, or even really audio. Up until 23.00, the mains voltage jumps around all over the place, but after midnight, it's far more stable. Thus, all our AC heaters are constantly having their temperature changed slightly and do not reach a stable equilibrium, similarly for unstabilized HTs.

An isolation transformer with E/S would be a very good start for getting rid of the RF hash. They're not expensive, so a 500VA or even 2kVA wouldn't be ridiculous. Because the mains often has a DC component (which saturates cores easily), a bigger transformer would be better. Unless, you have one specially made, and ask for a gapped core to prevent saturation due to DC.

However, an isolation transformer won't do anything that a properly designed mains transformer in the equipment should do. It's penny-pinching that hardly any modern kit has an E/S screen on its mains transformer.
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Old 7th May 2003, 11:07 AM   #24
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Quote:
It's penny-pinching that hardly any modern kit has an E/S screen on its mains transformer.
Luckily DIY'ers don't have such a problem...All my transformers torroļdal or EI have such a screen



Quote:
However, an isolation transformer won't do anything that a properly designed mains transformer in the equipment should do
Wouldn't they give you an extra 40dB reduction in capacitive coupling of noise?

That said spec's aren't everything. I'll just wait till I strike the jackpot with some or other lottery before I kit out my house with Isolation transformers all round. Then again I might just get a moderate one and see what it does..There is no substitute for experience.

Regards,
Bas
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Old 7th May 2003, 02:25 PM   #25
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Hi Tim;

>>>...I highly doubt it's line noise...<<<

No offence intended, but the difference between better line isolation on my CD player was "night and day", literally. And it's not like I had a big investment one way or the other (thus no psychological imperative that "I paid a gazillion $$ on this thing so it BETTER work") - the first isofilter I tossed together was just a pair of RS 25.2VCT trafos and some AC rated caps - all of which were on a breadboard and all of which were 'recyclable'.

In that same vein, the addition of a 90 cent "X2" 250VAC rated, UL Listed AC mains filtering cap to the mains in of my 2A3 yielded an instant improvement in the sound. Again, if it's not line AC noise, I'm darned if I know why.

Hi Bas;

>>>...I'll just wait till I strike the jackpot with some or other lottery before I kit out my house with Isolation transformers all round. Then again I might just get a moderate one and see what it does...<<<

I'd love to read the results of that experiment! Just wish I could afford to try it over here!!

All the best,
Morse
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Old 7th May 2003, 02:34 PM   #26
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Hi Morse,

I'll keep you posted once it happens.

Regards,
Bas
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Old 7th May 2003, 04:52 PM   #27
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mrothacher says:

Quote:

I've always felt it was primarily the result of these effects:

1. Far less power line noise at these hours
2. Far less ambient noise at these hours.
3. Our auditory acuity peaks at night, and arguably more so in the critical midrange.
#1... OK. I agree to an extent. I once plugged my TV into a computer grade line filter. Picture seemed better. But... with capacitance in the power transformer (TVs nowadays use direct connected AC, no step down/up transformer), and 1.5H and up choke, and 20-100µF capacitance.... it is difficult for 60 or 120 Hz to get through, let alone the kilo to megahertz frequencies. I would argue that one. But it is possible.

#2... I agree moreso. During the day there is much disturbance in the force... uh... much noise around from cars and planes (I live about 5 miles from a private airport) and birds and neighbors. At night it is much quieter. Has the "feel" in the ears like being up in the mountains (Blue Ridge/Appalachains to be exact. Not too high up, just very quiet). Very quiet.

#3... very interesting. I did not know this.

Thanks for the input so far folks!
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Old 7th May 2003, 06:55 PM   #28
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Default CORNER CUTTING...

Hi,

Quote:
However, an isolation transformer won't do anything that a properly designed mains transformer in the equipment should do. It's penny-pinching that hardly any modern kit has an E/S screen on its mains transformer
This is oh so true....it seems that a lot of manufacturers try to save money by cutting corners in the wrong places.

For us. DIY or on demand maunfacturers , knowing how to specify a good transformer or having a good xformer manufacturer who actually knows his stuff can be crucial to the endresult.

For my own projects I always have them custom made and I've never regretted this approach one minute.

Benefits are:

-absulotely dead quiet.
-no excessive heat.
-good regulation.
-good isolation from the mains.

There is more to a good PSU than just that but it's a darn good place to start.

Cheers,

P.S. Fellow member Nania started a thread on powerxformers for audio about a month ago, have a look if you like.
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Old 7th May 2003, 07:04 PM   #29
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Ive seen it stated here that our audio acuity becomes better at night. Is the assertion that this is because it is night, or because we are subject to less noise allowing the acuity to grow.

Would 20 minutes in an NC-10 anechoic chamber have the same effect on our hearing?

If this is the case it would argue well for listening environments with greater outside noise isolation. NC-10 would be a bit too extreme. It would also argue well for preconditioning ourselves before critical listening.
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Old 7th May 2003, 07:14 PM   #30
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Default Re: Middle of the night bloom

Koinichiwa,

Quote:
Originally posted by Gabevee
Any thoughts, theories, opinions?

For those who don't know what I mean, it is a phenomenon that occurs when listening to our systems at night, from about 11:00 PM to 5:00 or 6:00 AM, where everything seems to sound much better and wider and deeper, etc.

It is simple.

Ever since I started to use circuits that keep DC out of my Mains Transformers and PSU circuits that really isolate from mains born noise, I have found the sound of the system to be VERY consistent. There may still be a slight variation with time of day, but in general, my magic hours have increased to about 24 out of 24 Hours....

Sayonara
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