another power conditioner thread

[unheardof]

I just finished reading an article on power conditioners in the latest issue of EQ magazine (which I only read because I get it for free). When I got to the end I realized it was written by none other than Garth Powell of Furman Sound.

Now I fully understand the importance of surge supression, but what I can't understand is how any noise in your power would even make it to your audio circuits. Provided you have big enough PSU filter caps, how could noise in your AC have ANY effect on your audio? Am I missing something?

Oh, and can anyone recommend a good surge supression circuit that would be cheap to build?

 

[alk509]

[quote author="unheardof"]Provided you have big enough PSU filter caps, how could noise in your AC have ANY effect on your audio?[/quote]

Just guessing here, but maybe because of the large PSU caps (which have a little leakage inductance) high frequency crap gets to circuits? Now, how does HF crap gets through the power transformer in the first place? Lemme guess: it couples itself capacitively from primary to secondary?

Power supplies themselves can have a measurable effect on the final sound and noise level of a unit, but the stuff that comes through the wall, I have no idea... Having said that, something obviously is getting into circuits, or computer power cables wouldn't have those big chokes near the end...

I'm sure someone who actually knows what they're talking about will be with you shortly ...

Peace,
Al.

 

[unheardof]

[quote author="buttachunk"]If wall voltages run low, little 78XX/79XX power regulators can turn into noise generators. if you want to hear what dirty power sounds like, rent an older portable AC generator. :shock:[/quote]

Interesting... do other voltage regulation circuits, used instead of IC regs, have the same problem? And how low are we talking about here?

And Al, thanks! Valiant effort! :wink: Kidding, I think you are on to something with the leakage. But couldn't you get rid of that with a small cap in parallel with the large cap? Sure seems a lot cheaper than a huge power conditioner designed to remove all noise from the AC line.

I was also wondering about noise getting into your gear via the ground prong. Is this a concern?

I just remembered I have an "EMI Line filter" that I pulled out of an old scientific/medical device a while back. I wonder if it might be useful in a preamp or something. I'll check out the specs and see how much power it can handle.

 

[alk509]

[quote author="buttachunk"]since noise is a major factor in audio, the AC line must be as smooth and clean as possible.[/quote]

That's the question, though: Why? How does the crap in the AC line get past a power transformer with dismall frequency response above ~200-300Hz, a bunch of big caps shunting it to ground, 60 or so dB of reduction by a regulator, and whatever PSRR the circuit itself has?

Peace.
Al.

 

[sodderboy]

Even though AC in is hitting a transformer, the AC signal itself is unbalanced. The neutral is not an inversion of the hot but the signal return. Which is connected to Ground in the breaker box.
So noise on the power line can get into the chassis and signal returns of unbalanced audio signals.
This is especially apparent in large MIDI or semi-pro installs.
That is why it can be a help to install balanced AC. It is the same as balancing audio- where you have a balanced 120 or 240 VAC output, and ground is the center tap, just like a 20-0-20 type PSU transformer. It is a big transformer rated for so many VA. The result is true cancellation of noise into equipment PSU transformers.
I have found that it is a good solution for smaller installs, and I sometimes use one in home theater jobs where there are tons of SCR type dimmers up the AC line. Right? Just try to explain to a client that they need to have variac dimmers instead of a SCR dimmer controller!

The SCR dimmer is the recording studio's nightmare as far as dirty power is concerned. It backs-up harmonic spike sewage onto your sine wave! Especially when in between 0 or 100% brightness.
I'll dig around for some links or docs on this :grin:

 

[rafafredd]

The BEST way to run power in a studio is to regenerate a clean 60hz sine wave, free from external interference.

Come on. It´s not practical...

Do you really do like this?

I´ve seen audiophiles doing it for small home hifi systems.

 

[alk509]

Butta,

I understand all that. But assuming that image is an actual measurement of AC, notice that all the noise present in it is of much higher frequency and much lower level than the AC itself. So what I'm wondering is, how does it get past a power transformer, enough capacitance to pretty much kill 120Hz, a voltage regulator with around 60dB of ripple rejection, whatever extra filtering the circuit may have, and the circuit's own PSR? I'd just like to see some numbers, you know what I mean?

(I think) I can hear a difference when I use faster rectifiers than the standard 1N400X in power supplies, so **** can get through. But ideally what I would like is some numbers, a description of the mechanism by which it happens, and an explanation of how a power conditioner improves the numbers.

Peace,
Al.

 

[sodderboy]

Butta,
the only times I saw line voltage look like that was when I was using a bad neutral ref. for the scope. SCR's put a single, ringing spike on the leading edge of the AC sine. What you are showing is a pretty picture, but not found easily at anyone's outlets. It indicates a problem with electrical wiring perhaps, but not of real-world AC borne noise.
Al- check this out
http://www.equitech.com/articles/bpng.html

It shows and explains the unbalanced AC problem much better than I did before! :?
Mike

 

[bcarso]

Another thing too: take a look at your local outlet a.c. waveform on a scope (be careful to identify hot before inadvertently clipping something tied to safety ground to it!). If it looks sinusoidal you are a lucky and rare exception to the typical.

Most times now the positive and negative peaks are severely clipped due to lots of cap input power supplies loading the line, especially the ones that rectify the line immediately with a bridge or doubler, before high frequency switching through a transformer provides isolation.

The result of this is that a piece of equipment anticipating a sinusoid to provide the peak value of square root 2 times rms and then be rectified and filtered for your equipment needs, will suffer a considerably lower d.c. unregulated output, maybe one right on the verge of your regulator dropout.

 

[sodderboy]

[quote author="bcarso"]Another thing too: take a look at your local outlet a.c. waveform on a scope (be careful to identify hot before inadvertently clipping something tied to safety ground to it!). If it looks sinusoidal you are a lucky and rare exception to the typical.
[/quote]
Folks, ground-lift those scopes!!! This test has burned many a scope probe. At the least. You really should mod a power cord to get AC to a scope in a controlled, safe, tech-stylee.
OT, I had a 3 prong AC cord out to alligator clips tucked away in a studio shop. I came one Monday and those clips were MELTED and charred. My little experimenter never surfaced. . .
I get good sine just about everywhere. AT the breaker box. Down-line is different, and is why we exist as techs. Exceptions include fat-cat waterfront in the US and almost everywhere in the Carribeen. Commercial and residential boxes in UK and Europe has been spot-on in my limited experience.

I just searched g**gle for "AC line noise" and found tons of info. Not sure if any of it is white sheet caliber though. Look around.
Mike

 

[bcarso]

[quote author="sodderboy"]OT, I had a 3 prong AC cord out to alligator clips tucked away in a studio shop. I came one Monday and those clips were MELTED and charred. My little experimenter never surfaced. . .

Mike[/quote]

AC cords with clip leads are about the most dangerous accessories in the lab!

I remember a guy in a physics lab at UCLA who severely damaged the only decent scope they had. He said he wanted to get a signal on the screen so he used the line cord with clip leads, clipped to the shell of the BNC jack and to a wire in the center pin, and plugged in the a.c. cord....

It took a big ugly chip out of the jack before the breaker blew, and the jack was a muy expensive custom one from Tek. The guy who worked with him, my friend Shelton, since those days moderately famous for work on adaptive optics, had to do the repair so he could use the scope. A bit later the two of them got into a fairly damaging fistfight :shock:

 

[CJ]

Power line considerations and the equipment to handle them have been around for many years.

Where do you want to jump in?
Todays technology will probably be difficult to understand.
I suggest you start from the beginning and work your way up for a complete understanding of power quality and the way it has changed over the years.

You could easily write a thesis on this subject.

We use a sine wave generator here, but that's only because the waveform at our old building was bad, and someone was stamping fenders down the street.

K-bang--- K-bang---which caused huge voltgae sag spikes evertime the press came down. Or whatever it was.
The new building is much betrter, but we still use the auto variac into the generator for a clean, non distorted and regulated sine wave.

 

[unheardof]

CJ,

Sounds like you have a great power setup there, but I don't think it would be practical (or maybe even necessary) for most low budget project studios in residential areas.

I'm not really interested in learning the whole history of power quality. Actually, I am, but unfortunately I don't have the time. What I would really like to know is if AC line noise can really get past all of the filtration in a well-designed PS and affect the audio. If so, how, and to what extent?

From what some of you are saying, it seems the biggest concern for audio gear is not so much low-level AC line noise, but spikes and power surges or brownouts. What is the most practical and affordable way for dealing with this? What DIY solutions are available?

 

[CJ]

Look at the frequency rainbow.
When is ac capable of wireless transmission?
My AM dial starts at around 600 K CPS.
I have measured transformers that will pass this.
I think there are some hammies below that.
Whats 10 Meters translate to?


You think all the upper harmonics of a 15 K CPS note are confined to the wiring of your preamp?

If things are real bad, there is no supression circuit in the world that will help.
I used a cheap switcher and a car battery to run a JVC tape deck recently.
Sounded like a herd of killer bees heading up the road.
The square wave and it's associated array of spikes, transients and damped harmonics infiltrated every part of that deck.
The buzz was 50 db louder than the signal I was after.

So can you use a switcher in audio?
Of course!
A high quality model and about ten pounds of mu metal, so you end up at the same place and price as an analog supply, so why bother?

 

[CJ]

I haven't read this yet. It looks cool. Tell me if it's any good.
cj

http://vacuumbrain.com/The_Lab/TA/Power_Supplies/condition_2.jpg
http://vacuumbrain.com/The_Lab/TA/Power_Supplies/condition_3.jpg
http://vacuumbrain.com/The_Lab/TA/Power_Supplies/condition_4.jpg
http://vacuumbrain.com/The_Lab/TA/Power_Supplies/condition_5.jpg
http://vacuumbrain.com/The_Lab/TA/Power_Supplies/condition_6.jpg
http://vacuumbrain.com/The_Lab/TA/Power_Supplies/condition_7.jpg

 

[Kit]

OT, I had a 3 prong AC cord out to alligator clips tucked away in a studio shop. I came one Monday and those clips were MELTED and charred. My little experimenter never surfaced. . .

Haha.
Reminds me of that time i fixed a broken "switcher" weld at work.
The feedback circuit for the regulator was broken and after fixing it i decided to test the weld. Unfortunitly, we didnt have any welding-pins at the shop, so i figured i would just mesaure the output with my multimeter. :roll:

Snap, crackle and pop.....
Learning by breaking.

 

[Rob Flinn]

In the Handbook for sound engineers(modern edition) by Glen Ballou there is quite a good section on power conditioning. It has quite good discussion on the benefits or lack of.

From memory I believe it says that depending on where you put it in the chain determines it's effectiveness. I think it says in some places they are a waste of time. It also says that some power conditioners don't really work too well at all.

 

[bobkatz]

I just bought a Topaz transformer from Skycraft Surplus. $125 for a new condition 2.5 kva transformer. It looks like it's never been used. 120 or 240 in and out with electrostatic shield on each winding. There's another one there if anyone is interested. The nameplate is off of it, however, I have no idea why, so I'm curious what the capacitance rating between the windings is.

Is it just a matter of putting my capacitance meter between primary and secondary windings?

BK

 

[bobkatz]

[quote author="bobkatz"]I just bought a Topaz transformer from Skycraft Surplus. $125 for a new condition 2.5 kva transformer. It looks like it's never been used. 120 or 240 in and out with electrostatic shield on each winding. There's another one there if anyone is interested. The nameplate is off of it, however, I have no idea why, so I'm curious what the capacitance rating between the windings is.

Is it just a matter of putting my capacitance meter between primary and secondary windings?

BK[/quote]

I don't want to be obnoxious, so if you already saw my post, I deeply apologize... so does anyone know how to measure interwinding capacitance? Just use a capacitance meter?

BK

 

[PRR]

> Is it just a matter of putting my capacitance meter between primary and secondary windings?

Should tell you something. Shouldn't matter which lead you use. Should matter how you ground the core or shield.