So, how does a standard amplifier power supply (tx-bridge-caps) actually kick junk back onto the mains ?.
I can see that the impulsive power draw (caps charging periods) will cause mains supply peaks flattening which could then affect/effect other items connected to the same mains circuit.
With snubbering of the secondaries, is there no oscillatory behaviour of the secondaries to feedback to the primary side supply ?.
With sec snubbering, does the transformer/primary appear as a resistive load during the charging periods, and only cause mains supply circuit IR losses/droops/flattening ?.
As I understand it, the sudden current demands and sudden current shutoffs causes half cyclic IR drop (no big deal), BUT also excites harmonic ringing in the mains supply system, due to parasitic reactance in the supply system.
So, this pulsed load ought not by itself present as a problem, except for real world conditions, ie MEN distribution system cabling and cable routing, including proximity to metals.
Ringing on the mains is a consequence/by product of the pulsed load, and it is this mains supply modulation that finds it way into audio gear.
Different mains leads could well change the coupling between the pulsed load and the reactive mains supply, and the (minor) changes in mains harmonics then affects/effects the other audio gear on the circuit differently.
Just ask Mark Johnson, the cure for ringing is snubbering...... at each connection/interface to the supply chain, ie amp mains input, wall socket, meter box breakers, street wire mains entry connection !.
The question is what snubber values across the mains are appropriate ?.
Has anybody tried any of this ?.
Dan.
I can see that the impulsive power draw (caps charging periods) will cause mains supply peaks flattening which could then affect/effect other items connected to the same mains circuit.
With snubbering of the secondaries, is there no oscillatory behaviour of the secondaries to feedback to the primary side supply ?.
With sec snubbering, does the transformer/primary appear as a resistive load during the charging periods, and only cause mains supply circuit IR losses/droops/flattening ?.
As I understand it, the sudden current demands and sudden current shutoffs causes half cyclic IR drop (no big deal), BUT also excites harmonic ringing in the mains supply system, due to parasitic reactance in the supply system.
So, this pulsed load ought not by itself present as a problem, except for real world conditions, ie MEN distribution system cabling and cable routing, including proximity to metals.
Ringing on the mains is a consequence/by product of the pulsed load, and it is this mains supply modulation that finds it way into audio gear.
Different mains leads could well change the coupling between the pulsed load and the reactive mains supply, and the (minor) changes in mains harmonics then affects/effects the other audio gear on the circuit differently.
Just ask Mark Johnson, the cure for ringing is snubbering...... at each connection/interface to the supply chain, ie amp mains input, wall socket, meter box breakers, street wire mains entry connection !.
The question is what snubber values across the mains are appropriate ?.
Has anybody tried any of this ?.
Dan.
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Attached is an FFT of the noise from a power supply. Odd order harmonics are created by transformer saturation. Even order harmonics are from rectification. The HF bounce is from the filter capacitor's resonance. This is passed by the transformer back to the AC line, limited only by the transformer's bandwidth.
I have lots more measurements but they pretty much all look like this whether you are measuring voltage or current before or after the transformer.
The AC source is a low distortion (.05% or less) power amplifier driven by an even better signal source.
I have lots more measurements but they pretty much all look like this whether you are measuring voltage or current before or after the transformer.
The AC source is a low distortion (.05% or less) power amplifier driven by an even better signal source.
Attachments
Thanks.
So MJ's secondary snubbering ought to reduce some of that ringing stuff ?.
Have you tried measuring what happens when snubbing is added ?.
Dan.
So what's up with that graph? Shouldn't the line frequency be referenced to 0dB with the resulting harmonics falling off to the right? Just wondering (or wandering!
).Mike
If -30dBV on that plot corresponds to 32 millivolts of unwanted "signal" on the power supply rail, and if the circuit being powered has modest PSRR of, let's say, 30dB, then the equivalent unwanted "signal" at the input is 1 millivolt. Big enough to completely swamp out a phono cartridge input, even a high output MM cartridge.
Conclusion: when building a preamp, use one or more stages of well-designed, well-implemented voltage regulator(s) to drop the mains noise significantly ... AND/OR design high PSRR circuitry, much higher than 30dB.
Conclusion: when building a power amp, apply additional filtering / regulation / capacitance multipliers to the first stage(s) to increase their PSRR ... AND/OR design high PSRR circuitry, much higher than 30dB.
Conclusion: when building a preamp, use one or more stages of well-designed, well-implemented voltage regulator(s) to drop the mains noise significantly ... AND/OR design high PSRR circuitry, much higher than 30dB.
Conclusion: when building a power amp, apply additional filtering / regulation / capacitance multipliers to the first stage(s) to increase their PSRR ... AND/OR design high PSRR circuitry, much higher than 30dB.
Mark,
Unbelievable (For this thread) you got it all right and I completely agree with your conclusions.
Please note a second R C stage can drop the power supply noise by easily another 30 dB. This should hint (like a sledge hammer to the side of the head) that preamp power supplies should have different designs than those for power amplifiers.
ES
Max, Mark's transformer resonance damping does do a nice job on ringing, but the converstaion here is on all noise being generated.
It also has hit me many are confused about the fuse resistance variation. To properly consider the fuses's contribution we only look at the other power line resistances and the load current. So if 15% of the total line resistances swing with load, we only need to know the load current to predict the swinging voltage drop. (I think the trolls are confusing the issue by mentioning inductance etc.)
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Let's try again:
What is the voltage drop across the fuse when the transformer is unloaded?
What is the voltage drop across the fuse when the transformer is loaded to rated maximum current?
What was the net effect of fuse heating on line voltage seen by the transformer primary?
What was the effect of the tiny change in resistance in the primary circuit, on the secondary voltage? How much does it differ from the same transformer without a fuse?
My answer to all of those questions is "hardly any at all".
Using a fast blow fuse of 5 amps in a 3AG size with a current surge of 24 amps for an full cycle current of 5 amps and an average current of 1 amp, the peak voltage drop is around 1.5 volts on the AC peak voltage of 170 volts. For a power amplifier this would be a 2% power loss. Measurable but in a well designed amplifier most likely not an issue.
However to do a well designed amplifier requires one to be cognizant of the issues. The same amplifier with a 2.5 amp time delay fuse would drop around 4 volts from the fuse and a bit more from the rest of the power source resistance. Possibly enough to hit a perceptible level.
So the actual design will determine what drop is a problem.
Now if you are doing a bench test to measure one of the last generation of monster amplifiers you had to be sure it actually was fed from the correct line voltage. The newer ones use switching power supplies, so that if the voltage drops the current increases to keep the power available to the inner guts constant.
Well if you worked on gear as badly designed as some of the stuff you might need almost magical cables. In your world there are these nice premade filters that work better than just the power cord filter. There also are EMI standards you have to follow. Most consumer gear is exempt and audiophile level never paid attention anyway.
If I get the chance I'll cite a few of them. But yes they are all audiophile. Who da thunk it. Oh you did.
Not all are pre-made filters, though I did point some to the nice Vicor and Picor filters which would be far cheaper than most audiophile products of a similar ilk.... A lot of filtering is done on board as layout is critical especially to avoid capacitive (and inductive) coupling of any noise across the filter.
Found this humerous pile...
http://www.lessloss.com/docs/QA-on-Skin-filtering-and-the-Idea-of-Power-Cord-Performance.pdf
Well Audio is real time and sensitive industrial gear isn't Hmmmmm! What a larf.
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Not filtering, loop areas etc. Jneutron has given us plenty of related info on this as well as others, its limiting the noise pick up. A good document added to my collection cheers.
I think Hans Polak's article in Linear Audio Vol 10 is also very much to the point here with his recommendation for One End Only in some circumstances.
Hans Polak, Pin 1 revisited, adding OEO to an accepted rule
https://linearaudio.net/article-detail/2239
Jan
Hans Polak, Pin 1 revisited, adding OEO to an accepted rule
https://linearaudio.net/article-detail/2239
Jan
I suspect H.Polak had another fault that responded to cutting off one end of the screen.
In a balanced impedance system the screen/shield should be connected to the chassis at both ends. The screens/shields are NOT part of the audio system, they are extensions of the enclosures.
I was skeptical this would work, but sprayed this stuff:
https://www.amazon.com/gp/product/B000BXOGNI
in the fuse holders of my speakers, I was amazed
at the improvement in micro details. Seems to last about
two weeks.
Watching a football game on my home TV system...now hearing the stadium announcer clearly, sound of the band ricocheting across the stadium, clearly hear QB calling signals, etc... None of these details were heard prior to this treatment, or they were very muffled and unintelligible.
https://www.amazon.com/gp/product/B000BXOGNI
in the fuse holders of my speakers, I was amazed
at the improvement in micro details. Seems to last about
two weeks.
Watching a football game on my home TV system...now hearing the stadium announcer clearly, sound of the band ricocheting across the stadium, clearly hear QB calling signals, etc... None of these details were heard prior to this treatment, or they were very muffled and unintelligible.
Goiing to the thread title, I was thinking the best fuse for audio is the same one I use for my Little British cars. ATO. So you have a large surface area, and only the two end mechanical contacts. I have actually seen fuses in my lab with oor internal connection. Of course limited in values, and only fast-blow.
The way I understand this to work is Vcm is being shunted away from the receiver thru the shield, thru the 3.3nF caps, and back to the signal source? Interesting. I'll have to try this.
Note: The spray treatment also helps on the power cable connectors (to a lesser degree)
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