As you say the severity of outcome differs. If I think that polished stones and magnets can repair my broken leg, I may well end up permanently disabled. If I think that polished wooden cable supports at £50 a go improve my hifi, the only loss is to my bank account. Which is potentially false claims etc, but there you are. If 76% of a sample of 107 audiophiles felt it made their inky silences silenter and their hair visibly shinier, then crack on.
Don't let anyone tell you mains supply doesn't matter
- Thread starter kjb
- Start date
Message back:
"I'm having a couple of days off and staying off social media, please do me a favour and post this as a precis:
Malicious? Far from it. The note was a placeholder to a longer article pending some other data, which I now have. What does it mean for hifi? Nothing. For 3 reasons:
1. The power transformer is at line frequency.
2. The impedance will be stepped down according to the step down of the transformer squared, so a 24V secondary will have 1/100 of the impedance of the primary. This also holds for SMPS.
3. Reservoir caps are the actual supply to the internal circuitry.
A sensible designer designs for good PSRR, which makes power supply considerations irrelevant beyond it being actually broken or inadequately sized.
The 3 factors above render consideration of fuses impedance misguided."
I'm sure Martin can expand on this at his leisure if he feels the need.
Sue Pertwee-Tyr
Accuphase all the way down
Gracious of you.
mansr
Objectionist
Much better. In fact, I agree with all of that, and I apologise for the "malicious" remark. In an area infested by snake oil salesmen, it is all too easy to see ill intentions even where there are none.
Blackmetalboon
pfm Member
I am guessing your radial circuits are on 16A or 20A MCB’s? If they are on a higher rated MCB that would be an issue with hardwired mains leads to your equipment.
Cookers and showers are classed as stationary or fixed appliances. Due to their current rating (although some cookers are suitable for connection via a 13A socket) they are hardwired to a dedicated circuits as a domestic ring main is not designed to take such single heavy loads.
Hifi equipment would be classed as either a movable or stationary appliance, there are a couple of factors which will determine which class of appliance it falls under. Rack mounted equipment (fixed in a commercial rack) could be classed as a fixed appliance. All accessories (switched fused connection units, double pole switches, flex outlet plates etc..) that allow for hardwiring flex into also provide strain relief to prevent the flex from being pulled out of the accessory. How are your mains flexes connected to the circuits?
Isolating hardwired equipment, such as your hifi, means that the circuit should be provided with general isolation, emergency isolation and functional switching. While a MCB will technically give you all the above, under the circumstances we are discussing, I would consider it bad design. A plug and socket will give you general isolation and functional switching but not emergency isolation. There is a loophole where it’s is allowed but the circuit should not be designed to use it as a sole means of emergency isolation. In all the categories of devices for providing isolation there is not one mention of an IEC mains lead.
Arkless Electronics
Trade: Amp design and repairs.
Ah so Martin hasn't lost his marbles!
Yep I agree with all of that and it's just what I and all other people who know what they are talking about have been saying from the start (oh and on every such thread ever!)... and coincidentally what every book on electronics says!I wonder... do Mike and Steve et al have special books on electronics with chapter headings such as "Divination by cockerels entrails and it's importance in power supply design"?
Sue Pertwee-Tyr
Accuphase all the way down
Ah so Martin hasn't lost his marbles!
I wonder... do Mike and Steve et al have special books on electronics with chapter headings such as "Divination by cockerels entrails and it's importance in power supply design"?
I don't recall that being the title of my A level physics textbook, but it was over 40 years ago so I suppose it could have been, that being the Dark Ages and all that. And my memory of such things is a bit hazy, because I've never used the basic understanding I gained as to how a psu works, in Real LifeTM since school, so have largely forgotten what I knew. And I never mock you for not understanding the things I'm actually an expert (professionally) in, but it seems acceptable for the techs to do that to those of us who are less technically clued up
. Maybe it's that thing about geeks lacking social skills, or something. But if you're so inclined, I'd appreciate a little layman's explanation of something that does bug me. The power supply provides power to the voltage rails in the amp, and this is modulated by the signal to provide the output. That means, presumably, that the current draw on the 'demand' side of the psu modulates with the signal, similarly. Now I know that power comes from the reservoir caps, which discharge and are 'topped up' at every charging cycle (ie every 0.01 second). There's a degree of ripple, which can vary depending on the extent of the discharge for every cycle. Presumably, if the music signal is very dynamic and energetic, the reservoir caps are discharged a little deeper, so the top up has to be a little more powerful (and the ripple is of greater amplitude). Which suggests to me that the 'supply' side of the psu will also be modulated, at least to some degree, in keeping with the signal because it has to top up that little bit more on those particular cycles.
mansr
Objectionist
The amount of discharge between two 100 Hz top-ups depends on the power delivered during that time, not on the frequency of the output signal.
Joe Hutch
Mate of the bloke
I can promise that I will never theorise about physics or electricity, which to me is basically magic without playing cards or doves. I didn't even fail the O level; I wasn't allowed to sit the exam as my marks in the mock exam were so poor. We had brand-new textbooks for the O level course. Within days of getting mine, a bottle of ink broke inside my schoolbag and completely ruined the cover. Fortunately we were required to cover all textbooks with brown paper, so the mishap was never revealed. Until now.
Anyway, mains, as you were.
Anyway, mains, as you were.
Sue Pertwee-Tyr
Accuphase all the way down
Well yes, but it’s still modulated by the signal, just by the power in the signal, not necessarily the frequency.
mansr
Objectionist
It's modulated by the low-passed power of the signal. If the power varies at a high frequency, multiple peaks will occur between consecutive top-ups and appear as one to the transformer.
Darth Vader
From the Dark Side
..........and also the rating of the mains xformer and the reservoir caps........ Smaller ripple Voltage means higher input current via the mains xformer and rectifiers into a suitably robust electrolytic capacitor (can I say condenser?).
In case anyone is wondering although the DC pulses into the reservoir caps appears to be 0.01s it isn't! If you are providing say a 100V to the output devices at 1% ripple then the caps are only charged during that portion of time when the half mains cycle exceeds 99V and that is a mere fraction of 0.01s. Reduce the ripple further and you must increase the charging current = bigger, heavier and more expensive xformers and correspondingly associated rectifiers and condensers. My two power amps have between them 4 off 1.2KVA xformers ta daa! These amps weight in at 42Kg apiece and they are class AB not A!
Cheers,
DV
Arkless Electronics
Trade: Amp design and repairs.
And I never mock you for not understanding the things I'm actually an expert (professionally) in, but it seems acceptable for the techs to do that to those of us who are less technically clued up
But if you're so inclined, I'd appreciate a little layman's explanation of something that does bug me. The power supply provides power to the voltage rails in the amp, and this is modulated by the signal to provide the output. That means, presumably, that the current draw on the 'demand' side of the psu modulates with the signal, similarly. Now I know that power comes from the reservoir caps, which discharge and are 'topped up' at every charging cycle (ie every 0.01 second). There's a degree of ripple, which can vary depending on the extent of the discharge for every cycle. Presumably, if the music signal is very dynamic and energetic, the reservoir caps are discharged a little deeper, so the top up has to be a little more powerful (and the ripple is of greater amplitude). Which suggests to me that the 'supply' side of the psu will also be modulated, at least to some degree, in keeping with the signal because it has to top up that little bit more on those particular cycles.
I don't know what you do professionally Steve but I wouldn't continuously query even the most basic tenets of it on a pretty much daily basis and even after being told by not only yourself but several of your professional peers as well that what I was saying was complete nonsense!
You appear to have grasped the basics to some extent... but not the relevance of the various factors!
Before returning to it I'll pose a little homework for you; How come you don't hear the ripple?? I have an Onix OA21 on the bench right now and can tell you that even completely at idle (no signal) there is 100mV of ripple present on the smoothing caps. This should be VERY audible! Under load it will go up to probably a Volt or 3... There should then be a whole Watt of 100Hz buzz coming from each speaker then?
mansr
Objectionist
I thought it was implied that we were talking about a given power supply under varying load conditions. More generally, you are of course right.
Sue Pertwee-Tyr
Accuphase all the way down
If you can find where I've ever said what you said was complete nonsense, please show me because I don't believe that, so why would I say it? And if I challenge what is said by the techy side, it's because the explanations more usually granted to us are along the lines of 'because I said so'. Alternatively 'I can't be arsed going through this again, I've said all this stuff so many times before, saying it again won't make a blind bit of difference so I can't be arsed'.
Well, that bit's right, because saying 'because I said so' yet again, won't help one jot.
Well thank you. I do enjoy being patronised, that's the only reason I ask questions. I've no idea.
Is it my turn now, do I get to ask you what you think about the 'Five Chief Constables' case and its implications for the retention of criminal conviction records in the UK?
Sue Pertwee-Tyr
Accuphase all the way down
Does this not suggest, then, that the current pulses on the supply side will occur at frequencies considerably in excess of 100Hz. The spikes, of very short duration, surely represent a harmonic overlaid on a 100Hz 'carrier', or something broadly conceptually similar? Which is not what mansr said.
All these contradictory bits of wisdom. Is it any wonder we non-techies are confused?
mansr
Objectionist
It's difficult to condense years of education plus decades of experience into a three-line forum post.
Sue Pertwee-Tyr
Accuphase all the way down
Well sure, so when we speculate, or (as I did) ask questions to try to understand, we get fobbed off and patronised. And then we get told off for keep coming back with the same questions. It's because 'because I said so and I have years of experience which I can't explain to you' isn't a proper answer.
Is it?
mansr
Objectionist
Did I not try to answer your questions?