haha there's one in every group. at least yer reading it! but a little too literal
(I meant post 19)
(I meant post 19)
Since when?
Hydrogenaudio Forums - Portal is the place to be when you want to take the sceptic aproach.
Well its very eazy to make cables sound different when using badly designed equipment. That´s why you measure first. If it fits the target curve, then you start doing listening tests. So dbt are benificial to both camps: Wanting to reproduce the input acurately or puting up pink sunglasses. Ofcause one of those groups don´t really trust science.
So are there properly designed soundsystems that could bennefit from exotic cables? NO (propperly designed means here designed to reproduce the input as acurately as possible with no audible artifacts)
Are there soundsystems that change their sound when changeing cables? Yes, but these systems produce loads of artifacts, witch could sound nice to some.
DC and other resistance is relevant because resistance helps damp any resonances. Amplifier transformers don't see a nice resistive load but a near open circuit for most of the time and a near short circuit for part of the time (when the rectifiers conduct). During the latter period the net effective resistance and leakage inductance play a role, together with stray capacitance.
If the transformer has a low resistance, then the mains lead resistance becomes more important. If equipment has good PSRR, good EMC performance, and good internal layout and wiring (e.g. no big loops) then I would expect different mains leads to make little difference. Otherwise, the resistance of the lead will affect the shape of the charging pulses and this will affect the DC supply and cause induction of mains harmonics into audio circuits. Note that this means that sensitivity to mains leads is a sign of poor design, not 'fine discriminatory' design.
If the transformer has a low resistance, then the mains lead resistance becomes more important. If equipment has good PSRR, good EMC performance, and good internal layout and wiring (e.g. no big loops) then I would expect different mains leads to make little difference. Otherwise, the resistance of the lead will affect the shape of the charging pulses and this will affect the DC supply and cause induction of mains harmonics into audio circuits. Note that this means that sensitivity to mains leads is a sign of poor design, not 'fine discriminatory' design.
I could not agree more, DF96. How is it possible for a length of cable to cause something, either by commission or by omission, that the ensuing power supply (=a full-fledged circuit with transformers, rectifiers, capacitors, chokes, ICs, tubes, transistors, and whatever else a designer might choose to use) cannot take care of??? Now if a power supply is poorly designed and/or implemented, that's where the fault and the blame are. A designer should shoulder all the responsibility and the wherewithal to make sure that their device operates with a perfectly stable, clean, imperturbable DC voltage all the time, come what may. Surely the electronics art can be relied upon to provide as much in Anno Domini 2011! If perchance they cannot, they should specify exactly what kind of cable is needed, make it so, and include it with the device.
Hi
Recently a maker of replacement mains leads in the UK was taken to the
Advertisng Standards Agency over claims that his cable helped reject RF
and so make equipment sound better. The agency hired someone to test out
the claims and the maker in turn hired out an "expert" to substantiate the
claim. The outcome was that the ASA upheld the complaint and directed
the maker to change his advertising.
Having seen both submissions Im not entirely sure that justice was done
but it did show that it is very difficult to prove or not whether design of a
mains cable can affect sound. I wonder if it would be a good thing
if other claims in advertising were challenged this way.
Recently a maker of replacement mains leads in the UK was taken to the
Advertisng Standards Agency over claims that his cable helped reject RF
and so make equipment sound better. The agency hired someone to test out
the claims and the maker in turn hired out an "expert" to substantiate the
claim. The outcome was that the ASA upheld the complaint and directed
the maker to change his advertising.
Having seen both submissions Im not entirely sure that justice was done
but it did show that it is very difficult to prove or not whether design of a
mains cable can affect sound. I wonder if it would be a good thing
if other claims in advertising were challenged this way.
twisted, or even better star quad for the AC could cut radiated magnetic field - maybe helpful with signal, power, player's, pre/amp's cords all jumbled together
also cuts RF suceptability - but except next door to a AM transmission tower I would'nt think it should matter for the power cable
conducted EMI/noise still needs filtering in the PS - ferrite on the power cord can sometimes help a little on common mode - maybe more useful with a "technical ground" setup
also cuts RF suceptability - but except next door to a AM transmission tower I would'nt think it should matter for the power cable
conducted EMI/noise still needs filtering in the PS - ferrite on the power cord can sometimes help a little on common mode - maybe more useful with a "technical ground" setup
That is way over simplified circuit theory. Do you care to look at conduction angle?
That wasn't the question. It was what is the actual winding resistance. A 750 watt stereo amplifier at full power with a large capacitor bank would try to draw 125 amps except for the inductance in the transformer and other losses, that will typically limit it to around 40 amps peak during the capacitor charge time. That is low enough it will not trip a 20 amp breaker.
But your power cord voltage loss would typically be .92 db. referenced to full power. That is with a decent cord and connector. Throw in wiring to the outlet and an extension cord and your loss could exceed 3 db.
Simon, you said "The power amp on my bench has a DC resistance of .6 ohms. That is less than the power wiring in many locations." That is what I was refering to. Also, losses in power cords are not maesured in dB.
Mike
Mike
(bwahahaha)
But what about unshielded ground wires.
They just sit there in the walls like AM antennas.
(end catalyst statement)
But what about unshielded ground wires.
They just sit there in the walls like AM antennas.
(end catalyst statement)
A dB is just a ratio, so any losses can be expressed in dB. I'm not sure I would use dB to express mains power losses, but there is nothing wrong in principle with this.
The resistance in the circuit is the only thing which damps resonances. Together with the transformer leakage inductance it limits the current rise rate when the rectifiers switch on. The incoming mains does not see a nice clean resistance, calculated from the average current draw. It sees a network of low impedance resistors, capacitors and inductors, with a switch being flipped 100/120 times a second.
The resistance in the circuit is the only thing which damps resonances. Together with the transformer leakage inductance it limits the current rise rate when the rectifiers switch on. The incoming mains does not see a nice clean resistance, calculated from the average current draw. It sees a network of low impedance resistors, capacitors and inductors, with a switch being flipped 100/120 times a second.
Not sure what point yer trying to make throwing all these random numbers around. You do realize what 3dB power losses amount to? using 3dB is unreasonable ie very lossy and hot branch circuit and /or power cord. I think using power efficiency would be better expressed here. And please don't mix transient start up and steady state conditions this has little to do with SQ.
I know that dB is a ratio, but in this case it was misapplied, try telling your local electrician there's a 3dB power loss at your outlet and see what kind of response you get. In the same vein, the engine in my car is rated for 126769 watts, but I wouldn't say it that way to the person behind the counter at the local auto parts store.
Mike
Mike
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Real simple. If you push a high power amplifier that is connected to an extension cord, it may only be able to produce 1/2 of it's rated power due to the AC supply line losses.
This has been observed and measured many times.
If you have a very small 250 KW power plant and want your losses to the 120 volt outlet to be less than 5%, what is the effective impedance of the power line?
Just read any high power amplifier review where they have to check the AC input voltage, or any of the numerous examples on this site. Or you could even hook up an amplifier yourself and look at the current draw. You could even look up cable resistance tables and see how high the extension cord losses are.
The actual current draw of amplifiers has also been posted before.
Losing half of the power in the power cord? Pure rubbish. Let's say your high power amp is rated for 500 watts. At full power and 60% efficiency it would draw around 835 watts, that would make the impedance of the power amp itself a little more than 17 ohms. To lose half the power the amp could deliver would then require the cord to have approximatly the same resistance. Now, if you own any cords that are like that, my advise is you throw them away, they are defective, and they are a fire hazard.
Mike
Mike
No the impedance of the stereo 500 Watt amp during the charging portion of the cycle is closer to 2 ohms.
You can lead a horse to water....
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