Why digital seems to be affected by power and cables

[Zaphod Beeblebrox]

Is your wife into shoes?

Mine collects orchids. I built her a couple of orchid houses and, most recently, a raised deck just for her plants. I am, therefore, able to justify quite ridiculous amounts of money to be spent on woodworking tools. Test equipment is slightly easier to justify.

[Steved]

Mine collects orchids. I built her a couple of orchid houses and, most recently, a raised deck just for her plants. I am, therefore, able to justify quite ridiculous amounts of money to be spent on woodworking tools. Test equipment is slightly easier to justify.

OK, confide in her that  you are actually getting the bits together for your time machine.................  

Edited February 23, 2016 by Steved

[CraigS]

<off topic> = on

 

Oh - woodworking tools.  Apart from collectomania with test equipment, I also have a pretty fully equipped woodworking shop.  I did a couple of months training in cabinetmaking about 6 years ago - but all the capital expenditure is done.

 

The other collecting thing is slide rules.  And fountain pens.  At least they don't take up much room.

 

In fairness, most of the collecting thing is over and done - there is very little I either want or need in any of those now.  What I am really concentrating on is off-shelving a whole bunch of electronics and woody projects which are part finished.  I have a great tendency to start something, and then something else etc "ooh shiny!"

 

Mrs S is not a collector.  Doesn't have much time for it anyway as CEO of a significant charity http://www.brendoncare.org.uk/ .

 

<off topic> = off

[BioBrian]

Slightly back towards topic, does anyone have comment on Jaycar's WB1508 Electus mono shielded cable? It's core is 45 strands of 0.12 mm^ OFC, and the shield is a copper braid and aluminium foil.

 

Is it any good for

 

 - Digital spdif?

 - Analogue ICs?

 

 

I've recently tried RG6 for digital spdif, and it appears to work better, but not sure...

 

[CraigS]

At an impedance of 65 ohms, it is not a good match to the 75 ohms of SPDIF, which is possibly why RG6 works better.

 

Double shielding (braid *and* foil) is a good thing; see http://www.rane.com/pdf/ranenotes/SCIN_Shield_Current_Induced_Noise.pdf

 

Vis a vis SPDIF cables - longer is better.  If (as is usually the case) there is an impedance mismatch, a long cable will give reflections that are later than the transition time.  Reflections in and close to the transition time cause jitter.

 

Think about it - suppose the transition time is about 10 ns 10-90% (which is typical).  The time for a reflection to get back is twice the length of the cable at the speed of light, slowed down by the cable itself.  Suppose you have a typical 1 metre cable.  Round trip time is 6ns times cable factor, so around 10ns, bang where you don't want it.  If you make the cable 3 metres long, the reflection will come back about 30ns later, so well away from the transition and out of harms way.

[Red MacKay]

So that is the reason a longer digital cable is more desirable.  Thanks.

 

What about losses etc from 3 times your typical digital cable length?

 

It is such a small signal, how do those losses stack up vs no reflection in transition time?

 

What is usually the best compromise here?

[Red MacKay]

No, they are not. Power cable differences are utterly insignificant.

 

I'm sorry, I can't agree with you in that one.  Power cables can make quite a difference, but not in every system, imho.

[CraigS]

The glib answer is that there is no downside to increasing length of a digital cable.  Of course that breaks down ultimately if the cable is sufficiently long (a hundred metres or so) and the frequency sufficiently high (order 1GHz) - cable type dependent of course.

 

Just as an example, RG6A/U has an attenuation at 100MHz of 9.5dB per 100 metres (just from the spec sheet).  So a 3 metre length has an attenuation of 0.28dB, which is entirely insignificant (3%!).

 

Why have I picked 100MHz?  100MHz corresponds to 3.5ns, so faster than the vast majority of SPDIF rise times.  And even so the 3% attenuation at that frequency of a 3 metre cable is insignificant.  If it was not so, CATV would not work, and your FM radio antenna on the roof wouldn't work (both of which use RG6A/U cable)

Edited February 23, 2016 by CraigS

[BioBrian]

Thank you Craig!

 

Edit - more testing needed

Edited February 23, 2016 by BioBrian

[CraigS]

I'm sorry, I can't agree with you in that one.  Power cables can make quite a difference, but not in every system, imho.

 

See my much earlier post regarding RF pollution entering equipment via the mains.  Which means that it is location dependent and cable dependent.  Someone living in the sticks is probably in good shape for RF, but someone living in a city or suburbs receives a vast amount of RF garbage on the mains, made much worse by powerline ethernet which spew all sorts of wideband garbage into the mains - and then there is CFL and LED switched mode supplies....I could go on.

 

This is an effect that is fundamental and well-known to precision measuring instrument makers.  I got involved in this quite some years back on a device called a Cryogenic Current Comparator Resistance Bridge, in which currents are compared using SQUIDs. This beast http://www.npl.co.uk/electromagnetics/electrical-quantum-standards/products-and-services/cryogenic-current-comparator .  To get mains borne garbage low enough, first there was a double shielded isolation transformer mounted through the bulkhead.  After that was a triple box shielded toroid in three nested shielded cases.  Through careful construction the interwinding capacitance was less than 1pF.  Nothing got through that.

 

But in the real world of audio where rather simple (for cost) mains processing is used with interwinding capacitance of up to 100nF. To run through why mains cables are important - anything RF that gets into the casework of your audio gear radiates in there and is picked up and demodulated by every semiconductor junction.  Ever heard your mobile trying to seek a station and heard Zzt-zzt-zzt?  That is 800MHz getting into your audio gear and being heard by precisely that effect.  Mains inlet filters are useless, since they are only specced to 30MHz, and mains RF extends to GHz (powerline ethernet, for example).  

 

The problem is that a mains cable operates in a mismatched impedance environment.  It matches neither the installed cabling in the walls, nor the complex and time-dependent impedance of the power supply in audio gear.  Looked at as a transmission line, you get a comb filtering effect, where the frequency spacing of the comb depends on the electrical length of the cable.  So - depending on where the principle interfering frequencies are, and the electrical length of the cable, you can fortuitously get a match between a comb frequency null and that interfering frequency.  Which explains perfectly why different people swear by different mains cables.

[Martykt]

I must say @@CraigS your additions have been invaluable in this discussion.

The biggest question/issue most people have when dealing with power cables is that "How can the last metre make a difference when you have x metres of cheap cable in your walls?". The best answer that I have had till now was the theory that the metre or so coming out of the amplifier or component kind of acts like an antenna.

While this is obviously a simplistic explanation for what is going on, you have managed to help expand and clarify my knowledge here.

Can you please expand on how we can use this information in the real world audio situation in regards to power cables and their impedance and capacitance properties. I would like to hear your opinion on shielding in power cables and braided or twisted cables to cancel rf.

I'm also curious to know more about the double shielded isolation transformer you talked about and what possible DIY options may be beneficial and possible?

I too have heard the difference in power cables and while understanding what is happening is difficult to say the least, hopefully this extra information can help us to take more objective approaches father than trial and error when building the power sections of our systems.

[BioBrian]

And Craig, can you suggest anything we can do about hum from amplifier transformers, which I am told is caused by DC in the 'mains'?

[andyr]

And Craig, can you suggest anything we can do about hum from amplifier transformers, which I am told is caused by DC in the 'mains'?

 

Small power transformers like source components generally have (up to 160VA) generally don't show mechanical hum from the transformer itself.  Rod Elliott has an explanation for this on his web-site.

 

However, large power transformers in power amps having linear power supplies can certainly buzz - and, yes, it appears a DC component on the AC mains is the problem,  The culprits (producing the DC) can be a number of things - your (or your neighbour's) solar power inverter ... and SMPSes powering washing machines / routers / PCs / TVs / Foxtel boxes / wifi devices ... .

 

You can stop DC getting into your power amp(s) by plugging them into a 'device' which is then plugged into the wall-socket:

1. a 1:1 isolating transformer, or
2. a DC blocker.

The problem with #1 for a power amplifier - if it's 100w or more - is that the transformer needs to be a big one, so that it doesn't restrict the power flow into the amp.  Big transformers are a. physically large and b. expensive.  You would need to experiment whether the isolating transformer had a negative effect on SQ which outweighed the benefit of removing the transformer buzz.  I would suggest you'd need a transformer which has a minimum of 10x the VA rating of the amp, to not get any current restrictions.

 

So #2 is probably more appropriate for power amps.  Rod Elliott has a design on his web-site which @@guru used as the basis for his product (as I did).  With the correct choice of parts, these can pass 10a continuous - so they should be appropriate for most power amps out there.

 

 

Regards,

 

Andy

Edited February 24, 2016 by andyr

[CraigS]

It is 1am here, so I'm a bit bushed.  But you don't need DC on the mains to make a transformer hum.  

 

If the transformer has been built either with the winding pack or core laminations "loose" - by which I mean the wires are not properly stuck together, the wires or core laminations can flap around and cause a buzz.  

 

The other main cause are imported goods from the US, where the mains frequency is 60Hz.  If the transformer has been designed for 60Hz and you then use it at 50Hz (like Aus and UK) the core is operating with 60/50 times (ie 20%) more flux, which can push a core into non-linear behaviour.  Now a core in its linear region generates sound via magnetostriction (any core material does this) - but at 50Hz, which you can't hear.  But if pushed into non-linearity with too much flux it generates harmonics of 50Hz - so 100, 150, 200 Hz etc - which you definitely can hear as a buzz.

 

I had an Audio Research valved power amp, and earlier a Krell, in which the mains transformers buzzed because of precisely that reason.  I had the Audio Research amp on the same rack as the record deck, and with the stylus sitting on a record without the record rotating there was an irritating buzz.  The mains transformer in the power amp was vibrating so much it was coupling through the rack to the deck.  Banishing the amp to a different rack entirely cured the problem straight off.

 

But I have a massive fan cooled 1kW professional amp, made in the UK with a truly huge toroid that buzzes like crazy - and that falls into the category of loose winding pack or core laminations (so a faulty transformer).

 

But DC on the mains doesn't help for sure - this is usually caused by 2nd harmonic distortion on the mains - so each cycle top (or bottom) is flattened.  But distorted mains, whether generated by 2nd harmonic or not is not a good thing - because the harmonics will cause core buzz via magnetostriction.  I measured my mains by using a small transformer and hanging my distortion analyser on the secondary, and got 2% during the day and 0.6% at night.  I suspect that is why some transformers buzz more during the day than at night.

 

The other approach is to overrate the transformer.  I get mine made by a guy called Paul Houlden - last ones were UKP90 each for 2-off custom multiwinding 750VA toroids to my spec.  He does an ultralow noise audio option which are truly silent - well you can hear a slight hum if you press your ear onto the transformer itself, but that is all.

[CraigS]

Small power transformers like source components generally have (up to 160VA) generally don't show mechanical hum from the transformer itself.  Rod Elliott has an explanation for this on his web-site.

 

However, large power transformers in power amps having linear power supplies can certainly buzz - and, yes, it appears a DC component on the AC mains is the problem,  The culprits (producing the DC) can be a number of things - your (or your neighbour's) solar power inverter ... and SMPSes powering washing machines / routers / PCs / TVs / Foxtel boxes / wifi devices ... .

 

You can stop DC getting into your power amp(s) by plugging them into a 'device' which is then plugged into the wall-socket:

1. a 1:1 isolating transformer, or
2. a DC blocker.

The problem with #1 for a power amplifier - if it's 100w or more - is that the transformer needs to be a big one, so that it doesn't restrict the power flow into the amp.  Big transformers are a. physically large and b. expensive.  You would need to experiment whether the isolating transformer had a negative effect on SQ which outweighed the benefit of the removal of the transformer buzz.  I would suggest you'd need a transformer which has a minimum of 10x the VA rating of the amp, to not get any current restrictions.

 

So #2 is probably more appropriate for power amps.  Rod Elliott has a design on his web-site which @@guru used as the basis for his product (as I did).  With the correct choice of parts, these can pass 10a continuous - so they should be appropriate for most power amps out there.

 

 

Regards,

 

Andy

 

I agree with the isolating transformer - often also set up to make balanced mains.  But they do need to be several times higher VA rating than the amplifier power.  And alas they too can buzz! (been there, got the badge).

 

Interesting article on Rod's site.  With the proviso that you need to know what you are doing monkeying around with mains gizmos.  I clearly don't need one with Paul's transformers which are silent as the grave, but it might have helped with the wayward Audio Research or Krell power amps (both now sold - so someone else's problem!).

[Guest Eggcup The Daft]

See my much earlier post regarding RF pollution entering equipment via the mains.  Which means that it is location dependent and cable dependent.  Someone living in the sticks is probably in good shape for RF, but someone living in a city or suburbs receives a vast amount of RF garbage on the mains, made much worse by powerline ethernet which spew all sorts of wideband garbage into the mains - and then there is CFL and LED switched mode supplies....I could go on.

 

This is an effect that is fundamental and well-known to precision measuring instrument makers.  I got involved in this quite some years back on a device called a Cryogenic Current Comparator Resistance Bridge, in which currents are compared using SQUIDs. This beast http://www.npl.co.uk/electromagnetics/electrical-quantum-standards/products-and-services/cryogenic-current-comparator .  To get mains borne garbage low enough, first there was a double shielded isolation transformer mounted through the bulkhead.  After that was a triple box shielded toroid in three nested shielded cases.  Through careful construction the interwinding capacitance was less than 1pF.  Nothing got through that.

 

But in the real world of audio where rather simple (for cost) mains processing is used with interwinding capacitance of up to 100nF. To run through why mains cables are important - anything RF that gets into the casework of your audio gear radiates in there and is picked up and demodulated by every semiconductor junction.  Ever heard your mobile trying to seek a station and heard Zzt-zzt-zzt?  That is 800MHz getting into your audio gear and being heard by precisely that effect.  Mains inlet filters are useless, since they are only specced to 30MHz, and mains RF extends to GHz (powerline ethernet, for example).  

 

The problem is that a mains cable operates in a mismatched impedance environment.  It matches neither the installed cabling in the walls, nor the complex and time-dependent impedance of the power supply in audio gear.  Looked at as a transmission line, you get a comb filtering effect, where the frequency spacing of the comb depends on the electrical length of the cable.  So - depending on where the principle interfering frequencies are, and the electrical length of the cable, you can fortuitously get a match between a comb frequency null and that interfering frequency.  Which explains perfectly why different people swear by different mains cables.

I'm trying to get my head around this.

What you appear to be saying, is that mains borne interference can only be treated at the power supply at great expense.

Also that there may be an effect from a mains cable wouldn't come from things like shielding or special materials, but simply a fortuitous impedence match to something else  (and even then, if it's the power supply, only some of the time). 

 

So, questions.

Firstly, how much would you say it would cost to actually isolate an audio product from these effects? Am I being unrealistic in expecting proper power management (assuming it's necessary) in an amplifier at a retail price of, say, $2000? $20000? $200000?

 

Secondly, does using a screened lead - or any of the other exotic construction methods used in "audio" power leads - make any difference to what you are describing? You seem to be simply talking length and impedence.

 

Thirdly, could this effect happen, benefically, elsewhere - for example in a length of cable between a mains socket and a powerboard to which audio equipment is attached, or even between another device that may be outputting a problem frequency and its attached mains outlet? in other words, is the power lead to an item of audio equipment "special"?

 

Fourthly, is it necessarily luck? Could a mains cable manufacturer reliably make a cable to always "match a comb frequency null to a common interfering frequency" no matter what the impedence mismatch is? 

 

Finally, what are the chances of this sort of thing actually being audible? Can cancelling one common frequency make a difference in a mass of RF garbage? And wouldn't airborne RF garbage be a bigger issue?

 

Sorry if this seems a lot to ask, but as a regular consumer, I'd prefer to be trusting to engineering, than "fortuitous" effects,,,

[Zaphod Beeblebrox]

See my much earlier post regarding RF pollution entering equipment via the mains.  Which means that it is location dependent and cable dependent.  Someone living in the sticks is probably in good shape for RF, but someone living in a city or suburbs receives a vast amount of RF garbage on the mains, made much worse by powerline ethernet which spew all sorts of wideband garbage into the mains - and then there is CFL and LED switched mode supplies....I could go on.

You could, BUT, I see a major flaw in this argument. Let me first state that it is possible (but highly unlikely) for any RF to enter (and cause problems) a product via the mains supply. IME, the vast majority of RF interference problems occur via speaker cables, through the global NFB system of amplifiers.

Anyway, back to the issue of RF interference entering an audio device. The difficulty I have is that 2 Metres of mains cable is diddly-squat, compared to the dozens of Metres of unshielded cables within the home, which is then connected to the dozens of km of cable between the home and the nearest sub-station. Certainly, RF will be impressed upon all this stuff, but, in the vast majority of cases (probably all) that RF will be severely attenuated by the inductance of the mains wiring itself. A low loss cap and, perhaps a common mode inductor should mop up anything that remains.

Mains power cables make no difference whatsoever. Ever.

I invite any listener who imagines that there is a difference, to subject themselves to a double blind test. I doubt that any will.

[EDIT] Just to add my experience into the mix:

Many years ago a mate lived in a suburb not far from one of Sydney's larger TV transmission towers. Frame buzz permeated his system. The only cure was found to be to use shielded speaker cables. This almost completely eliminated the problem.

Many years later, I was called to a client's home because he had problems with his system. He lived across the road from the same TV transmission tower. Even shielded speaker cables failed to eliminate the problem. Many different amplifiers were tried. Some, better than others. I offered to try a zero global NFB amplifier. Problem solved. He didn't even require shielded speaker cables.

Edited February 24, 2016 by Zaphod Beeblebrox

[Slartibartfast]

Reminds me of a VHF oscillation problem that I was trying to solve in an power amplifier. It was only after several hours when I'd given up and switched off the amp that I noticed that the waveform was still visible on the cro, albeit at reduced amplitude, and it dawned on me that I was looking at AM television RFI

 

Problem was solved by inserting a ferrite bead on the vas transistor emitter,which limited the gain above 40MHz.

 

The need for the bead only existed because the star earth traces were sufficiently long enough to act as antennas. Also, mkt film caps used for HF  bypassing are next to useless at VHF.   

Edited February 24, 2016 by Slartibartfast

[Zaphod Beeblebrox]

Reminds me of a VHF oscillation problem that I was trying to solve in an power amplifier. It was only after several hours when I'd given up and switched off the amp that I noticed that the waveform was still visible on the cro, albeit at reduced amplitude, and it dawned on me that I was looking at AM television RFI

 

Problem was solved by inserting a ferrite bead on the vas transistor emitter,which limited the gain above 40MHz.

 

The need for the bead only existed because the star earth traces were sufficiently long enough to act as antennas. Also, mkt film caps used for HF  bypassing are next to useless at VHF.

That's why God gave us cheap and cheerful ceramics.

[CraigS]

I'm trying to get my head around this.

What you appear to be saying, is that mains borne interference can only be treated at the power supply at great expense.

Also that there may be an effect from a mains cable wouldn't come from things like shielding or special materials, but simply a fortuitous impedence match to something else  (and even then, if it's the power supply, only some of the time). 

 

So, questions.

Firstly, how much would you say it would cost to actually isolate an audio product from these effects? Am I being unrealistic in expecting proper power management (assuming it's necessary) in an amplifier at a retail price of, say, $2000? $20000? $200000?

 

Secondly, does using a screened lead - or any of the other exotic construction methods used in "audio" power leads - make any difference to what you are describing? You seem to be simply talking length and impedence.

 

Thirdly, could this effect happen, benefically, elsewhere - for example in a length of cable between a mains socket and a powerboard to which audio equipment is attached, or even between another device that may be outputting a problem frequency and its attached mains outlet? in other words, is the power lead to an item of audio equipment "special"?

 

Fourthly, is it necessarily luck? Could a mains cable manufacturer reliably make a cable to always "match a comb frequency null to a common interfering frequency" no matter what the impedence mismatch is? 

 

Finally, what are the chances of this sort of thing actually being audible? Can cancelling one common frequency make a difference in a mass of RF garbage? And wouldn't airborne RF garbage be a bigger issue?

 

Sorry if this seems a lot to ask, but as a regular consumer, I'd prefer to be trusting to engineering, than "fortuitous" effects,,,

 

The expensive way of isolating an audio system from the mains is to use a mains regenerator.  Basically a regular large power supply followed by a low distortion 50Hz sine oscillator and power amplifier.  It can either be left like that, using high power high voltage transistors, or run at lower voltage and then a second transformer to boost to 230V or whatever.

 

There are cheap'n'cheerful ones that use class D amps (like a regular UPS) at a few hundred somethings, right up to huge audiophile units at tens of thousands somethings.

 

The odd thing is that some of the sonically best mains cables I've made myself are the cheapest by far.  My wife can clearly hear the difference with me blind swapping (she is not at all technical) between this and a kettle lead.  Basically use a length of the same cable that is in the wall - twin and earth.  Wired between a mains plug and an IEC.  No comb filtering, and theoretically ought to let stuff straight though.  Maybe it is because the physical construction is the same, with the ground wire between live and neutral.  But it costs next to nothing to try it out.

 

I've tried screened leads (no real effect), a balanced construction based on two coaxes - cores to live and neutral and shields to ground (modest effect) and woven (Kimber) which was clearly better.  The Kimber is woven with the ground through the hole down in the middle of the weave; it is very high capacitance and almost vanishingly low inductance.

 

I have to declare something of a professional interest in this.  There is a variety of Kimber mains cable (from Russ Andrews) that uses something I developed.  Basically it gets rid of the nulls, and simply gives broadband attenuation without ferrites or inductors. Between 10dB and 25dB (as compared with a kettle lead) at up to 1GHz, tested at 3C Test http://www.3ctest.co.uk/ so the result is qualified.  Not cheap alas.

 

On balanced signal cables, I always use Neutrik EMC series, which include a ferrite bead and array of surface mount capacitors to prevent shield and pin 1 RF from entering the enclosure.  Cheap (like most Neutrik connectors are).  I'm pretty anal about the RFI problem.

Edited February 24, 2016 by CraigS

[CraigS]

Reminds me of a VHF oscillation problem that I was trying to solve in an power amplifier. It was only after several hours when I'd given up and switched off the amp that I noticed that the waveform was still visible on the cro, albeit at reduced amplitude, and it dawned on me that I was looking at AM television RFI

 

Problem was solved by inserting a ferrite bead on the vas transistor emitter,which limited the gain above 40MHz.

 

The need for the bead only existed because the star earth traces were sufficiently long enough to act as antennas. Also, mkt film caps used for HF  bypassing are next to useless at VHF.   

 

I'm  a real fan of the pro audio company Rane.  Their technical note http://www.rane.com/note165.html describes precisely this problem, where a few cm of inappropriate ground wire gives RF breakthrough.

[CraigS]

You could, BUT, I see a major flaw in this argument. Let me first state that it is possible (but highly unlikely) for any RF to enter (and cause problems) a product via the mains supply. IME, the vast majority of RF interference problems occur via speaker cables, through the global NFB system of amplifiers.

Anyway, back to the issue of RF interference entering an audio device. The difficulty I have is that 2 Metres of mains cable is diddly-squat, compared to the dozens of Metres of unshielded cables within the home, which is then connected to the dozens of km of cable between the home and the nearest sub-station. Certainly, RF will be impressed upon all this stuff, but, in the vast majority of cases (probably all) that RF will be severely attenuated by the inductance of the mains wiring itself. A low loss cap and, perhaps a common mode inductor should mop up anything that remains.

Mains power cables make no difference whatsoever. Ever.

I invite any listener who imagines that there is a difference, to subject themselves to a double blind test. I doubt that any will.

[EDIT] Just to add my experience into the mix:

Many years ago a mate lived in a suburb not far from one of Sydney's larger TV transmission towers. Frame buzz permeated his system. The only cure was found to be to use shielded speaker cables. This almost completely eliminated the problem.

Many years later, I was called to a client's home because he had problems with his system. He lived across the road from the same TV transmission tower. Even shielded speaker cables failed to eliminate the problem. Many different amplifiers were tried. Some, better than others. I offered to try a zero global NFB amplifier. Problem solved. He didn't even require shielded speaker cables.

 

Oh I totally agree with the speaker cable thing - as I've said before on this list.  

 

But I'd submit myself to any test you like on mains cables - in a heartbeat.

[CraigS]

I must say @@CraigS your additions have been invaluable in this discussion.

The biggest question/issue most people have when dealing with power cables is that "How can the last metre make a difference when you have x metres of cheap cable in your walls?". The best answer that I have had till now was the theory that the metre or so coming out of the amplifier or component kind of acts like an antenna.

While this is obviously a simplistic explanation for what is going on, you have managed to help expand and clarify my knowledge here.

Can you please expand on how we can use this information in the real world audio situation in regards to power cables and their impedance and capacitance properties. I would like to hear your opinion on shielding in power cables and braided or twisted cables to cancel rf.

I'm also curious to know more about the double shielded isolation transformer you talked about and what possible DIY options may be beneficial and possible?

I too have heard the difference in power cables and while understanding what is happening is difficult to say the least, hopefully this extra information can help us to take more objective approaches father than trial and error when building the power sections of our systems.

 

Single shielded, but http://airlinktransformers.com.au/product-category/balanced-power-supplies/ have a variety of balanced mains units with single shielded toroidal isolation transformer up to 5kVA (for AUD894).  This the Aus outpost of a UK company http://www.airlinktransformers.com/ .  Havn't bought one, haven't tried one - but I'm pretty tempted at the price.

[Red MacKay]

How about a more "basic" problem we have here in OZ..., of mains phase inversion with US male plugs and AU male plugs.  The active and neutral are swapped and opposite to each other, only the Earth is common.

 

I'll put my hand up here!  Until about a year ago I was unaware of this.  I auditioned a respectable US manufacturer's mains cable fitted with10A moulded plugs at both ends.  Man, I put some hours on that thing, ran it on a fan for a week etc, but just could not work out why it sounded worse than my bog standard cable.

 

Returned it to the shop and told them of my woe, to which they asked if I had changed the polarity before the plug.  Changed the what???

 

So I was running it with the Neutral as the Active and the Active as the Neutral.  No wonder the poor sonic result.  And safety?

 

How many people actually check for correct phase at the end of their IEC plug?  The wall socket will be wired to AU Standards (hopefully!), but where is your phase after you have run through an adaptor, or through an American power board, or even an AU one?  The only way to find out is to check it!  You might be surprised.

 

Not rocket science this one.

[SdP]

I don't understand. Do power cables make a difference or not?