Domestic electromagnetic compatibility

[47137]

I have an old-fashioned sort of music system: a Rega P3, Elys 2 cartridge, an Arcam Alpha 3 amplifier (20+ years old) and two Mordaunt-Short loudspeakers. Very British. I also have a smart TV, and a Solwise 'Homeplug AV' thing which takes my local area network through the mains wiring to the TV.

 

The Solwise thing causes constant interference to the amplifier (especially when switched to its phono input) and the record player sounds a whole lot better when I unplug the Solwise box.

 

Why?

1. The record player is excessively susceptible to mains-borne noise?

2. The network over mains wiring idea is silly if you want hi-fi?

3. The emc standards are inadequate?

4. The emc standards have changed a lot in the last twenty years, and are now oriented towards digital sound not analogue, least of all turntables?

 

I haven't a clue, but I know emc testing and accreditation is the most intangible and frustrating side of electrical engineering to me. I can run in a cable for the network to sort my domestic issue, but I want to know "how" the providers of emc standards arrive at what they impose on industry.

 

- Richard.

[zarniwhoop]

No.2  For decent hifi sound, the power supply  is critical.  Polluting the mains with radio frequencies is a bad idea.

 

General electrmagnetic Interference (particularly from wifi) is also a bad idea.

 

A magnetic cartridge puts out somewhere between 1 and 10mV at 1KHz. And I think it puts out about 20dB less at 20Hz / 20dB more at 20KHz. That is for nominal full-volume sounds, and you can will hear noise 60dB or 80dB below that. It produces tiny signal levels so interference has much more of an effect than on line-level signals.

 

If it's any consolation, setting up a hif--quality audio streamer turns out to be *much* more susceptible to mains interference (and, to a small extent, also to wifi interference).  I swear by *some* of the products from Russ Andrews, but other people regard him as a purveyor of snake oil.  There are a number of other people selling mains cables, and I dare say there are other people selling alternative ways of trying to reduce interference. Then again, some people think that any cable will do and refuse to believe that listening to a system is a valid test. I think that your system is good enough to hear the differences between cables and, strange as it may seem, better mains cables usually help more than better interconnects.

 

But as to what standards are imposed, I have no idea and no interest - what matters is the real-life state of everything where/when we are trying to listen to the music.

 

len

[Dagworth]

No.2  For decent hifi sound, the power supply  is critical.  Polluting the mains with radio frequencies is a bad idea.

 

General electrmagnetic Interference (particularly from wifi) is also a bad idea.

 

A magnetic cartridge puts out somewhere between 1 and 10mV at 1KHz. And I think it puts out about 20dB less at 20Hz / 20dB more at 20KHz. That is for nominal full-volume sounds, and you can will hear noise 60dB or 80dB below that. It produces tiny signal levels so interference has much more of an effect than on line-level signals.

 

If it's any consolation, setting up a hif--quality audio streamer turns out to be *much* more susceptible to mains interference (and, to a small extent, also to wifi interference).  I swear by *some* of the products from Russ Andrews, but other people regard him as a purveyor of snake oil.  There are a number of other people selling mains cables, and I dare say there are other people selling alternative ways of trying to reduce interference. Then again, some people think that any cable will do and refuse to believe that listening to a system is a valid test. I think that your system is good enough to hear the differences between cables and, strange as it may seem, better mains cables usually help more than better interconnects.

 

But as to what standards are imposed, I have no idea and no interest - what matters is the real-life state of everything where/when we are trying to listen to the music.

 

len

Sorry, but the comments about power feeds to hifi are a load of cobblers! The power supply of the units themselves (i.e. the on-board transformers/rectifiers/capacitors/regulators) are critical but what noise is borne on the mains itself is completely irrelevant as a well designed power supply within the equipment will produce as near to pure DC as you can get without a battery.

As for Russ Andrews my comments would get me moderated so I won't say anything except that I work in the pro audio and lighting industry and no-one who KNOWS what they are talking about would dream of having any of his garbage anywhere near our kit. Changing the mains cable to one made of some allegedly superior material has no effect at all on the umpteen metres from the substation to the fuse box and around your house... how can one two metre cable make any difference? Mains is mains!

 

With regards to the OPs problem I'd start by looking at the earthing of your turntable to the amplifier.* The signal put out by the turntable is so low that earthing is vital to keep the interference out. Note that I'm talking about magnetic interference NOT mains noise. There is probably no connection at all between any of the powered part of the record player and the output, I know that in my tables the output from the cartridge goes directly to the phono connectors with no electronics in the turntable at all (apart from that involved with making the table rotate).

*Not the mains earthing but the earth wire alongside the phono leads of the output from the record deck.

 

My system here consists of a Technics 1200 turntable, Technics CD and tape deck, an Alesis graphic, a Sansui amp (also over 20 years old), a pair of mordant-shorts and a pair of Mission cabs. I also have ethernet over mains and wifi in the same room. My system is totally silent when set to phono with the stylus lifted from the record.

 

Andi

[raymw]

Drop an email to Steve Mace at Solwise - see if he has any ideas.

 

Best wishes,

 

Ray

[ZiderHead]

As for Russ Andrews my comments would get me moderated so I won't say anything except that I work in the pro audio and lighting industry and no-one who KNOWS what they are talking about would dream of having any of his garbage anywhere near our kit.

 

No comments required - £196 for a kettle lead speaks for itself ...

 

http://www.russandrews.com/product.asp?lookup=0&region=UK&currency=GBP&pf_id=1542&customer_id=PAA2193080713261YPWRVHBRRSIOCNZP

 

[Robert]

I won't get into a discussion about Hi-fi, but these power line adapters are horrible things which IMHO should be banned.  Yes, that's a sweeping statement - but it is becoming a big problem.  The RSGB has been trying to address various EMC issues for years.  As a radio amateur - if I was to generate the sort of interference that these things do, then the authorities would come down on me like a ton of bricks.

 

If you are technically minded, then here is a report about the problem: http://rsgb.org/main/files/2012/11/EMC14-final.pdf

 

It may be that the adapter is introducing noise through the mains supply - in which case a ferrite on the mains lead may help.  Nothing expensive is needed - just a simple clip on ferrite which can be had for a quid or so.  If that doesn't help - then relocating the adapter may be the only solution.

[47137]

This was a local RF interference problem. I have moved the Solwise box to the other side of the room, away from the turntable and the amplifier, with a longer ethernet cable running across the carpet to the TV, and the interference has gone. It cannot be a mains-borne problem, the whole room is on the same ring main.

 

Thank you for the various suggestions. The Arcam amplifier has a knurled earth terminal next to its phono inputs, but there is no equivalent terminal on the turntable - so no option of adding an earth wire there. I hadn't heard of Russ Andrews until now ... found some really plush kettle leads for £3,000+ and ... well, I have never had a post moderated and I don't want to start now.

 

Regarding other special cables, I worked with someone who used to work for a British hi-fi company, and he had a colleague there who actually could hear the difference when a directional speaker cable was turned end for end. However there was never any suggestion that one direction was 'better' than the other - just different.

 

I have never heard a radio amateur say a good thing about ethernet over mains arrangements, but fortunately I don't see any aerials near my house! At the time, the cost of my Solwise purchase was just about identical to the rather circuitous cable run I would need to get from the back of the TV to the router, but with a five minute install instead of I suspect most of a day. They also work well and didn't need any setting up. However, I can't live with the network cable across the middle of the floor, so maybe the bank holiday weekend will get me into the loft with a reel of cable ...

 

- Richard.

[34theletterbetweenB&D]

It's quite funny reading this on a model railway forum. As some will know, the one time statement  'blood on their hands' relating to a model railway product would count as an innocuous passing comment in the high fidelity sound battlespace. Recollections of 'The Abso!ute Sound' as digital recording emerged as a consumer product?

[Suzie]

EMC is all about identifying the level of interference that can be managed by affected devices so that the interference generated can be kept below that level.

 

Modern equipment with its digital interconnects which are often fibre optic are much less susceptible to interference than old fashioned unbalanced screened cables, and modern switch mode power supplies are much better at filtering out mains borne interference than linear ones, so the standards of how much interference devices can generate allow much higher than they once did. The standards are based on what interference suppression can be easily achieved in devices that might be affected using modern techniques, not those of the 1940s.

 

At the end of the day Hi-Fi if it is worthy of the label will be designed in a way to eliminate all interference entering via interconnect cables and the power lead, if this is not the case it is just simple audio equipment regardless of how much it costs. Interference has always been around, you are probably very familiar with hearing pops whenever you turn a light on or the boiler starts up, the interference generated by the network device is probably significantly less, it just happens continuously and not just now and then.

 

If the Hi-Fi is very old think about getting the power supply checked out. If the capacitors have dumped their contents they will not be doing much filtering any more and even a £3K mains lead will not help you much. Even some cheap consumer-grade audio equipment comes with balanced interconnects using what was once strictly for the professionals XLR connectors, so it is well worth thinking about upgrading to equipment with balanced interconnects if you are going to continue with analogue sources otherwise you might find you get a nasty shock should anyone put a mobile phone anywhere near your phonograph.

 

Without doubt the best advice has already been given. Install ferrite cores on ALL of the cables to your amplifier and phonograph as near as possible to where they enter the screened enclosure. Many older devices will not be adequately screened (made of wood etc.) so you might need to add extra screening to make this work. Speakers, mains or low voltage power cables, interconnect cables whether screened or not all need to be done. Maplin N94AB ferrite cores will be ideal in most cases.

 

If the manufacturer still exists ask them for details of the EMC testing that was done and the results. Twenty or more years ago it is likely to be very minimal if they bothered doing any at all.

 

To answer your question then, basically '4'. Record players were invented in an age of no potential interference and they on the whole have not been upgraded to keep pace with the introduction of interference-causing modern technology like taxi radios and such like which started to come about in the 1950s. Magnetic cartridges are on the whole balanced and well shielded devices, it is the circuitry which follows that is not up to the job, and being obsolete technology there is little effort being made to improve things when better alternatives for sound reproduction are already available.

[47137]

Suzie, I agree with most of your sentiments, especially the idea of tired electrolytics ... but I would prefer to remove the source of the problem (which I have done) before I go spending money on ferrites or equipment servicing. The thing had to have a new cartridge last year, which cost as much as quite a decent Bachmann or Hornby loco ...

 

I do feel the technology is 'well-established', or 'mature' if you prefer, but it is not obsolete; there are many recordings not available in more modern formats, and new recordings are still released onto the market, though in newer formats too of course. To me, obsolete means things like 405-line television (but not 625-line, still useful with analogue modulators) and 16mm cine film (plenty of projectors out there, but nigh on impossible to make a new recording). Also the word 'better' sounds a bit subjective ... for example the modern media are not so good at holding my attention for a whole 'side' ...

 

- Richard.

[Suzie]

Rest assured that will not be the only source of interference, just the main source. All sorts of things will be getting into the sound path and increasing the background noise level masking ever more detail in the recordings. Ferrites are not expensive, and now that you have a good source of interference for EMC testing you should be able to make your installation a bit better to be the first line of defence against the next wave when it comes. 4G and power transmission will be the likeliest candidates, and all those little pops are not good for your tweeters.

 

Get it fixed so that at least you will have peace of mind that your enjoyment will not be marred by things that you could have avoided.

[QWILPEN]

No comments required - £196 for a kettle lead speaks for itself ...

 

http://www.russandrews.com/product.asp?lookup=0&region=UK&currency=GBP&pf_id=1542&customer_id=PAA2193080713261YPWRVHBRRSIOCNZP

 

if you thought £196 was expensive look at this one again just a jumped up kettle lead for £399.00 ....... yes thats £400

http://www.russandrews.com/product.asp?lookup=1&region=UK&currency=GBP&pf_id=1548&customer_id=PAA2193080713261YPWRVHBRRSIOCNZP

 

#

[47137]

Ferrites are not expensive, and now that you have a good source of interference for EMC testing you should be able to make your installation a bit better ...

Given the problem was RF not mains-borne, I guess the various cables are working like receive aerials, and the ferrites stop or attenuate this. So may I guess I should plan on one ferrite on the amplifier mains lead, near where it enters the amp; and another ferrite on the audio from the turntable, near where it enters the amp?

 

Or should I be putting two on every cable, one at each end, and include the DVD player, video recorder and television and their various interconnects too? I don't mind spending say £15 or £20 to make things better, but no more. The speakers give out a huge thump whenever I turn on (and especially turn off) the turntable motor if that helps. Perhaps the filtering capacitors in the amp are tired, it is about 20 years old now.

 

- Richard.

[raymw]

You could always try this - http://www.james-audio-sales.co.uk/index.htm  - worth reading the whole of the site.

Or, a bit cheaper, If you have a double wall socket for your hifi, plug it into one socket, then in the adjacent plug in a lumpy low voltage power supply unit, one for charging batteries, say, not one of the lightweight solid state units, but one with a decent sized transformer. It may well absorb some of the supply voltage spikes, etc. Maybe mu-metal is your friend.

 

Best wishes,

 

Ray

[Suzie]

Given the problem was RF not mains-borne, I guess the various cables are working like receive aerials, and the ferrites stop or attenuate this. So may I guess I should plan on one ferrite on the amplifier mains lead, near where it enters the amp; and another ferrite on the audio from the turntable, near where it enters the amp?

 

Or should I be putting two on every cable, one at each end, and include the DVD player, video recorder and television and their various interconnects too? I don't mind spending say £15 or £20 to make things better, but no more. The speakers give out a huge thump whenever I turn on (and especially turn off) the turntable motor if that helps. Perhaps the filtering capacitors in the amp are tired, it is about 20 years old now.

 

- Richard.

It is not clear exactly how the interference is getting in to the amplifier so you need to suppress all the entries because it could be any of them, but chances are that it is getting in via the mains cable because that is where the highest concentration of the network-over-the-mains signal is. Any unbalanced cable can act as an aerial, especially if it is not terminated correctly with a suitable circuit at both ends and this is especially true of many phonographs with balanced cartridges connected directly to an unbalanced cable with no balanced input pre-amp to drive the cable. The low impedance of the magnetic cartridge just feeds any RF picked up on the outside of the screened cable straight back into the inner conductor. The way you describe the effect of switching on the motor would indicate that this is a problem in your case. If the coupling was inside the deck you would expect to get some hum or something similar while the motor is running.

 

It should not be necessary to put a ferrite on both ends of the interconnect between the phonograph and the amplifier - just do the amplifier end, but other devices which contain electronics like the DVD player might benefit from having a ferrite at both ends, it all depends on how good the DVD player is (again price is no indication of Quality - I have seen some real junk optical drives from Cambridgeshire that cost a fortune!) If I find a device that is suceptible to interference I tend to blitz it with a ferrite on every cable that goes into it, and you will need to treat your amplifier that way for sure. Television set top boxes tend to need the same treatment more often than not because of the amount of interference that leaves them via the mains lead and then leaks back in via the other cables. DVD players (and especially recorders) are likely to be in a similar position. Be very wary of anything in a plastic or wooden case.

 

£20 should buy you enough ferrites to do the job (£2.99 each from Maplin), getting your amplifier checked out might cost a bit more, but then you might not need to do that if you are not getting any hum.

[47137]

Well ... I've bought four ferrites from someone on eBay (£5 post paid), and put just one on the power lead to the amplifier, about two inches from the IEC inline socket ...

1. For a few hours, the small speaker thump from switching on the turntable motor was almost gone, and the rather bigger thump from turning the motor off was much reduced. But later yesterday evening (and now, the following morning), these noises are back as they were when I started.

2. There is (and still is) a real improvement to the sound of the system, especially the clarity of vocals. The size of the improvement is comparable to what I got by moving the turntable from the top of a bit of cabinet furniture to a home-made but very sturdy shelf.

3. There is no difference at all to the interference from the Solwise box. But as I wrote before, I can replace this with a long network cable. It's the only thing in a plastic box ...

 

Putting a pair of ferrites on the amplifier end of the audio cables from the turntable made no difference so I took them off. Putting one ferrite on the power cable to the turntable motor at the turntable end seemed to make the power on/off thumps worse, so I took that off too. A shall have another play over the weekend .. I shall probably start by unplugging everything except the turntable, amplifier and speakers.

 

So at the moment, one £1.25 ferrite is getting me better sound - and so a big thank you.

[ZiderHead]

One of my mates had a planar from new and it always did the pop/thump thing when switched on. I'd be amazed if there isn't an easy mod to fix that since its not in the audio path (small cap across the switch?), theres plenty of audio forums to search through.