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June 2012 Issue

Article Index
June 2012 Issue
page 2
page 3
page 4
page 5
page 6 (Digital Cables)
All Pages

World mail June 2012 issue

 

Write to us!  E-mail –>     This e-mail address is being protected from spambots. You need JavaScript enabled to view it

 

Letters are published first in the magazine, then here in our web archive. We cannot guarantee to answer all mail, but we do manage most!

 

Or  comment in the Comment section at the bottom of each page.

 

Your experts are -
NK Noel Keywood, publisher; PR Paul Rigby, reviewer; TB Tony Bolton, reviewer; RT Rafael Todes, reviewer (Allegri String Quartet); AS Adam Smith, reviewer; DC Dave Cawley, Sound Hi-Fi, World Design, etc.

 


 

 

imf-external

IMF Reference Standard Professional Monitor  loudspeaker

 

 

 

SINGING PROFESSIONAL

My system has grown somewhat haphazardly in recent years but I’m now homing in on a definitive set up - or trying to. There is one cast in stone element, which I’m loath to change. At the end of the signal path, and occupying two corners of my living room is a pair of IMF Reference Standard Professional Monitor Mk IVs. These transmission line monsters are even bigger than the IMF TL80s by some margin, and something of a family heirloom, being my dad’s before I got my hands on them. They were purchased as liquidated stock from the Hi-Fi Surplus Store in the early 80s, when IMF sadly went out of business. So big were they, that we had to put one speaker in the back of my dad’s Capri with the seats down and tailgate open, and one on the roof rack!


Fortunately I have no near neighbours so they can be used loud, which is a good thing because they need to be moving a lot of air before they really get going. Feeding these hungry beasts I have a pair of Conrad Johnson Premiere 12s.


So far so good. I love the IMFs, but I’m aware that they are a bit on the slow side, but really nothing quite gets those low furniture vibrating bass notes quite like these do. I like all sorts of music, but have a fondness for Prog for which the IMFs excel, particularly if there’s a bit of Moog or Mellotron action.


Moving forward and this is where it all starts to get a bit messy. I’m currently between pre amps, having jettisoned an Audio Research SP – I can’t remember what one (it was the valve hybrid one)! It never really sounded convincing to my ears. In temporary residence is a Hitachi HCA 8500 Mk2, which is actually pretty good, but not exactly in league with the CJs. It has a surprisingly good phono stage with a good choice of gain settings for various cartridges, but that said I’m using a World Designs phono stage and power supply.


Finally there is the Technics SL-120 Mk2. It’s a lovely thing in excellent condition and was fitted from new with an SME Series III S arm, which I realise is a limiting factor. I’ve fitted my trusty Dynavector Karat 17D3 and have so far modded the Technics with upgraded feet and mat from Sound Hi-Fi. At the moment the deck has the pace that I was expecting, but is a bit bass light, which I put down to the arm. Certainly CDs currently have more oomph, but I’m fairly clear on the upgrade path, which will involve retaining the Dynavector and fitting a more up to date SME and probably remote PSU and upgraded main bearing.


I’m quite keen on having a punchy, metronomic and up-front turntable set up, because frankly I think the IMFs need to have something to think about, or they’ll just wallow. Equally, I do wonder whether the CJ 12s really have the grunt required. Would the IMFs benefit from some serious horsepower to get the best out of them? I’m thinking of the big engine analogy here. I’m not wedded to valves and my inclination is towards a big sound, which the IMFs deliver, but with some wallop and control too, which currently they don’t quite manage.


And of course in the middle of all this is the pre amp. Which way to go? If I’m sticking with valves, then the only pre that has really caught my attention is the Icon Audio  LA-4 and frankly with the way high-end audio is going these days price wise, £1000 is about the maximum I’m willing to spend. Of course there is always the second hand route.


So any advice gratefully received. I suppose it all comes down to the speakers. If you guys had a pair of these monsters in residence, how would you get them to perform at their optimum?

Steve Bennett,

Hoxne,

Suffolk


 

imf-internal

Inside the IMF Reference Standard Professional Monitor loudspeaker. A KEF B139 bass unit was acoustically loaded by a long, damped transmission line, ported at the front of the cabinet. This gave big bass that ran deep, a feature of IMFs, but they need high damping factor amplifiers for control.

 

 

 

technics-sl1200mk2upgrade

 

Technics SL-120 Direct Drive turntable. It has metronomic timing and suits the IMFs. Fit it with a good, modern arm like an SME309, we suggest.


Hi Steve. Those are great loudspeakers. Your dad was brave to buy them; they are rare birds and produce bass like few others. The KEF B139 bass unit loaded by a long ‘Transmission’ line is quite a load and demands current. Of all the loudspeakers that need the grip and current delivery of solid-state, this is the one! You would be best off siting a monoblock power amp near each one, but suitable models like the Electrocompaniet Nemo don’t come cheap. NAD will be updating their M2 Class D technology power amplifier soon, so an old M2 might become available at low cost and Nu Force make technologically advanced Class D power amps with a tight, clean sound.


I am not saying Class D is better, but generally they sound dry and tight. You just have to be aware that many have rotten transfer functions that modulate distortion terribly and they have nasty treble and are none too detailed or delicate. Hypex modules are an exception with  a clean sound and can be found in Channel Islands amplifiers.


Roksan make amplifiers with the right sort of balance for your IMFs, meaning punchy, dry and very controlled. Their M2 power amplifier would be a very good choice. But don’t get a Naim, as they have a low damping factor and will not exert enough control.


If you use an integrated amp., site it reasonably close to the loudspeakers and use stout loudspeaker cables.


Try and audition before buying as many won’t cut it with those loudspeakers, and don’t buy blind from eBay for the same reason.

In front of your solid-state power amplifier use a valve preamplifier, or possibly a passive preamp, or even a Music First Audio transformer preamp., if your budget can stretch that far. The Icon Audio LA-4 may well suit; it’s 6SN7 small-signal triodes are the smoothest, most relaxing valve you will ever hear, but it has fulsome bass and I am uncertain how this will suit your big IMFs.


You are spot on with your turntable upgrade suggestions. Get an SME309, a lovely arm by any standards and upgrade the SL-120 with Sound Hi-Fi parts. Consider a Benz Micro Ace (low output) MC cartridge at least if you want to move up from the Dynavector.

NK


 


A TOUCH BETTER

Thanks for your very interesting comparison of digital streamers in your March edition. I’ve been running one flavour or another of a networked Squeezebox for a few years now and never looked back. It’s a boon in convenience and I find the sound quality excellent (digital output from my Touch to Lyngdorf digital amps into Perigee ribbons or Final electrostatics / Lyngdorf corner woofers).


Keeping the music library in order though does take a bit of time and effort and, to be fair, users of Squeezeboxes and the like are usually expected to have a modicum of computer savvy. It’s really cute too to be able to access my music from the comfort of my IPad!


Anyway, I came across the suggestions below and applied them a year ago and they did make a very noticeable improvement (I haven’t changed the power supply as I had tried that with a previous Squeezebox and, to be honest, heard no difference).


I’ve recently upgraded to v3.0 of the firmware modifications which has been a real step change improvement. The instructions may look a bit disconcerting at first, especially to a novice, but the whole revision took about an hour. The instructions are actually quite easy to follow and you can ignore various sections depending on what you want to do. Perhaps you might want to try them on your own Touch and re-evaluate. Might move the score up a notch or two!

Stephen Judge

 

 

logitech-squeezebox-final

The popular Logitech Squeezebox can be tweaked to improve its sound, says Stephen Judge.


DIY-AUDIO SBT Modification Thread http://www.diyaudio.com/forums/pc-based/168871-squeezebox-touch-modifications.htm


A TURN OFF

I listen mainly to classical music, most of the time late at night, so with reduced volume. And my problem is: for some reason the music is not involving. I know that is a difficult and personal description, but it is the only way to put it. I am sure that everything measures very fine, but in the end I often switch off the music after an hour or so.


My setup is: KEF 203 Reference loudspeakers, MBL 7008 amplifier, Olive 4 music server (just used as digital output), North Star 192 MK2 DAC. Power and ‘speaker cabling from Cassiopeia, XLR interlinks (DAC to amplifier) from John van Gent and Kimber Select KS 2020 digital interlink.

I don’t fancy going analogue (LPs) as I have zero LPs and 500+ CDs (real CDs and/or downloaded). Due to physical restrictions, I cannot use a tube amplifier or separate pre/power amp.


Do you have any suggestions what might be wrong with my system? Why does it make me so listening-fatigued? Any suggestion what I could try to change? Or is it just me, between the ears?

Kind regards,

Serge Wallach

Amsterdam

Netherlands

 

 

 

kef-reference-203

 

KEF Reference 203 loudspeakers

 

 

We have all suffered this and I know what you are experiencing. The KEFs are good but can be a bit clattery in their treble and this does not suit the items you are using to drive them. The MBL amplifier is not a good subjective match; it has a rather soul-less and dry delivery, if clean and powerful. I suggest you replace it with a Creek Destiny II integrated amplifier – this will make a big difference. As transistor amps go it is smooth as silk, almost warm, but big and muscular in character. NK

 

 

 

creek-destiny-2

Creek Destiny 2 amplifier has an easy, enjoyable sound, but is powerful and suits KEF Reference 203 loudspeakers.


 

MISSING MUSIC

I read with interest the letter ‘Missing Music’ in the March 2012 issue. The fact that Christopher Warrender's copy of Eric Clapton’s Unplugged album on vinyl had some music missing did not really surprise me. You published a letter by me in late 2010 in which I complained about the poor quality of vinyl pressing produced by the major labels and it seems that things have not improved if Mr Warrender’s experience is typical.


I would take issue, however, with his assertion that reissues should be avoided. I buy a lot of reissues on vinyl, mostly from specialist reissue labels such as Doxy, Sundazed and Music On Vinyl and the quality I find on these LPs is always superb. It would seem that the majors who reissue their own stuff on vinyl just don’t care about quality and are just out for the quick buck. That view is counter productive of course, because “once bitten, twice shy” as the saying goes, so you don’t buy their reissues a second time.


I have to say that I was surprised that Hi-Fi World did not follow up Mr Warrender’s email to Warner as surely you have a better chance of squeezing a reply out of them, being the respected magazine that you are!


Keep up the good work, although I’m not very keen on the increasing emphasis you are giving to digital.

David Jarvis

 

 

sundazed

 

Re-issue labels such as Doxy, Sundazed and Music On Vinyl are superb, says David Jarvis.


 

The music business is its own world, one having a difficult time as music sales slip downward and once-great studios close. With engineers adding distortion to give music “graunch” and compressing and balancing recordings to sound loud on a small radio or in a car, it can be depressing to even attempt any discussion about quality, and often a waste of time. This is one of those horrible generalisations; for every engineer that has become functionally brain dead after spending years in front of giant studio monitors cranked to max volume, there is one that uses electrostatics. But we visited a West London studio not so long ago where they cut vinyl and upon asking how they replayed the result to check quality they sheepishly admitted they did not bother. We suggested they buy at least a little Rega turntable and an Ortofon 2M Black to hear what they were doing. NK

 

 

NAPPED

I have a fully Funked Sondek/Ittok 2/Dynavector 10x5, Naim NAC32/NAP160 and a pair of Harbeth HL monitors Mark2. I am thinking of replacing the preamp with a valve based unit, hoping to smooth off a few rough edges and open up the soundstage. I’ve read some favourable reviews of the Croft micro basic and the Micro 25 preamps and I’m hoping for some advice as to whether or not they are electronically compatible with my NAP 160. If they are, would you advise going for the 25 which has a phono stage or the basic, which is £350 cheaper, and use a separate phono stage.

 

A couple of dealers have suggested the Icon Audio LA4 and I remember reading NKs review of this preamp a couple of years ago where he mentioned compatibility with Naim power amps, although in its current form its about £300 more than it was then and I’ll need a phono stage as well.

I haven’t heard either but I will before I make a decision. Advice about these preamps and any other suggestions would be welcome.

Steve Wright

 

 

icon-audio-ps3-phonostage

Icon Audio phono preamps have a volume control, so can drive a power amplifier like the Naim NAP160, owned by Steve Wright, direct.

 

 

Hi Steve. You get what you pay for here. The Crofts are fine and inexpensive and we hear they drive a NAP160 successfully, but we have not tried it and cannot be sure. Technically, there is no matching problem but you do have to beware of having enough gain in the system to drive the NAP160 from a turntable. The Icon Audio products have sufficient gain (x3000 MC) and that is partly what you pay for. Don’t forget that you can drive a power amplifier direct from an Icon Audio phono stage, because it has a volume control. Whether it will get the NAP160 to full output we do not know but it will almost certainly go very loud at full volume. You could then get an LA4 preamp for extra gain and input switching later. NK


KANDY MAN

Perhaps you could offer me some advice on my next upgrade. I currently use a Roksan Kandy K2 amp/CD player with new Monitor Audio RX6 speakers. These are connected with VDH cables and I listen to LPs using a Project perspex turntable fitted with a Goldring 1042. The sound is very good, but I will soon have in the region of £2k to spend, and am thinking of buying a Creek Destiny 2 amp. Everyone says that this amp has a valve like quality and I am wondering if I would get a better standard of reproduction by changing amps? I would keep the Kandy CD player.


Also, is the MM add-on phono stage for the Creek as good as the inbuilt Kandy stage, or would you suggest a stand alone unit? Would I also gain a lot by changing the Goldring for the Dynavector DV10X5 pick up?


My musical tastes are very wide, from classical to jazz, but no boom boom stuff! Room size is approx 13’ x 14’.

Any help would be welcome.

Many thanks,

Cliff Millward

Tipton

West Midlands

 

 

quad-24-p-phonostage

A Quad QC-twentyfour P phono stage has a lot of gain, so is a good match for an integrated amplifier with limited gain (low input sensitivity), like the Creek Destiny 2.


The Creek Destiny 2 would be an upgrade for your Roksan Kandy, but having said that Roksans are very good. You would be going from good to slightly better, and from a dry, yet solid sound to a big, fulsome delivery. Try and audition first to see if this change of character suits. And yes, the Destiny 2 is as close to a valve amp as you will get from transistors.


To be frank Dynavector cartridges are not my greatest love and the DV10X 5 was surpassed long ago. High output MCs are not a very good idea and few sound special. Stick with MM and upgrade to an Ortofon 2M Black, which will give you a more technically correct if arguably less funky sound than the excellent Goldring 1042, or do it properly and upgrade to MC. You would then need to consider an external phono stage for the Creek, perhaps their own, or a Quad QC-twentyfour P, and at least a budget MC – see our group test in the May 2012 issue.


And a quick word of advice on high output MCs – avoid them! Always go for the low output option. These have the fewest turns of wire, the least wire coloration, the lowest output impedance and the lowest effective tip mass, meaning they track best. To compensate you need a quality preamplifier with low noise and plenty of gain, but you are spoilt for choice nowadays. NK


 

AGING NAIM

After many happy years with my Naim CDI CD player, it has developed a fault where it will not read some discs and has problems skipping forward to other tracks. I can only imagine the worst, that the laser is going. So if it is not a fixable problem I can only assume it’s time to dig deep and find a replacement. My musical tastes are from the dance/electronica spectrum, you maybe familiar with bands like The Prodigy, Shpongle, Infected Mushroom, High Contrast, but I also like hip/hop such as Jurassic 5, Doctor DRE and Fort Minor. I just love the way the Naim musically engages me with this style of music, I think this is partly due to it’s rhythm and timing capabilities. If I could find something equally as good or better that would be great. My budget is around £1000, Naim CD5i2? Or maybe Rega Saturn?


I live in a large flat with high ceilings. The rest of my equipment is a Jungson JA88D Class A amplifier and Yamaha NS1000Ms speakers. These speakers sit on Atacama SL300 stands, shot filled. And the equipment rests on Russ Andrews Tortlyte stand, I use Kimber 4TC speaker cables and an interconnect which beat Kimber’s pure copper select series (can’t remember the name). Both pieces of equipment run from pure silver 14 awg mains cables (these again beat the top copper mains cables from Kimber). Any advice would be greatly received.

Many thanks,

Mark Skinner

Ramsgate

Kent

 

 

naim-cd5xs_front

Get the classic Naim sound from a Naim CD5 XS CD player, if your old Naim has died.


I would suggest you either have the CDI serviced or replace it with another Naim, like the CD512 you mention, or a CD5 XS perhaps? You will not easily get a CD player that is clearly better unless you spend big wonga, say for a Canor (with valves) or perhaps a Chord Electronics DAC64 second hand (if there are any!). Then of course you will need a transport, as yours is on its way out. It makes most sense to have it serviced Mark, and then perhaps use it as a transport with an external DAC, or sell it and get a new Naim. NK


MEDIA MATTER

I read your article on media players with great interest and agree media players have a lot of potential to create great music and perhaps will become the modern CD players of the future. But for those of us wanting to get the best out of the humble computer, all is not lost.


There are three ways I can see getting the best of computers for audio purposes.

1)      Build a dedicated system. You could pay someone to do this for you. It requires a lot of technical knowledge around system building, but will guarantee very good sounds.

2)      Use a Linux based system. Basically Windows is doing many functions that takes away from the sound quality, using Linux greatly reduces this.

3)      Use JPlay in full hibernation mode. This will allow Windows users to get their computer sounding like a dedicated high-end Transport system.


Over recent times I have learnt that the more you can get your computer to just function on the sound quality, the better it will perform. It goes back to the old mantra of “source first”, and in this case perhaps the DAC is not as critical as we used to think, perhaps it’s the quality of the signal going to the components that really matters.


I know people will argue “data is data” and yes, I agree, but its having less in the way of getting that data so it is managed without timing issues. The results are clearly evident in the listening.

John Cahill

 

 

 

jplay

 

 

Use JPlay to turn your PC into a digital transport, says John Cahill.

 

 

Thanks John. I suspect the ‘build it yourself’ route is still the best, if time consuming. My home built PCs have consistently been more reliable than the commercial PCs (and Macs) we run at Hi-Fi World. I am due to build a new one, but the world is changing and I am unsure building your own PC makes much sense nowadays. My local computer shop will assemble a computer to my spec at no extra charge, saving me the time, and they know what the best bits are as this is their business (they are Epsilon computers in London’s Tottenham Court Road, see www.epsilonpc.co.uk).


Computers are general purpose devices running a lot of background services, like anti-virus and content cataloging (e.g. Spotlight on Macs). There is a lot to disable, as a peep inside ‘msconfig’ on a PC (type this at the command terminal) reveals. Media players avoid all this complexity, as well as the horrors of long Cat 5 cables that really are not a clever idea when it comes to transmitting digital music signals. NK


NEW SMOOTHIE

I would like some advice. I’m thinking of changing my CD and amp. I would like something very smooth sounding for a budget of £600 for the pair. I recently upgraded my speakers so I want something to do them justice.

Many thanks ,

Chris Close

Lincoln

 

 

nad-326bee

For a budget smoothie, get an NAD 326BEE amplifier.

 

 

 

The smoothest sound you will get for that price comes from NAD in the form of their 326BEE amplifier. An alternative is an Onkyo like the A9377. Both NAD and Onkyo produce good quality amplifiers having a smooth sound and good bass. I think it best if you then choose a matching CD player. NK



DENON DAY

I’m a regular reader from Singapore. I recently bought the Denon PMA 1510 amplifier. The rest of my system consists of the Marantz 5003(CD), Wharfedale Diamond 10.1 loudspeakers, Chord company speaker cable and Van den Hul interconnect. I listen to Vocal, Pop and Music like David Foster, Chris Spheeris etc.


I found music details were missing and bass weight is light with the mentioned combination. Could the missing details be caused by the CD player? I’ve thought of upgrading the CD player to an Audiolab 8200 or Marantz Pearl Lite or any recommendation?


Most importantly can you recommend some floor standing speaker that can sing well with the PMA1510? I can spare £500 to £1000 pounds for the speaker. Thank you in advance.

Regards,

Sng Boon Seong

Singapore

 

 

audiolab-8200-cdq

 

An Audiolab 8200CDQ CD player will pick up the sound with great bass and it is available in Singapore.


 

An  Audiolab 8200CDQ CD player, available in Singapore, would certainly offer punchier bass and a more open sound. It is an impressive player.

Floorstanding loudspeakers will give the bigger bass you want and I would suggest you listen to Castle Knight 3 or 4 loudspeakers, which are also available in Singapore I believe. Audition Triangle loudspeakers too, available in Singapore, as they are very well engineered and have a great sound – the Altea may well suit you. NK


TANNOY UPDATE

I read Noel Keywood's review of the Tannoy DC8T with great interest. (page 46. March 2012 issue). The DC8T has been updated. Well I have updated my own Tannoys.


In 1976 approx, the National Hi-Fi Exhibition was conveniently held in Harrogate and within 5 minutes walk of my house!


That was one of the best days of my life leading to the purchase of the Arcam Delta integrated. amplifier, tuner and CD player the following week.

Whilst looking and listening to demos all day long I happened to enter the hotel ballroom as Tannoy held a demo and when the Westminster Royals played I felt as well as heard the music. That session impressed me so much that I became the proud owner of a new pair of Tannoy 12” concentrics.

In May 2011 I sent them to Lockwood Audio to be re-coned and now they sound magnificent again!

Yours sincerely

Paul H Metson

Harrogate

Yorkshire.


ON STREAM

It was great to see the review of streaming media devices in the March issue. I’ve long believed SACD/DVDA/Blu-Ray were the wrong “delivery mechanisms” for hi-resolution content – nobody really wants yet another incompatible silver disk format and it is great to see the hi-fi manufacturers are catching up with the geeks (myself included). I might even pass my Squeezebox Touch and Cambridge DAC combo on to the kids.


With my electronic engineering hat on, can I just clarify the oft-repeated comment that S/PDIF cannot carry audio above 96kHz sampling rate? I may be wrong but, as far as I am aware, the S/PDIF spec does not limit the sampling rate. My copy of the AES/EBU spec (dated 2004) lists 22.05, 24,32, 44.1, 48, 88.2, 96, 176.4 and 192kHz sampling rates, and all at 16, 20 or 24-bit depth. Admittedly, there have not been many chipsets around to support higher sampling rates; until recently nothing much went above 48kHz – but they are now readily available, just Google “192kHz digital audio receiver”. That said, I agree that the practical difference between 96kHz and 192kHz is not exactly night and day...


Might it be worth mentioning that HDTracks accept PayPal outside of the USA? For those with broad musical tastes, the B&W / Real World Society Of Sound is a great source of 24-bit downloads at a little over £1 each album for an annual subscription. I have no vested interest in either, but I recommend both.

Regards,

Steve Fenton

Cambridge

 

cirrus

 

Google '192kHz digital audio receiver' and you come up with a chip, the Cirrus Logic CS8416, that sends 192kHz via S/PDIF, Steve Fenton says.

 

 

 

Thanks for that Steve. You are right – there is no stated limit, as far as I am aware, only an actual one imposed by hardware. But if we state you can get 192kHz down S/PDIF someone will complain bitterly we misled them!


Try buying from HDtracks and your order will be rejected on the basis of your IP address. This is a Copyright issue and David Chesky confirmed by telephone from N.Y. that they do not sell outside the States. As you are the third person to tell us you can buy using PayPal I suspect something might have changed since you tried it. NK

Steve Fenton replies -

I designed an AES3 receiver / transmitter (mainly implemented in FPGA) about 10 years ago for TV studio use, so it was only ever for 48kHz sampling rate. My 2004 spec lists another eight reserved sampling rates but, given it already covers half, double and quadruple of both 44.1 and 48kHz, it isn’t easy to see what they might ever be. Cirrus and Texas Instruments, for starters, both list 192kHz devices. Doubtless, before long, so will everybody else.


I think HDTracks have tightened their restrictions recently. I downloaded Steve Earle and Isaac Hayes in the UK (payment via UK PayPal) but had to get Cat Stevens via my employer’s US-based server – I’m lucky that I can get round the IP restriction.

Cheers,

Steve


 

LASER LIGHT

I read with interest your articles on network streaming and USB to S/PDIF converters and about the weird variations in jitter you saw on your analyser vis. dirt and reversing the connections on the optical lead. I think I can throw some light on these, excuse the pun.


The TOSLINK is basically just a fibre optic cable – but in the fibre optic timeline it’s pre-stone age. It consists of a glass or plastic core of approximately 1mm diameter, covered by a cladding of more glass or plastic of a higher refractive index. This protects the core from scratches and contains the light in the core. The refractive indices of the core and cladding are chosen such that total internal reflection occurs over a wide range of angles that the light rays make at the core/cladding boundary. This ensures that the maximum amount of light makes it to the other end. The light source is a red LED, which means that a spread of wavelengths from about 650nm to 850nm are introduced into the core. At the time of TOSLINK’s introduction, a LED was the only practical source, its’ large emitting area dictated a large core fibre unless costly bulk optics are used.


The problem is, the larger the core of an fibre optic cable, the worse its’ performance! Rather like a waveguide, large cores allow large modal spread – from the ray that theoretically travels down the axis of the fibre to the one that bounces off the core cladding interface thousands of times. The response to a step function – the LED turning from off to on for example – will cause light at thousands of different modes and several different wavelengths to be sent down the fibre, and of course they will arrive at the other end at a range of different times. The effect at the detector will be to turn the step into a slope.


This slope (neglecting electrical effects in the detector) is thus caused by modal spread and varies according to how many bends and coils are in the cable. If you can measure optical power with your analyser you will have noticed how sensitive this is to bends in the cable. This modal effect limits the theoretical bandwidth of TOSLINK cable to about 10Mbps per metre. If four or five turns of cable are wrapped around a, say, 100mm mandrel (piece of plastic pipe?) the high order modes will be dispersed into the cladding and only the low orders will make it to the end. The optical power will be reduced considerably but the recovered signal should be a lot cleaner and – in theory at least – less jittery.


Sorry for the lengthy preamble but the effect that you’re seeing is I believe caused by a phenomenon known as return loss. TOSLINK connector ends are flat polished, which means that some of the light gets trapped inside the cable and bounces around with a whole new set of modes. Some of these modes escape at both ends to be reflected by the LED source and the sensor back into the cable again. This effect is strongly dependent on the cleanliness and condition of the connector end faces – the two ends are never going to be exactly the same. Cleaning, polishing and swapping the cable ends over will affect the magnitude of this return loss factor. This adds to the modal chaos in this large fibre and I believe will be measurable as jitter.


Large cores are good for tolerance to dirt and misalignment in connectors, but bad for everything else. The industry standard multimode fibre in general use has a core diameter of 50μm – 20 times smaller than TOSLINK. It’s bandwidth is typically 1Gbps per kilometre (a bit different!) So-called single mode fibres – the kind that our information superhighway is built on and the Government and BT baulk at the cost of installing – has a core diameter of 9um and a bandwidth 50 to 100 times as great as multimode. You get huge bandwidth and huge distance, but the quality of the installation and components has to be high. So-called ‘fibre to the home’ has floundered on the component cost required to do this reliably. The light sources are lasers though, which have the advantage of being both monochromatic (usually IR, 850nm to 1500nm) and of very small cross sectional area and can thus inject into very small cores. Considerable efforts are made to minimise return loss as well, by using angled, domed ended connectors.  A short multimode cable isn’t necessarily better than a long one, as the long cable increases the chance of high order modes being dissipated. It may be therefore, all other things being equal, that a 10m cable sounds better than a 1m one.


Apart from DVI/HDMI, I can’t think of another digital protocol that is time contiguous – data is always time stamped and packeted these days. And as we don’t see in the same way as video is transmitted, I think this makes audio unique – and uniquely vulnerable!


It would be great to make an optical link using single mode fibre, laser source and narrow band detector. The parts aren’t hugely expensive, but too expensive for manufacturers, I expect (pounds, not pence!). And TOSLINK isn’t going away because the automotive sector have picked up on it – because it’s cheap!


The telecoms sector fibre optic market eclipses all else into insignificance. As a result it is surprisingly difficult to optimise fibre optic systems that don’t fit into its’ value set. In general manufacturers are not too interested in making low volume ‘specialty’ parts at marginal profit when they can make a far bigger one in the telecoms business. I suspect this may be a reason why TOSLINK has had such a long life – it’s not economic to replace and in bare data rate terms, has sufficient capacity.


Hope this makes some sense at least. Please continue with your investigations as I think you’re breaking new ground here.

Kind regards,

Keith Stickel

 

 

cinnamon_optilink

 

Audioquest Cinnamon optical digital TOSLINK cable uses a high purity polymer fibre with low dispersion to lessen jitter, they say.

 

 

Thanks for that detailed insight Keith. It saves us all from a lot of unknowing speculation on a topic that is obviously well known about outside audio – and its Stone Age cables and connectors!


The irony here is that digital cables do measurably affect audio quality, when it has been firmly believed until now that they cannot do so by the very nature of digital. Since the restricted bandwidth of long electrical cables introduces jitter by lengthening the zero crossing transition it seems we are dammed in both camps!  The following letter on the problems of Cat5 adds to our woes in this field, but also points again to fibre optics.


I can’t help suspect, however, that because the audio market will pay for a good product, better fibre optic cables and terminators will become popular in due course. I know they are appearing now and I expect somewhat more mail about all this very soon! NK


NETWORKING DIFFICULTY

I was interested to read Noel Keywood’s article ‘Media Message’ in the May 2012 issue. I was particularly interested in his comments regarding signal degradation due to passage over network cables. As a computer network engineer, I am well aware of signal problems due to the poor shielding qualities of standard (CAT5) network cables. Poor cable installation is a very common cause of poor network performance, and can be hard to diagnose unless you know what to look for and/or have the right test equipment. So if you are using network cabling in your hi-fi system, the cable installation needs to be considered carefully.


CAT5’s ability to prevent external noise interfering with the signal, comes from the signal leads being twisted in pairs; each signal lead twisting through 360 degrees continually along it length. This means that if wireless noise hits the cable in one orientation, it will also hit the cable in a 180 degree opposite orientation very nearby. Thereby, any alteration of the signal caused by noise in one orientation, is cancelled out by the same noise passing through the cable in the opposite orientation nearby.


Relying on twisted pair signal leads, to prevent interference, is not a good way of avoiding signal degradation, but for the vast majority of network installations it is good enough. The leads are cheap and easy to install, which leads to good enough being just that - good enough.


So what do good network cable installers do to avoid signal degradation? The key is maintaining the twists. As the twisting provides the only shielding, if the twists stop, so does the shielding.

 

So what are the common causes of untwisting:


Over-tight cable ties. Cable ties can pinch the cable, causing the twists to straighten out. A good rule of thumb is that you should be able to push the cable back and forth through the tie. If the tie pinches the cable so tight that you cannot move the cable through the tie, then it is also tight enough to straighten out the twists, and you’ve lost the limited shielding twists provide.


Over-tight bends. Cables need to go round corners in smooth curves. If you see a cable pulled taught around the corner of a wall, or wrapped into tight bunches, then there is a good chance the twists have straightened in the bend.


Too much bare wire at joints. This is common when people make up their own cables. The cables need to be untwisted to enter the joints (end connector, punch boards, and mounting plates). Where the cable is straightened shielding is lost, so it needs to be minimised. For example, the straightened cables need to be totally within the end connectors. If you can see bare signal wire entering the connector, then the connector has not been made up properly and signal degradation will result.


Another thing to consider is avoiding noise sources. Try to avoid laying CAT5 network cables alongside or past RF noise emitters:


Do not run network cables through the same conduits as mains cables. Mains cable emit electrical noise. Running a main cable alongside a CAT5 network cable is asking for trouble. If the network cable has to cross a mains cable, try to do it at 90 degrees.


Where cable runs pass though ceiling spaces, keep them away from fluorescent lighting units. Avoid passing cables near to electrically noisy devises such as refrigerators.


However, there is one simple way of overcoming all these problems: don’t use CAT5.

 

So what are the alternatives:


Coax. Twenty years ago network cables consisted of coax cable connected via BNC connectors. It was thick and therefore difficult to install, but it was also much better at shielding noise, as it contained a continuous metal shield around the cables. Unfortunately, this style of cabling was only commonly used on slow ethernet (10Mb/s as compared to modern 1Gb/s - 100 times faster), and finding modern equipment that will use this style of cabling is unlikely.


Part of the reason for there being a lack of modern coax network equipment, is that there is a much better alternative: fibre. Fibre optic cables can support very high transmission speeds and are immune to RF noise interference. However, it is more expensive and harder to install, so tends to be used to connect between networks, or where there is no alternative.


Saying that, fibre optic cable is the best medium for transmitting network signals, and if they could, network engineers would use it everywhere.

Which begs the question: why isn’t hi-fi equipment using fibre optic network connections?


Network switches with fibre optic ports are more expensive than standard switches, but not that much more – an HP E2520-8 8 port switch costs around £260 pounds and has two SFP ports that can take fibre modules (from around £60 each). A fibre network card to fit into a computer can be had for around £70. When you are looking at hi-fi music streamers costing hundreds if not thousands of pounds a go, that’s hardly a lot of money.


So how long will it be until server to network player connections follow the same trend that CD transport to DAC connects went through - from copper to fibre? Surely it has to happen. I only wonder why we haven’t seen it yet!

Rob Nichols

Evesham

 

fibre-card

A StarTech fibre optic PC card available for £96, allows data to be sent down optical fibre.

 

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