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NET NOTES

Studio wiring By Martin Walker
Published June 2001

The Digital Pro Sound web site has lots of articles for the musician, including a survey of the different types of screened audio cable available.The Digital Pro Sound web site has lots of articles for the musician, including a survey of the different types of screened audio cable available.

Studio wiring may not be the most fascinating of subjects, but a little knowledge can go a long way when it comes to sorting out cable‑related problems. Martin Walker rounds up the best of the wired web.

While audio processing becomes ever more sophisticated, thanks largely to advances in computer algorithms, the quality of the audio in our studios can still be compromised by rather more mundane factors, such as the hums, crackles and RF interference caused by poor mains and audio cabling. In the past, anyone trying to solve such problems might take a trip to the local library, which would probably yield a few dry textbooks on the whys and wherefores of electrical wiring. However, now we have the Internet, which provides a wealth of information on the subject from seasoned professionals.

Cable Talk

Rane provide a comprehensive audio glossary and lots of technical notes about grounding and shielding on their web site.Rane provide a comprehensive audio glossary and lots of technical notes about grounding and shielding on their web site.

Choosing decent cable can make a noticeable difference to audio quality, particularly with low‑level signals such as those from guitars and microphones. However, with so many types of cable available, choosing between them can be extremely confusing for the beginner. If you want to learn about the different basic types of interconnect, speaker and digital cables, look no further than Paul White's 'Wires and Wherefores' article on the SOS web site (https://web.archive.org/web/2015..." target="mainframe), which also includes brief details of unbalanced and balanced operation.

Digital Pro Sound also maintain a useful set of articles at www.digitalprosound.com/1splash/..., and if you scroll down to the Electrical/Electronic section you'll find all the basics about different types of cables in 'Good Connections', how to choose the correct type of cable for your application in the 'The Right Connection', and a discussion of how to rid your system of hum and buzz in 'Keeping Quiet'.

Rolling Your Own

Of course, you may never need to know about cables if you always buy ready‑made ones, and there are plenty of companies, such as Studiospares (www.studiospares.com) that sell high‑quality audio cables of various lengths, terminated with a range of connectors. However, anyone who needs an unusual combination of cable and connector, or who wants to save some money, and has some time and a suitable soldering iron, can indulge in a little DIY. Paul White wrote a useful introduction to soldering back in SOS March 1994 (https://web.archive.org/web/2015..." target="mainframe). Some people prefer to use solder with a small percentage of silver in it for audio connections, and such solder is available in short lengths or by the reel from various hi‑fi and electrical outlets. Sometimes it's better to avoid solder if possible; there's a helpful description of the relative merits of soldered versus crimped connections at the Cardas Audio site (www.cardas.com/insights/solder.html).

The Cardas site offers lots of general information regarding the company's own audio cables, plus discussions of the relative merits of solid core, stranded, litz, tubular stranding, and even Constant Q Golden Section stranding! They also tackle explanations of such thorny issues as cable break‑in — why many new cables (in particular, speaker cables) sound better after being used for several days.

George Cardas holds US patents for some of his cable, microphone, and connector designs, but many musicians still regard hi‑fi cable designs with great scepticism, particularly when they see some of the prices! Still, more and more audio professionals are accepting that the quality of materials used in cables, and the type of construction chosen, can affect overall sound quality. There are plenty of companies advertising ready‑made cables constructed from exotic materials, such as silver and platinum (try www.kimber.com or www.purenote.com, for instance), but musicians mostly use cables terminated in either quarter‑inch jack or XLR plugs, and while both aforementioned companies offer XLR termination as an option, most others don't, and jacks aren't generally available at all.

If you want to see if you can hear the difference in your studio without spending lots of money, why not try making your own exotic cables? For some practical advice based on solid engineering principles, by someone who has presented AES papers, take a look at Jon Risch's web site (members.nbci.com/Jon_Risch). Jon has undertaken a huge number of tests over the years, using many different types and brands of cable, and presents a preferential list of conductor and dielectric materials ordered by audio quality.

He also recommends specific standard cable types from the huge US Belden company (www.belden.com/), mainly using standard copper conductors and foamed PTFE (Teflon) dielectric. Top favourites are apparently type 89259 for making up unbalanced cables, and 89207 for balanced cables. By the way, if anyone sells these by the metre in the UK please let me know, as I'd like to try some for myself!

There are also plenty of web sites offering recipes for home‑brew cables (see the comprehensive Hi‑Fi Tweakings site at www.tntÐaudio.com/clinica/tweaks.html, for instance), but since most of these involve creating cables from individual wires threaded down or wrapped around dielectric tubes, they're not very practical in the studio, even if you accept the claims made for them. However, you might want to try one for a short critical connection between mixer and amp, or DAT recorder and mixer, for instance.

If the pursuit of DIY cable excellence interests you, the real cable fanatics tend to frequent the Cable Asylum forum, which is one of many that together form Audio Asylum (www.audioasylum.com). Others are devoted to Pro Audio, Digital, and Music, while anyone into DIY Hi‑Fi Tweaks will revel in the dedicated Tweaker's Asylum. There is also a large and useful set of Audio FAQs at www.audioasylum.com/audio/faq.html.

Staying Grounded

Meanwhile, many of the more down‑to‑earth amongst us are still struggling with that most annoying of problems — the ground loop. When two or more items of audio gear are connected together to a common ground (or earth) point through different paths, you get one of these, and the resulting currents can cause 50/60Hz background hum, background noise, or even equipment damage in extreme cases. They will certainly prevent you getting the best results from modern 24‑bit soundcard converters. If you understand the causes of ground loops, it makes them far easier to track down and solve, and a little understanding might also save your life if it prevents you disconnecting earth wires inside a UK mains plug.

Paul White covered all the basics in the wonderfully titled 'Ground Control of Major Hum' in SOS August 1994 (https://web.archive.org/web/2015..." target="mainframe), and Tomi Engdahls covers much of the same ground in his Ground Loops page (www.epanorama.net/documents/grou...). He also provides a set of links to more specific grounding topics for the studio, such as rack installations, digital audio interfaces, and video installations. Whether you are an absolute beginner with a hum or an experienced engineer about to install a new studio from scratch, there's a link here that should cover what you need to know.

If you're not sure what some of the technical terms mean, Rane have a very comprehensive glossary in their Professional Audio Reference www.rane.com/digi‑dic.html), as well as a useful library (www.rane.com/library.html) that includes several detailed PDF articles about grounding and shielding. Further down on this same page is a list of technical notes, number 110 of which covers 'Sound System Interconnection'. Although this provides yet more information concerning ground loops, it concentrates on the right and wrong ways to connect your gear together, including transformer isolation, specially wired cables, and ground lifting, and has lots of useful diagrams. While the HTML version is the quickest to view, it's well worth downloading the 251K PDF version, since the diagrams are a lot larger and clearer.

RF Interference

Our planet is now almost totally bathed in radio frequencies, and while this may help us to keep in touch with world events and each other, it doesn't help audio quality at all, since both audio and mains wiring acts as an aerial, letting unwanted RFI (Radio Frequency Interference) into the audio chain. Problems can range from the obvious sounds of police radio messages and passing taxis appearing on our monitor speakers in extreme cases, to increases in audio background noise and distortion.

The majority of audio cables are screened to keep such interference at bay, but it may be worth using braided rather than lapped screen cable if you suffer from major RF problems, since this provides better screening coverage. You can also buy or make up screened mains cables (try www.tnt‑audio.com/clinica/merlino.html for a DIY one, using standard Radiospares components obtainable at www.rswww.com), although the benefits of this are debatable (more later).

Mind you, even if we screened our entire studios we wouldn't escape, since RFI is also generated by digital gear, from CD players to computers, albeit hopefully at the low levels approved by various standards authorities. Even if you hear no obvious audio problems, you can test for RF generation near audio equipment using an AM radio (www.audiotweaks.elosoft.com/Set0...).

Sometimes studio RF problems can simply be due to the existing screening and earths not making good connections with each other. You can remedy the fault by cleaning the offending contacts with proprietary contact cleaner/enhancers, such as Caig's DeOxit, for general use, or ProGold for plated surfaces (see www.caig.com for more details).

Persistent problems can also be cured by placing a ferrite clamp around the offending cable at the entry or exit point of the gear in question — at the output if you suspect the gear of generating RF, or at the input if external RF is getting in. You can buy these from many electrical retailers, including Radiospares and Studiospares.

Mains Wiring

For those building a studio from the ground up, Paul White and Hugh Robjohns's 'All About Studio Power And Wiring', in SOS August 1999, covers mains wiring in a straightforward way, helping you to make such decisions as whether to install a Spur or Ring main, and discussing the merits of RCBs (Residual Current Breakers) and the best way to distribute mains power around the studio.

But even with properly implemented mains wiring, you can still suffer from audio problems due to poor mains power quality. Interference can piggyback on the 50Hz/60Hz pure sine wave most of us expect the mains to provide, and unless this is filtered out it can get into circuitry and downgrade audio.

In the UK, Russ Andrews (www.russandrews.com) has spearheaded the attack on mains quality problems, and his range of cables, power conditioners, and mains filters is one of the best. He and Ray Kimber (www.kimber.com) also market plaited mains cables that capacitively filter out existing interference. Another site that discusses mains filtering is that of cable manufacturers Magnan Audio (www.magnan.com).

To take things a stage further, there are specially designed isolation transformers to remove common‑mode distortion (where identical interference is superimposed on both live and neutral lines). Read about the SmartLight Power Conditioner at https://web.archive.org/web/2015..." target="mainframe. Tice Audio (www.ticeaudio.com) have both US and UK models.

To bypass such problems altogether, you can instead use balanced power (also useful for running foreign studio gear ). A power amp and oscillator are used to generate local power, with a perfect sine wave at the desired frequency. Equitech (www.equitech.com/) claim to be the pioneers of this technique, while the PS Audio site (www.psaudio.com) also offers lots of info.

With quality cabling, good grounding, freedom from RFI, and clean power, your audio quality should improve significantly.

Quick Solutions

For a quick guide to signal problems and how to avoid them, look no further than Paul White's previous SOS article of the same name, which covers missing and intermittent signals, non‑computer‑related crackles and pops, hiss and hum (https://web.archive.org/web/2015..." target="mainframe).

Even if your studio is working well at the moment, there are things you can do to keep it that way. 'Preventative Maintenance In The Studio' (https://web.archive.org/web/2015..." target="mainframe) discusses the best way to keep your gear clean, your sockets and other contacts in good order, your power points reliable, and your fan‑cooled equipment properly ventilated.