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Minimising Noise In Electric Guitar Rigs

Guitar Technology
Published August 2006
By Dave Lockwood

Above: A properly screened Strat-type guitar. To make a significant difference, the whole surface area of the pickup and wiring cavities must be covered and connected to the earth side of the circuit. There must be electrical continuity throughout, and in this example, every join in the copper foil is bridged with solder.Above: A properly screened Strat-type guitar. To make a significant difference, the whole surface area of the pickup and wiring cavities must be covered and connected to the earth side of the circuit. There must be electrical continuity throughout, and in this example, every join in the copper foil is bridged with solder.

Electrical noise — hiss, buzz and hum — is something that plagues every electric guitarist to some degree, but noise comes in a variety of forms and it is important to establish exactly which kind(s) you are experiencing in order to devise an appropriate solution. Most noise in an electric guitar rig emanates from one or more of five different sources: amplifier self-generated hum and/or hiss; hum or buzz picked up by the guitar itself; self-generated noise from any pedals/processors in the circuit; gain structure-related noise, such as cascaded distortion stages; and ground-loop-related hum. If you think you are suffering from noise that isn't generated in one of these ways, I'd like to hear about it!

The most efficient way to track down noise in a guitar system is to think of the amplifier or studio monitor system as the end of your signal chain and work systematically back from there. If you don't do this, you have no idea whether the noise you are hearing from the amplifier is being generated within the amp itself, or being picked up by the guitar and fed to the amp. You could end up taking steps to solve a problem you don't have, as well as completely failing to solve the one you actually do have. If your amp or monitoring system hums or buzzes excessively with no input connected to it, then you've got an equipment malfunction. That is beyond the scope of this article, so for these purposes I'll assume that that part of your rig is clean. From here on, I'm also going to treat amps and recording processors (Line 6 Pods and the like) as the same, because it is the 'upstream' noise of the guitar itself and related systems that we are interested in.

Left: A small tag of copper foil is used to continue the screening onto the underside of the shielded scratchplate. Passing one of the scratchplate screws through it ensures consistent contact.Left: A small tag of copper foil is used to continue the screening onto the underside of the shielded scratchplate. Passing one of the scratchplate screws through it ensures consistent contact.

When tracking down noise it always pays to initially reduce your system to the minimum number of components, so begin by connecting your guitar directly to a single amp or recording processor via a screened cable, set the volume of the amp or monitor system to a normal operating level, turn the guitar's volume control all the way down and just listen. If there is any more noise than there was before the guitar was connected then the cable is at fault. With nothing connected, the amp's input jack will be automatically short-circuited to ground; with the guitar connected, but turned down, the input is again shorted, but at the other end of the cable, so the cable is the only variable.

Assuming all is well with the cable, now turn up the guitar's volume to maximum, hold the strings in a normal playing fashion and listen again. If you hear no more noise than before, congratulations; you must have a fantastically well-screened guitar and the perfect guitar-recording environment. The rest of us will be hearing at least a bit of buzzing and maybe a bit of 50/60Hz hum as well. Move the guitar around over an area of a few feet either way to see if the hum goes away. The level of hum is usually directly related to the guitar's proximity to any large mains transformers in the room. If you are using conventional (non-hum-cancelling) single-coil pickups and you are within the radiated field of a mains transformer, you will get hum. Exactly how much depends on the gain in your system and your proximity to the source. If you can't work out the origin of the hum field, try switching off everything except your amp (or monitor system, if you are DI'd) and then switch things back on one at a time to see when the hum reappears. When it does, see if you can re-site the offending item further away. The only solution is physical separation, as the amount of additional screening required to keep induced hum out of the pickups would actually prevent the guitar working at all. Of course, if you are using humbucking pickups, you are in the clear on this one, but the chances are you'll still have some 'buzz'.

Buzz has a lot more high-frequency content than hum. If you are unsure which you have, try turning your guitar's tone control all the way down; if the noise mostly goes away, you are dealing with buzz rather than hum. Buzz will also often be greatly reduced when you touch the strings or any other metal part of the guitar, sometimes accompanied by an audible click, whereas hum will remain unchanged. The common explanation for why noise goes away when you touch the strings or metalwork is that you are adding to the overall amount of screening. I'm not so sure about that, because certain types of noise actually get louder when you hold a guitar close to your body without touching the strings. This suggests to me that the player's body is, effectively, conducting the interference into close proximity with the guitar. The noise goes away when you touch the strings because that interference is safely conducted away to ground.

Unlike hum, which is generally induced directly into the pickup coils themselves, buzz gets in everywhere, so any bit of unshielded wiring can be the source. Even guitars with humbucking pickups will often still buzz. This is, understandably, very frustrating if you've just shelled out for a set 'noiseless' pickups for your Strat and find out the instrument is just as noisy as before; it no longer hums, but the amount of buzz is unchanged because the noise is getting in via the control cavity and the unscreened wiring rather than the pickups. The only answer is to screen every part of the internal electronics with copper foil or conductive paint, which is then connected to the earth side of the circuit. Do not attempt to screen the pickups themselves, or even the pickup covers, however, as this will alter the sound.

'Noiseless' single-coil pickups, such as these models from Kinman and Dimarzio, will cancel hum effectively, but noise can still get into the system via the wiring and controls.'Noiseless' single-coil pickups, such as these models from Kinman and Dimarzio, will cancel hum effectively, but noise can still get into the system via the wiring and controls.Screening will make a major improvement, but if you are using single-coils with a high-gain setup or lots of compression, you will still have some noise pickup. Buzz is often sensitive to the angle at which you hold the guitar, however, so you can always try to find the 'null point' at which the noise is least intrusive and simply do your best to keep the guitar at that angle whilst recording. It sounds crude, I know, but pro Strat and Tele players have worked that way in the studio for years because, until recently, there were no hum-cancelling single-coil pickups that sounded enough like the real thing to make the trade-off worthwhile.

The most common sources of buzz are TVs and CRT computer monitors, computers themselves and lighting dimmer switches. Just occasionally you'll also find a poorly designed external power supply for some piece of equipment in your rig that puts buzzy noise back onto the mains and thereby affects everything in the room. So, switch the TV off, use a flat-screen (non-CRT) monitor if possible, site your computer over four feet away, dump any noisy PSUs and use only conventional incandescent lighting.

If you've done all of those things and you've still got a nasty, edgy-sounding buzz, then the chances are that there is a lighting dimmer involved somewhere. The trouble is, it doesn't have to be your dimmer — lighting dimmers can affect you from an adjacent room, or a room above or below you. And it doesn't even have to be the dimmer itself — the cable running between the dimmed lamp and the dimmer control can also emit interference and this is often routed across the middle of the room within the ceiling void. Dimmers make most noise when they are actually dimming, so the noise will improve slightly when you turn the dimmer all the way up, but only switching it off altogether will make the interference go away. Dimmers that work on an entirely different principle and do not create electrical interference are just starting to appear on the market — watch this space for news.

Over the next few issues we'll tackle sources of noise beyond the guitar itself: pedals, cascading gain stages and earth loops. Dave Lockwood

Guitar Grounding Practicalities

If touching your guitar's metal jack socket when your guitar is connected to the amp kills the noise, but touching only the strings doesn't, then you may have a faulty grounding connection inside the guitar. Invariably there's a wire connected to the back of the pots or the cold side of the output jack that connects to the bridge directly or via the tremolo spring anchors, so check that this is intact. If you're not sure, make a temporary connection with another piece of wire to confirm your suspicions. Pretty much anything will do. If the hum goes when you fit your piece of wire, then the existing ground wire is broken or detached somewhere.

If you hear electrical noise (including crackling) when you move the tremolo, that's probably because the tremolo springs or some other non-moving part of the tremolo is grounded, but the strings are connected to it only via the tremolo pivot points, and if these don't have a very low electrical resistance at all times, you'll get noise that will vary as the resistance varies. Spraying a contact enhancer such as DeOxit on the pivot points can help, but in some tremolo designs it may be best to use a thin, very flexible wire to ground the moving part of the tremolo providing you can find or create a suitable attachment point, such as a tag washer fixed under one of the existing screws.

Strat Pickup Combinations

You can combat both hum and buzz in Strat-type guitars by using a reverse-wound, reverse polarity middle pickup (as the name suggests, the magnets are the other way up and the coil is wound the opposite way) and most modern (non-vintage reissue) Strats are now wired this way as standard.

When used in combination with either of the other pickups, the RW/RP pickup creates a parallel-connected humbucker. Noise, which is induced into the coils only, is cancelled out as the two coils are, effectively, out of phase, whilst the strings are sensed by the magnets, initially out of phase (due to the reverse polarity of one of the pickups) and then restored to in-phase by the reverse winding. The net result is a clean signal with no noise. It works a treat, but only in switch positions two and four, which, ironically, are the ones that you would rarely choose for high-gain work.

Carl Martin Surf Trem, Crush Zone & Red Repeat

Effects Pedals

Designed by East Sound Research of Denmark, Carl Martin's Vintage range of pedals is designed to offer both tonal quality and mechanical longlevity, hence the chunky cast metalwork, chicken head knobs and mechanical bypass switches. All three models reviewed can be powered by means of a standard 9V battery or an external power supply, and the battery compartment is easily accessible without tools by means of a lift-out flap on the underside of the case. Rubber feet keep the pedals from creeping and they're heavy enough to stay put without being too heavy to carry around in your gig bag. The input and output jacks are on the edge of the case away from the player.

Finished in surf green, the Surf Trem (£54.99) is the simplest of the pedals and has just two controls other than the mechanical bypass switch and red indicator LED shared by the other models in the series. This is a straightforward tremolo effect, taken directly from the Carl Martin Tremovibe, with depth and speed controls that cover all the range you're ever likely to need. Depth adjusts the amount by which the level is modulated while Speed sets how fast the level wobbles. While this pedal doesn't do anything unusual, it does work extremely smoothly with no obvious noise or unwelcome thumping, and the bypass switch seems pretty quiet too.

Guitar TechnologyThe Crush Zone (£54.99) is an old school distortion box with controls for output level, tone and distortion. It has a raunchy, raspy character reminiscent of the old MXR Distortion Plus that straddles conventional overdrive and fuzz. A tone knob can be used to smooth out the tone but even at the minimum drive setting, you can't really clean up the sound by backing off the guitar's volume control, so this is definitely a 'step on it and blaze away' kind of pedal. Within its genre, Crush Zone delivers exactly what is expected of it. It's great for power chords or solos but is perhaps less well suited to blues or country rock.

There's little detailed technical info on the Red Repeat (£79.99). Apparently it was derived from the Carl Martin Delayla pedal and, from the sound of it, it is either an analogue (charge-coupled delay line) delay pedal or an extremely good emulation of one. My money is on true analogue, though none of the available literature comes out and says it in so many words. In addition to controls for Echo Level, Time and Repeat (feedback), it also has a tone control that can be used to darken the sound of the repeats. At long delay times (the longest of which is 600ms), there is a little background noise in evidence, though rolling off the top end using the tone control masks this pretty well. The repeats get darker and grittier each time around, which is actually a lot more musical than the pristine delays of a standard digital delay pedal, and at more practical delay times of 400ms or less with just a bit of top rolled off, the effect is exactly right.

Unlike tape echo units (or their solid-state equivalents), which may use multiple heads to produce multiple delay taps, this one generates a single delay that can be made to repeat to a greater or lesser extent using the Repeat control. If you crank this up too far you get the familiar swirling, out-of-control effect so beloved of dub producers, but normally you'd keep away from such extremes. The old analogue delay sound is definitely something special and the Red Repeat captures it perfectly.

While these pedals offer nothing radically new, they are sensibly priced, extremely solidy built and the sounds they produce are exactly right for their respective genres. It is still worth checking out the usual suspects such as Boss, especially where distortion is concerned, as that company offer so many different variants of fuzz, distortion and overdrive. However, I respect the 'built like a tank', no-nonsense approach taken here, and I can see no reason why these pedals shouldn't outlast their owners. Paul White

SUMMARY: Retro sounds and styling from a well-respected effects designer. 

First Line +44 (0)1392 493429.
www.carlmartin.com

Published August 2006