Having a quiet guitar rig brings the magic, while a noisy rig can ruin the vibe, especially for high gain players. As always, we try show folks cost-effective ways to have better rigs. How to reduce noise using simple power supplies is part of that effort.
The helpful info on this page applies to all guitar rigs, whether you use or not. We offer the three examples below for a reason: If you understand these three, then you can figure out most any isolation or ground loop hum problem.
Digital pedals produce some of the best effects around, especially in clean, time-based modulation type effects. But a few of them can be noisy on power chains.
Ground Loops And ........ Social Distancing
They are, for the most part, very quiet pedals as well. And they keep things around them quiet by good filters on their power lines.
But some don't keep things around them quiet. They let their clock noise escape into their power lines. So if connectoed to a power chain, a special kind of whine noise can find its way into the audio lines of other pedals on the chain.
So, like a problem child, these noisy digital pedals must be isolated from the other children. The problem pedal must be powered by itself on its own isolated power transformer.
Pedalsnake: Isolation And Grounding
With , when isolating power, use two separate MF1-H Single P-Line Pigtails, or MF2-I (or MM2-I) Dual Isolated P-Lines on the white 5wire channel. Any 2 isolated power supplies, or power isolated outputs, will work. When isolation is not required, MF2 Dual P-Line can power pedals of different voltages, like an 18V pedal mixed in with 9V pedals. Use only isolated DC power supplies with MF2.
Slightly different grounds can exist in devices, even if they are plugged into the same outlet. This is worse when one or more of the devices draws a lot of AC current from the wall, like a tube guitar amp.
Tube amps draw a lot of current, and their power transformer can induce small voltages into the grounded metal chassis. When different ground voltages are connected together, either through audio lines or pedal power chains, and audible hum can result. Stereo amps are often the worst offenders.
Ground Lift On Amp Di Revisited (gk Content)
NOTE As with the example below that uses two amps, isolating with two power supplies can help with FX Loops too. This is needed more often in higher powered all-tube amps. Using two separate isolated power supplies—one for the chain of pedals going to the amp input, and another for the FX Loop pedals, can keep grounds currents out of the audio lines and reduce hum.
Because they are the most common offender, we will use two stereo amps here as our example. In the first case, a pedal power chain is the culprit that ties the grounds together.
If the grounds of two stereo amps are tied together by a power chain, and the induced ground voltages are slightly different, 60Hz ground loop current will flow in the grounds of the audio guitar cords. Hum is the result.
Fixing Ground Loop In Stereo Tube Amp Setup
We are often told the only way to fix this is do away with the power chain. We must rush out and buy an expensive power supply with multiple isolated outputs. Yes, that will fix it, but it is also expensive.
In fact, due to the currents induced into the chassis by the transformers, voltages can even be slightly different at different points on the same metal amp chassis! So it can sometimes help to reduce hum by isolating power chains going to the same amp. Use one isolated power transformer for the amp-input chain, and another for the FX Loop chain.
The analysis here is the same as for Power Chains (above). Slighly different grounds can exist in devices, even if they are plugged into the same AC power outlet.
The How's And Why's Of Ground Loops
This is worse when one or more of the devices draws a lot of current from the wall. Tube amps draw a lot of current. This current flows in the windings of their power transformer, which can induce small voltages into the grounded metal chassis.
If the grounds of two amps are tied together by a stereo pedal, and the ground voltages are slightly different, 60Hz ground loop current can flow between the amps in the ground wire of the audio guitar cords. Hum again is the result.
Unless one output of a stereo pedal is isolated with a signal transformer, the grounds are being tied together by the two guitar cords going to each amp's input. So ground currents flow in the audio signal ground, causing hum.
When The Guitar Amp Didn't Came With A Ground Wire
When isolating audio with , you must keep the grounds of the cables separate. So if the audio transformer is on the pedalboard, use two separate RS1 Single G-Line Pigtails to go from the board to the two amps. Do NOT use an RS2 Dual G-Line, because the 2 lines share the same ground wire.Years ago I touched a guitar that was plugged into an amp against a radiator, and it blew the amp and melted the guitar string. Afterwards someone told me that this was caused by a ground loop, but I've never actually understood what that means.
Technical Editor Hugh Robjohns replies: That wasn't a ground loop — that was a faulty amp with a missing safety earth. There was no loop, because there was no earth at all until touching the radiator provided the missing link. Had you sat on the radiator and then picked up the guitar, you might well have been playing Emaj7 on a harp on a fluffy white cloud by now!
This is a distressingly common and life-threatening situation often caused by guitarists (or their so called 'technicians') in a futile effort to stop audible hums.
Q. What Is A Ground (earth) Loop?
A ground loop is different — it occurs when there is more than one ground path between two items of equipment. Usually, one path is the screen of an audio cable connecting the two pieces of equipment and the other path is via their chassis safety earths in the mains plugs. Inside the equipment, the audio screen earth is often linked directly to the chassis earth, hence the possibility of a loop. If the two bits of equipment are plugged into the same mains socket, their chassis safety earths are effectively tied together at the same potential, and so there is unlikely to be any circulating ground current, despite the apparent ground loop. However, if one item is plugged into a different mains socket, its chassis safety earth might be grounded some way away from the other equipment's earth, and there can be a small difference in potential voltage between them. Silly as it sounds, earth is not the same everywhere. The potential voltage difference between their two chassis earths can cause a small current to flow, and since the earth provides a reference for the audio electronics, that flowing current causes the earth reference voltage point to vary slightly. This can be heard, usually as a low-level hum or buzz.
Ideally, the solution is to make sure that everything is earthed at one central point, so that everything shares the same common earth reference point. The easiest way to do that is to plug everything into a star arrangement of plug-boards fed from a single socket (assuming suitable power capacity). If that can't be done, the safest solution is to break the loop by isolating the audio cable screens at one end. The cable is still screened, but there is no longer any possibility of a loop, so the hum currents can't flow around it. Inserting transformers in the signal path can also break the loop, and this solution is common in outside broadcast and live sound rigs. DI boxes feature transformers for this purpose too.
Problems arise when uninformed people decide to break the loop by removing the safety earth in the mains plug instead. This does break the loop, obviously, so any related hum will disappear. But it also means that the equipment is no longer earthed, and thus any fault that occurs in the equipment is now life-threatening! Sometimes you don't even need a fault to cause dangerous problems, though. Most equipment has filtering on the mains input to stop mains-borne noise getting in (or out). If you disconnect the mains earth in the plug, the nature of that filtering is such that the (previously earthed) chassis — and everything connected to it — 'floats' up to half mains voltage (making it about 115V in the UK). This means everything that should be safely earthed — all the exposed metalwork, including guitar strings — now carries a life-threatening voltage.
Klotz Ground Lift Adapter, Xlr, 0.2m At Gear4music
Going back to your guitar incident, the strings on the guitar are supposed to be earthed through the guitar lead to the socket on the amp. That, in turn, is usually connected to the amp's chassis earth, and thus through the mains plug to the mains safety earth. Metal radiators are connected to the mains safety earth point too, as is all house plumbing.
So if you have a guitar amp with the safety earth disconnected in the plug, the chassis
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