Ripple (specifically ripple voltage) in electronics is the residual periodic variation of the DC, or direct current voltage, within a power supply using an AC, or alternating current, source, like the electrical outlets in your home or studio. If you're curious, you can read all about DC versus AC current at electrical4u.com/dc-current.
Ripple is wasted power, and has many undesirable effects. It heats components, causes noise and distortion, and may cause digital circuits to operate improperly. Ripple can be reduced by adding the aforementioned electronic filter into the circuitry, to ensure that the pedal is getting the proper juice. There are parts called electrolytic capacitors that do a lot of the heavy lifting in this section of a circuit. You can learn more about capacitors at a variety of websites, including Wise-Geek.com, Techcircuit.org, Beavisaudio.com, and coda-effects.com, and you can see what they look like above.
Ripple is wasted power, and has many undesirable effects.
Those of us who love and cherish old amps know all about capacitors. The first thing I do when I acquire a gem from yesteryear is take it to a qualified amplifier technician to have it thoroughly inspected, and to have the power filter capacitors replaced with new ones. The reason for this is that over time these capacitors can dry out and cause the amp to not function properly, or to just simply stop working. In a worst case scenario, it can even cause electric shock.
When an electrolytic capacitor is going bad, it can appear to be deformed, sometimes bulging out at the ends. If the power filter capacitors—or really any of the electrolytics—look like this, it's a sure sign that it's time to take the amp to a tech for them to be replaced. In some cases, there might not be any visual indication at all when a cap goes bad. Most amp technicians I have dealt with say that a good rule of thumb is to replace these capacitors every seven years or so.
For reference, here's what caps can look like when they're blown:
The electrolytic capacitors in effects pedals also wear out over time. As in amps, caps in pedals are used for multiple purposes. Coupling capacitors let AC pass through them, but not DC. And RC (resistor-capacitor) filter caps cut off frequencies above or below a certain threshold. But the classic role is the one we're discussing here: smoothing out ripples in the power supply. Capacitors have what is known as an "end of life cycle." This means that the manufacturer only guarantees them to remain fully functional for a certain amount of time. That time frame can typically range anywhere from 1,000 to 5,000 hours.
There have been a few occasions when I have purchased a vintage pedal I had been trying to find for ages, only to get it plugged in and find it unusably noisy and/or dull-sounding. I usually re-cap these old circuits before I do anything else to them. This usually brings the pedal's power back to its former glory, ensuring that the unit will behave as it was intended to for another decade or so. I would say nine times out of 10, replacing these capacitors creates a massive difference in clarity and sound. Take a look at one of my recapped circuit boards:
Keeping your pedals healthy internally is a great way to ensure that they will last lifetimes. Having them re-capped is one way to help maintain the integrity of the circuits inside. I am so glad I discovered this when I was early in my career as a pedal user and builder. It has certainly given a few of my formerly fallen soldiers a new lease on life.
Fig. A
Oh, how I wish that was the only means of making a ground loop! Tennyson certainly didn't have ground loops in mind when writing that nature was red in tooth and claw, but as someone who has built guitar rigs for around 25 years, it is hard to shake the idea that they serve a merciless and maniacal natural force that actively resists the pristine and well-ordered world of quiet, toneful pedalboards and rack systems.
These loops are made by the way we wire our stompboxes and the environment around them. The ones in this month's ground loop fest may be a bit more identifiable than the loops in the multi-amp scenario. In that case, part of the loop is hidden in your venue's installed power cabling. This time, we're going to discuss loops that exist wholly and entirely in your pedalboard itself.
"Tennyson certainly didn't have ground loops in mind when writing that nature was red in tooth and claw."
The first ground loop we'll discuss is a potential loop created by using daisy-chain power cables, where one power supply feeds multiple pedals. In this setup, you can make a loop via the power cables connecting two pedals and the audio cables connecting them. There is a clear ground path in Fig. A that goes from stompbox to stompbox via the audio cables. If that were the only path, there would be little chance for a loop to be formed. But if you add in the ground path made by the power cables, you can now see a circuitous path that connects the first and last pedal through the audio cables and then doubles back through the power daisy chain. This circle of wire is our loop.
A second loop type is shown in Fig. B. Most loop switchers tie the ground connections of the send and return jacks together, and when the loop switcher is connected to a stompbox, the audio cables make a ring of ground conductors. So each loop switcher loop can actually make a ground loop. Yay!
There are countless loop switcher-equipped boards out in the world. Why don't all of them hum? Ground loops can generate hum when they are driven by an outside electromagnetic field. (Bill Whitlock's Audio Engineering Society treatise "Ground Loops: The Rest of the Story" gives great theoretical and experimental explanation of EMF—electromotive force—induced ground loops.) When the ground looped cable encircles an EMF field, that field can develop a current in the wire that can translate into audible hum in your rig. So if your power/audio cable loop or your loop switcher loop wraps around a power supply transformer or a high-current, noisy power cable at a venue or in your home, you may get an induced hum that you can hear in your amplifier's output.
Fig B.
So, what can be done? Fig. A shows how daisy-chained power can make a giant ground loop susceptible to picking up stray EMF. Using isolated power for every pedal will break this loop and keep it from generating noise. If you must share power amongst pedals on your board, make sure they are next to one another in your signal chain so that the loop size (and associated hum) is minimized.
For Fig. B, the cables to and from the pedal can be as short as possible and run as close to one another as possible. This too will decrease the area encircled by the loop and commensurately minimize the induced current. Special care should be taken to make sure looping cables do not surround or run near power supplies or wall warts. The type of power supply can make a difference as well, since those from Truetone or Strymon switch at higher frequencies that are less likely to be induced in the first place, and less likely to be heard if they are.
While this is hardly a 100 percent complete picture of the cruel world of ground loops, you hopefully are armed with enough knowledge to have insight into exactly what could be causing those wayward noises and buzzes in your rig and how to clear them out to make way for a much more gratifying set of buzzes and noise.