Hum and Noise: It seems like there is a lot of talk and problems associated with hum and noise so lets go over these. I am an electronic engineer that specializes in music reproduction. I primarily make and design tube guitar amps, audio and digital audio products.

Ground Loops: This term came to be used for say you have your pedal board plugged into an outlet A and your amp into outlet B. Their common ground maybe at the panel and the hum that is caused is because there is an imbalance of current at the ground and that is now radiating through your system. See with single ended connection (i.e. TS) the ground is the reference for everything signal flowing through your rig.

Now this kind of hum can also be caused by the amplifier power transformer being wired inverted. Use a orange cheater plug and flip the power to see if the hum goes away.

Hum can also be caused by using a single outlet on your pedal board and daisy chaining that supply to numerous pedals. Not enough isolation is the cause of this problem. Some pedal companies (including some of my designs) have isolators built in such as the GigRig Isolator or Noise Cancelling Filter. Most pedals do not have isolated power.

Hum resides at either the root frequency of your mains (i.e. 50 or 60Hz) or 2x that frequency. If you hear 2x the frequency (i.e. 100Hz or 120Hz) then this is sometimes caused by your amp or power supply because most power is derived by what is called full wave rectification. Kind of like an octave up pedal, it multiples the frequency by 2 and smooths that into a DC voltage.

The best way to solve these problems is not very fast. Plug your guitar or bass directly into the amp. No hum then it is probably something leading up to your amp. If you have hum here then it is probably either some wrong with your amp, poor design or so much gain that anything close to the amp is being amplified.

Side Note Gain: Guitars put out very low signals, most companies represent a guitar as 10mvAc RMS output, but Barenaked Ladies front man Ed Robertson owns a Dennis Fano made guitar (#1) that outputs almost a volt. Anyway… So lets say you have a 25W amplifier then the gain required for full output is 1414 or 63dB. That is a crazy amount of gain so noise is a big problem for guitar rigs. Anything in and around and amplified that much will be crazy.

So back to solving these problems: isolate you pedal board and plug in pedals one at a time until the problem starts. Yes I know this is a pain in the ### but really that is what needs to be done. Look at your powering of your pedals if daisy chained then try an isolator. Solving hum with an active pedal should really be your last step. There are a lot of isolated power supplies but they are not really isolated. Yes they offer regulated separate outputs but most of them have common ground. I am waiting for someone to wind a power transformer with X# of secondaries to make a completely isolated power system. On your pedal board you have both a signal ground and a power ground that are tied together. So in some cases you are creating tiny ground loops on your pedal board. Again noise x 1000 = loud noise!

The key is isolation and sometimes that means a transformer. Which is how GigRig’s HumDinger works. Take a look at Dan’s work over at GigRig and how the power is taken from a single output and feed to a distributor that feeds isolators that feeds pedals.

High frequency noise: Lets face it we live in a world of RF these days with Cellular, WIFI, Bluetooth, switching wall warts you name it. Power is at an all time dirty. Plus again we are amplifying everything by a 1000 or more. Amplifiers that have tube rectifiers will block a lot of this. But cables, high gain pedals, switching supplies, DSP pedals (yes processor make noise) are all possible sources of this noise before it even hits the amplifier. Fuzz pedals and overdrive pedals are boosting the signal high enough to overcome the diode effect to creating clipping. That is enough to make some pretty nasty noise. If the pedal designer chooses to filter say high frequency energy then it changes the character of the pedal. Tube pedals that have DC to DC switching supplies inside (and yes all good ones do this). I would say powering Tube pedals from a separate supply is a really good idea in most cases. I made one that draws 32ma (based on the 6418 directly heated tube) and that works just fine in my system. But think of it this way…. any 12A(X, Y, T, U)7 tube is going to draw 300ma for the filament itself. Then you have to boost the 9V (or 12 in some cases) up too what 150-250V that takes a lot of current. So maybe any pedal that draws between 250-500ma should be powered from a separate power supply. This may not always be true but with testing may prove to solve your problem.

Know your pedals: Make a spread sheet or less geeky cheat sheet with all the power requirements and make sure your power source can handle it.