FUQ (eff -yu - cue) - FAQ's with an EDGE

Tagged As: Randall Guitar Amp

Question:
What causes an amp, a new one at that (Randall RX30D) to have a background hum and a bit of static? - Even at low volume/gain levels. More importantly, how do I get rid of the hum/static? Or, at least reduce it.

Answer:
First elminate any ground loop issues. A ground loop is a situation where you may be inadvertently grounding a device in multiple places at varying potentials. Because the impedances of these grounds are different, an ac current can still flow in the ground path causing hum. Guitar cables, effect cables, mixers, etc. all provide paths to ground in your signal chain. Unplug anything in the effects loop, and inputs, volume pedals, etc. IOW unplug all signals. Does the amp still hum with everything unplugged? If so move the amp to a more isolated location. Does the amp still hum with everything unplugged? If so, take it in for warranty work or exchange, it's probably the amp, unless your house is crawling with emi. If no hum with everything unplugged, then start by just plugging in the guitar. Did the hum come back? If yes, then make sure that same guitar does NOT hum with a differnt amp in the same general location. If it's not the guitar then it's the way that guitar interacts with that amp, try a pre-amp in front, different guitar, etc. If no hum move on to any effects... IOW, simplify, to try to isolate the hum and find a potential ground loop. Other hints: Use a single power strip for all devices in your chain. Keep things far enough away from stray AC fields especially for single coil PUP's, (these new energy efficient compact flourescent light bulbs make horrendous amounts of line noise and horribly ugly light too). Motors, computers, tv's all can emit near field em. If using a complicated array of parallel effects, or a long array of serial effects, try to make the first effect in the chains the ones with the healthiest output signals, or use a uncolored transparent buffer pre-amp first in the chain. Test your grounded outlet with a polarity tester (small plug with LED's available from home centers). This is more a safety issue, but an open ground or reversed neutral is not good. If it's a tube amp, then swap power tube sets with a new set, check for hum. If it still hums swap the pre-amp tubes one at a time. (do power tubes as a matched set though).