SYMPTOM
NOISE (LOW FREQUENCY HUM) IN AUDIO
1. Defective instrument cable or problem with bass wiring (unplug instrument cable from amplifier, if hum goes away, this means
that the noise is entering from outside the amplifier. Try known good instrument cable and/or bass)
2. Power source wiring is not grounded/earthed (check all wiring for missing grounding/earthing pins, have qualified electrician
check building power wiring for missing ground/earth connections and correct as necessary.)
3. External stray magnetic field present coupling into the pickups, especially single coils (one clue that this may be the cause is when
the volume level of the hum changes with position of the bass. Possible causes are large power transformers located near the
performance area, if this occurs when you get close to another instrument amp it may be due to stray field from its power supply)
SYMPTOM
NOISE (HIGH FREQUENCY HISS AND HASH) IN AUDIO
1. If the noise goes away when the instrument cable into the amp is unplugged, the cause of the noise is external to the amp (pos-
sibly an active preamp with the treble turned all the way up, a failing battery, defective on board preamp)
2. If there is neon or fluorescent lighting close by, it’s possible that EMI is radiating into the pick-up wiring (try turning off such light-
ing to see if noise goes away. If so, it could be an arcing secondary wire on neon lighting, failing ballast or tube on fluorescent
lighting, radiated EMI getting into instrument pick-up)
3. Power source wiring is not grounded/earthed (check all wiring for missing grounding/earthing pins, have qualified electrician
check building power wiring for missing ground/earth connections and correct as necessary.)
4. Tweeter turned all the way up in a quiet room (may need to turn tweeter down under such conditions, especially if the sensitivity
of the tweeter greatly exceeds that of the low frequency drivers with tweeter turned up)
SYMPTOM
PROTECT LED TURNS ON
1. Disconnect all cables except power cable, if the amp is no longer in protect, try plugging in just the speaker cable. If the amp
goes immediately into protect, one possible cause is a defective or damaged crossover that is presenting an illegal load to the
amplifier and the protection circuit is working correctly. (Try a known good speaker cabinet from another manufacturer to rule
this possibility out. If the amp works correctly with another speaker cabinet, call customer service for assistance. This is more
common with “do it yourself” speaker projects with incorrectly designed crossovers. ALL amps with PWM carriers are sensitive
to stored reactive energy in defective crossover tank circuits.)
2. Protect circuit shuts down amp while playing at low to moderate volumes (possible shorted speaker cable, try known good
speaker cable)
3. Protect circuit shuts down amp at moderate to high volumes (Verify that total load to the amplifier has not fallen below 4 ohms (or
2 ohms on models that support 2 ohms with the impedance selector switch set to 2 ohms). Possible causes are incorrect pairing
of multiple speaker cabinets, incorrectly labeled speaker cabinets that were repaired or modified without relabeling, defective
driver that has shorted voice coil turns as voice coil warms up.)
4. Power source voltage falling dangerously low due to improper wiring or extension cable that is too long for it’s wire size. (correct
problems as needed with the help of a qualified electrician)
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