Humming or buzzing noise:
Unplug the guitar cord from the input and unplug any cable used for jumpering the two
inputs. If the buzzing stops, try replacing the cord. Be sure to use only guitar cables, not
unshielded speaker cables! If in doubt, unscrew the connector and look to see if there is
a shield around the center connector. Some smaller speaker cables are easily mistaken
for guitar cables. Fluorescent lights and light dimmers can be a source of hum/buzz, as
can computer monitors.
If the buzzing only occurs when using effects or a tuner, the problem is likely a ground
loop hum (in particular, the Korg rack mount tuner seems to be susceptible to ground
loops). If this is the case, the hum/buzz will go away if the guitar is plugged straight in to
the amplifier. The solution is to use a ground loop hum eliminator (there are a few on the
market) or make a guitar cord with a "telescoping shield" to go from the output of the
effects to the input of the amp. This is a cord with the shield cut on one end. The cut end
should go into the amplifier input jack, and the end with the shield must go into the output
of the effects unit/tuner. In a emergency, a ground lift plug (three-prong to two-prong
adapter) can be used on the tuner/effects box, but this is not recommended due to safety
concerns. If you do use a ground lift adapter, you should check to see if there is any AC
voltage present from the chassis of the rack effect/tuner to the chassis of the amplifier. If
so, do not use the adapter!
If the buzzing only occurs when playing the guitar, try replacing the speaker or plugging
the amplifier into an extension speaker cabinet. A buzzing noise from the speaker can
indicate a blown speaker, or one with a warped frame. Buzzing noises that occur only on
certain notes can be indicative of a cabinet problem. Check all rear panel screws, handle
screws, and chassis mounting screws to insure they are tight. Check to insure there are
no speaker or reverb cables rattling against the baffle board. Check the two screws that
hold the nameplate to the front of the amplifier, as the nameplate can cause a rattle or
buzz if it is loose enough to vibrate against the front panel board. If the nameplate
buzzing cannot be stopped by tightening the screws, a small piece of double-stick tape
affixed to the rear of the nameplate will dampen the vibration. Some speakers are known
to exhibit "cone cry", or "ghost noting", which is a second, out-of-tune note that occurs
only when playing certain notes on the guitar. If this is suspected, try another speaker to
see if the problem goes away.
Some preamp tubes are more susceptible to filament-induced hum than others. The
ECC83/12AX7 is a dual triode (two tubes in one package), and some tubes will exhibit
hum in only one of the two sections, or in both. Try replacing the preamp tubes with
different ones to see if the hum decreases. The JJ/Tesla ECC83S is the least
microphonic and least noisy current-manufacture tube we have found, but are a bit
compressed sounding compared to longer-plate tubes, and as such, may not be
preferred by everyone. The Chinese 12AX7s are a good compromise between low
microphonics and a more “open” tone.
Hissing noise:
A small amount of hiss is a characteristic of higher-gain tube amps, and is generally
unavoidable. Excessive levels of hiss are usually caused by bad preamp tubes.
Some preamp tubes have more hiss than others. Try replacing the preamp tubes with
different ones to see if the hiss decreases.
IntruderMKIIManual.doc 06/17/13 Page 15 of 17
Copyright 2004-2011, Aiken Amplification, Inc.
