Grounding Issues
Guitar rigs are complex electrical systems, and rigs with switching systems are among the most complex. The more
complex the rig, the more likely you are to encounter grounding issues. Every audio path in the system must be
shielded, with a good connection to ground, or you may get audio hum or buzz due to electromagnetic interference.
However, if there are too many connections to ground, you can get a ground loop, which also causes hum.
So, if you’re experiencing hum, what do you do?
Step 1: Press the Gnd Lift button on the back of the Rack Gizmo. This will either connect or disconnect the ground
connection to the Rack Gizmo’s metal enclosure. (In means disconnected (lifted), out means connected). If you’re lucky,
that will solve the problem.
Step 2: Are you using either the buffer or Click Stopper? If either is connected in your audio path, then you can skip to
Step 3. If neither is connected, try using the buffer. This may provide a needed path to ground. Also, for this test, make
sure that the Gnd Lift switch is in the out (connected) position.
Step 3: Check what you’re using to power your effect pedals. A multiple output power supply that doesn’t have
isolated outputs is a common source of ground loops. Power supplies that have “daisy chain” power cords, where there
are multiple power connectors on a single cord are definitely not isolated, and there are many other non-isolated
culprits on the market. You can test for isolation by unplugging the power cable from every pedal. If the hum goes
away, you need to upgrade to a better (isolated) power supply!
Step 3: If you have more than one amp connected, disconnect the audio connection(s) to one of the two amps. If the
hum goes away, you need an isolation transformer to isolate either the audio or power connection on the second amp.
Step 4: If you’re running a split effects setup where some pedals are connected to the amp’s input and others are
connected in the amp’s loop, you should try to use an isolation transformer on the lead running from the amp’s loop
return to the Rack Gizmo. Alternately, you can use a ground lift cable
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- it can work as well as an isolation transformer.
Step 5: If none of the above steps have helped, you’ll need to do some detective work. Begin disconnecting your
effects, starting with any rack-mounted effects. At some point, the hum will stop (at least, we hope so!) You will need to
use an isolation transformer or ground lift cable on the lead coming out of the effect’s output (and possibly the input as
well). Do this for the last effect you disconnected, and start reconnecting everything. If the hum comes back, isolate the
last effects device you just connected. Repeat this until you are hum free.
This is only a brief guide giving you the basic steps – there are, unfortunately, many other ways for ground loops to find
their way into your rig. If you can’t figure it out, you may need to enlist the services of a competent tech – someone
who’s used to chasing down these kinds of problems.
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A ground lift cable is an audio cable that has the shield or ground disconnected on one side. They’re very useful to have around
when building a guitar rig!
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