GROUND ISOLATION SWITCH: This mini-rocker switch is extremely useful in reducing the hum
and buzz caused by ground loops which occur in rack installations. Ground loops occur when there
is more than one path for grounds between electronic units. There are three main type of ground
loops: each one contributes its own trademark component of buzz or hum. The three types of
ground loops are:
1) Grounds are connected via the ground lugs of the power cords on the units. The rule-of-thumb
here is that one and only one unit in a rack should have a connection to the AC power ground; all
the other units in the rack should have their grounds lifted by using 3-to-2 adapters on their AC
plugs.
2) Ground loops occurring because of two or more audio cables connecting two components. The
most common solution is to disconnect the shield from the sleeve connection at one end of some of
the inter-connecting cables, so that only one cable between each device has an intact ground shield.
Some experimentation is required to find which cable is best for conducting the ground, and which
cables are best suited to have the special "clipped ground". We recommend trying the intact-ground
cables for the signal path which flows, say, from the Preamp’s Effects Send to an effects unit; and
trying the clipped-ground method on the cable which connects the effects output back into the Effect
Return on the Preamp.
3) Ground loops created by the physical contact between the metal chassis of the components and
the steel rack rails. It is for this third type of ground loop that the Ground Isolation Switch was pro-
vided. The switch effectively lifts the electronic circuit ground from the metal chassis ground
(which otherwise must be done manually by disconnecting a wire inside of the Preamp). Here
again, the rule is that one device in your system - and usually only one - needs its circuit ground
connected to its metal chassis ground; all others should be lifted (in other words, disconnected) for
quietest operation. (Some effects units provide similar switches; some are constructed such that the
input ground and the output grounds are permanently separated; in other cases, the method used to
isolate the grounds is unclear). Again, some experimentation is vital to discovering which combina-
tion of "lifted" and "grounded" works best in your rack....and out
Ground Isolation Switch makes it much easier.
NOTE: If the Studio Preamp is operated outside of a rack installation, the switch should generally
be set to the Normal position, or else squealing, buzzing and oscillation may occur. Always check
this switch before thinking that something has gone wrong with your Preamp!!
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