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If your speaker cabinet is 8 ohms (this information is usually on the jack plate of the
speaker cabinet) simply set the impedance switch to 8 ohms. The same applies for a
single 2 or 4 ohm cabinet.
If you are using two 8 ohm cabinets in parallel (both connected directly to the
back of the amp), the impedance value is halved, and the impedance switch should be
set to 4 ohms. For two 4 ohm cabinets, set the impedance switch to the to 2 ohm
setting.
Your amp needs to be set at the proper impedance for full power and reliability.
Fan Switch:
Rear Panel
The fan is ultra quiet, and is always on to provide the necessary cooling to the
components. There is a low speed setting for use in the quietest environments. We
recommend using the high speed whenever possible as this will help facilitate the
longest tube life.
Signal Ground Lift:
The signal ground lift jumper, located on the rear panel, connects the audio circuit
ground to the chassis ground (earth). This should be left in place under most
circumstances. An exception would be if connecting an external preamp to the DB
728 causes an audible ground loop. In this case removing the signal ground jumper
will eliminate the ground loop. Note that this can be done only when an external
device is connected to the input of the DB 728. With the signal ground jumper
removed, the DB 728 will hum in the absence of a connection.
