Så här står det i manualen.
A NOTE ABOUT POWERING THE BASS COMP
For maximum headroom and performance, the Bass Comp should be powered using the included 18V, positive tip adapter. However, for a situation where the 18V adapter is unavailable, the Bass Comp can be powered from a standard 9V, negative tip power supply provided the included red polarity reversing cable is used. The polarity reverse cable should not be used with the supplied 18V adapter for normal operation.
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