[mikethedruid]

The battery holder holds 8 1.5V batteries, and provides 12 volts total, as does the AC adapter. The positive goes to ground and the negative goes to one side of the power switch. See the diagram at the very lower right of the schematic. You will need a very low noise power supply putting out 12 volts DC and 45 ma MINIMUM. On the auction site I see a suitable power supply for less then $10, 12 V DC at 1.5 A. You may have to adapt its connector, and add a large filter condenser to the output, say 1000 mfd, 25 V, but it should work OK.Be sure, when you make the power adapter, that the positive goes to ground and the negative goes to one side of the switch. If there is currently an input jack for this, check how it is polarized.