My Rolls RM65b works - sometimes. The internal plus and minus 12V supply is powered from an external ("wall-wart") transformer via a 2-conductor plug. That means the plus and minus supply is is developed _without_ using a transformer center tap. I do not approve of this method, since the input voltage of either power supply regulator (7812 or 7912) with respect to ground can drift in voltage depending on the load. In my unit, the positive regulator will shut down on power up about half the time. I suspect, but I do not know, that this is due to the lack of a center tap connection.

Purchased new and have been using it live for over one year with no problems at all. It is so compact and inexpensive for a made in usa mixer I could not be happier.

My Rolls RM65b works - sometimes. The internal plus and minus 12V supply is powered from an external ("wall-wart") transformer via a 2-conductor plug. That means the plus and minus supply is is developed _without_ using a transformer center tap. I do not approve of this method, since the input voltage of either power supply regulator (7812 or 7912) with respect to ground can drift in voltage depending on the load. In my unit, the positive regulator will shut down on power up about half the time. I suspect, but I do not know, that this is due to the lack of a center tap connection. To be fair, I have not yet contacted Rolls service for resolution of the problem. Also, the schematic posted on the Rolls site shows a discrete-input circuit using 2n5087 transistors. These are not used in the unit shipped to me.

My Rolls RM65b works - sometimes. The internal plus and minus 12V supply is powered from an external ("wall-wart") transformer via a 2-conductor plug. That means the plus and minus supply is is developed _without_ using a transformer center tap. I do not approve of this method, since the input voltage of either power supply regulator (7812 or 7912) with respect to ground can drift in voltage depending on the load. In my unit, the positive regulator will shut down on power up about half the time. I suspect, but I do not know, that this is due to the lack of a center tap connection. To be fair, I have not yet contacted Rolls service for resolution of the problem.