UPDATE: I received an email from Aguilar regarding the use of 9V power supply and I quote, "...do not use 9V power supply. While the pedal will power up - you are not getting the full head room capabilities of the preamp - plus, this could cause damage to the unit in the long run." Suffice to say, I will be getting a 18V PSU and informing the staff at Sam Ash that they are incorrect telling customers that it works with 9V.I just bought the Tone Hammer and even though it calls for 2(9v) batteries or the 18V PSU, mine seems to be operating fine on 9V daisy chained with my other pedals on one PSU. Right now I don't how the 9V is impacting the performance of the pedal versus the performance with 18V.