Interesting...the date on the circuit board says 02/03/04. I'm guessing this is the manufacturing date? Is this still a mark I?
Also, could you give an explanation as to why you think the parallel loop knob is constantly on? Can it be fixed?
Ps. Used it live for the first time last night..it was awesome!
Cheers from Melbourne Australia!
The Herbert MK2 production started in late 2010 so your Herbert is definitely a MK1 model. There maybe some confusion about that because some people called older models also MK2 because of the differences concerning bias adjustment from outside. Officially however everything prior late 2010 is Herbert MK1.
The parallel loop poti acts as a mixer between the dry preamp signal and the processed effect signal. It doesn't change the signal amplitudes. The parallel loop gets activated when you plug something into its jacks.
Hope that helped a bit.