... check the input jack impedance rating at full attenuation / half attenuation & no attenuation (levels at 0, 5 & 10) respectively? I have a problem with my MASS 150w that when I put the levels lower than 5 the impedance on the input jack increases from 12 (halfway) to 25 ohms (full attenuation). I use an 8 ohm cab / head so the head is suffering from a 3-1 impedance mismatch, and this is quite bad for the power amp section of my tube amp. I want to be sure this is only a problem of my Weber and not some faulty design. I also found that the lower switch (high/low switch) of my model is in the way of the MASS motor causing a dent in the speaker. So if anyone could check that too that would be great. :AOK Edit: I have a Weber MASS 150W btw.