Power Amplifiers

Pass Labs X1000.5 Monoblock Power Amplifier


The Design of the Pass Labs X1000.5 Power Amplifier

Pass uses what they call Supersymmetry in the circuit design. What this means is that the input stage is fully balanced, which eliminates some of the distortion, and the input stage drives the output stage which consists of 72 output transistors. So, the output is single-ended. This combination of a balanced input stage but single-ended output stage is very unique, and it allows them to manipulate the input stage in such a way that the final sound can be made to be "just right". In Pass' case, this tends to be a spectrum that has a bit more third order harmonic than second. Again, this is unique to the Pass philosophy, as most designers tend to try and get the harmonic spectrum to be primarily even ordered, and mostly second order.

At 27" in length and 183 pounds in weight, these monoblocks are not easily placed. If you have a dedicated music listening room, then you probably want them center stage as they are quite nice in appearance. Otherwise, they could go behind the speakers.

The rear panel is shown below. There are two sets of speaker binding posts, but they are designed to accept bare wire or spade lugs, not banana plugs. However, Pass will supply you with a pair of banana-to-spade adapters if you wish. My cables are all terminated with bananas, so I wished. At the top are an RCA jack and an XLR jack. If your preamplifier is XLR out, and you want to connect it to the X1000.5 with an XLR cable, you first have to remove a U-shaped pin from the XLR jack. Leave it in if you are using the RCA inputs.

The on/off power toggle, three-pin grounded AC receptacle, and a trigger connection round out the panel features (along with the handles for lifting the amplifier).