Power Amplifiers

Pass Labs XA30.5 Stereo Power Amplifier

ARTICLE INDEX

Design


The XA30.5 is quite an amazing piece of equipment. The amp weighs 75 pounds, even more than one of my 500 W Emotiva XPA-1s. The toroidal power transformer is huge. I'm not sure what its power rating is, but it looks as large as the 1200VA transformer in the Emotiva. The XA30.5 uses 20 output transistors, 5 for each leg of the balanced output. The 500W Emotiva uses 24. The biggest XA amp, the XA200.5 monoblock uses 80, yes eighty, output transistors per channel. The transistors run at only about 20% of their rated output power, so they never are pushed hard. Inside the amp, an input board located at the rear of the amp contains the supersymmetry input stage. The Aleph output stages (4 per XA30.5) are mounted on boards on either side of the chassis, bolted to enormous extruded aluminum heat sinks. The floor of the amp houses the power supply PC board and the toroidal transformer. A blue-lit current meter that measures the bias current through the devices dominates the beautifully machined front panel. While operating in class A, this meter doesn't move. When the amp transitions into class AB, it will begin to wag a bit as more current is drawn.

The rear panel houses two pairs of binding posts for the speakers (that do not accept banana plugs, by the way). An third binding post pair is used for a 12V trigger input. Power is supplied through a standard IEC jack, with a main power toggle switch. Thankfully, a pair of very sturdy handles are mounted on either side of the rear panel for carrying the amp. A front panel switch toggles the amp between run and standby. It takes about 30 minutes for the amp to warm up to the point that the bias current stabilizes. The heat sinks stabilize at about 50 degrees Celsius in about 1 hour. Every bit of this amp is top notch, with no compromises in design or execution. It certainly looks like a $5500 product.