- Written by John E. Johnson, Jr.
- Published on 01 December 2011
The Design of the Pass Labs XP-30 Preamplifier
Compared to the XP-20, which is also a fully balanced line-stage preamplifier, the XP-30 has a larger power supply followed by electronic capacitance multipliers, has better noise suppression, a different circuit board layout, the capability to daisy-chain other XP-30 preamps if you wanted to use all XP-30's in a multi-channel sound system (SACD, DVD-A, etc.), and the ability to blend the stereo channels into a mono output through the use of a balanced cable connection on the rear panel. This is said to give improved resolution over simply connecting the outputs together through a mixer.
The power supply chassis also contains the digital circuits, while the other two chassis have the analog gain stages (two gain stages for each channel). On the front panel, besides the input selection buttons and main volume control, there are smal trim dials in the right top corner. These are used to balance the sound of the blend when using the preamplifier to produce a mono output.
Below is a photo of the rear panel. You can see that having the two analog stages of each channel in a separate chassis allows for more connections. Each of the output chassis has a 25 pin jack which connects to the power supply (the bottom chassis) and a second 25 pin jack for daisy-chaining. On the right are five sets of RCA unbalanced and XLR balanced input jacks, a Pass Through RCA/XLR set for passing the signal through when using a separate pre-pro for surround sound, a tape loop RCA/XLR set, and a Mono RCA/XLR set.
The power supply has a trigger, which looks like a pair of speaker binding posts, and which is set to receive a 12 volt signal to turn the preamplifier on or off, a grounded AC jack, and the two 25 pin power output jacks to feed the pair of analog gain stage chassis.
The remote control is the same one as used with the XP-20. It is made from routing the center of an aluminum block. The rear cover is aluminum with a small screw to attach it.