Passlabs Amplifier Projects

Balanced Line Stage

This was built specifically to drive the Son of Zen, however, following subsequent projects I can say it drive the Aleph series of amplifiers very nicely indeed ;-)

The project file can be downloaded from the Passlabs site.

The SoZ is different in really requiring a balanced input for optimal performance, so the real use of this pre-amp is not as a gain circuit, but as an unbalanced-to-balanced converter. For this reason the default setting for gain is to a minimum, ie R15 = 120ohm.

The line stage from the front, showing left and right volume controls and the main power switch to the bottom right.

The rear showing 2 sets of gold RCA inputs, the XLR output sockets and 2 switches. One switch selects the input, the other is a gain adjust switch, effectively altering the value of R15 from 120ohm to 120+300ohm, with the former being the default.

Looking inside the top the layout is standard, with all attempts made to separate the AC and signal wiring.