The Manley Variable MU with T-bar Mod is a high-end limiter compressor known for its unique tube-based gain control, versatile compression modes, and superior performance in mastering and final mix applications.

The Manley Variable MU has been a best-seller for many years, becoming a staple in mastering studios and contributing to numerous hit records. "MU" is tube-speak for gain, and Variable MU is the registered trademark for this limiter compressor. It uses the "remote cut-off" or re-biasing of a vacuum tube for compression, similar to the vintage Fairchild 670. The 5670 dual triode is central to its peak-reducing and compression action, constantly re-biased by vacuum tube rectified side-chain control voltages for smooth gain changes.

Compression Modes

The COMPRESS mode offers a soft-knee ratio of 1.5:1, while the LIMIT mode starts at a sharper knee ratio of 4:1 and escalates to 20:1 when limiting over 12dB. Interestingly, the knee softens with increased limiting. Users can creatively use distortion by increasing the input and decreasing the output with minimal compression.

Stereo Input Control

The Variable MU Limiter Compressor features a ganged input control, but it remains stereo-friendly with separate thresholds and output controls for compensation. The stereo input control's advantage becomes evident in LINK mode, excelling in final mix, 2-track, or mastering limiting and compression.

The T-Bar Modification

The newer Variable MU units use 5670 tubes instead of the scarce and often problematic 6386 tubes. While the 5670 sounds similar to the 6386 up to about 6dB of limiting, beyond that, it tends to sound more "squashed." The T-Bar Mod, solves these issues by using a pair of 6BA6 pentodes wired as single triodes to replace each dual triode 5670 (or 6386). This modification ensures perfect matching of each phase-halves section and stereo set, provides low noise and low microphonic sets at a lower cost, and closely resembles the smooth 6386 limiting curves.