Vacuvox U23m Mastering Vari-Mu Compressor/Limiter #080 (Used)

The Vacuvox U23m is a mastering version of the U23 vari-mu compressor/limiter building upon the legacy of the Vacuvox CL-2 for which the Rohde & Schwarz U-23 broadcast limiter served as a basis. Several improvements have taken the design and functionality of the CL-2 a step further while preserving the euphonic sound of the original. The Vacuvox U23 has an all Class A vacuum tube audio path, and side-chain path based upon the original circuit of the Rohde & Schwarz U23. These ensure unparalleled performance and provide unrivaled headroom and transparency.

DESIGN AND FUNCTIONALITY

The Vacuvox U23m mastering compressor/limiter is assembled entirely by hand and uses high-quality modern components. The custom-made transformers are faithful recreations of the original, sonically excellent, Rohde & Schwarz transformers. The four audio transformers are made of permalloy with 80% nickel and 20% iron content. The chokes and power supply are made of SiFi. The power transformer is upgraded for better noise performance and stability. A front panel layout, a modification of the output gain and the thresholds and two extra gain stages are the most significant improvements that have been incorporated in the Vacuvox U23m.

21-stepped switches for input, output, attack, release, and threshold are used for the U23m mastering version. These extend the use of a pair of U23m compressor limiters to critical stereo applications for many different genres of music. Even jazz and classical material can be mildly compressed with a perfect stereo balance and without sacrificing the sense of dynamics and producing unwanted artifacts.

The various gain structure options from the Pad, Input, Gain and Threshold offer the possibility to create different kind and levels of saturation subtly. Therefore the sound can be varied between transparent, dense and fluid by lowering the threshold, driving the input transformer or driving the tubes.

The above features are included with both the U23 and U23m, the following are specific to the U23m:

• Ratio: 7-step rotary switch with ratios 2:1, 3:1, 4:1, 5:1, 7:1, 9:1, 12:1
• Input: 21-step attenuator switch with 1 dB per step
• Attack: 21-step rotary switch with time settings between 1 mS and 50 mS
• Release: 21-step rotary switch with time settings between 0.2 S and 1.2 S
• Output: 21-step attenuator switch with 2 dB per step for the first 5 steps and 1 dB per step for the last 15 steps
• Selectable output level (normal or +6 dB) of the output transformer