The Vacuvox CL-2 is a compressor/limiter designed for use in sound recording studioís. It is a modified Rohde & Schwarz U 23.

Details considering this apparatus could be found by searching the web using the keywords Braunbuch NWDR, vintage German modules, Rohde & Schwarz U 23. A link is provided on this site to (click 'braunbuch' below). This is a very usefull site, but you will only get proper acces if approached via keywords in Google or another search engine.

The original Rohde & Schwarz U 23 had very limited possibilities as its only purpose was preventing overmodulation of a broadcast transmitter. In the Vacuvox various controls were added, such as variable attack- and release times and a variable compression radio. Also the circuit was modified, resulting in a more stable operation over a wider range.

During the development the lowest possible distortion was not a design goal and when the gain is being reduced some higher harmonics become audible. This has the effect of making the sound appear louder that it really is (most musical instruments increase their harmonic content with increasing volume). The result is a natural sound, the musicianís original level changes remain clearly perceptible, irrespective of the compression.

Many of the original parts of the U 23 are used, among which the transformers (most important) and the chassis, which is not to 19 inch standard, so rack mounting is not possible. Most capacitors are paper-oil of good quality, in most cases replacement is not required. Resistors are carbon film and may drift somewhat, but this can be easily checked by measuring the DC voltages.  


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(TdW 29-12-2012)