Golden Age Project - COMP-54 (1-ch 2254/64-style compressor)

The COMP-54 is a one-channel vintage style compressor. The signal path uses only discrete components like resistors, capacitors and transistors. The input and output are transformer balanced and the unit also uses a third interstage transformer. This is the way audio components were built before integrated circuits became available. IC´s are small and cheap and they are widely used in most modern designs. It is clear though that audio components built with modern technology doesn´t always provide the best perceived sound quality or character that the modern user desires. On the contrary, the subjective sound quality delivered by vintage equipment is often prefered over the one delivered by modern units. This is the reason why so many vintage audio components are cloned and produced again and also why the vintage originals are often very expensive on the second hand market. The class-A circuit used in the COMP-54 is similar to the one in the classic 2254 compressor that was designed in 1969. It quickly became a legend due to it´s totally unique sound character that is warm, smooth, sweet and musical. These characteristics have been heard on countless recordings through the years and it is a versatile sound that works very well on many sound sources and in many genres. The essence of this sound is now available at a surprisingly low cost, making it available to nearly everyone.

The signal first enters the input transformer, a damping network and is then passed on to the diode bridge where the actual gain reduction is taking place, it is followed by balanced FET-transistor stage. Then follows an interstage stepup transformer that feeds the side chain circuitry and a three transistor gain stage followed by the GAIN potentiometer. The signal then goes to the output stage. This stage again uses only three transistors, the last one in the chain is a hefty 2N3055 power transistor running in class-A mode, driving the output transformer. So, all in all, the complete signal chain only contains a maximum of ten active elements. Compare that to the big number of transistors that are usually used in one single integrated circuit!

It is true that there are some great IC´s available today that achieves very low levels of static and dynamic distortion.The simple circuits that the COMP-54 uses, and even more so the transformers, cannot match the low distortion specifications of modern IC´s. It is the distortion components that imparts a sound character to the audio signal and, if the distortion components are of the right sort, this is a good thing since it makes the recorded voice or instrument sound “better”, more musical, more pleasing to the ear. This is one reason why vintage style units are so popular today. Sometimes, transparent units are prefered over colored ones. It´s all about taste and it depends on the genre. For most modern music styles though, color and character is definitely a good thing. And isn´t it great to use audio components built according to the old, minimalistic approach where one can follow the signal flow from one discrete component to another?