Build your own classic compressor

For nearly a decade Hairball Audio has partnered with talented PCB designer Mako Natsume.  The partnership, based on a passion for quality design, has yielded some of the best DIY projects on the market today.  The FET/RACK compressor series is no exception.

These kits include only the highest quality USA made custom enclosure and transformers. All components are carefully selected by ear to match the original units and create the most authentic recreation available on the market.

In summer of 2016 we released the next generation FET/RACK. After nearly a decade of working together, we were convinced we could make a kit that was more elegant, more build friendly and most of all MORE ORIGINAL. The new FET/RACK maintains the classic front panel and sound of the classic FET compressors from the 60’s and 70’s.  What’s changed is that we’ve taken the build experience and detail to a whole new level.  The authenticity and sound of the new FET/RACK is unparalleled.

Metalwork made in the USA:

Our custom 2U enclosure was designed for Hairball Audio and is made in Seattle, USA from 18 gauge steel. The floating PCB allows top and bottom PCB access for ease of install and troubleshooting.


The new PCB design is a nod to the classic layout. The audio transformers now mount directly onto the main PCB. The attack and release network, previously the trickiest wiring in the build, is now on its own small PCB that easily mounts to the main board with the supplied connectors.

JST Connectors

A standard in pro-audio, JST connectors have allowed us to eliminate the complicated wiring. What little is left is made simple with pre-assembled connectors. The wiring of the kit, which used to take several hours, can now be done in only a few minutes. 


Our transformers, custom designed by Ed Anderson, are meticulous recreations of the original UTC 0-12 input, 5002 output transformer, and 11754 power transformer.  Modern recreations from larger transformer winders tend to focus on improving specifications, which washes out the original character and tone that made these compressors so famous.


FET/RACK complete kits feature only the best board-level passive components carefully selected by ear to impart all of the original color and tone of their original counterparts.  We spent weeks listening to original units and auditioned almost 100 capacitors to select a compliment of authentic sounding components.

Our focus was not to manufacture products overseas in places such as China to keep our costs low. Rather, our focus is to provide only the best parts available and to never compromise. Hairball Audio prides itself in creating the highest quality kits, while keeping design elegant and simple.

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