Desktop Passive Monitor Controller

A compact, desktop item custom built for a client who was fed up with this active desktop monitor controller not weighing enough, being pulled off the table by its own cables, and various other issues.

Considering known source and destination impedances with proper unbalancing and grounding, we were able to make this controller entirely passive without the need for transformers. Contained inside are just gold plated switches, resistors, wire, and mass. Eisen Audio has found that passive circuits can in some cases sound more transparent than anything active when properly designed and implemented, which can be helpful when monitoring.

DFA Model DFX 3-2JM DJ Effects Mixer

Eisen Audio was hired to design and build a rackmount submixer, which is patched into the tape loop of a vintage (and primitive) Bozak DJ mixer, providing effects integration and monitoring capabilities as part of the Despacio Sound System.

Discrete transistor circuitry was employed exclusively, with extensive “tuning” by-ear, in order to blend in with the construction and tonality of the aforementioned vintage Bozak mixer. All of the signal routing and switching is done using photo resistors so that it’s always safe to make daring on-the-fly mix moves without fear of “pops”, “clicks”, or “bad edits”. All of the rotary faders are high quality conductive plastic, selected over a dozen competing offerings for minimum noise.

Two different mixer prototypes have been constructed thus far, based on end-user requests and feedback, and are touring the world. We hope at some point to revisit this project – down time and budget permitting – in order to develop a special-order product from it that could be useful to many other DJs who are committed to the vintage rotary mixers.

Despacio ADA-8 Analog Distribution Amplifier

Eisen Audio was hired to design and build a rackmount distribution amplifier for a touring sound system, the heralded Despacio Sound System.

This box accepts three different kinds of stereo input sources, scales their levels, sums to L-C-R, and feeds eight transformer-balanaced output amplifiers, each capable of driving hundreds of feet of cable to the individual powered speaker stacks.

A key-switch activates silent opto-mute circuits, so that the speakers don’t “pop” during changeover. This was crucial, because the speaker stacks are operated without any compression, limiting, nor overload protection in order to maintain the highest fidelity.

Given just two weeks notice and a modest budget, we were able to draw and have fabricated a custom front panel and PCB, while reusing our NLA System 8000 chassis, and fortunately we had a stockpile of Jensen output transformers on hand. Two identical units were constructed so that the tour had a backup and/or the larger system could be split into two rigs.

Design/build goals included:

– utmost reliability
– ability to be powered from any mains voltage across the globe
– transparent sound quality
– quiet operation
– ground isolation

NonLinearAudio ( is a manufacturing brand of Eisen Audio, co-owned by John Klett of Tech Mecca, Inc.