Understanding the Role, Noise, and Evolution of High-Density Dimming
Somewhere in most auditoriums, there’s a dimmer rack — a metal cabinet about 2 feet wide, 2 feet deep, and 3 to 6 feet tall. It is often found in an electrical room near the stage, on stage in the wings, or tucked in an alcove near the stage. If your venue is running on older gear, you may want to explore upgrade options for legacy dimmer racks to keep things running safely and reliably.
So what does this beast do?
Why are those fans so darn loud?
And seriously — who puts something that noisy onstage?
Let’s break it down.
What Is a Dimmer Rack?
Dimmer racks take in large 3-phase power feeds (typically 120/208V AC at 200 amps or more) and convert them into multiple dimmable 120V AC circuits — usually 48 or 96.
These circuits are controlled by:
- Lighting consoles
- Architectural control stations
Both systems send signals to the processor inside the dimmer rack, which adjusts the output of individual dimmers. The output of each dimmer controls the intensity of connected lighting fixtures.
Each dimmer powers one or more lighting fixtures, allowing granular intensity control across the venue.
High-Density Dimmer Racks: The Beginning
The first modern dimmer rack, the Strand CD80, was introduced in 1980. It centralized processing in one location and used modular “dumb” dimmer modules to handle power. These modules contain:
- SSR (solid state relays)
- Circuit breakers
- Filter chokes to reduce lamp noise
The reduction in for CD80 vs. previous technology made dimmer per circuit systems affordable. The 1960’s design of room-sized racks of 6k and 12k dimmers with a patch bay became obsolete. CD80 systems connected every plug in the theatre to a dedicated 20amp dimmer…in a dimmer panel no larger than a refrigerator.
Not surprisingly, legacy manufacturers like Kliegl, Electronics Diversified (EDI), and Electro-Controls scrambled to catch up. If you’re working with one of these aging systems, see common dimmer rack failure signs and learn how to extend your system’s lifespan.
High-Density Dimmer Racks: Evolution
Through the 1980s, a wave of competitive systems entered the market:
- EDI Mark VII
- Kliegl K96
- Colortran D192 & ENR
- Electro-Controls EC-Quad
- ETC/LMI L86
- Strand CD80AE (CD80 with updated electronics)
While many of these racks entered the market with custom control protocols (K96, ECMUX, CMUX, AMX-192, etc.) they were updated to include DMX-512, a now-standard protocol for communication between dimmers and consoles.
In the 1990s a 2nd wave of high-density racks was introduced as technology evolved:
- Strand CD80SV updated CD80 with rack/load status monitoring and “System Wide” presets
- ETC Sensor and Colortran iSeries updated the design introduced by Colortran’s ENR
- EDI MX replaced the aging Mark VII offering with digital electronics and a reduced footprint
- Entertainment Technology (ET) launched Capio, a trailblazing IGBT (chokeless) dimming system.
The 2000s: Ethernet Control and LED Compatibility
The 21st century brought networking and LED adaptation:
- Strand C21 added ethernet-native processors and sinewave dimming to the CD80SV design.
- ETC released Sensor+ and Sensor 3 with expanded features.
- Colortran and EDI were acquired and phased out.
- Strand Lighting absorbed the Entertainment Technology (ET)/ Lightolier Controls product line, blending IGBT dimming into their ecosystem.
EDI’s Mark VII and MX systems were discontinued, but many still operate today — learn how these legacy racks work and how to maintain them with our deep dive into EDI dimming history.
High-Density Dimmer Racks Today
Today, ETC and Strand Lighting (now Vari-Lite) continue manufacturing dimmer racks and offer upgrade paths for LED-based systems, including:
- Processor replacements
- Relay modules
- Power-thru modules
Companies like JSI Manufacturing (Johnson Systems) and Parlights (VisionLynx) now support legacy systems with:
- Replacement processors
- Fan assemblies
- Relay module conversions
For a full list of supported racks — including EDI MX, Colortran iSeries, Capio, Kliegl K96, and EC-Quad — explore our EDI dimmer rack upgrade services.
Why Are Those Fans So Loud?
Because they have to be.
Controlling thousands of watts of power generates serious heat. That heat must be moved — fast.
Dimmer racks like CD80, Sensor, Mark VII, and MX use high-speed fans to force airflow through modules. Even “quiet” models like the EDI MX produce enough noise to be heard through solid doors.
Who Would Put Something This Loud Onstage?
Honestly? People who didn’t know better.
Many post-1982 venues were designed by architects or engineers who had never worked backstage. They didn’t realize that fan noise would bleed into performances.
In older theaters (pre-1982), the original dimming systems were convection cooled — silent by comparison. When those systems were replaced, the new racks were often installed in the same location as the patch bay on stage, introducing unexpected noise.
Need Help with Your Dimmer Rack?
Parlights offers service, repair, and upgrade solutions for nearly every dimmer and control system still in operation — including legacy and unsupported racks.
📞 Call us: 301.698.9242
📧 Email: service@parlights.com