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EMT 250 / 251 Reverb Repair and Service

Shipping your EMT to us for servicing

EMT 251 Digital Reverberation System
David Kulka in his shop in Burbank CA
Visitors to our shop are often surprised to see an "R2D2" --an EMT 250 or a 251-- in the service area. Well, hardware reverbs weren’t always rackmount boxes with lights on the front! The history of studio reverb is fascinating, and EMT’s important developments in the field deserve special mention For decades the only way to create studio reverb was with an echo chamber. This was a special room with reflective surfaces, isolated from its surroundings, that contained one or more microphones and speakers. (Recording pioneer Bill Putnam is credited with building the first echo chamber in 1947 at Universal Audio, his studio in Chicago. Read the whole story at www.uaudio.com.

Good echo chambers were difficult and expensive to build, especially in urban locations where real estate was expensive and extensive sound isolation was needed to keep out traffic and other noises. Tape loops were sometimes used but they didn’t provide the random, complex reflections that were needed to replicate real reverb in an acoustic space. As for springs...well, they sounded like springs.

Original EMT 140 owner's manual
In 1957, EMT introduced the 140 Reverberation Unit. The 140 consisted of a large piece of sheet metal, suspended from a heavy steel frame. An electrical transducer (similar to a miniature speaker) transmitted sound energy to the plate, which along with its drive and pickup amplifiers, was built into a large wooden enclosure. The 140 was about 4 feet tall and 8 feet long, and weighed about 600 pounds. A damping plate, controlled by a servo motor, allowed adjustment of the reverb time. Though it was much smaller than an echo chamber it was still sensitive to ambient noise, and had to be kept in an isolated space. Still, the “plate” was a great advance. Instead of building 8 echo chambers, a large facility could put 8 140’s in a small iso room. It was the first cost effective answer for smaller studios, where actual chambers were not feasable. EMT 140’s didn’t sound exactly like a real room but they sounded very good, and remained the most popular studio reverb for many years. The early ones used tube electronics, but in the 70’s EMT began shipping them with transistor circuitry.

In 1972, EMT released the very first digital reverb, the rack mount 144. The capabilities of this early unit were limited, and few survive. But just four years later, EMT blew a lot of minds by introducing the 250 Electronic Reverberator Unit. It looked like something from an UFO, and sounded fabulous. A free standing unit, it was three feet tall with black “radiator” heat sinks on three sides and a large, bright red power supply assembly. On the upper control panel, 4 oversize levers resembling aircraft controls adjusted main delay/decay time, LF and HF decay times, and added delay to the send. The software also included delay, phasing, chorus, slap, and “space echo” programs. It had one input and either 2 or 4 outputs, depending on the version ordered.

Despite it’s early 12 bit architecture, the 250 had a beautiful sound. Its design was a joint effort between EMT’s engineers in Germany and a small firm in Massachusetts called Dynatron. EMT designed the converters, I/O, and power supply, while Dynatron designed the main digital/processor board. The Dynatron effort was led by Dr. Barry Blesser, then a professor at MIT (and later an AES President). The finished unit had nearly 500 IC’s, and 3 cooling fans. To protect its revolutionary design, the part numbers and identification were scratched off most of the IC’s on the digital board.

EMT 251 Digital Reverberation System
EMT 251 Digital
Reverberation System
EMT 250 Electronic Reverberator Unit
EMT 250 Electronic Reverberator Unit
The Electronic Reverberator Unit utilized a memory board that held 80 “2102” IC’s -- a popular 1k (!) static RAM chip that was also used in Radio Shack’s TRS-80, the first popular home computer. In accordance with Moore’s Law (which predicted the doubling of transistor density every year) later models used a RAM board with just 32 IC’s. The new board used the 4044, a 4K RAM chip. About 250 250’s were built, and they sold for about $20,000 each. I’m not sure whether EMT recouped their investment, but the machine was a huge milestone that heralded the dawn of digital audio in the recording industry.

Four years later EMT released the 16-bit 251. Along with a new reverb program and an LCD display, the 251 had extended frequency response, more parameter controls, more programs, and a remote control port -- all in the same striking “sci-fi” package.

The EMT digital reverbs were something else. They were “Manhattan projects”, the result of intense efforts in a short period of time. Despite their high costs they were very successful, and remain one of the few digital technologies that stand the test of time, for one simple reason — the sound.

Though just a few hundred of these old girls were produced, it seems a safe bet that most units are still floating around -- who would throw out such an amazing looking machine? But as 250’s and 251’s pass the three decade mark, the attrition rate has caught up. Power supply problems, failed capacitors, aging ribbon cables, sluggish fans, dying RAM chips...those R2D2's can develop a lot of problems. Fortunately, they are all fixable and repair is well worthwhile.

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