MCI JH-500
MCI's "automation-ready" flagship console - a desk that arrived with the VCA plumbing already installed, waiting for the automation that was still coming.
Overview
The JH-500 wasn't one fixed desk. It was a frame you configured. MCI built it in two sizes: the JH-528, which took up to 28 inputs, and the JH-542, which went to 42. Around that frame you picked from eight custom meter panels - VU or bargraph, with DIN peak, VU, or accumulate ballistics, and a phase meter option in the mix. The standard patchbay shows how seriously the desk was meant to be wired: 504 patchpoints on the 28-input frame, 756 on the 42, tielines and switchable mults included.
The channel strip is where MCI spent its money. Four-point EQ, which the company's own literature described as offering 140 million possible curves, switchable between monitor and channel path, with a pre/post EQ patchpoint and an EQ-only solo. High frequency could be shelved or peaked at 8, 10, 12, or 15 kHz, ±10 dB, with a separate shelf at 30, 60, 100, or 150 Hz. Low frequency gave ±10 dB. Mid-range I covered half-octave steps from 150 Hz to 7 kHz at ±14 dB. Mid-range II ran 180 Hz to 8.5 kHz, also ±14 dB. There was a switchable 20 dB pad on the mike input with a 30 dB trim range. Six sends for echo or cue, each with its own pre/post switch: two mono sends on 45 mm conductive-plastic slides, two mono sends on rotary controls, and one stereo send.
Every straight-line fader in the desk was conductive plastic. The monitor fader was a 45 mm quad unit with front/back and left/right pan, mute, and a wet/echo switch. Detented monitor and send trims, an alternate producer monitor center, and meters that follow the monitor were among the features MCI singled out as unique to the line.
What set the JH-500 apart at launch was what it already had inside. The control switches for automation and the voltage-controlled amplifiers for the channel and echo-return faders were built into the standard desk. The mute system was designed to be driven by automation too. So MCI sold you a console that was waiting for its brain. That brain, the JH-50 automation system, came later. MCI announced it as a release in Recording-Engineer (February 1976, p.46), where the JH-500 was billed as a programmable mixing desk and "a whole generation ahead of any mixing desk previously available." The company's pitch was that the desk worked as a signal processor first, and automation could be added in a few hours without modification.
The automation was no throwaway add-on. MCI's design notes describe a digital update scheme with a bounce time of roughly 1.2 milliseconds per pass. The system reads the VCA value off the multitrack master, processes it digitally, and writes the result back in the same scan, so full eight-bit, 256-step resolution comes easily. Cumulative system error was quoted at 0.4 dB across unlimited passes, and it does not accumulate. Scan time was 102 ms, which is not a delay and does not accumulate either. Bounce delay, at 1.2 ms per pass, is a delay and does stack with each update pass. Data rate was 9600 baud, roughly 14 kHz of bandwidth. MCI stored automation data on the audio master tape rather than a separate digital device. The company argued this saved the three to five thousand dollars a synchronized digital storage system would have added, and gave automatic synchronization as a side benefit.
The retrofit path was laid out per frame: JH-50-416, JH-50-428, JH-50-528, and JH-50-542 kits for the corresponding consoles. Tapes cut on an automated JH-400B or JH-500 would play back on any other automated JH-400B or JH-500.
The VCA at the heart of the channel path was the 1537A, which MCI's own spec sheet called the only monolithic Class A voltage-controlled attenuator then on the market. Bandwidth was DC to 50 MHz, THD 0.004% typical, IMD 0.03% typical, noise −90 dB worst case, and more than 100 dB of attenuation at +20 dBm from DC to 200 kHz. For owners who wanted the improvement without buying a new desk, the VCA 500A dropped a 1537A into the existing JH-500 channel for $89 per single, a few minutes of plug-in work per channel. The VCA 505, also $89, was an expanded version of the same attenuator in a 15-pin card-edge package with multiple buffered control inputs.
Studio-Sound (May 1978, p.37) reported that a Billboard survey of studio equipment had confirmed MCI as the number one manufacturer of consoles in the U.S.A., and that the JH-400 and JH-500 Series had become "the recognized standard of the industry." That's advertising copy riding on survey data. Two years earlier, Recording-Engineer (October 1976, p.13) ran a full-page ad joking that Beethoven would have flipped over the JH-500.
For anyone maintaining one today, the picture is the usual MCI story: conductive-plastic faders that wear, VCA cards that can be swapped, patchbays that need cleaning, and automation that either works or is a project. The modular layout that made the desk configurable in 1976 helps here. The VCA 500A upgrade path still exists in the used market, and the automation interface boards plug in rather than requiring surgery. A JH-542 is a large piece of furniture, and the 756-point patchbay means a correspondingly large harness. Power came from a separate supply - +5 V at 5 A and ±15 V at 3 A on the automation side, with line requirements of 100 V, 120 V, or 240 V at 2 A (1 A on 240 V). The processor, digitizers, and power distribution boards for the automation lived in a case that mounted underneath the console.
Collectors and studio owners chasing JH-500s today are usually after either the channel strip - the four-point EQ with the switchable monitor/channel path and EQ-only solo is the reason people want these desks - or the automation hardware, which is increasingly hard to find complete. A bare desk isn't useless without the JH-50, but a lot of desks were sold with the promise of automation that never got installed.
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