MCI JH-45 AutoLock
A microprocessor synchronizer that let two MCI transports chase each other to within a few dozen microseconds - and turned a pair of recorders into a 46-track studio.
Overview
The JH-45 AutoLock is not a tape machine, a console, or a monitor. It is the box that made MCI's tape machines behave as one. MCI's own product literature describes it as a microprocessor-based synchronizer/generator that locks two tape transports together with extremely low displacement, typically within ±50 µsec absolute. Fifty microseconds of drift between two machines is roughly the width of a single cycle of a 20 kHz tone. That is tight enough that a doubled guitar part or a stacked vocal stays phase-coherent instead of smearing into a chorus effect. Engineers who ran synchronized MCI rigs knew the AutoLock as the difference between "two recorders in the same room" and "one recorder with double the tracks."
The unit reads and writes SMPTE/EBU timecode as well as video drop-frame code. That put it in the film and broadcast workflow of its day, not just the music side. MCI's literature notes that the high-speed reader for the chase function requires no wideband amplifiers, and that the reader handles odd and even video fields plus vertical serration, with user-programmable behavior for video work. In plain terms, the JH-45 could chase a video deck, not just another audio transport.
The JH-45 carries ten memories, programmable user bits, and the AutoLocator and shuttle functions from MCI's standalone locator line. Record punch in and out points are programmable, and the unit displays master or slave position and offset in real time. MCI's advertising was explicit that the AutoLock could be interfaced to virtually any professional recorder/reproducer, not only MCI's own. That mattered for a synchronizer sold into rooms that already owned Ampex or Scully transports.
What the JH-45 bought a studio was track capacity without a second control room. MCI's own promotional copy pitched exactly that: lock two MCI recorder/reproducers together for maximum track capacity, or separate them to serve two studios. In the Bee Gees' South Florida facility, per a Recording-Engineer (February 1981, p.9) advertisement, the rig ran two JH-24 multitracks with a JH-45 AutoLock synchronizer alongside a JH-556-LM automated console and JH-110B stereo recorders - the canonical MCI "Ultimate System" configuration of the era. The same period copy placed the JH-45 at the center of MCI's automated console ecosystem, pairing it with the JH-556C recording/remixing console, which was designed for dual multitrack work with two JH-16 machines.
The JH-45 was a new product announcement in the UK trade press in late 1978, when MCI's British arm ran a teaser in Studio Sound (November 1978, p.63) promising full technical specs in the following issue and offering advance information to anyone who wrote or phoned. By the end of the following year, Recording-Engineer (December 1979, p.65) was listing "plug-in ready for use with MCI JH-45 AutoLock (SMPTE synchronizer)" as a bullet-point selling feature of the MCI 8-track. The synchronizer had become a reason to buy the recorder, not the other way around.
The AutoLock was not a standalone island. MCI's JH-110B Series literature lists compatibility with the optional microprocessor-based RTZ III and/or the JH-45 AutoLock as a standard line item. The JH-110B's three-speed, fully DC servo-controlled transport with variable speed capability and Manual Velocity Controls was built with synchronized use in mind, and the JH-45 was the intended partner for it. The same is true across the JH-16 and JH-24 lines.
One practical caution for anyone servicing a JH-45 today: the surrounding MCI transport electronics of this generation are not self-correcting. A period service note in the Archive's files calls out the use of 748 op-amps in place of 741s as a recurring source of oscillation. The 748 lacks the internal compensation of the 741, so the substitution can destabilize a circuit that was never designed around it. Swapping back to a 741-type device is the documented cure. The same note flags intermittent tension, odd servo lock, and erratic wind and locate functions as symptoms usually traceable to cold solder joints on the Molex pins of the motherboard. Those joints can look like a proper solder cone until a dark ring around the pin gives them away. On a synchronizer whose entire job is to hold two transports in lock, a marginal motherboard connection shows up as a sync problem and sends owners chasing the wrong box. The note also records a specific modification: when the JH-45 AutoLock is in use, R1 must be jumpered out, and the minus 15V feed to the transport switches - both on the transport and on the remote - must be isolated by a 4K7 resistor or greater. Anyone pairing a JH-45 with a JH-114 should also know that early-1980 JH-114s shipped with a ground trace left off the circuit board, causing the machine to lock into MVC mode or drop into it intermittently. The documented fix is a jumper from the upper left-hand corner pin to the top of the upper left-hand resistor.
Original pricing for the JH-45 itself is thin in the surviving record. What does survive is the secondhand market: a period classified listing in the Archive's files offered a JH-45 autolock synchronizer in like-new condition at $3,000, and a later dealer list priced two JH-45 AutoLocks at $1,200 each. Those two figures, from different years and different sellers, bracket what the box has traded for on the used market - a fraction of what the transports it synchronizes now command. The synchronizer is the cheapest part of a synchronized MCI system and the part most likely to be missing, because it was sold as an option and because studios that broke up their rigs often kept the recorders and let the AutoLock go. Buyers chasing a complete period MCI setup should expect to hunt for the JH-45 separately. Finding one with intact timecode reader circuitry and a motherboard that has been re-soldered rather than merely re-flowed is the hard part.
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