The Atlantic City Midmer Losh organs is one of the most incredible musical instruments ever created by man. Because it is being rebuilt in phases over time, the phases are not necessarily aligned with what would be ideal from a control system perspective. Most control systems require console information (inputs) to be relatively close together, but until the 7 manual console is rebuilt, it is actually spread around the building. Hall effect keystrips were retrofitted into the keyboards, providing a source of keying in the console. Linear transducers are also retrofitted to the original swell shoes in the console. Coupling originally occurred in Reisner-Style keying trays in the console that suffer from corrosion, so coupler stop signals are available in console junctions. Regular (non-coupler) stop signals do not junction in the console at all, and are wired to junctions in the basement (pictured). A small card panel in the right side blower room collects the stop statuses and forwards them back to the console via a PipeBus link.
There are currently 7 chamber relay panels with a total of nearly 100 I/O cards just driving pipes. Another dozen cards are used in the collection of stop source data from various locations around the hall.
There are a number of features that were original to the instrument, including melody couplers, pizzicato couplers, and floating divisions. These are all recreated in software to work exactly like the original pneumatic units.
Some fun facts:
There are 87 “global” couplers in the organ. Global couplers affect all controllers. In addition, some controllers have as many as 20 “local” couplers; these are couplers that only affect a particular chamber controller card.
One of the largest causes of dead notes we found during an early survey of the organ was key contacts. Because one key contact can take out many pipes, these become very important to eliminate as a source of trouble. The hall effect key strips on the manuals are impervious to humidity and automatically adjust for changes in physical key caused by seasonal climate changes.
A subject of great interest is the DC requirements for an organ of this size. A brief summary of expected major requirements using modern estimation methods follows:
Main Console 600 Amps
Aux Console 320 Amps
Left Main Chamber 180 Amps
Right Main Chamber 180 Amps
Other Chambers 100 Amps
This totals a potential current draw of 1380 amps. This isn’t a huge surprise since the consoles were built with electric action (the next largest organ uses a vacuum console to avoid this problem). The subject of great interest is that the Generator (pictured) is only good for about 10% of that. There are no signs of other generators (and even if there were, they wouldn’t be able to significantly contribute from other places in the building). In fact, listening to the 1998 CD, a sharp ear can hear notes dropping out as more stops are added. The generator is still in place and powers the entire right chamber (including the Opus-Two components), the stop tabs (for the sense action), and the Opus-Two stop collector panel in the basement. The generator also provides the signal that tells the Astron Rectifiers to sequence on.
The drawing shown is a block illustration of the various components of the Opus-Two control system for the Midmer-Losh organ. This is a “logical diagram” and is taken directly from the documentation book for the organ. This allows a technician to visualize the flow of data from the various components. A common question relates to how the various panels “talk” to one another. The panels that are listed “above’ the C-IV in the diagram sit idle until the CVA requests their data. The CVA sends the request over the PipeBus port, and the panels reply with the state of the attached IO cards. The CVA can poll them as often as is necessary as the communication occurs at an extremely high speed. Each panel is polled every time a data frame is sent to the chamber controllers, ensuring they have the most accurate information available. If a sub-controller doesn’t answer in time, it’s previous response is allowed to ‘fill the gap’ until it comes back online (this is helpful for panels that run from a generator and may experience short power outages).