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 ever built 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. While it is true that these generators are known for putting out several times their nameplate rating briefly, this fact alone would not likely “fill in the blanks.” There are no signs of other generators or batteries, although the possibility remains that their power junctions have long been covered up by an old renovation. 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 very short power outages).

The addition of a combination action in 2019 was one of the most labor-intensive parts of the project. Additional data collection points were added inside the console to capture piston presses, piston rails were re-wired (re-using original contacts and pistons), and the stop collection panel in the basement was expanded to included every single stop tab in the instrument. Featuring the current-standard CVA combination action (10,000 levels), it is one of the first projects to use the new Nano Controller. From piston press to tab movement is less than 10ms, with absolutely no interruption to the continuous pipe processing.