Jesse and I spent last Saturday working to fit the new intercom. This is the third intercom ordered from Spruce (fast forward - I made 2 consecutive ordering mistakes, which led to me getting intercoms which were not suitable).
The latest intercom from FlightTech is still in the small aluminum box, which means it fits perfectly in the same slot occupied by the current mono intercom. Paying another $60 for the stereo version also got me a set of installation instructions that could be read without a magnifying glass. The mono intercom (since returned for credit) came with the instructions duplicated on 2-ups with faint printing, which required me to scan and enlarge the pages before they could easily be read.
Along the way it emerged that the headphone circuit on the existing intercom had been wired in series. This might explain the propensity of the intercom to distort when 2 headsets were in use. The 20XL and 3G headset combination that I currently use has made the distortion worse, possibly due to those headsets having different internal resistances. Because we had been given all new headphone and microphone jack hardware (for 4 places) with the intercom we decided to replace all of the existing hardware, which was probably 13 years old.
The main installation and wiring challenge (which Jesse seemed to have no trouble with) was attaching the wires to a set of extremely tiny Molex connectors to go into a 24-pin plug which connects to the intercom board. Those connectors are so tiny I swear I almost needed a magnifying glass to see them...
We hit an issue towards the end of the wiring with the PTT circuits. Jesse could not properly make sense of the instructions, which appeared to be inconsistent. The wiring diagram said one thing, the written instructions appeared to contradict the wiring diagram. We also had to remove the canard to try and trace several of the wires from the PTT circuit on the front stick. The wires were not clearly labelled, so we had to pull out the multimeter to make sense of the wiring.
We ended up suspending work at around 4.00 pm. Jesse took the installation instructions home and tried to match/compare them with the installation for the current intercom. After determining that, yes, the new intercom instructions were internally inconsistent, he ended up calling FlightTech support. They confirmed that the wiring diagram is right, and the written instructions wrong. (NOTE for use by anybody installing a FlightTech intercom).
The wiring diagram shows that the PTT circuit needs to be fundamentally rewired since more of the PTT processing capability resides in the intercom. For example, the previous PTT processing was operated by a single stick switch, but if the rear seat passenger was talking at the same time as the switch was pressed, that would be broadcast on the radio. With the new intercom, the passenger mike is not connected if the pilot is pressing the PTT. Only the pilot voice is transmitted.
The result is that Jesse will be completely re-wiring the PTT circuits between the radio and the intercom. This will probably involve discarding the existing wiring, since, in this type of situation, it usually takes less time to discard the wires and run new ones, compared to tracing all current wiring to determine which wires are connected to which devices. The wiring runs are only 24-36 inches long in any case.
Because the pilot PTT switch will not activate the co-pilot/passenger mike with the new intercom, I have ordered a second PTT switch from Spruce to fit in the rear seat stick. This will be wired into the intercom on a separate circuit so that the rear seat passenger can talk on the radio if required.
This intercom is beautifully small and compact, and if it works as well as it looks, the plane's communication system will be transformed. If it doesn't work, I might be learning some new Anglo-Saxon words in the weeks to come...