Thanks for your replies to date. The very nice Ed from Arcam support did just send an email that he got back from the "designer". Some nice insights from the man involved in the original.
From Ed: I have a reply from the original designer which should hopefully prove useful:-
"Wow that's nearly 40 years old! I am not sure why the computer system doesn't have the schematics etc on it and I don't think I have them at home, though I will look. Originally they will have been stored in some kind of A4 binder for access by support/service and if that's been lost we have no records I imagine.
A group was set up around 1980 to do this and agree levels, pin outs etc so you could use a given speaker with different electronics. It was somewhat pretentiously named ALSO = the Active Loudspeaker Standards Organisation. Original members Arcam, Linn, Naim, Nytech and ARC.
The active crossover for the Arcam One was designed for the original Arcam Ones that had a set of crossover links on the back with IIIRC 8 terminals in all; this allowed us to bypass the actual crossover components and access the drive units directly by removing bridging metal strips. It will not work (properly) for the later (taller) Arcam Ones that have only 4 terminals on the back as one can't get the passive crossover network out of the signal path. Similarly the ARC speaker had a removable external crossover "brick" - unplugging it exposed the 4 terminals connected to the speaker treble and bass units.
The crossover board fitted in the SA60 was a universal PCB designed to be configurable by fitting components for one pole crossover slopes (6dB/octave), 2 pole (12 db/octave) and possibly even 3 pole. Again, IIRC, the Arcam One was set up for 2 pole crossover, as was the ARC101. The Tangent was different and I don't recall how, but was possibly linear phase single pole. There will be preset pots on these boards to set up the relative gain between treble and bass (factory set for the right nominal values). Of course you can't change the chosen crossover frequencies for each speaker system without changing parts on the PCB, nor should you need to.
To get it going one retro-fitted a small A60P board to the A60 at the point of entry to the power amps, i.e. post volume, tone and balance controls. This was fitted with a 5 pin DIN connector with ins and outs from memory and replaced one of the original DIN sockets, probably the 3rd (AUX) socket. This was connected with a 4 way DIN cable to the optional crossover board in the SA60 - it provided a stereo full bandwidth feed to the crossover PCB and a single channel treble and bass (filtered) return to the A60 to drive one loudspeaker. The SA60 then took care of the other channel. I can't remember which amp took care of L and which R!
That's about as much as I can tell you right now. You need to confirm which Arcam Ones the enquirer has before anything else. Feel free to pass on this email to him.
It worked pretty well by the way in sonic terms and was only abandoned because we needed to design a new PCB every time a speaker design was modified so it became very complex to support. Linn and Naim kept theirs running for a long time but that was because they had direct control of their own speaker models."
I did reply to let them have my thanks and that also the Arcam One has nine terminals on the back. The original A60AP drives the left, the SA60 drives the right.
Happy tinkering and listening. I will let you know when I actually get it powered up.
Julian
