Quote:
Originally Posted by Synchrodyne
Quote:
Originally Posted by Craig Sawyers
It is not such a bad idea - pin 2 goes high on mono, resulting in about 1.4mA of collector current in TR101. Quad fitted several types of transistor depending on availability, with BC550C being an equivalent. That has a beta of 400 - 800. So it will pull a pretty insignificant 3.5uA to 1.75uA from pin 2 on mono.
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I was of the impression – perhaps wrongly so - that the separate mono output, via emitter follower Tr101, was independent of anything that was happening in the stereo decoder IC (MC1310) - available regardless as it were. And that the DC conditions at pin 2 (MC1310 input) were not conditional upon what mode the decoder was in.
Quote:
Originally Posted by Craig Sawyers
Having met the guy who designed the FM3 (the late great Mike Albinson) he would have thought that through long and hard before deciding on that way of doing mono.
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I had wondered who had designed the FM3. Was it Mike Albinson’s first major job at Quad? I think that Quad had been without a designated RF person since John Collinson had left, which might be why the FM3 was somewhat late in appearing.
Cheers, |
According to Peter Baxandall (in a long letter to Doug Self reproduced in Baxandall and Self on Audio Power, Linear Audio Special Edition) Mike Albinson joined from Murphy Radio in about 1966/7. His first contribution was the input circuit of the 303 power amp. But the next three products were the FMII, FM3 and AM3, which I reckon were all Albinson's.
When I met him he described the way he did radio PCB's. He'd commandeered a toilet to be a circuit board prototype facility. He had a camera lens screwed in the toilet door, and he put a 4x taped up master on the end of a Dexion component store rack. This was all arranged to produce a correct size image on the wall of the toilet. He'd wait for a sunny day, go into the loo and lock the door. Tape a piece of resist coated board on the loo wall and wait a guesstimated time. He reckoned that was the only way to get an RF layout right. Iterate the layout until it worked as designed.
He'd then send the x4 master to the board house.
I asked him what audio system he had at home, expecting something Quad. "No interest in listening to audio - that is work. I really enjoy fixing up classic motorbikes"
Real character!
Craig