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Speed control- the journey continues... Using a Linn Axis power supply (getting technical now!)...

Posted by Dman (A) on April 15, 2015 at 08:06:48

Well, it seems that maybe one or two of you are actually following my dilemma here.

So the journey continues- I got the nerve up to actually measure things out on the Linn Axis PSU, and have discovered what I believe is the REAL problem!

The oscillator(s) is/are not set correctly. This may come as no surprise to those who have owned an early production Linn Axis table; Linn themselves owned up to the fact very early on (as I stated in a previous post) that they "goofed". They suggested some resistor value replacements. I did those many years ago; while it made SOME difference, certainly not enough to make things right (meaning CORRECT speed).

Ah, yes! The measurements! Here they are-

Spec states that for 33.3 rpm, the PSU should be outputting 50hz. As as measured at the output to the motor, I get 48.035Hz (0 phase), and 48.040Hz (90degree phase). Hmm... Not quite right (3.93% slow, if I did the math right!).

Spec for 45 rpm should be 67.5 (45rpm), but as measured at the output to the motor, the number is 66.100Hz (at both the 0 phase and 90degree phase). Again, not quite right (2.07% slow).

So, the tricky part. While I have a great respect for Electricity, some time to "play" with this thing, and of course a schematic, I am at a bit of a loss with this type of oscillator (a quadrature oscillator), and obviously there needs to be some changes made.

Anyone willing to help out?

Dman
Analog Junkie

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