FM Acoustics and their Phono Master

[Dave2002]

The longer the arm the less the geometric (angular) tracking error when compared with the ideal of the cartridge always being tangential to the disc, since the cutting head moved along a radius. That is why SME, for example, offered a 12" arm as well as a 9" one.

Agreed, but those arms in the EMI test room looked a lot longer than 12". Longer arms aren't always good news, as they generally increase mass, and affect resonances. Perhaps that didn't matter for the applcation, which was mainly for detecting pressing flaws, and the tested discs were possibly not sold - but found their way to others related to the company who might want them.

Gordon has pointed out the additional link connected to some form of data logger - I did wonder what they were for.

[Gordon]

Given the purpose of the system it is hard to see why such a long arm is used. It's only a guess but perhaps the extra leverage from the tracing stylus was needed to drive the logging mechanism on the extra arm?

Gordon has pointed out the additional link connected to some form of data logger - I did wonder what they were for.

For the production statistics files? They'd wish to keep a log of the faults and if no-one is actually noting where the click ocurs the automatic system needs a way of recording the results for each disc tested. Some of those discs might also be stored in archive as examples - just for the record - together with the log!

I'd still like to know what they do for CD production quality control. I have only ever had 1 CD affected by pressing defects. Apart that is from those unfortunate Hyperion [+ a few others] discs some years ago that suffered a chemical problem and turned a bronze colour after a while and then failed to play. You would not catch that in a factory test!!

[Dave2002]

s tillliketo nwo = still like to know?

bws - dave

I do have one CD with a very minute hole in it, which gives a barely audible click. Other CDs may have holes in - hold them up to the light - but I only found one where the click (very slight) was audible.