Established in London, Soundlock Engineering repairs, services and refurbishes old sound equipment.

The company was recently challenged with refurbishing two Studer A800’s, tape machines introduced in 1978. Upon investigation of these broken machines, it was clear the ball bearings used needed replacing.

To repair tape machines of this type, engineers need to heat parts up to make the metal more malleable, before putting bearings and other components in place. This means the ball bearings used must be manufactured to tight tolerances. The SMB Bearings technical team advised Soundlock Engineering on the right bearings to use, which in this case were EZO bearings of various sizes, including 6900s and 6203s.

To validate the bearings and refurbishment once installed, Roberts performed a ‘wow flutter’ test on the equipment. This industry-standard measurement quantifies the amount of frequency wobble in audio tape machines caused by irregular tape motion, which can be caused by imperfect bearings. The measurement must fall under the specification given by the manufacturer of the machine, which Studer set at 0.04%.

Following the refurbishment of both Struder A800s, the wow flutter measurement was well within acceptable levels.

“Replacing the Struder A800 bearings with substandard bearings — while they may have fit initially — wouldn’t have provided the longstanding premium recording quality usually associated with these machines,” said Chris Roberts of Soundlock Engineering.

Chris Johnson, managing director of SMB Bearings said “We don’t solely provide bearings for analogue recording devices, but specialise in supplying for many niche projects requiring small or miniature bearings. In fact, we store 2.6 million bearings in our warehouse for businesses just like this, who cannot foresee which bearings will be required for the next job.”