...unless mine is non-standard.
The problem (- or just skip to....)
With the mains supply to all equipment disconnected there's an audible low frequency "dong" bell-like sound from the deck after the on-button is firmly pressed, but not the off button.
With the system live, the stylus lowered onto the motor-unit itself outwith the platter and the mains supply disconnected from only the motor unit, the bell sound can be heard plainly through the speakers. It takes just a small touch anywhere on the deck to excite it. This situation is begging for acoustic feedback problems, which I do have and is what prompted me to begin poking around.
I thought it would be caused by the unsuported idler wheel tension spring ringing like a guitar string. There was no similar sound after pressing the off button, when the spring is under more tension. Won't do any harm to thread a section of soft silicone rubber impregnated glass-mat tube (intended for high temperature electrical insulation). This noticeably damped the spring while not affecting its operation. Made no difference to the problem at all.
I played an LP and allowed the stylus to remain in the run-out groove. There was the usual 33rpm thump - which had its usual unique sound depending on which LP. Through the speakers the thump had a quiet but plainly audible dong after it. On simply unplugging the mains power to the motor the platter gradually slowed. The thump lowered in pitch but the dong didn't. Interesting little problem here.
Having a good poke around under the platter I noticed the metal strip which moves with the on/off switches and is bent up at its end to withdraw the idler arm and idler from the motor and platter.
With the machine in the 'on' position it went "dong" when I tapped it. When the machine was set to 'off', it didn't. This was because in the off position the end of the strip was in contact with the idler arm and therefore damped, and when in the on position it was a steel strip supported only at one end.
...the Solution.
I wrapped some handy Velcro "One-Wrap" around the metal strip so that it ocupied the small distance between it and the motor unit's cast chassis. Anything soft could be used. It completely stopped the dong. There was a slight increase in the pressure needed to push the on and off buttons as the One-Wrap rubbed against the chassis.
Obsevations
Absolutely amazing that the 'small beyond belief' stimulus from acceleration of the mass of the stylus in picking up the run-out thump was enough to excite the resonating metal strip, and for that to be so plainly reproduced through the speakers.
It just goes to show just how precise and sensitive these instruments are. A real learning experience. Maybe there's a bit less snake-oil involved in the HiFi business than I thought there was.
The problem (- or just skip to....)
With the mains supply to all equipment disconnected there's an audible low frequency "dong" bell-like sound from the deck after the on-button is firmly pressed, but not the off button.
With the system live, the stylus lowered onto the motor-unit itself outwith the platter and the mains supply disconnected from only the motor unit, the bell sound can be heard plainly through the speakers. It takes just a small touch anywhere on the deck to excite it. This situation is begging for acoustic feedback problems, which I do have and is what prompted me to begin poking around.
I thought it would be caused by the unsuported idler wheel tension spring ringing like a guitar string. There was no similar sound after pressing the off button, when the spring is under more tension. Won't do any harm to thread a section of soft silicone rubber impregnated glass-mat tube (intended for high temperature electrical insulation). This noticeably damped the spring while not affecting its operation. Made no difference to the problem at all.
I played an LP and allowed the stylus to remain in the run-out groove. There was the usual 33rpm thump - which had its usual unique sound depending on which LP. Through the speakers the thump had a quiet but plainly audible dong after it. On simply unplugging the mains power to the motor the platter gradually slowed. The thump lowered in pitch but the dong didn't. Interesting little problem here.
Having a good poke around under the platter I noticed the metal strip which moves with the on/off switches and is bent up at its end to withdraw the idler arm and idler from the motor and platter.
With the machine in the 'on' position it went "dong" when I tapped it. When the machine was set to 'off', it didn't. This was because in the off position the end of the strip was in contact with the idler arm and therefore damped, and when in the on position it was a steel strip supported only at one end.
...the Solution.
I wrapped some handy Velcro "One-Wrap" around the metal strip so that it ocupied the small distance between it and the motor unit's cast chassis. Anything soft could be used. It completely stopped the dong. There was a slight increase in the pressure needed to push the on and off buttons as the One-Wrap rubbed against the chassis.
Obsevations
Absolutely amazing that the 'small beyond belief' stimulus from acceleration of the mass of the stylus in picking up the run-out thump was enough to excite the resonating metal strip, and for that to be so plainly reproduced through the speakers.
It just goes to show just how precise and sensitive these instruments are. A real learning experience. Maybe there's a bit less snake-oil involved in the HiFi business than I thought there was.
Last edited:
