Today I am in the mood to try on the preowned Bang & Olufsen ( circa 1970's) vintage belt-drive turntable, Beogram 3400, which I chanced upon in the local flea market some time ago.
A very well-designed, elegant looking so-called 'sprung' turntable, the main bearing and the tonearm of Beogram 3400 are mounted on a sub-chassis suspended on three springs to isolate it from most interferences. The motor assembly is also mounted on the sub-chassis, but with another three springs to prevent the motor vibrations from reaching the tonearm and the platter. It is interesting to note that one of the spring that holds the motor even acts to counter-balance the push/pull force of the rubber belt, enabling the sub-chassis to centre itself easily.
The sub-platter and platter are made of aluminium with strong anti-resonance patterns; the platter is further isolated from the sub-platter with three pieces of felt, 120 degrees apart at the bottom of the platter surface.
All the pulleys are of metal type - brass and aluminium. The motor pulley drives an idler which turns the rubber belt to spin the sub-platter/platter combo. Combination of idler and belt reduces the motor vibration from reaching the rubber belt, hence the sub-platter.
The 33.3 rpm and 45 rpm speeds are adjustable through eddy current effect ā la Thorens TD124.
Before getting the Beogram going, I have checked and rectified the following :
1. The dented and corroded 5-pin Din plug to be changed to RCA plugs.
2. The rubber belt and the idler, both are still surprisingly in good conditions.
3. The main bearing and idler bush bearing are lubricated with light oil ( sparingly) and the metal pulley of the motor is cleaned with alcohol using a cotton bud .
4. Three pieces of 2 mm x 19 mm circular cork are added to isolate the platter from the sub-platter(the original felt isolators had already been fully compressed and lost the effective isolation property). Moreover, the cork has 'anti-slip' property allowing effective energy transfer to platter. Another four pieces of 8 mm adhesive clear bumpers are also stuck on the bottoms of the turntable supports to reduce ground-borne interference.
5. The MMC20EN cartridge stylus is cleaned with stylus cleaning solution.
6. A Thorens rubber/cork mate is added to tame the platter resonance.
Finally, with the AC power on, I check the speeds for both 33.3 rpm and 45 rpm. To my surprise it is quite easy to achieve the accurate speed desired.
The turntable is now ready to be tested on its performance. I can't wait to put on it my favourite record ..... AND..... press 'go' .......
Amazing ....... ! It's still sounding so good after such a long hiatus ......!
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