Taming of the “Syrinx” PU2!!!!!!!!!!!!
So, with both the plinth and “fully suspended” turntable perfectly level, the “fully loaded” perfectly balanced unbiased tone arm set, all is now ready to load the tracking weight, set the bias and go! – or is it?
Our “vinyl friends” can have various masses either by design (180g) or simply determined by the dollop of vinyl placed between the poised pressings. Under the above conditions, if the arm is placed in the mid position over a “heavy” record on the turntable, the arm will move slowly toward the spindle. There will be similar situations, reducing in severity of reaction, when records with varying but smaller masses are used. With a “light” record in position the arm will tend to maintain its position. If a record clamp is used then the loss of arm control and the rate of change in position will increase. It is quite inconvenient and perhaps too difficult to set the turntable up for one weight of record or another, and/or for use with or without a record clamp! Even if the arm is properly balanced and the recommended bias is applied the introduction of the record/clamp mass will compromise the expected tracking condition.
Why does this happen? An explanation is that the sprung suspension system of the turntable resides around the periphery of the platter whilst the arm is mounted in a “satellite” position outside the perimeter of the patter. Not that this is a problem once the turntable is levelled with the tone arm fitted. But place a mass about the spindle centre with no change of mass in the “satellite” position for the arm, and an imbalance occurs and the platter/chassis system tilts.
This means the attitude of the arm pedestal is no longer perpendicular, the centres of the top and bottom bearings are no longer coincident with a centre line through them, and because of the split inertias of the PU2 bearing system together with the un-damped arm, the total lack of lateral balance kicks in and the arm will gently swing toward the turntable spindle – not what is wanted.
Is there a resolution? With a 180g record in place the left side of the platter was closer to the plinth than the opposite side when viewed from the front of the turntable. A 10g brass weight was placed on the arm board – not enough to redress the imbalance. Tried a 20g weight, much better – the platter was perfectly level with the 180g record on board and the arm maintained the set position. For the first time it appears that predictable control of the unbiased arm was achievable. A lighter record was placed on the platter and the clamp fitted to the spindle. The 10g weight was placed on the arm board closest to the platter – the arm very slowly moved toward the spindle, tried again with the weight placed furthest position possible on the arm board away from the platter – much better, platter level – once again the arm remained in position, unbiased control achieved. Over a trial period of time it was found that the use of the 10g, 20g and (together) 30g weights on the arm board, allowed easy, simple adjustment for a wide variety of platter loads, whenever the need arose. Similarly, the easy, simple adjustment of the bias could now be applied knowing that the setting can be used for different platter loads.
Thing is, with proper control of the bias the rest of the front end set-up will be correct. Now the finer points of the arm bias can be fully appreciated – who knows, this approach may also apply to other turntable/tone-arm set-ups!!
Hmm - Dunlop Systemdek Transcription Turntable/Syrinx PU2, golden oldies!!!!