**Unipivot mod (lengthy, how and why)**
Hello Sandro and all Mayware users,

looked at the pixes meanwhile and found my supicion proved.

The tonearm almost certainly has not enough rotational intertia.

A very common disease among unipivot tonearms.

Without damping, the torque exerted by the stylus on the tonearm's rotational inertia (imagine it as as rotational "effective mass") triggers rotational oscillations of low freqency, but not low enough. With damping, the arm is coupled to its pivot base, the coupling increases with the frequency going up. Of course, there is considerrable damping already at the resonant frequency and the amplitude peak of the oscillation is low. But as it is the case with all mechanical dampings, the more damping we have, the lower the Q factor and the less steep the resonance decoupling curve, the transfer function, is falling.

Which means: a low rotational inertia and considerable damping together do not make the arm near as stiff in the range of 20 to 80Hz as if the rotiational inertia would be sufficiently high and no damping is applied. Because in the latter case, the Q factor is very high, the resonant freqency is low enough (say, 1 Hz) not to disturb the audible range. In reference to the excitation, the transfer function of this oscillating system, its "output" goes from unity (below resonant freq.) to a peak way higher than unity (@ resonant frequency) and with further increasing frequency of the excitation, it drops to waaaayyy less than unity, so fast that at 20Hz (more than 4 octaves higher) it has already reached -60dB or more.

Which means in short: the arm being ultra-soft against rotational excitation at 1Hz is very stiff against them already at 20 Hz and few audio systems make it to that basement. It is superstiff at 50Hz.

Another important fact: any mass added to the arm affects the arm's effective mass in proportion to the square of it's distance to the arm's center of inertia.

As a practical result, i would carry my unipivot arm (id i 'd own one) to a mechanic wizard and tell him to mount two small rods exactly at the height of the pivot point and in rectangular orientation to the tonearm wand, or better, rectangular to the headshell's offset angle. On these rods i would mount slender, lengthy weights then to achieve a rotational resonace frequency as low as possible.

[disgressing, <tonearm resonances>]:

remember i used slender weights, the arm's effective mass in vertical direction is increased only by a tiny amount as the the slender weights have almost distance zero in reference to the arm's pivot axis of up-and-down movement. Effective mass in lateral direction is increased more and thus vertical and lateral tonearm resonant frequencies are pulled apart for which i am very grateful as a lowered lateral resonance improves tracking. Many folks believe tonearm resonance has to be between 8 and 12 Hz. I agree for the vertical resonance, a resonance too low makes the stylus jump grooves and, too high, it muddens the bass. But think a bit which triggers lateral resonance: disc excentricity (0.55 Hz at 33rpm, up to 2.5mm amplitude) and groove feed (< 1Hz, 50µm amplitude). Methinks that a lateral tonearm resonace as low as possible but above 3Hz is ok. Airborne linear tracking tonearms, particular the DIY Ladegaard arm would not work if this opinion would be dead wrong, Poul Ladegaard thought the same and proved it by his arm.

[/disgressing]

The weights should be equal and adjustable in distance to the pivot: Eeezy azimuth adjustment with high resolution is the payback

.

I would have a mechically skilled person do the modification, the arm looks soo neat

Who got lost in my description (nobody i hope

..

) and/or wants further proof: please track the web for Stax tonearms. Some of them have such side-weights and they work extremely well, are considered to be the best unipivots by some.

A buddy bult himself a unipivot with high rotational inertia and high effective mass too: he wanted to make his Denon DL103 track 1st class and he succeeded. He had the side-weights not at the pivot but agreed this would be better and said this would be the next development step.

Consider, the Denon has a compiance of only 5 µm/mN . A challenge for any tonearm, not only for a unipivot.

All for now, if questions arise, pester me