tonearm theory & importance
The priority of low level signal purity
It is difficult to appreciate why a mechanical modification to
the rear end of the OL1 or Rega tone-arm should have such an enormous
influence on tonearm resonance and hence the overall sound. To
explain this phenomenon, it is helpful to grasp firstly, that the
signals
generated
by the
cartridge
cantilever are extremely small. These signals are then amplified
thousands of times to produce the output at the speaker. It follows
that the slightest source of unwanted vibration and resonance is
also magnified equally. Not only can unwanted vibration be introduced
(coloration), but this vibration also affects the cantilever movement
to cause distortion. It is the elimination of this spurious vibration
that results in the large differences that exist between mediocre
and high end arms.
The cause of unwanted vibration
To minimize vibration it is often recommended to match the tonearm
effective mass to the stylus compliance. However it is found in
practice that the arm effective mass is not very relevant if it
has an inherently very
low resonance.
As the cartridge stylus negotiates its tortuous way through your
record grooves it undergoes forces measured in tons per sq. inch.
This sends shock waves down the arm tube. What happens to these
shock-waves normally? - Some of the energy is transmitted down into
the deck, but much of it meets the counterweight structure and is
reflected back down the arm tube to the cartridge - this is highly
detrimental for good sound quality due to the aforementioned facts.
There is a secondary reason why the rear end of the arm is an extremely
critical area - The counterweight represents by far the highest
moving mass in the arm and affects an arm's performance in ways
that are hard to imagine. The counterweight is excited into resonance
by the motion of the arm. This means that it should be decoupled
and yet also remain rigid to the arm (to avoid introducing other
problems). The beauty of the Origin Live modification is that it
acts as a shock absorber, for waves traveling down the arm from
the cartridge and it also acts to de-couple the counterweight, whilst
maintaining rigidity
e.g. - why the structural upgrade works wonders
The upgrade involves removing the rear end stub. This stub is just
screwed into the end of the arm - far from ideal! Origin Live then
replace the old stub with a new stub. The new stub is torqued onto
the arm by a thin high tensile bolt. The new stub is also designed
such that it presents a low contact area onto the arm tube and is
therefore decoupled, yet far more rigid than the original. This
change also allows the counterweight to be rigidly clamped onto
the stub using an Allen bolt. An unmodified arm should not have
the counterweight rigidly coupled in this way, due to the old vibration
characteristics of the standard arm / rear stub joint. This ingenious
modification elevates a good arm into the same league as the super
arms and at an insignificant outlay. |