Hi, please find previous posts ref Aro setup, follow these to the letter and, with the advice as advised above by Simon and others, you will be OK.
All,
Below are my previous posts regarding bias adjustment for the Naim ARO.
In addition, I’d like to add the following:
- Cartridge/arm bias adjustment is not an exact science. There are too many variables to be able to get it right for every record, or even over the playing surface of a given record:
a. The compound of vinyl used
b. How ‘hot’ the tracks are cut
c. The thickness of the record. This changes the stylus rake angle, the vertical tracking force (when using a statically balance arm like the ARO) and the stylus azimuth in the groove
d. Stylus profile
e. Horizontal and vertical compliance of the stylus/cartridge suspension system varies non-linearly and non-coincidentally across the frequency spectrum.
- Assuming an LP12, the horizontal plane of the platter and the horizontal plane of the armboard MUST be parallel. Leveling the plinth is the first step, but overall this isn’t as easy as it sounds to get right even with a level plinth. The standard Linn top plate is bowed, which makes it difficult to have a reference. With a flat top plate (I have a Tiger Paw Kahn) you can slip a small stack of business cards under the platter’s edge at the points close to where the suspension springs hang, and adjust the suspension so at the three points the bottom edge of the platter just touches the top of the stack.
- Remembering that the centre of gravity of the platter/armboard/subchassis/suspension system is not coincident with the record spindle, when you’re leveling the platter/armboard the platter needs to be loaded with a mass equivalent to a typical record. If you have a spare heavy ARO counterweight, you’ll find that it weighs 139g and works perfectly if placed centrally over the spindle. The bubble level that came with the ARO can them be centered on top of the heavy counterweight as a double-check. You’ll likely never get everything absolutely perfect, but when the platter is rotating you can get it so that the bubble only moves very slightly, and certainly stays within the black scribed circle on the Naim bubble level.
- The lead-out wires that go from the ARO bearing cup to the socket on the armboard should be teased into a position where they do not touch the bearing cup or the armboard mounting collet over the arc the arm describes over the playing surface. The positioning of these wires will also affect the cartridge azimuth as the arm moves over the record and it’s quite a chore to get those wires into a position where they make the minimum change in azimuth from the outer to inner grooves. This will take patience and several iterations. Then you put on a record of a different thickness and find that everything has changed. As I inferred at the start of this post, you’ll have to aim for the best compromise.
- Changing the mass of the bias weight may change the azimuth of the cartridge. This is because the bias force applied to the bearing is not on the same horizontal plane as the stylus, and so there will a be a slight tendency to rotate the arm with the stylus as the pivot point. This is a small effect but can be clearly seen and heard if the mass of the bias weight is changed by a large enough amount.
Below is a diagram to help you see what I’ve done with the bias hanger, and why I tried this route. But first some background:
a. The ARO bias weight weighs in at 1.65g
b. There should be 40% - 50% greater bias force at the end of the record as at the beginning. Interestingly, this is NOT due to the reaction force from the centripetal acceleration trying to throw the stylus outwards, as that force is an order of magnitude lower than the force pulling inwards due to headshell offset and friction. It is, I believe, primarily due to the amount of information (undulations) per unit length of groove being higher at the inner grooves than at the outer.
c. The standard ARO (and most other hanging weight bias systems) have the exact opposite of what is required in (b) above due to the angle of the line attaching the gradated bias arm to the bias weight (see diagram below)
d. The simplest way to get things at least approximately correct is to set the bias hanger as in the diagram, use the first groove of the gradated bias arm, and add mass to the bias weight (I use Blu-Tak) to make up for the lost leverage.
e. Knowing that mass of the bias weight it is straightforward to calculate the right amount of mass to add using force = mass x distance.
I have empirically tested this method both with the HFN test record (I knew I’d use it someday) and a PC software oscilloscope and obviously by listening too. The main benefits are that the music is more ‘centered’ in both musical and hi-fi senses across much more of the playing area. It is now very difficult to tell which part of a record is being played. There is also considerably more detail at the start and end of a side, as one might expect.
Obviously, this experiment involves maligning the bias hanger, so be careful. I take no responsibility … yada yada yada.
Added Information
The bias hanger needs to be bent so that the bottom of the ‘U’ shape where the bias cord crosses it causes the cord to be level with the main axis of the gradated bias arm. This adjustment should always be done as a matter of course anyway.
Too get the best angles, the ‘U’ shape of the bias hanger should be only 1 to 2mm away from the gradated bias arm when the arm is at rest with the arm tube parallel to the side of the armboard.
With the ARO’s arm tube on its rest and parallel to the side of the plinth:
- The bottom of the ‘U’ of the bias hanger where the bias weight filament hangs is mid-way between the 4th and 5th notches on the bias bar.
- The bottom of the ‘U’ is at the same height as the middle of the bias bar.
- The distance between the front edge of the bias bar and the bottom of the ‘U’ is 1-2mm
If you now have the bias filament on the first notch, the angle between the bias weight filament and the bias bar will be close to 90 degrees with the stylus at the start of an LP.
I’ve tried a lot of different permutations and to my ears and oscilloscope, this set-up gives the best compromise.
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