A million years ago (well nine actually) I posted about setting up a cartridge. As it has now receded into the dark recesses of posts past, I thought it might be useful to repost it.
These days my system is a lot more modest than it was back then, but that doesn't change the thrust of the post, but it's worth bearing in mind that the comments I make in the post relate to an Orbe with an SME V and a Clearaudio Accurate cartridge. I have had some further thoughts about setting the bias (anti-skate) since then, but I will make a separate post on those later.
Here it is, and it's a bit long
OK, here are my thoughts on cartridge alignment, and I'm sorry if this is a bit long. Everything written here assumes the cartridge's internals are all in alignment with each other and with the body. This is sometimes not the case, but as an extra complication, that can be dealt with another time.
There are two parts to cartridge alignment, one is to get the diamond aligned in the groove, and the other is to get the generator centrally set (and that means horizontal and vertical). This second one is less frequently discussed, but in my opinion is fundamental to getting the best dynamics out of the cartridge.
Cartridge alignment is about geometry. First up, overhang and offset angle:
What we are trying to achieve is minimal tracing distortion across the record surface. This is not the same as minimal degrees deviation from tangential across the record surface, as more distortion will be created for a 1deg deviation at the centre of the record than at the outer edge. In other words we can afford to deviate from the tangential to a greater degree at the outer edge of the record than we can at the centre.
Ok, I just made a statement that is at odds with the various protractor types. Looking for minimal distortion is only one way of approaching the problem, and would generally be represented by a Loefgrun protractor (null points 70.3mm and 116.6 mm).
However, the Stevenson protractor (null points 60.33 mm and 117.42 mm) is looking from the viewpoint that as tracing distortion is worse at the end of a side, then that is where the null point should be.
The Baerwald viewpoint is that the maximum distortion (start, middle, and centre of record) should be broadly equal. This gives null points of 66.0 mm and 120.9 mm.
Max Townshend used to make a protractor that measured the distortion across the whole record side, the idea being that you would play with the parameters to get the minimum, even if your tone arm offset angle was incorrect. I have one of these, and I have to say it isn't the easiest thing to use. Having persevered though, I ended up with null points that appeared to match the Loefgrun ones almost exactly, but I did have to twist the cartridge a little in the mildly oversized holes in my SME V. Seems SME know their stuff when it comes to geometry, and no surprise there I guess.
Deviation from tangency is not only affected by the offset angle, but also by the overhang. It is interesting to note that a slight inaccuracy in offset can be compensated for by changing the overhang. It's not quite as good as having both correct, but pretty close.
The stylus must sit exactly perpendicular to the record surface for the best results. There are two reasons for this: firstly so that the stylus will sit correctly within the groove walls, and secondly so that the generator is correctly aligned with the modulations. On a stereo record, a sine wave that is in phase and equally recorded on both channels will create a horizontal movement of the stylus, and one that is out of phase will create a vertical movement (which is of course a bugger to track). You want the generator to move precisely vertically in the out of phase situation, otherwise you will get channel imbalance.
For those that have an oscilloscope, the HFN test record can be used to check azimuth by using the lowest level out of phase cut and checking the output is identical in amplitude. (Please remember I said I was talking about correctly made carts.)
Downward Force (playing weight):
When all is said and done, the correct downward force is the one that centralises the position of the generator inside the cart. Problem is it is very difficult to determine this, and what's more it changes with the ambient temperature. If you live somewhere very hot, there might be a problem with the appropriate downward force being too little to give good tracking. Some manufacturers tailor their suspension for export to hotter climes, others are designed in such a way that good tracking can be reached across a wide range of temperatures with a standard suspension. Neither is right or wrong.
These days I try and pretty much set the initial downward force by use of a big illuminated magnifying glass and a sheet of Perspex. By sitting the Perspex on the platter with a corner overhanging, I can then place the cart on the overhanging part and view the position of the cantilever right up to the suspension. Thus it is possible to see where it sits. Very minor tweaking by ear then ensues.
I might add that by using this technique I realised that I had been using too little downward force, and there is a reason for this. In my arm/cart combination, there is a point where the downward force is too little BUT the bass thickens up considerable. I now put this down to resonance, but I previously erroneously laid it at the door of too much tracking force, and backed off. Now I am using a heavier force, I have pushed it through this point, and the bass is now forceful, fast and tuneful as it should be, but the dynamics have increased remarkably.
There is no doubt in my mind that small adjustments to the VTA can make a large difference to the perceived sound. The problem is that I am no longer sure that the mechanisms involved are fully understood. Whilst most people have concentrated on the match between the cutter head angle and the stylus profile, cutting angles can vary from record to record by as much as 10 degrees (ok that's a maximum, but still 3-4 degrees would be a good median). To make a variation of that size would require a lot more VTA adjustment than is available.
I used to perform record by record adjustment, using the Ringmat system, but I've stopped because it was getting in the way of the music. I've now decided to go for the best VTA for a middle thickness record and hang the consequences. Interestingly, now I have the downward force where I believe the generator is correctly centred, I have found the best position to be, ahem, when the arm tube is parallel to the record. Hmm wasn't expecting that, to be honest, or perhaps we should be trusting the guys who make this stuff a bit more!.
If I had on the fly adjustment (because I've also stopped using the Ringmat), I think I would mark off a setting to make the arm parallel for each record weight, and leave it at that.
Bias (anti skate):
Because of the offset angle, the pull on the stylus is not passed through the bearings, but through a point to the right. This creates a moment, and so the arm is pulled toward the centre. As the stylus is locked into the groove, it does what Newton wanted, and resists equally and oppositely. This results in two things. Firstly there is greater stylus pressure on the inner groove wall, and secondly as the cantilever compliantly mounted, its position is deviated to the right.
This force is also dynamic in nature, responding to the transients on the record. I imagine if you knew the lateral resonance of a tone arm / cart combination, you could create a disc that would excite that not by having a tone at that frequency, but by having spaced impulses that would add drag at the correct resonant frequency. My guess is the stylus would pretty quickly leap out of the groove!!
This dynamic nature makes it difficult (impossible?) to set the value for the bias. However, we really want the cantilever to be tangential to the groove at the null points, because we just spent an age setting the cart that way to get the minimum distortion. Too little or too much bias will undo all that good work. Alright it might not mistrack, but we will still be getting a percentage of distortion that we don't want. In my case it's back to the big illuminated magnifying glass, and check to see if the cantilever is riding central.
The longer the arm, the less the offset angle, and the less the pull toward the centre of the record. I strongly suspect that 12" arms are liked more for this reason than for the reduced tracing distortion.
i.e. only in the horizontal plane. I have really changed my mind about this recently, having spent a lot of time recently researching the whole subject on the web and at home. I now believe the main advantage of lateral damping is not to cut down resonance, even though it does. I now think the main benefit is to cut down on the dynamic nature of the bias. The damping fluid will resist the fast acting inward pull created by a transient on the record. This will keep the bias required a lot more consistent, and allow the stylus to get on with the job at hand i.e. tracing the groove.
I have gone for full damping on my SME since I reset all the other parameters described above, and I believe the sound is more dynamic and clean than it has ever been. I don't believe the sound sounds "damped" at all, which is the usual criticism of damping. I may be suffering from "expectation bias".
Off-centre records may be adversely affected by lateral damping, as the fluid resists the arms ability to swing to and fro.
Vertical Damping reduces resonances in the vertical plane, but it also acts to slow down the arms reaction to vertical movement, such as when the record is rippled or warped. This translates as continuous change in the downward force, and may be why damping is disliked by many. I have little experience of vertically damped arms.
Many arms cannot be laterally damped without being vertically damped.