The Korf Blog

The inside story: our research, development and opinions

21 August 2018
Azimuth Adjustment Myths and Reality, Part I
While we are getting ready for new prototypes and new measurements, I think it might be interesting to revisit static alignment, which we talked about more than a year ago.

Recently, a friend of ours bought a remarkably expensive cartridge, a full set of protractors, and an electronic "azimuth adjustment tool." His own efforts at alighnment resulted in the cartridge being twisted more than 5° in azimuth, and sounding quite a bit worse than the rebodied Denon DL-103R it was meant to replace. We were called to help.

I think this little job is an excellent reason to revisit what is considered common knowledge in azimuth alignment, and see if there's any truth to it.

Let's recap this common knowledge first:
Azimuth is a normal and standard alignment procedure, just like overhang, SRA, tracking force, antiskating etc
Correctly assembled quality cartridges require azimuth alignment to sound their best
Consequently, any tonearm that does not have azimuth adjustment is severely deficient
There is only one correct azimuth alignment for a given cartridge
It is achieved by rotating the cartridge along its longitudinal axis until crosstalk between channels is at a minimum

I have drawn a simplified schematic representation of a moving magnet cartridge to help us with our azimuth investigations.

The cartridge is shown as if viewed from the front. The information in the right channel is reproduced by the stylus moving along the axis a, and in the left channel by the movement along the axis b.

The stylus is connected with a rigid cantilever to 2 generators, A and B. Generator A's axis is perfectly parallel to a, and perpendicular to the groove wall. Generator B's is to b. Thus, in theory, stylus moving along the axis a only excites generator A, and likewise for b.

In practice, of course, everything isn't nearly as sunny, and a degree of crosstalk is inevitable. However, this is a reasonable picture of a perfectly assembled cartridge in perfect alignment. What can go wrong?

There are 3 possible scenarios:
The whole correctly assembled cartridge is incorrectly mounted, being rotated along its longitudinal axis away from a perfect position
A cartridge is imperfectly assembled, introducing an angle α between the axis of a stylus and a generator. It is aligned in such a way that the generator's axis is perpendicular to the groove wall.
Same imperfectly assembled cartridge is aligned in such a way that the stylus is perfectly vertical in the groove.

Let's start with (a).

Rotating the whole cartridge along its longitudinal axis introduces the angle α between a tangent to an LP surface and a cartridge's own vertical axis.

This rotates the stylus out of alignment, and also rotates the generator. Now the stylus movement along the axis a doesn't only excite generator A. It also excites B, proportional to \( \tan \alpha \). As a result, part of a signal meant for generator A appears in B.

Consequently, the easiest way to return our cartridge here back to alignment is to measure said crosstalk and to rotate the cartridge until crosstalk is at minimum for both channels.

In real life, it is a bit more complex than that. Rotating the stylus in the groove in effect reduces it to a less advanced shape, and this impacts crosstalk too. We'll cover this in more detail in the next post.
There's an important corollary from above that sounds like an utter platitude, but please bear with me.

If a correctly designed and installed tonearm is not equipped with azimuth adjustment, there is no way to introduce the angle α and thus rotate the cartridge out of alignment. Hence, in our case (a), the cartridge will always be perfectly adjusted for azimuth.
In a correctly designed and adjusted playback system, the only source of static azimuth error is imprecision in cartridge assembly
Let me rephrase that a little bit. If we limit ourselves to correctly assembled cartridges, having an azimuth adjustment on a tonearm is a disadvantage. It can only introduce an error where there was none.

And there's a second corollary. In a correctly designed and adjusted playback system, the only source of static azimuth error is imprecision in cartridge assembly.

And this is probably the reason why, in the otherwise encyclopaedic AES Disk Recording Anthology, azimuth is only mentioned a few times, and always in connection with cutting, rather than playback, of LPs. It was considered a solved problem: "Why, you just build your cartridges correctly, and that's it!"

Unfortunately, nowadays it isn't so. While most mass-market manufacturers have decent quality control (for example, I've never ever had to adjust azimuth on an Audio Technica cartridge), smaller operations probably lack the necessary tools and expertise to make sure the cartridge is assembled correctly. Azimuth (and SRA) errors of 10° are not unheard of.

I personally think that the cartridges requiring azimuth adjustments are defective and should be returned to seller. However, I am clearly a minority here, and most sellers refuse to accept back cartridges that were opened and mounted.

In the next blog posts, we'll examine what exactly happens when the azimuth error is introduced during cartridge assembly, and whether anything can be done about it.
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