The Korf Blog

The inside story: our research, development and opinions

29 August 2018
Azimuth Adjustment Myths and Reality, Part II
In the previous blog post, we have started discussing azimuth alignment. We've seen the 3 typical cases of how it might go wrong, and have covered the first one in detail.

Today, we'll compare the 2 types of azimuth adjustment with poorly assembled cartridges, and decide which alignment is better: when the stylus is aligned and generator isn't, or when generator is aligned but stylus is askew? We will also see what exactly happens on the mechanical level when the stylus azimuth is wrong.

In the previous post, we came to the conclusion that in a correctly designed and adjusted playback system, the only source of static azimuth error is imprecision in cartridge assembly. Such alignment issues are, unfortunately, fairly common in expensive cartridges made by smaller companies.

Just how bad are these errors? Here is a photo by our reader Marco, who generously allowed us to use it. The cartridge shown is aligned like in case (c) so that the stylus is precisely vertical. This results in the body (and the generator) of the cartridge being slanted 3.3° left. I would say it is rather typical and isn't the worst case by far.

Assuming a specified channel separation of about 25 dB, slanting the generator 3.3° will decrease it by 6 dB to 19 dB. This is worse than a $35 AT95E, makes a joke of manufacturer's published specifications, and reinforces the argument that the cartridges with assembly azimuth error are defective.

What is better? Having a slanted generator or a slanted stylus?
So the effects of the alignment like in case (c) are pretty clear. Worse channel separation, more crosstalk. But what would happen if we align the generator perfectly and eliminate this crosstalk component? The stylus will be slanted by the same angle α, but it is that bad? What exactly happens when the stylus is not vertical?
It depends a lot on the stylus shape. For the following illustrations, we've taken the elliptical stylus as an example. With a conical (spherical) one, not much happens when the azimuth is off 1-5°. With more advanced shapes like line contact, Shibata, Gyger etc, the illustrations become too complex and detract from the gist of the matter.

Here is the normal perfectly aligned position. The stylus contacts the groove walls in two spots. When the stylus is vertical, those spots are symmetrical.
When the angle α is introduced, the shape of contact spots changes. In our case, the right one becomes shorter, but remains narrow. The left one, however, moves up the stylus, and thus becomes broader.
Cartridge designers try to minimize the width of contact spots for many reasons. Introducing an azimuth angle, in effect, changes the stylus shape on one channel to a less advanced one. What are the effects?

First of all, high frequency reproduction is impacted. Broader contact patch equals earlier HF rolloff.

Second, harmonic distortion rises. The broader the contact patch, the more harmonics of a pure recorded signal are generated during playback.

Third, the tracking becomes worse. These small undulations in the groove wall that the broader contact patch can't trace push the stylus up, out of the groove.

And last but not least, channel separation degrades too. That additional unwanted vertical motion of the stylus is, by definition, registered in both channels. The effect is smaller than with a slanted generator, but it does exist.

So in effect we have a choice:
b)
worse HF reproduction
more harmonic distortion
worse tracking
worse channel separation
c)
worse channel separation
I think the answer is clear. And with more advanced stylus shapes, the effects in (b) become much worse.

But what tools can we use to align the cartridge like in (c) above? Measuring and minimizing crosstalk will give us (b) — and this is exactly what happened to our hapless friend whom we mentioned in the introduction to the previous post. How to do it right?

In the next blog posts, we'll share the tools and procedure we use at Korf Audio to achieve correct azimuth alignment. Stay with us!

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