The world of vinyl manufacture and reproduction is an imperfect one, and I’m reminded of a spoof engineering paper which “proved” that bumble bees can’t fly.
I don’t know if anyone has ever “proved” the impossibility of vinyl playback, but when you consider all of the barriers to reproducing music by employing a rock to scrape across a piece of plastic, the results we have achieved are nothing short of amazing.
Vinyl Playback Perfection in a Physical Universe?
I’ve never encountered the perfect tonearm, and I doubt I ever will.
With respect to cartridges, consider vagaries of affixing a tiny stylus to a cantilever. In my recent introduction to the AnalogMagik software, I referenced comments by Jonathan Carr of Lyra. Jonathan noted that his cantilever supplier will not guarantee better than +1.5 / -1.5 degree precision for stylus positioning.
Lyra uses Ogura Jewel for their cantilever/stylus assemblies. Ogura supplies Koetsu and many other top line Japanese cartridge builders. It doesn’t get better than this.
In the record pressing industry, I’m unaware of any cutting angle standards, and as Jonathan mentions in the above link, cutting angles range from 91 to 95 degrees..
This is why we use microscopes and other sophisticated tools to set up our cartridges, and even that is a moving target for the above reasons.
A Statistical Norm & Some Exceptions …
In my experience, the vast majority of cartridges tend to set up in the range from a “level" headshell (the mounting plane of the cartridge parallel to the platter), to one where mounting plane angles upward toward the bearing pivot - a “tail up” orientation.
In the past few months, I’ve experienced a perfect storm of sorts, encountering several cartridges requiring a “tail low” setting.
From the perspective of most tonearms and turntables, an "extreme" tail low setting like this is not a problem. These two cartridges however, began to push the limit of the 4Point-9's downward adjustment range.
When mounting a Kuzma CAR 40 cartridge to a 4Point-9, our microscope guided us toward a “tail low” setting to achieve the 92 degree SRA as shown in the the microscope photo, and the dimensioned side view photo (above).
I’m loving the Kuzma cartridges and will have more to say about them in the coming days.
The 4Point-9's Operating Range
In the above dimensioned photo, the 4Point-9's "tail low" orientation is achieved by lowering the bearing by about 7mm (14 turns of the VTA screw) from a starting position of a horizontal headshell (cartridge mounting surface). This lowers the SRA by 1.75 degrees.
At this point, we began to approach the limits of the 4Point's working range.
Set at this height, we noticed a slight increase in cueing resistance (upward) as the headshell rose a few millimeters above the record surface. In other words, if the arm was tracking a severe (very severe - borderline unplayable) warp, the tracking force would increase.
This wasn't a problem in normal use (playing LPs - even warped ones), but it was a bit too close for comfort.
What to Look For
The arrows in this photo point to the parts requiring clearance in order to track records correctly.
This photo shows an installation where the headshell is approximately parallel to the platter (it's slightly "tail up").
After establishing your SRA, ensure that there's visible space (clearance) when the stylus is cued about 5mm above the record surface. This will permit free upward movement when tracking record warps.
As noted above, such a "tail low" orientation is extremely unusual, but it is possible, and it's something to check when setting up your cartridge. Without a USB microscope or other means of establishing the correct SRA, the typical user is unlikely to set their tonearm up in this manner.
A Simple Solution
The solution is simple – an angled shim which allows us to raise the 4Point to the middle of its operating range while retaining the 92 degree SRA.
Stay tuned, as we're tooling up to release these as a product. They'll come in a package of 3:
- Angled (7000 series aerospace grade aluminum): to solve tonearm height problems.
- "Flat" (light and heavy): to tune tonearm mass. The light shim will be 7000-series aluminum, and the heavy one will be marine brass.
You don't know when you'll need these, so having them in your toolbox, will come in handy.
We modeled these in our CAD program, and the light shims (angled and "flat") will weigh about 4 grams and the brass version will weigh about 8 grams.
Straight and angled shims can be combined for mass-tuning flexibility.
The production versions will have a 1.5 degree angle. For any smaller angle, you wouldn't need it. If a larger angle is required, your cartridge is likely out of spec.
A note about the prototype
There's a bit of "false precision" in the angular dimensions shown here, so consider these 3-decimal dimensions to be approximate.
There wasn't much point in changing our CAD software drawing defaults for this exercise.
To draw the reference lines and measure the angles, we imported the photos into our CAD software and "traced" the lines.
We did our best to eliminate parallax in the photos, but a bit remains, and with it, a bit of uncertainty.
Teach a Man to Fish
While the concept of angled shims is by no means revolutionary, we felt obligated to point out its efficacy in this particular application.
It's important to point out the importance of energy transfer and material interfaces. Cartridge designers take this very seriously, and one key assumption they make (and condition they test for), is the headshell material - whether it be removable, or integral with the arm wand.
The vast majority are aircraft grade aluminum, although there are some exceptions (stainless, wood, carbon fiber).
Change the cartridge interface and you have altered the cartridge design.
This may sound overblown, but every time we've made a radical departure in material interfaces, the sound has changed - whether it be a headshell shim, an armboard material, or a layer in our platters.
We mention this, because there are some services who will perform a remote setup for you, and they accomplish this by fabricating shims to set SRA and Azimuth.
We applaud this idea, but there's one important consideration (you guessed it) - the shim material. We advise asking them what material they use to fabricate these shims.
Last year, we considered fabricating "one-off" custom shims from 6061-T6 aluminum, but it this is both impractical (costly) as well as subject to long lead times. With the advent of 3D printing with metal, we may return to this at some point.
So, an alignment achieved with a composite shim may indeed improve your setup (alignment matters), but know that you are only part way there. The cartridge no longer behaves the way the designer tested it. You might get lucky, and the stars might align for you, but be aware that you're now in "design mode", with its inherent pitfalls.
Our preference is to teach you how to perform your own setups, although we realize that not everyone is inclined to this sort of activity. If you are up to it however, we're happy to guide you through the tool selection process along with relevant techniques, tips, tricks, and best practices we've established over time.
Our downloadable setup report has some tool information in the appendix, including a guide to fabricating your own azimuth gauge. Subscribers to our mailing list can download it. Scroll to the bottom of any of our web pages to sign up.
Perfection? Not in Our World
I need to restate: no tonearm is perfect, and I won’t be shy about pointing out anomalies as I encounter them.
Please take my criticisms in the collaborative spirit in which they’re offered.
In my “best tonearm” blog post, I comment about tonearms being tools, and depending on your work style, some may be a better solution for you than others.
The Kuzma 4Points and Schröder CB tonearms remain my reference tonearms, with Kuzma’s ease of adjustability being second to none (and matching their performance).
It took me 10 years to encounter this anomalous situation with the 4Point, and about an hour to fabricate a solution. The winners? Our customers.