Electrical Zenith Setup

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dave slagle
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Electrical Zenith Setup

Post by dave slagle »

I use Analog Magik to setup my zenith electrically and here is my simple procedure for initial cartridge setup.

First you must understand that it is 99% likely that your diamond is not set precisely 90° to your cantilever so protractors are useless. The idea is that the amount of intermodulation distortion measured from the diamond not tracing the groove properly can be electrically measured. I have found that using the VTA test in analog magic is surprisingly effective in aligning a cartridge for the desired null points. It is all about finding the nulls in distortion and then placing them where you need them I find that if incorrectly set, the Zenith will dominate and confuse everything else that the software can measure so this should be the first step in cartridge setup.

Step 1

Get a copy of Analog Magik (i'm a dealer so get it from me please) and understand this is not a crazy scheme to make me millions. :-) You will also need the $99 ART USB Phono Plus and will need to install the drivers from AM and not the ones supplied by ART. Other methods of measuring IMD are acceptable but require more work on the user front. AM makes it quick and easy.

Step 2

Print an arc protractor for your desired alignment. I use the template generator from Conrad Hoffman Set up your cartridge to properly sweep the tracing arc. you can set the cantilever close to the alignment line as a starting point but this is the adjustment you will be making electrically.

Step 3

Set AM to the VTA setting and measure / note the distortion at the beginning of the track and at the end of the track. Also pay attention to if the distortion value is high or low. This is a relative thing and I consider anything more than 5% high and the goal is below 3%.

Step 4

If the distortion increases by a fair amount (1-2%) rotate the cartridge anti-clockwise from the top and repeat.

If the distortion decreases by a smaller amount then rotate the cartridge clockwise from the top.

repeat steps 3 & 4 until you identify and place a null near the end of the test track which coincides with a typical outer null point.

some key observations.

-Zenith has the most severe impact on the distortion numbers and VTA is secondary. Distortion imbalance between channels is generally due to improper Azimuth.

-This is the process distilled down to the bare essentials and making minor adjustments to the zenith is tough and takes time getting used to.

-It is very important to measure both the start and the end of the track to see which direction the distortion is going so you know which direction you need to rotate the cartridge it is entirely possible to go too far past the null and get a similar number and make you think you didn't move anything. Measure the start and finish of the track every time.

-You are looking for a null or the lowest measured distortion so make note of the absolute lowest measured value you see throughout the process.

-The end of the track is in the vicinity of a typical outer null point so you want to see the distortion drop to the lowest value just as the track ends.

-The VTA also has an effect on these numbers so once you find the lowest number by zenith adjustment make try increasing/decreasing the VTA to see if further improvements can be found.

-If the left and right channels are substantially different from each other check / adjust the Azimuth.

-The key factor here is the changing distortion across the track is due to the fact that the zenith angle changes across the record face. You are in fact seeing the change in zenith as the distortion numbers change. This is to be expected and whether the number is going up or down is a key indicator in which way the cartridge should be rotated. The only way the value should remain constant is if you have a linear tracking arm.

dave
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dave slagle
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Post by dave slagle »

some of the back story....

I became a dealer for Analog Magik because I wanted to find a repeatable method to set SRA for cartridge comparisons. Over the past few years in building cartridge prototypes, I have realized that setup often dominates the sound. If trying to compare two different suspension materials, the better set up cartridge will sound best. I had the thought that since I am using diamonds with the micro-ridge profile which are heavily reliant on SRA settings it would be nice to be able to quickly adjust cartridges to the same SRA electrically to better isolate the variable being compared.

Analog Magik uses an IMD test of a 60Hz+7kHz tone with a 4:1 ratio. You then filter out the 60Hz and look at the FFT of the signal and the level of the sidebands at 6940Hz and 7060hz tell you the amount of IMD. If those levels are 40dB below the 7kHz fundamental then the IMD is 1%.

This is not a new testing concept. The Ultimate Analogue Test LP has instructions and a test track for setting VTA using this exact procedure and both the CBS STR-110 and the Shure TTR-103 lay out this test for mistracking. I stumbled upon this using Analog Magic's VTA setup and quickly realized that the zenith if slightly misaligned dominated the distortion measurements and a zenith error of 1.2° assures that a null point will never be hit on the playable record surface.

In trying to use this test to set VTA, The distortion was >5% and I could never obtain meaningful numbers by any amount of VTA change. I saw reference to try another alignment geometry so I twisted the zenith a bit and was shocked how much the measured distortion numbers changed. I then began initially setting the Zenith first by using the VTA test outlined above. After a null in distortion was located in the vicinity of where the null point should be I them proceeded to then adjust VTA to further lower the distortion numbers and the world made sense again. It turns out that the distortion caused by the improper Zenith was so high it was obscuring the minor changes seem by VTA adjustment. I needed to codify this behavior so I did some IMD plots of both a micro-rigge and a conical vs. zenith angle.

reliably setting zenith to 0.5° increments was a challenge so a laser was glued to the cartridge to project a dot on the wall 110" away and every 1" of dot movement was ~0.5°. I could then carefully lock the arm in the armrest and adjust zenith bu 0.5° and remeasure.

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Once the data was captured for a range I repeated several of the measurements to check for consistency and am confidant with the testing methodology and the plots are below.

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It is clear that there is a null for both the conical and the micro-ridge and it is interesting how the conical gives a V and the micro-ridge more of a parabola. Since a conical does not have a zenith the fact that the cantilever angle still changes distortion points to two different mechanisms at work here. It appears as if the null for the conical occurs when the cantilever is aligned properly to a protractor but lets take the case where the zenith of a micro-ridge is 2° off from the ideal 90°. You now have the choice to align electrically for the diamond or visually for the cantilever. Well I have listened to both and have found that hands down the electrical method wins.

This is a capture of a cantilever on a traditional Löfgren alignment that measured under 2% IMD with analog Magik. When aligned in the traditional manner the IMD was in the 8% range and visual inspection of the diamond confirmed an approximately 2° zenith error.

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I started listening to this cartridge at the 8% number and it sounded good. I was shocked at how much better things got when I got the number down to 2% and how crooked things actually looked on a protractor. I have since set up 20 more cartridges for zenith with this method and distortion below say 3% has given consistently good sound across the entire record face independent of what the protractor says.

Lets assume for a 12" arm that the Zenith change over the face of the record is 2° for a Löfgren alignment. Looking at the distortion plots above you also see that the width of the null is also close to that 2° range so it becomes clear that if your nulls are not aligned properly, inner/outer groove distortion can get exceedingly high rather quickly.
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dave slagle
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Post by dave slagle »

Lets look at this whole Zenith thing a bit more closely and assume a 12" Schick arm with a Löfgren alignment. Here are the numbers from the Conrad Hoffman Arc Template generator and the plots zenith angle and distortion from John Ellison's excel spreadsheet.

The key thing to look at is the box in the upper right corner that allows for the zenith error to be entered.

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OK so now the world makes sense but look what happens if the diamond is set to either 89.5° or 90.5° which introduces a 30' zenith error. (30'=30 minutes=0.5°)

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Those null points sure end up in different places don't they? Now lets get crazy and look at what a full 60 minutes of error in either direction looks like.

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With a 1° zenith error in either direction the null points are essentially off the face of the record. The problem here is two fold. First it is exceedingly hard to repeatedly set a cantilever to a line with better than 0.5° accuracy and the typical specification from the people who set the diamonds is ±5°. I do not have any info beyond the test data sheets provided by one of the manufacturers on the actual variability of diamond set. The best of the measured results of the 9 samples measured (3 samples each from 3 different runs) was 1° 50'.
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It seems that this whole subject of incorrect zenith set is coming out of the shadows into the light. Many are trying to toss the cartridge manufacturers under the bus as being incompetent which i think is unfair since more often than not they buy the complete diamond / cantilever assemblies from one of the three places in the world that make them (Ogura, Namiki, Gyger) and if the companies that cut and polish the tips have a ±5° spec, can we really expect 10X better accuracy across the board? Will the market stand for 10 cantilever assemblies to be purchased and 9 discarded in order to find one good one? I think not. The better approach is to accept that the days of setting a cantilever to a line belong in the past. I for one feel that electrical alignment of zenith should be the first step in dialing in a cartridge.
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Post by dave slagle »

knowns and unknowns.

These days there seems to be two warring factions around analog setup. You have those that measure and those that listen and each faction thinks their way is the best. Within the measurement clan there appears to be an emerging divide between those who use the electrical and those who use the visual. The visualites use optical tools and software to determine angular relations to the ideal and the electrites use audio analyzers to meet the same end. Ultimately both then rely on listening to affirm how well they did their jobs. Both methods are prone to errors and lets dig a bit deeper into what they actually are. The first set of errors common to both are the unknowns. The two big unknowns here involve sra and zenith. Setting the sra to a mythical 92° angle makes the assumption that all records are cut the same. Whether the SRA is set visually or electrically the possibility of error from album to album is the same. The zenith situation is actually worse since nothing guarantees that the cutting or playback stylus is exactly 90°. To further complicate things, while SRA changes are repeatable and show an identifiable pattern, zenith changes are far more cagey to identify. Visual inspection of the playback diamond can point to errors on that end but only the electrical can test for sample to sample variation of the cutting stylus. The achilles heel on the electrical is the test record becomes the reference and nothing guarantees that it was cut at a 90°:00’:00� angle. Before anyone cries foul on the cutting stylus angle, it is important to know that the cutting stylus typically lasts 10 hours before it is replaced and in looking at the way it is set in the cutterhead leaves a big window for variability.

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Beyond the unique sample to sample unknowns hidden in the groove there are also two distinct differences between the visualites and the electrites. Lets stick with zenith for the rest of this since it represents the final frontier and is about to become the “it� thing for analog. I have visually noticed that the zenith of the diamonds with relation to the cantilevers often seems askew. I have optically measured and put a number on the apparent zenith error and that angle has coincided with the visual skew of the cantilever when set up electrically so both methods are viable but each has its own unique set of unknowns.

The Electrical method gives you a single number that encompasses three dimensions of possible error so the great unknown becomes which error are you looking at? To further complicate things, in many setups, adjusting for one parameter often changes the other two so while you could be moving in the right direction for one axis you might be going the wrong way on the others. Put another way, the numbers are always correct but it is often difficult to figure out exactly what they mean.

The optical method has the distinct possibility of human error. Lets take the case of the zenith error mentioned above. If I carefully measure the zenith of the diamond on a controlled environment and attach a number with a precision the easy part is done. Now taking that number and trying to replicate with the needle on a record surface to the same precision is a herculean task. Lets assume the "best case in an ideal environment� the zenith can be assessed to ±15’ and then lets replicate those numbers in aligning the corrected cantilever to the same ±15’ accuracy. This makes the window of final zenith setup error ±30’ or 1/2 a degree. Being realistic in the capabilities of the average vinyl enthusiast I would expect the setup error to double the initial measurement error and lets call them 20’ and 40’ for a possible zenith error of ±1°

Hey everyone gets lucky and even a blind squirrel is bound to find at least one acorn in its life. For us somewhat clear sighted lemmings, lets look at what a skewed zenith of 1° does. First we need to make a few assumptions so lets stick with a 12� Schick and a ideal Löfgren A alignment. This happens to give roughly a +1.5°, -0.5° range of zenith across the record face and if aligned to the null in the picture below the IMD will be under 5% across the side. Rotate the zenith by a degree either direction and suddenly the 2° window shifts left or right and you are in the 8-12° range at some points. This makes it clear to me that the optimal setting for zenith with the advanced profiles is surprisingly small and the possibility of human induced error is very real.

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Moving back to the electrical realm it appears as if not all of the parameters are created equal and thus far I have found that even if slightly off, the IMD caused by zenith error is both easily measurable and clearly audible. Once the zenith is reasonably dialed it the effect of incorrect SRA on IMD starts to become visible. Azimuth errors seem to show up as differences in distortion levels from left to right. SRA follows the same pattern of a null that the zenith does and it just takes a few times back and forth between the two to further refine the null. Toss in an occasional peek at the azimuth and things get to the point where further refinement is best done by ear.

The good news here is if you make a mistake during the electrical setup... the numbers immediately let you know. A similar human error in the visualite world only sometimes becomes apparent after listening to a few album sides. Living in the electrite I have consistently found that once you get a feel for it, after a quick general visual setup, the electrical procedure results in good sound across the entire album side with a minimum of stress and to me that is a huge win.
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Daniel
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Post by Daniel »

How did you go about changing zenith without changing overhang? The old loosen one screw, adjust and as the change in overhang is so minute don't care about it?
dave slagle
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Post by dave slagle »

The overhang change will happen and this happens whether you are aligning your zenith electrically or visually. This is why I use armpods for my tonearms since it allows for the focus of the tracing arc to be changed independently from the zenith.

At this point I am not convinced that the overhang is that critical.... or even matters at all. Overhang is just a variable added to another parameter (pivot to spindle) to get to the required number which is pivot to stylus (effective length). The two parameters at play for null point alignment here are the tracing arc and the zenith so why add complication when it is not needed? Thus far, the first step is to simply print out an appropriate tracing arc and then set the diamond to follow it. Next align the zenith to hit the outer null. In a perfect world if you set the zenith to hit the outer null, the inner null will also be hit. Often after several attempts at zenith adjustment the tracing arc is not followed perfectly but I have yet to get anything but positive results from setting zenith to the outer null even if the diamond ends up having a 1mm error in the arc tracing.

I am not saying that accurately tracing the arc is not important but I will say that a 1mm error in the tracing arc seems to have a much smaller effect than say a 0.25° change in zenith. I should add at this point, everything I am saying here has to do with profiles that try to mimmic the cutterhead profile. I see similar measured pattern of results with conicals but have limited ears on experience since friends don't let friends listen to conicals. :-)

dave
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