More Anti-Skate Testing

The Feickert test disk has a serious of tracking tests.  The last one breaks up horribly at my previous antiskating compensation setting of 3.1g.  Dialing the antiskating down to 2.2g passes the test.  At 1.5g antiskating, it begins to get ugly again.  It's fairly decent from to 1.8-2.7g.

On the silent groove, 2.65 is as low as it can go without pulling toward the center.  It can go as high as 2.9g without strongly pulling outwards, which it does do at my previous setting of 3.1g.

The overlap between these two tests being 2.65-2.7g, that's where I set the antiskating compensation.

Later I took out the "Orion Test Record."  It has a very intense trackability test.  My cartridge with the above settings was breaking up somewhat on the second to last series and skipped the middle frequency on the last series

Checking the antiskating blank space it seemed like the Linn antiskating adjustment followed the tracking force almost perfectly.  This blank space is much larger than the one on the Feickert disk and you can try different spots more easily.  Though I wonder if the Feickert has some special "roughness" that makes it more correct.

With this in mind I tried lower and higher tracking forces than my usual 2.2g, with the antiskating set the same.  Lower tracking forces resulted in worse tracking (as expected, but I wanted to be sure).  Forces higher than 2.3g sounded no better (I tried 2.5g and 2.7g and it was the same or possibly worse).  It might have improved a tad still further with 2.4g antiskating.  At 2.5g it was pulling toward the side on the blank grove and no better on the trackability test.

So as of 8pm, this is the setting: 2.3g tracking force (on the Linn dial, measures 2.26g) and 2.4g antiskating compensation.  This is only a hair above the 2.2g recommended maximum tracking force and therefore I think it's OK.

The cartridge still skipped the middle frequency of the last series.  I think this test record is damaged from previous testing and I ordered a "mint+, possibly unplayed" one on Discogs.

 

New "Stacked" Headshell Mass

The new mass looks and sounds much better than before.  I aimed for 4.5g added mass but actually ended up with 4.7g after stacking a fair amount of hockey tape on top of the lightweight "headshell" of the Linn Ittok arm.  I also removed some hockey tape from the arm which was getting too close to warped records.  I added a single layer of hockey tape around much of the cartridge too (which was not easy to do) in the hopes of attenuating a high frequency resonance apparent on the Hifi News frequency sweep test.

Sonically I'm feeling I now have turntable reproduction in the big leagues, like the megabuck turntables at shows.  Probably most of what they do is simply getting the basics right, such as effective arm mass for the cartridge.

In order to test turntable speed, I brought out the Feickert test record, which works with the PlatterSpeed app on my Android phone.  Sadly it does not appear there is an equivalent app for iPhone anymore.  The iphone apps have you place the phone on the record, which introduces a lot more weight on the platter and therefore may change the speed slightly on a Linn (which it seems to do) because the suspension is pushed down, changing the angle with the motor pulley and hence speed.

The Feickert record also has a low frequency spot frequency test which seems easier to read visually than the Hifi News low frequency sweep.  The announcer announces each frequency, and it appears my low frequency resonance starts and is very intense at 8 Hz, then just a bit at 9 Hz, and gone at 10 Hz.

The previous measurement based on examining the measured response of the Hifi News test because visual inspection was not revealing, with the larger 6.1g mass, was that the lateral resonance went down to 7 Hz, which is why I decided to use less mass.  But perhaps even less is called for, perhaps 3.5g added mass.

Some say 7-14 Hz is OK.  Others recommend 9-11 Hz for best performance.

Here is some excellent research on arm/cartridge resonance.  The usual spring/mass model is an oversimplification.  Also the specs provided are not as useful as they would seem.  Ultimately you must do measurements and mass adjustments to get the arm/cartridge resonance correct.

 

New LP12 adjustment speed accuracy

 Platterspeed app using Feickert test disk shows my LP12 now at +0.11% speed error, not much, but not as good as the +0.02% it had been a few years ago.  But still very tiny.  I had figured the new much improved suspension alignment would make a slight difference, and it did.  But it would probably be pretty hard to see the error with a strobe disc.

Linn LP12 specification is 0.03% accuracy.  It can be made that good, or even better, if you adjust the motor screws well enough to get the pulley tilt just right.  The synchronous motor is controlled by a very accurate oscillator in the Valhalla board.

1000 Hz reads as 1001.1 Hz, with raw -.31% to +.19%.  Which means if you looked at any tiny bit, it might go in the other direction, you have to get a long term average to see the 0.11% fast.

Wow and Flutter reads 0.009% using two different standards.  That's better than the specs of many top turntables.

Update: I see now that measurements may be even more accurate with the 3150 Hz test.  This shows an average speed of 3153.9, which is a 0.13% error.  The two wow measurments are 0.14% and 0.12%, still within the specs of the better turntables (the best are often spec'd at 0.15% if there is any spec at all).   The raw speed deviations are -0.47% and +0.38%.

Measurements on LP12 with Ittok arm and additional headshell mass

Additional Headshell Mass*

Upon getting my Linn LP12 fixed, and finding that I liked it slightly better with my 6.1g additional headshell mass, which is a squished roll of hockey tape,  I decided it was time to do some measurements with and without the extra mass, and with different levels of antiskate.

The results seem to indicate that the mass DOES improve the low frequency tonearm/cartridge resonance by lowering it considerably in frequency and slightly in level (except it increases the amplitude of the resonance in the right channel).  But it seems to have no measurable impact on anything else, including the 20-20kHz response using the 20 second sweep on Hifi News test record (HFNTR).  So how does reducing the resonance from 13Hz to 9Hz make the bass above 20Hz sound better?  Apparently not by a straightforward effect on the frequency response as such, but by reducing resonances that are intermodulating with the rest of the sound.  Note that a 20 second 20-20kHz sweep will also tend to downplay low frequency resonances which take a while to develop, a pink noise test (not yet done) may be more revealing.

Meanwhile, cranking the antiskate compensation up to 3.1 g (the maximum) seems to have no effect on the vertical resonance.  

The 3.1g antiskate setting also the cleanest performance on the maximum trackability test, which sounds slightly distorted at the 2.2g setting which would nominally match my 2.2g tracking force.  I have been using the 3.1g setting since discovering that it worked best two years ago.  The Ittok antiskate mechanism seems to add desireable horizontal damping as well as antiskating force, and both are useful to me up to the 3.1g setting.

I was motivated to test vertical resonance vs antiskate compensation specifically because of a strange channel imbalance in the vertical resonance.  There is much more vertical resonance in the right channel than the left channel.  This could mean the stylus is climbing the outermost side of the groove, which is what excess antiskate force might tend to do.  But no antiskate setting made any measured difference on the vertical resonance.

Here is a picture showing first the horizontal and then the vertical resonance test in the No Added Mass condition (on top) and the 6.1g Added Mass condition (on bottom).  Both resonances are clearly lower in frequency (desireable) with the added mass.  However, strangely, the vertical resonance in the right channel gets lower and perhaps slightly larger.  The marker is at 9Hz in the horizontal resonance test.

Horizontal and Vertical Resonances vs Added Mass (bottom)

You can see why I was motivated by this result to see if excess antiskating force was causing the increased right channel (bottom in Audacity) resonance amplitude with added mass.

But antiskate does not appear to be causing this issue.  The image below shows the result of testing vertical resonance vs antiskate.  There appears to be no change in the vertical resonance while varying antiskate compensation from 3.1g to 0g.  And it's always worse in the right channel anyway.

Vertical Resonance for 3.1g, 2.2g, 0g, and 1g antiskating compensation

Meanwhile, the Frequency Response sweeps show no bass difference from added mass (on bottom).  In the highs the added mass slightly changes the high frequency measurement (I thought it sounded better WITH the mass, but the graph does not make that look obviously better):

20-20kHz sweep without and with (bottom) added mass

Also the frequency response sweeps show no low frequency dependency on antiskating force level.  Once again I thought the highs sounded better in the 3.1g antiskating condition, but this is not obvious in the measurements.

Frequency Response vs Antiskating level (2.2, 3.1, and 0g)

These results suggest to me that the added mass should be somewhat smaller than 6.1g, perhaps 4.5g or so.  With 6.1g, the horizontal resonant peak is 9 Hz which is fine but has legs reaching down to 7 Hz, which is undesirable.  Also a lower mass might reduce the 9Hz or so increase in amplitude of the vertical resonance.  But without the mass, there is resonant garbage as high up as 16 Hz, which is clearly undesirable.

(*The photo is to show what the 6.1g mass looks like.  It is not fully authentic, because by the time I remembered to take a photo I had already removed the mass again and had started replacing it with a stack of hockey tape, which should work better.  I didn't remove the beginnings of that stack to take the photo,  I simply stuck the mass back onto the headshell again, so it shows quite a bit more hockey tape underneath the roll than there was before.  Prior to this week, I had never even measured the weight of the hockey tape roll either.   When I came up with the idea of rolling up a bunch of hockey tape and squishing it on top of the headshell 18 months ago, I had conceived it as only a temporary measure.  It would enable me to quickly figure out exactly how massive the mass had to be.  Or so I thought.  Somehow all the tests I did back then seemed inconclusive.  Especially just listening to the "warbling" as the test record instructs you to do is quite ambiguous, and then to compare one such ambiguous listening session with a much earlier one is just confounding.  I knew the mass was an improvement but it would be better larger or smaller?   I couldn't tell, and I didn't dare to make it much larger.  I had never gotten around to the much more precise visual analysis in this post, until now.  And so I like to think that in some ways I'm getting better.  And of course I rebalanced the arm whenever I either added or removed the mass.  The mass is to increase the tonearm+cartridge Effective Mass, not the tracking force.  The Linn Ittok is a low to medium mass tonearm.  For low compliance cartridges such as the Dynavector 17D3 moving coil, a high mass (most importantly, high lateral mass) tonearm like the Dynavector DV-505 or Fidelity Research is called for.  One can fudge this a bit with tonearms that have adjustable damping, like my medium mass Jelco 750L, which I haven't tested yet.)

Linn Sondek fixed and tested

My Linn Sondek LP12 was fixed by Mark last Saturday.

It broke over 6 months ago when, frustrated by the loose arm holder, I tilted the table up on it's side without removing the heavy platter.  That is a big no-no for an LP12.  The springs got twisted in such a way as to make the suspension constantly jittery.

The proper repair for a jittery suspension requires having a level jig for adjusting the turntable.  I tried but was unable to order a genuine Linn one last year from Symbiosis in UK (their computer acknowledged my order but I never got a follow up email).  When I first talked to Mark about the issue last year, he said he could probably fix it without the jig.  But on Saturday he brought his jig and gave my Linn an adjustment which seemed almost chiropractic.  He worked the springs over and over to get much of the "squeak" out.  And after that, he did a very precise level adjustment.

And it also helps that my stand is now pretty well leveled.  I thought it was perfect after I adjusted it a few months ago, but I've gotten better at reading these things and I now see it's off by about 0.1-0.2 degree, but that's much better than it was last year.)  The turntable platter shows the exact same 0.1-0.2 degrees as the stand, so it appears the turntable adjustment itself is "perfect."

When playing records now, the turntable is totally serene, as in riding on glass.  I see now the spinning platter helps to stabilize it a lot.

However if the turntable is NOT spinning, and you press down on the platter and let go, there will be some jittery movements.  So that test may be too difficult and it is confusing to interpret.

I've played many records now (including Blood On The Tracks and Fresh Aire II) and there has been no case where the audio sounded the least bit jittery.  So it seems that problem has been solved.

Mark also tested the speed with his KAB test record and said it was right on.  I myself adjusted that (using my KAB disc and other methods) a year ago, but slight changes in the suspension position might cause it to go out.

Mark also fixed the arm holder.  And just like me, in order to do that he tilted the turntable up to do that.  But unlike me, he took the platter off first.  And he only tilted it about 45 degrees.

He noted a sound in the bass (playing first track side two of Blood on the Tracks) that he called thuddish or thumpish.  I thought I noticed it too.*  He suggested I could use Mapleshade triple point feet on the Linn, or a better stand.

I didn't tell him I had removed a 6.1 gram additional headshell mass that I had been using before.  I removed it prior to the adjustment because I myself was unsure if it was doing more good than harm, and it was annoying how it always stuck to the underside of the dust cover.  I can see now that this mass or something like it (perhaps a tad smaller) is very much needed.  (See the measurements in the next post.)

(*To some degree it might also be a peculiarity of the percussion Dylan uses on that track.  Also Mark did not stay long enough to sit in my listening position, where the bass is much better balanced.  It's a peculiarity of my system geometry that the least bass is heard in the front central listening position and it gets too loud elsewhere in the room.  As of my last bass adjustment in July, the bass is optimized for the listening position specifically, more than I had ever done before, meaning it gets much worse elsewhere.  I need to dial down the bass when I'm showing movies to a group of people sitting in the back of the room, and even more than before.  But these effects would simply have made the problem more obvious...there was a problem and Mark correctly noticed it though I'm not keen on his solutions and I like mine better.)

He didn't use a clamp, which isn't too bad on a Linn, but I'm not sure if he removed the center felt washer I use for clamping.  I'm not sure if the record could have even played with the washer there and no clamp, though I seem to recall it WAS there after I removed the record--perhaps that's a false memory.  I didn't think the sound was THAT bad anyway, in fact I was listening to how nicely stable and solid it sounded compared to what it had been like just after I messed up the suspension.  But the bass didn't sound exactly right either, though I wasn't focusing on that until he mentioned it.

I really do want to redesign this headshell mass (it's a "squished roll" of hockey tape, and I want to make it a more stable "stack" of hockey tape, plus add hockey tape around the Dynavector D17 V3 cartridge itself which I think has a high frequency mechanical resonance that's not controlled well by the thin piece of carbon fiber that constitutes a headshell on the Ittok arm.  Possibly if the cartridge were attached to the heavy metal headshell of a Dynavector or Fidelity Research arm this wouldn't happen).

But for the time being I reattached the existing flattened-roll-of-tape mass.  (That had always been intended to be temporary, until I figured out how much mass was needed, but then I lost confidence in my ability to determine what mass was correct.)

With the added mass, I believed I heard the old cleaner bass I was familiar with.  However I should also admit that before I reattached the mass, I tried listening to the another record (Fresh Aire II) and my feeling was that there was no bass problem at all (in fact, it sounded fabulous, and was far more involving than the CD version).  So I think this "thuddish bass problem" is true but not really that big a deal, you might not notice it on everything including other records with bass, especially in the listening position.

And I feared that restoring the headshell mass might bring the jitters back.  In fact it was a bit worrysome that when Mark came over and did his first "bounce test" on the suspension, he said it didn't seem too bad.  This made me think of several alternative explanations:

1) Perhaps the jitteryness was caused by the added headshell mass, either as an arm destabilization, or because it offset the Linn suspension from normal leveled balance sufficienty--it is very sensitive.  Perhaps I didn't notice this at first until one day it was obvious from other factors being at the threshold too.

Two days of follow up experiments have demonstrated that this hypothesis was not true.  Reattaching  the headshell mass has not caused any kind of jitteryness either in sound or measurements.

Also I placed quarters on top of the platter where the cartridge would be tracking to see how they upset the table leveling.  They made no detectable difference until I reached 6 quarters, about 31g, and then they caused about 0.01 degrees of difference, in my best estimation.  Meanwhile the stand and table are off by about 0.1-0.2 degrees in the opposite direction.  If anything, more headshell mass would make the table MORE level.  But it appears not to make a significant difference at all, despite the incredibly sensitive suspension.

2) Perhaps they were caused somewhat by the table not being level.  Last year I fixed the table level and re-tested and the problem had not gone away.  But I can't remember if I did a real listening test, or just a table bounce test, and I apparently don't know how to do the bounce test or its interpretation correctly.

3) Perhaps the springs reset themselves by not being used for 6 months, by slowly releasing stored potential energy.

Anyway, as of now, either with or without the headshell mass, I'm feeling like I have the best turntable sound I've ever had.

Measurements of the table level with my digital level show that depending on axis it varies from 0.00 degrees to 0.15 degrees (with 0.05 and 0.10 in between).  I doubt I've ever got it this good before.  I think this is a significant factor in the current "best ever" sound.