Friday, February 7, 2014

Turntable Adjusting

Time flies when you are messing with a turntable.  On Monday night I thought some of the bass was excessive, suggesting either feedback or arm resonance.  On Tuesday, I had difficulty determining which of those, or neither, was true.  It might have simply been the recording I was listening to.  But then later, I decided that worse than feedback, I seemed might be having a serious tracking error issue.  On Wednesday morning I was playing Peter Sprague again, and in the final grooves it seemed to be silently skipping, sliding back a groove or so but without any obvious tick or pop.  THAT was an issue that immediately needed fixing, I decided, and no more records until it is fixed.

The first thing I did Wednesday night was to check the level.  I had leveled the table on Sunday night using a very small level of unknown quality.  I couldn't find my regular level, or my bubble level.  So on Wednesday I bought a level, and used it on Wednesday night.  I had leveled the table correctly on Sunday with the little level I had found then.  (The Rear feet are cranked up nearly an inch, it seems, but that's what it took!)

Then I checked the arm balance, and stylus force.  All were OK.

Then I got out an anti-skate test record, which has a 1 inch blank surface near the end of the record.  There was no skating whatever, suggesting my cartridge alignment was OK.  And since there was no skating force, that could not explain skipping anyway (regardless of how correct the alignment is, but it *is* probably correct anyway).

So then I got to something I've wanted to do for a long time.  I adjusted the height of the cueing mechanism.  The owners manual tells you to adjust this, and it should be set for 3/16 of an inch.  But when I turned the screw, nothing happened.  So I decided to take a chance and turn the screw all the way.  The screw came out!  Then I looked under the screw, and there is a little collar that the screw goes into.  When you tighten the screw, it's supposed to lift that collar flush with the surrounding metal (which is as far as it can go).  When you loosen the screw, it's supposed to fall back.  But it wasn't falling back.  The solution was to put the screw back in, and push the screw down.  With several pounds of pressure, it finally moved the arm to change the cueing height.  At first, I adjusted it a bit too low, then I adjusted just slightly higher than 3/16 of an inch (to allow for thicker records), and that worked great.  Turning the screw clockwise works great for raising the cueing, but counterclockwise requires a push so that the collar actually moves down.

Then I noticed something really weird.  When I had the cueing too low, the blank record now showed considerable skating towards the center of the record.  That would suggest that the arm had been made too long.  When I finally got the cueing adjusted right (just slightly more than 3/16 of an inch) there was no skating again.

So it seems the cueing adjust screw actually adjusts the arm tilt rather than the cueing arm itself!  Actually the manual does not even call this the cueing adjustment, they call it the stylus level adjustment.  Small changes in arm tilt affect (by a very small amount) the length of the arm when the stylus touches the record.  If I understand this correctly, it suggests my cartridge alignment is very exact, because even a small error introduces significant skating, and I have none.

I had some idea that adjusting the cueing was beneficial in this way: the cueing had been set so high that the cueing mechanism was actually pushing the arm up at points when it was in the groove.  That could explain the mistracking.  I'm not sure this is true, possibly the mistracking (which I thought I heard while in the bathroom) was just hearing the repeats in the music.  I had not tried to replicate the mistracking before I started testing and adjusting (because I wanted to get the job done, and I knew some things needed adjustment anyway).

The rest of the adjustment mainly involved getting the arm to land precisely in the arm holder after automatic arm return (this turns out to be VERY important on this turntable) and to get it safely into the lead in groove on automatic start.  These two adjustments require very fine screw turning, and they are said to interact (though I didn't notice much interaction, per se).

Here is why you need to get the arm to land precisely in the holder when it returns.  If the arm doesn't land precisely in the arm holder, it will get bumped either toward the record or away from the record.  Then, the arm will no longer be perpendicular to the arm rails.  So then if you put the arm on the record, when it lands (or before it lands) the servo mechanism will try to correct by moving the arm base.  This could cause the stylus to fall off the record (not good).

Now I had noticed from Sunday night that the servo mechanism was turning on above the record surface.  That could cause the arm base to move before the stylus falls into the groove, which is inconvenient if not dangerous.  I tried unsuccessfully to adjust that.  Actually, this particular adjustment was covered by what looked like factory applied black tape, which I needed to peel off.  That black tape is on both of my LT-30's.  Anyway, I peeled off the tape, but the small phillips screw underneath could not be turned by any reasonable amount of pressure.  I gave up, not wanting to break the arm.

But after I had adjusted the cueing height, the servo engagement system fixed itself.  Now the servo turns on at the moment the stylus reaches the grove.  That means even if the arm is not correctly perpendicular, it will fall where you want it, and not servo to some other position (which could be off the side of the record) before reaching the groove.

Then one more adjustment, because I actually feared all of the above (while useful) would not actually solve any mistracking problem (if there had been one).  I tried adding more mass to the headshell to change the arm resonance.  I first tried using the 4g weight, but that was too much because I could not get the arm to balance.  But the 2g weight worked fine.  I'm not sure if this is helpful, it seems I can see more relative arm to stylus jiggling than before.  But I think that might be good if previously the jiggling was at too high a frequency.

I've noticed no more mistracking.  But it sometimes seems like the turntable might be adding wow and/or flutter, despite the servo lock light being on, and the turntable not being affected by a little extra finger drag.  I've gone ahead to buy the Dr Feickert test record from Hong Kong through ebay as it is apparently not sold in the USA (not online anyway).  That should give me some objective results for wow and flutter and arm resonance.  An arm resonance could also be adding wow and flutter.

Friend came over on Thursday night and we listened to two records together.  She noticed nothing wrong and said it sounded great.  It's great to have a working turntable!  It's great to have friends too!

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