Adjust Your Anti-Skating With An Oscilloscope

[Grainger49]

Background that you can skip:

Joel In TN and his lovely wife just left.  He and I did some adjusting on his Rega table.  It was almost perfectly set up from the dealer but needed a little more tracking force and the anti-skate was not right.

Here is the important stuff:

The anti-skate was a pain to adjust.  It was hard to make small adjustments.  So we fed the table into a simple phono stage into my oscilloscope.  I found that using a pencil rolling the tip against the anti-skate peg would move the anti-skate slightly as needed.

Here is the BIG hint.  I used the old Hi-Fi News... test LP playing one of the anti-skate tracks.  I inverted one channel of the scope, hit add ch A and ch B and tweaked till the trace was all but a flat line.  This made setting the anti-skate very quick and straight forward.

I was all but amazed.  I know a number of Bottleheads have scopes and I would suggest trying this.

BTW, azimuth is adjusted the same way.  The lowest output with the channels inverted and added is when the stylus is dead center in the groove.

A new, EVEN BETTER, idea in reply #7 below.

[johnsonad]

I use a two channel scope and the Hi-Fi News LP to set every cart.  Friends are impressed at how quick and easy it is.  On this LP I use the three 300hz tracks on the second side at +15dB.  Just watch for clipping in one of the channels and adjust as needed.  If your scope has it, you can hit the X-Y button and watch for loops.  If it has a straight line through the entire track you are good to go. 

Though people talk crap about this test LP I find it easier to use than most including some classic LP's I use.  The Shure TTR103 tracability test record is another good one.  If you can adjust a R2R machine, TT's should be a cake walk.

[Grainger49]

There is a 3" thick manual on this scope that I admit I haven't read.  I don't remember an X-Y button but I will look.  Hey, it took me a couple of minutes yesterday just to get the second channel up.  It just wasn't selected.  I'd be embarrassed if I thought more of myself.

Are you describing a combination that produces a trace at a 45 degree angle, or a straight up line that becomes a loop when there is a phase (timing) difference between the two channels?

[johnsonad]

45 degree angle, please excuse my fast typing.  There is a longer word to desribe the test but it escapes me at the moment.  I prefer to look at both channels at the same time adjusting the gain to see them both on the screen at once.  I overlap them to adjust azimith.  Fun stuff!  I've got a lot to learn in using a scope but hopefully this helps some. 

[Grainger49]

I'm going to try the spelling of what I remember this being called: a Lissajous patter?

Just a couple of questions, do you use an RIAA Preamp before the scope or directly from the phono leads?

Does azimuth change the phase, and therefore timing, of the two sine waves? 

[johnsonad]

Here is my recipe for set up, mind you it is ever evolving as I learn more.

First I run a 300hz sine wave (though it could be any frequency) through the preamp via the aux jack and make sure the output is equal to the amp with a DMM (I'm using a SS preamp at the moment).  Second and after the VTF is set to optimal I set the antiskate as discused before.  Lastly I adjust the azimuth, mind you the headshells I use allow for rotation and I do not adjust the azimuth to comp for cross talk yet but hope to in the future (still considering purchasing the Adjust + software).  Using the same 300hz tone as was used for the antiskate I overlap the two channels of the sine waves and play the track.  I then adjust the headshell until the are at near identical output.  Then I fine tune the output by measuring the output voltage at the preamp outputs.  Usually using the scope I can get it pretty close though I've never got it identical in both channels. 

The HiFi News LP has a track specificly made for this and an easy way to do it (track 5, side 2).  I don't use this method because I question the cuts made for this track as it differs from every other stereo 300hz track on the LP (these discs seem to have a bad rep).

I'm still learning the different ways to do this but have been lazy lately and haven't refined my technique.  I've got a copy of the Ultimate Analogue Test LP which allows for isolating each channel and adjusting for cross talk.  If you want to learn more on the topic I recommend reading this:  http://www.audioasylum.com/cgi/t.mpl?f=vinyl&m=138751

[Grainger49]

That sounds like too many stages in there, just too many variables.  How about sending a 1k Hz signal into the phono stage, take the output and uncalibrate the V/div. spreading so that it gives you top to bottom (graticule) for a full cycle.  That will maximum the  spread.  Then try inverting one channel and adding to verify that you get zero output.  This guarantees that any channel imbalance is nulled out.

Then do the same thing with a test track that is not designed to make your cartridge mistrack.  That would eliminate the anti-skating tracks on the Hi-Fi News LP.  Sadly it will still not compensate for channel to channel output balance from the cartridge, we have to rely on the manufacturer's quality control for that.

[Grainger49]

I had another thought.  I could wire one channel of the cartridge out of phase for the test.  Then combine them like with a Y adapter and amplify with a phono stage.  Then the pure signal is already inverted and summed before it gets to the phono preamp.  Any downstream amplification is only one channel and works only on the already summed and inverted signal.  Only one trace of a scope is necessary.

But remember to swap back the channel you inverted before listening or it will sound very, very odd.

[johnsonad]

I'm taking it one step further and plan on purchasing a Cartright once Soundsmith releases it.  One box, simple to use and has all the adjustments I need.

http://www.sound-smith.com/cartright/index.html

[denti alligator]

I was noticing some inner groove distortion on my Rega recently, and adjusting anti-skate from below 1 to 2 made all the difference. I have no idea how to set it properly, though, without a test LP. Can it be done?

[Grainger49]

I'm taking it one step further and plan on purchasing a Cartright once Soundsmith releases it.  One box, simple to use and has all the adjustments I need.

http://www.sound-smith.com/cartright/index.html

Maybe so.  For $900 I can buy a lot of LPs.  And I already have the LP and oscilloscope.  But then the Fosgometer is $250 and only adjusts azimuth.

I was noticing some inner groove distortion on my Rega recently, and adjusting anti-skate from below 1 to 2 made all the difference. I have no idea how to set it properly, though, without a test LP. Can it be done?

The Hi-Fi News LP I referred to is the most maddening thing you can buy.  All of the higher velocity anti-skating tracks distort.  It isn't really good for adjusting anti-skate.  All you need is a pure test tone on an LP and access to a 'scope for my method.  Without that, if you don't hear distortion you are way ahead of a lot of guys out there.