Rega tonearms and the importance of azimuth correction

[Guest]

The standard simple way to check cartridge azimuth is to look at the reflection of the cartridge in a mirror placed on the platter, and make sure that the cartridge and its image are perfectly aligned. In turntables with adjustable azimuth, misalignment is usually cased by the headshell being twisted out of true, and is easily corrected. Of course this assumes that stylus tip is correctly aligned to the cartridge body, which assumes that both the cantilever is straight and that the tip is mounted squarely, and most often this is the case although not always. 

 

 

I recently did a Rega RP10 wiring upgrade (posted here:             #1741            )

 

When doing the cartridge alignment, one of the standard tests is channel balance and channel crosstalk. I noticed in the case of this turntable there was more crosstalk to the left channel than to the right, which is an indicator that the azimuth is not correct.

 

I also had trouble with setting the anti-skating force. To get the cartridge to track properly through all of the anti-skating test tracks, I needed more anti-skating force than normal. Usually the amount of anti-skating determined dynamically is similar to the amount required to hold the arm steady on blank 'land' on the record surface. In this case I needed so much anti-skating to keep the stylus in contact with both sides of the groove that when the stylus was dropped onto land, the arm swung rapidly away from centre.

 

On close inspection I could see that the reflection of the cartridge body was very slightly misaligned, and the cantilever looked perfectly straight. I could not see the contact surfaces of the stylus tip to know if they were symmetrical, however, I made the assumption they would be.  What to do - Regas do not have any azimuth adjustment and this tonearm was out.

 

There are two means to adjust the azimuth on a Rega tonearm: shim the tonearm base; or shim the cartridge. The base is easier to do, but has the disadvantage that the amount of adjustment varies according to the tonearm angle. In this case, I needed to lower the righthand side of the cartridge. Using a vernier calliper I estimated the amount of adjustment required would be about 0.05mm (about 2/1000s of an inch). Luckily I had stainless steel shim washer that was 0.05 mm thick and I also made another shim out of slightly thinner cellophane ~ 0.035mm. I tried the thinner shim first, then I fitted the thicker shim and then both. The closest match was the 0.05 shim. This is approximately 2 degrees of clockwise rotation, so that is how much this particular RB2000 tonearm was out.

 

After redoing the cartridge offset, overhang and vertical tracking force adjustments, I found that with the azimuth corrected, the ant-skating force was back to normal, and the tonearm holds position on 'land' with the same anti-skating setting that gives *perfect* tracking on the most severe test track. The crosstalk is also balanced left to right, and right to left.

 

Here's a heavily edited version of what the owner had to say when he tried the turntable:

 

Noticeably high frequency detail improvement, all over a lot cleaner, reduced background noise, pleasing imaging and stereo separation. The detail is very noticeable, I've played this record 500 times and heard things I've NEVER noticed before, not just one or two things either, very f'ing weird. Definitely a veil layer or two has been lifted. Seriously, thanks!

 

The picture below is before the correction (apologies for poor quality image). Does it look like the right hand side needs to be shimmed down?

Edited November 11, 2015 by Guest

[Happy]

Such a pity you're in Adelaide John. I'd have paid to get you over my place to inspect my Rega arm.

[andyr]

The beauty of a UP arm ... easy azimuth adjustment!! 

 

Andy

[Bush thug]

Hey john just wondering where you are located live to bring you my table.

Thanks steve