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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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In Reply to: Azimuth adjustment using Oscilloscope posted by Ungie on May 16, 2009 at 10:35:29:
HI All,
I have developed a method of critically adjusting azimuth using an oscilloscope and a sine wave generator. It is not difficult but while writing it up, in detail, I realized not many imates could take advantage of it. First, a decent oscilloscope and sine wave generator is needed. Most folks do not have the test equipment. Next, a good working knowledge of scope operation and an understanding of how to do measurements is needed. I did not want to write a book on how to make scope measurements. This would be needed for the average inmate. So, I'm going to compromise. Those who have the knowledge will understand the concept and take it from there.This idea is well proven over about 30 years and many cartridges. Conceptually, this test method is based upon the fact that a stereo cartridge will produce the same output from both channels when playing a mono record if the azimuth angle is zero. Therefore, if the same signal is on both channels then subtracting one channel form the other will produce zero output (the null point) on the scope display. An azimuth error will show up as displayed signal and the azimuth angle must be corrected to attain zero signal.
A scope is used to monitor the signals, do the subtraction via an inverted channel and the Algebraic Added vertical scope mode and, display the results. Any signal that is present is due to a non-zero azimuth angle. See note below. The signal generator is used to calibrate the test.
Some notes:
1. The preamp and the scope channels must be critically balanced. Absolute voltage accuracy is not important but all channels, both preamp and scope, must be calibrated to be exactly the same. That is, the scope channel gains must be exactly the same and the preamp channels must be exactly the same. Any errors here will give incorrect test results.2. A mono record with test tones will give the best results. But a normal mono music recording will also work, the difference being the music recording will make the null point (zero azimuth Angle) harder to identify. Try to avoid warps.
3. The null with music will show both amplitude and channel phase differences even at the null point. These are due to the fact that cartridges are not perfect transducers. Phase differences are caused mostly by the frequency response differences between channels. But they are minor. You will need to use some judgment to identify the null.
4. Cartridge channel amplitude differences do exist. The better the cartridge the more minor the channel differences. I know of no way to compensate for this. They are minor for better cartridges. If you have a cartridge with substantial differences between the channel outputs this is not a good method for your situation.
5. I have mostly used this technique with my Eminent Technology ET-2.5 linear air bearing arms. With these arms the null point is very defined. With my Graham 2.2 Deluxe unipivot arm the null is harder to identify. I think this is caused by the geometrical errors associated with pivoted arms. The difference between the two different arm designs is striking.
6. I know of no better way to adjust azimuth with test equipment that I have available to me.
Sparky
Edits: 05/18/09
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Follow Ups
- RE: Azimuth adjustment using Oscilloscope - Karma16 09:45:39 05/18/09 (0)
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