Sv: Rett VTA
Fra
Kuzmas hjemmeside:
Practical Suggestions for VTA and Azimuth Adjustment
As a basic rule, if the VTA is too high, the sound will be harsh, too open, thin, metallic and analytical at upper frequencies. Some people find this convincing.
If the VTA is too low then the sound tends to be muffled with a big bass and a more rounded sound.
When VTA is correct the sound falls into focus. In a good system correct VTA is easy to establish but if there are basic flaws in the system it can be difficult and frustrating.
I suggest that you listen to midrange sounds, preferably with a natural vocal recording. As VTA is different for each record, a compromise must be reached. Beware of falling into the trap of accepting a too HIFI sound as opposed to a less bright , less spectacular, but more correct sound.
To start adjusting VTA have the tonearm tube parallel to the record and try a few settings of 3-4mm below and above this reference point. Then mark the best sound and do fine VTA adjustments around this new marked level in the range of 0.5mm.(1/50 inch). The optimum height is often found when the base of the tonearm is lower than when the tube is parallel to the record surface. (If the tonearm has a conical tube, this parallel line is the imaginary one running through the middle of the tube.)
It is also advisable to check absolute phase by reversing all connectors to the cartridge where such a change has the biggest effect ( white with blue and red with green). Listen and check wheather the soundstage is deep and focused and presentation of singers convincing.
AZIMUTH
Correct azimuth will have a similar effect as correct VTA except it will be the same for almost all records. Incorrect azimuth causes lack of focus, distortion of loud passages and muffled details. Again, the better the system, the bigger the difference.
In order to adjust azimuth use of a mono recording and connecting leads to the cartridge in such way that we can hear minimum output from one speaker, is not good enough. This does not give correct azimuth.
It is possible to adjust azimuth by ear but extremely difficult. The correct and simple way is to use a test record and an oscilloscope. The oscilloscope should be dual trace (though this is not essential) so that we can easily observe both channels on a test record at the same time. The test record should have test signals of 300 Hz or 1 KHz or 3 KHz recorded separately for left and for right channels. (Separation tracks). With the oscilloscope we can see test signals and the aim is to adjust cartridge azimuth so that crosstalk signals are equal for both channels. That is, to make separation from left channel to right the same as from right channel to the left .
When we play the left channel we can see the sine wave of the full size signal while on the right channel we will see the very small signal which is the crosstalk from the left channel. By adjusting the oscilloscope so that both signals have the same reference zero and, with appropriate amplification of signals, we can observe the left channel signal which is so big that it is off the screen and the small crosstalk signal.Keeping in mind the size of the crosstalk signal, we then play the right channel from the test record and observe the crosstalk signal of the right channel. We will see that they are not the same. Changing azimuth will change both. One will be bigger, the other will be smaller. When the azimuth is correct they will be the same. Sometimes the differences are very small. Due to tonearm resonance the whole signal will jump up and down on the screen . Use of a filter below 200Hz makes reading of the signals much easier.
After finding the correct azimuth you should again listen to ensure VTA is correct and re-check absolute phase. Any change of VTA will affect azimuth (though not on the tower of our Stabi XL turntable) so this will need re-adjustment. By taking these small steps we will eventually obtain almost perfect cartridge set-up, providing of course that we do not change tracking force. Finding the sweet spot with tracking force and making appropriate adjustment necessitates repetition of the whole process. Now try to imagine the task of reviewing cartridges or even tonearms for magazines!
Have fun and remember, if changes in sound are very small then they are not important.
Franc Kuzma