Band pass filter for azimuth adjustment.

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TomWh

Member
Joined 2009
#1
Been playing around with cross talk adjustment on cartridge using a test record and fluke 87 DVM. It has been mentioned that a band pass filter would help stabilize the readings.

In building one how close would put the cut offs and what order filter would you use. If you have a diagram of one that has worked for you that would be great also.

I also have a dual trace scope but pretty much a novice on scope testing. Open to all suggestions on this azimuth adjustment with test equipment.

Thanks in advance
Tom
 
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#2
Bandpass filters of this sort have a Q, not cutoff frequencies, basically they resonate at the centre frequency providing gain. A multiple-feedback opamp active filter circuit is supposedly a reasonable choice for this. Google will find what you want given those keywords. Select a modest Q initially like 5, otherwise frequency drift / wow&flutter might present problems. I presume the test disc has just a single test tone frequency for alignment?
 
#3
First off, azimuth and cross talk really need to be considered seperately. Azimuth is whether the diamond is vertical in the groove. Cross-talk also takes into account generator alignment (and yes you may have spotted you can optimise one or the other, no free lunch).



Azimuth you measure with a vertical signal (usually around 300Hz on test records) sum and adjust for a null. If you have a scope you can also play a mono track, invert one channel and sum on the scope.



If you want cross talk you have the tricky situation that cross talk can be in or out of phase and different L-R vs R-L. You know you have crossed the optimum when one channel or both flips phase. But I don't think this is what you are after?
 
#4
The cross talk I did with the procedure that Michael Fremer wrote about. You use L track only 1 kz signal measure both speakers then use R track and repeat. Do the math and you got the results. You adjust the azimuth then retest.

I would also like to try your azimuth only solution with the scope but do not understand what you have written. If you could explain it to a novice on scopes or point me to book/site, I would like to learn how to do the above.

Thanks
Tom
 
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#5
The way I set horizontal azimuth is to use L and R 1kHz test tones. I use a fluke meter and measure the mvrms.


I measure the L channel with L tone and the L channel with R tone and calculate the dB. Then do the same with the right channel. I use the worst channel (calculated dB) and optimise it for the best cross talk.
 
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