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RE: Sound Hi Fi Jelco & SME arm mods for Technics 1200

I've been thinking about that ripple picture, too. I believe it is the ripple on the output of the regulator, but I believe the strobe might be contributing to its shape and amplitude. After making some measurements of my own, I can tell you that the motor provides a very light load to the circuit, but the strobe causes some significant ripple. I connected wires to the input of the regulator, J1, and the output, J3, and ran them out the hole in the bottom where the power cord exits. I also ran a ground wire out so I could make some measurement. What I discovered is that the strobe creates a powerful pulse at 101.111-Hz for 33.3-RPM and 136.5-Hz for 45-RPM that causes significant ripple at the output of the regulator. Consequently, I believe that the strobe disabler is an important modification. Furthermore, with regard to the Sound Hi Fi measurement, I have a feeling that the 101.111-Hz pulse combined with 100-Hz ripple from 50-Hz line frequency was responsible for the waveform in the report. I suspect they snapped the screen shot at just the right moment for the phase of each signal to produce maximum effect. That's just my guess anyway.

Here are some of my oscilloscope screen shots depicting 120-Hz ripple from the 60-Hz line frequency. With the strobe disabled and the platter spinning at 33.3-RPM, the ripple in my SL-1200 is only one-forth the amplitude of the Sound Hi Fi measurement. I used the same settings as Sound Hi Fi and I've included their screen shot for comparison.


......

Now, when the strobe is turned on, the ripple increases significantly. The first picture below is 33.3-RPM and the second is 45-RPM. I think the pointed bottoms on the Sound Hi Fi picture above are from the strobe pulses, which are nearly in sync with the 100-Hz ripple.


......

I have a number of other screen shots and measurements, but I can't keep my eyes open anymore. I must get some sleep and continue tomorrow.

Best regards,
John Elison



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