Yesterday I was adjusting the focus bias on an old Sony CDP-103 which lovely BU-1C laser mech.
Until now I have always adjusted for maximum peak-peak voltage of the eye-pattern waveform but yesterday I made the following observations which made me question that:
1) The most sharply focused eye-pattern occurred just before the maximum amplitude was reached. About 0.1v before maximum amplitude. I could get the waveform peak-peak voltage 0.1v higher but at this point the eye-pattern became a touch 'fuzzy'.
2) The laser was more noisy at the maximum amplitude and was quieter and seemed 'happier' at the point where the eye-pattern was best focused which was just a bit before maximum amplitude was reached.
So in these circumstances is it better to set the focus bias for maximum amplitude or for best focus which results in a quieter laser?
Until now I have always adjusted for maximum peak-peak voltage of the eye-pattern waveform but yesterday I made the following observations which made me question that:
1) The most sharply focused eye-pattern occurred just before the maximum amplitude was reached. About 0.1v before maximum amplitude. I could get the waveform peak-peak voltage 0.1v higher but at this point the eye-pattern became a touch 'fuzzy'.
2) The laser was more noisy at the maximum amplitude and was quieter and seemed 'happier' at the point where the eye-pattern was best focused which was just a bit before maximum amplitude was reached.
So in these circumstances is it better to set the focus bias for maximum amplitude or for best focus which results in a quieter laser?
There are often two adjustments, focus bias and focus gain.
White noise from the pickup can be caused by having the focus gain set to high.
Sony CDP790 and KSS240 Restoration Project
White noise from the pickup can be caused by having the focus gain set to high.
Sony CDP790 and KSS240 Restoration Project
Hi Mooly, thanks for the reply.
I'm familiar with the focus gain adjustment but that's not what I'm referring to here. I do mean focus bias.
Allow me to clarify:
When the focus bias is set to give the absolute maximum waveform amplitude the eye-pattern becomes very slightly blurred and the laser emits a slight white noise. Just before reaching the max amplitude, with the peak-peak voltage about 0.1v lower the eye-pattern is sharper, looks 'better' and and the laser is quiet.
So, is 0.1v more peak-peak amplitude the optimum adjustment or is a better focused sharper eye-pattern optimum?
I'm familiar with the focus gain adjustment but that's not what I'm referring to here. I do mean focus bias.
Allow me to clarify:
When the focus bias is set to give the absolute maximum waveform amplitude the eye-pattern becomes very slightly blurred and the laser emits a slight white noise. Just before reaching the max amplitude, with the peak-peak voltage about 0.1v lower the eye-pattern is sharper, looks 'better' and and the laser is quiet.
So, is 0.1v more peak-peak amplitude the optimum adjustment or is a better focused sharper eye-pattern optimum?
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