Re: Op-Amp RIAA Preamp with Tone Controls - Help!
Hi David, it's a Thorens TD150 Mkii.
Is there any linkage at the turntable between the signal cable braids and the turntable metalwork? Yes
Is the turntable earthed to its mains plug? No
is it fitted with a 2-core mains cable? Yes
Does the turntable have a pair of Y capacitors in some filtering arrangement?
Maybe, see attached image. But I think the caps are across live/neutral and on-off switch, not between line and earth.
Is there a ground wire from the turntable to the amplifier? No, earthing is via the coax braid only.
BTW I have rejigged the PSU - in a previous post on the pre-amp schematic I was using a single diode bridge taking the 15v rails from the + and - with earth return to the link between the two 9v windings (CT). I have now separated the windings and I am using 2 diode bridges as shown. Effect? Now I have 100Hz ripple instead of 50Hz. Odd, as I thought the previous arrangement was also full-wave rectification. Maybe I need to go back to power supply school.....I will be replacing the transformer with a 20-0-20v unit and adding LM7815/7915 regulators. Cheers, Jerry
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