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Re: Rega Power supplies

Hello Werner
Thanks for the tips.

"BTW, do you have any idea where the +12/-12V originates from? With only three big(gish) reservoir caps seen after the transformer, all of them at a positive voltage, this is odd, and fear arises ..."

+12 V is derived from the +15V on the cap closest to the toroid, C61.
-12V comes from the -15 V on the second cap, counting from the back, C25. 25 is connected with reverse polarity. You can easily confirm that by measuring the voltage at the diode pair output.
The first pair (located on the leftmost side of the board) outputs + 15V, the second pair outputs - 15V.

Amazingly, the +12V supply is regulated, the -12 is not! This unbalances the power supplies to the analog stage, probably introducing some second harmonic distortion, which will vary with AC line voltage.

I replaced a zero ohm jumper (beige component with black band) off C25 with a resistor and varied the resistor value until I measured less than 5 mV differenve beteen +12 and -12, measured at the analog IC pins.
This was possible because I have a stabilized AC supply.
Most households are affected by 5-10 V variation in the AC supply voltage.

Maybe a better idea would be to install a low dropout negative 12 V regulator. So far, I have not found a low dropout negative 12 V regulator with good specs.
The LM 2990 has excellent regulation but poor noise and ripple specs.
Maybe it will work with good, low ESR caps before and after the IC ?
All the best
Carlos





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