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Old 11th March 2021, 07:50 PM
bikerhifinut bikerhifinut is offline
Senior Member
Join Date: Jan 2006
Location: Penrith, Cumbria
Posts: 1,060
Default Re: Phono 3 noise issues

Correct me if I am wrong Damien.
You are using PSU2?
In which case the PSU3 is slightly different, I believe, in quite a few ways.
As it happens I have an unused spare PSU3 PCB lying round somewhere and if you're going to rebuild the thing, then this might be useful to you.
Let me know and for the price of a stamp its yours.

There are differences in stuff like the regulator for the heaters where PSU3 uses a 3 Amp LDO regulator rather than a 7805 with a couple of silicon diodes hung off the bottom leg.
And no zener diode regulator for the preamp HT if i remember right, again its not needed.
I think its got a better earthing scheme too.
Now the main thing as I found out, was to ensure the 100R earth lift resistor was in place and actually in circuit. This was the main glaring error on my PSU as bought and the Phono 3 hummed like an old AC/DC mains radio.
It's still sensitive to placement in regards to hum pick up from mains transformers etc.

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