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In the Forum: Analog Playback
In the Thread: The last phonocorrector: “End of Life" Phonostage

Post Subject: The hum is drooped significantly!Posted by AlexBerger on: 4/20/2010

Romy,

I try to remove the step-up transformers & short the input grid, the hum has gone.
Than, I did next changes:
1. Twisted wire from input RCA to step-up transformers. Connect transformers input & output ground directly (not thought ground bus as before).
2. Connect filament minus to the power supply ground directly (not with 100 ohm as before).
3. Connect wall outlet ground to the chassis thought 50 ohm, like in original EAR (not with 22 ohm as before).
4. Connect chassis to the RCA output ground point (not to the power supply ground point as before).

The result, the hum is drooped significantly to the acceptably level.
Actually, right channel no hum at all, the left channel has minor hum.
Maybe because, left channel transformer is 10 cm nearer to power supply than right channel transformer?

I going to put shielding aluminum plate between power supply and RIAA board. It will help?

Another question: what is the necessary accuracy of second tube grid resistor (2M). It's used in RIAA equalization?

Thank you again,
Alexander.

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