Grounding question in phono preamp with battery supply

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Hey,
I'm doing a phono preamp according to what is described here:
- DIY Phono Preamp : Recording Magazine -

I will use a battery pack for the dual supply and will mount everything in a metal casing.
My question is if the virtual ground created by the supply caps should be connected to signal ground? I guess it should as if I do not connect it I hear a lot of noises.
Why is this? What function does the virtual ground created from the batteries have here?

01Schematic.jpg
 

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the phono pre-amp is direct coupled.
That means that the input DC comes out of the Output.
It also means that when zero signal is present the voltage on the signal pin equals the voltage on the signal return pin and equals the voltage on the output return pin and since the amplifier is amplifying zero input signal the output signal voltage must also be the same as the Output return voltage.

For all these voltages to be equal, the Ground or Signal Return must be at the same DC voltage as the Signal input.
The Signal Return must be connected to the virtual ground.
 
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The caps themselves do not create a virtual ground. Your diagram shows the supplies as already being "split", i.e. a plus and a minus 15 volts with a centre tap.

To run this on batteries needs two identical ones, say of 12 volt each. These must be connected in series to give a total of 24 volts. The centre connection between the two batteries then becomes the ground point.

(Your circuit as drawn in post #1 doesn't include a virtual ground because it doesn't need one using the supplies shown. If your battery pack is a single unit then you need to add a virtual ground generator to emulate a split supply... which is easy to do :)).
 
Thanks for the help guys. It works now and is dead quiet (when no music is playing).

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For all these voltages to be equal, the Ground or Signal Return must be at the same DC voltage as the Signal input.
The Signal Return must be connected to the virtual ground.
So the supply ground is to have a stable reference(?).

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To run this on batteries needs two identical ones, say of 12 volt each. These must be connected in series to give a total of 24 volts. The centre connection between the two batteries then becomes the ground point.
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Ah okay. I was thinking it was meant to have a virtual ground to form a middle point in case the two battery supply sides drained a little differently creating a slight offset.

So you won't need a virtual earth, as it won't be a single supply.

The centre point of the supply caps should be connected to signal ground.

2 x 9V - 12V batteries will be fine.
Removing the resistors as you showed made a lot of sense to me as I received the desired supply voltage for the opamp. What would be the use of the resistors here? The RC-links formed would I guess filter something, but the cutoff frequency seems weird? Edit: Ow nwm, it pass pretty much only DC. Wasn't thinking
 
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The resistors combined with the capacitors filter out RFI garbage, & also mains hum & harmonics etc. Usually you might expect to see Much lower value resistors for eg 10R. That would help with RFI but not so much with 50/60Hz hum.

The problem with such high value resistors in those positions, is the power supply modulation to the OpAmps as they draw current = Not good. Using batteries eliminates the mains power supply issues. But if a mains PS is ever used for anything, it's better to use regulators to power the circuit.

All the best
 
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