How to feed reference voltage for two op amps inputs with different input signal each one

Question

Im building a Stereo Buffer and a Baxandall circuit together. In powering the circuit with a single supply of 9v, and i need to bias each four inputs with 4.5 volts. The question is: If i feed the four inputs with the same reference voltage line will a have problems with the signals that are different. Into the buffer the signal is the IN signal, but in the Baxandall input the signal is the output buffer. But if i used the same voltage reference i suposed that im going to have a mix of both inputs signals in the baxandall, im right? How i can fixed that thing?

Thank you for your answer!

Answer 1

Let's fix a few other things first.

Figure 1.

1. GND symbols should point down to the ground, not to the sky. The upward arrow is often used to signify connection to V_CC so it risks confusion.
2. You've AC decoupled in the wrong place move C2 from here to (3).
3. As wired here the pot is pulling your V_CC/2 reference to ground. Consider what happens when you move the wiper to the top of the pot.
4. Swap R10 and R11 and your V_CC and GND will be the right way up with higher voltages higher on the page and current flowing from top to bottom.
5. See (4).

We'll also fix the pot orientation.

^{simulate this circuit – Schematic created using CircuitLab}

Figure 2. The modified circuit.

• The pot is the right way up. Moving the wiper up will raise the volume.
• The pot GND (and all the others) are pointing down.
• C1 is positioned after the volume control wiper. This prevents the pot wiper affecting the non-inverting bias.
• If you're worried about DC coming in on the audio signal you can add another capacitor on the input.
• OA2 provides a "stiff" buffer for the V_CC/2 mid-rail supply. C2 keeps the voltage steady even if V_CC has some noise on it.
• R4, 5, 6 & 7 provide the bias to the other four op-amps. OA2's output is stable and low impedance so the audio signals on the other op-amps don't interfere. I realise I've set these resistors to 10k which may load the audio signal a bit too much. 100k or more should be fine.

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