# Design an OP AMP Power Supply for Audio Preamp

• neg_ion13
In summary, the conversation discusses the design of a foundation for an audio preamp powered by a single 9V battery. The speaker is using a voltage divider scheme to get a +4.5V and -4.5V reference voltages, but when a load is added, the supply voltages shift. The speaker is trying to determine the cause of this and is considering using two 9V batteries or using a DC-DC to invert the 9V to get a stable voltage. The conversation also mentions using two 10k resistors in the voltage divider and connecting the load to ground.
neg_ion13
Hello,

I am trying to design a foundation for an audio preamp that is powered by a single 9V battery. I am successful so far except the single power supply part. I am using the voltage divider scheme to get a +4.5V and a -4.5V reference voltages. With no load the supply voltages are close to even but when I add a load of say 1K the voltage shifts at the supply pins. The plus increases and the neg sides decreases. Do this mean the positive side is pulling more current and therefore dropping more voltage? The set up is 1mV AC input to non-inverting side with negative feedback for A = 100.

How much current do you need at the midpoint between 0 and 9 volts? You could use two equal series resistors (e.g., 10k ohm) and a LM324 (or LM358) as a voltage follower to get a stable voltage. It can source/sink up to 8 milliamps.

Bob S

Thanks for the suggestion. I would to keep the IC count low as I am running on a 9V battery. I'm not sure what current I need yet as I have not considered the next stage of the amplifier. The main problem I am having is; due to this voltage offset at the supply pins my negative half of the signal is clipping to early as I adjust the gain. What would cause the supply levels to shift like that? I am using 2 10k resistor for the voltage divider with ground referenced in the middle of the V divider and the voltage + and - at either end of the divider.

neg_ion13 said:
Hello,

I am trying to design a foundation for an audio preamp that is powered by a single 9V battery. I am successful so far except the single power supply part. I am using the voltage divider scheme to get a +4.5V and a -4.5V reference voltages. With no load the supply voltages are close to even but when I add a load of say 1K the voltage shifts at the supply pins. The plus increases and the neg sides decreases. Do this mean the positive side is pulling more current and therefore dropping more voltage? The set up is 1mV AC input to non-inverting side with negative feedback for A = 100.

Using 2 9V batteries would probably be cleaner. Or invert the 9V with a DC-DC to give you the negative rail.

neg_ion13 said:
Hello,

I am trying to design a foundation for an audio preamp that is powered by a single 9V battery. I am successful so far except the single power supply part. I am using the voltage divider scheme to get a +4.5V and a -4.5V reference voltages. With no load the supply voltages are close to even but when I add a load of say 1K the voltage shifts at the supply pins. The plus increases and the neg sides decreases. Do this mean the positive side is pulling more current and therefore dropping more voltage? The set up is 1mV AC input to non-inverting side with negative feedback for A = 100.

What value are the resistors in your voltage divider?

If one side of your load is connected to the output of the opamp, where is the other side of your load connected?

As I said in my first reply 2 10ks. The other side of the load is connected to ground.

Sorry, I missed your reference to the 2 10Ks.

Where is ground, at the junction of your voltage divider or -9V?

At the junction of my voltage divider. So I have +4.5 at the top, ground ref in middle and -4.5 at bottom. Also, I made sure my op amp output offset was zero volts with the non-inverting input connected to ground.

## 1. How do I choose the appropriate power supply for my OP AMP audio preamp?

Choosing the appropriate power supply for an OP AMP audio preamp involves considering the required voltage and current specifications of the OP AMP as well as the input and output signals. It is important to select a power supply that can provide enough voltage and current to meet the requirements of the OP AMP and also ensure that the power supply is stable and has low noise levels.

## 2. What type of power supply is recommended for an OP AMP audio preamp?

The type of power supply recommended for an OP AMP audio preamp depends on the specific design and requirements of the preamp. Generally, a linear power supply is preferred over a switching power supply for audio applications due to its lower noise levels and better regulation. However, a switching power supply can also be used if proper filtering and regulation techniques are implemented.

## 3. How do I calculate the power supply ratings for an OP AMP audio preamp?

The power supply ratings for an OP AMP audio preamp can be calculated by considering the maximum input and output voltages of the OP AMP, the maximum input and output currents, and any other components in the circuit that require power. It is important to also consider the power supply's efficiency and any voltage drops that may occur in the circuit.

## 4. What are the key considerations for designing a power supply for an OP AMP audio preamp?

Some key considerations for designing a power supply for an OP AMP audio preamp include ensuring stable and noise-free voltage and current outputs, selecting appropriate filtering components, and considering the thermal management of the power supply. It is also important to consider the cost and size constraints of the overall design.

## 5. Are there any specific design techniques for minimizing noise in an OP AMP power supply for audio preamp?

Yes, there are several design techniques that can help minimize noise in an OP AMP power supply for audio preamp. These include using low-noise components, implementing proper filtering and decoupling techniques, and paying attention to the layout and grounding of the circuit. It is also important to consider the location of the power supply in relation to the audio circuit and to keep any high-frequency components away from the power supply.

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