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#### coupe

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I'm an op amp! What do I do?!

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#### MrDeodorant

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You produce an output voltage proportionate to the potential difference between your inputs!

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#### coupe

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I read the wiki, but the terminology is not working well with me. I was wondering if anyone could set up a couple metaphors to make it a bit more easy to understand.

I haven't been able to grasp electrical engineering yet.

Love how people assume I haven't tried to learn myself....

#### lozanoa11

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It is the Amp part of an Amp. Basicly how I understand it, is it is a transistor. You have lots of power going in from the power supply, but it cannot go threw the opamp unless there is input. So you have your input from your sound source that controls the flow of the amped part.

If im wrong someone tell me.

#### RallyMaster

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An operational amplifier has many purposes, most of them being defined by how you place the resistors in relation to the inputs and output terminals of the opamp.

A single DIP-8 (8 pin package) opamp has five different, useful pins if you draw the circuit diagram representation. First, you have the power pins that allow a positive and a negative voltage (these voltages are typically equal in magnitude but different in sign). Second, you have the input pins. There's a positive and a negative input. Based on how you place the resistors relative to those pins and the output pin, you can adjust the gain of the circuit. By gain, I mean output voltage divided by input voltage.

Next, I'll draw up two fundamental opamp circuits for you to feast your eyes on. Input signal is a 1V amplitude 1kHz signal.

First up is the inverting amplifier. R1 is 1k, connected between signal source and negative terminal. R2 is 10k, connected between the output and the negative terminal. The gain of this is -(R2/R1) = -10. Notice that there is a 180Âº phase shift (positive input becomes negative output).
Circuit:

Output and Input as a function of time:

The other fundamental circuit is the non-inverting amplifier. In this case, the input is placed at the positive terminal but the negative terminal still does the biasing and adjust the gain. As the name implies, the output is not inverted and stays in phase with the original signal. In this case, the gain of the amplifier is (R2/R1)+1 = 11.

Circuit:

Output and Input as a function of time:

All simulations done with TINA, a tool provided by Texas Instruments utilizing the OPAy132 model.

Typically, adjusting voltage gain means you are making the speaker or headphone you're driving louder or quieter.

#### coupe

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when you say negative circuit. That just implies the ground... like closing the electrical circuit?

sorry I'm used to automotive electrical work.

#### coupe

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#### RallyMaster

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When I said inverting circuit, I mean it takes positive voltage and makes it negative and makes negative voltage positive. In other words, instead of pushing the speaker in the positive direction, it pushes in the negative. Frequency response and audio produced should theoretically stay the same, if a bit out of phase.

Are you talking about the negative terminal? If you are, which circuit are you referring to?

Terminology:
Closed circuit. This means the switch is connected and the circuit is on.
Open circuit. This means the switch is not connected and the circuit is off.
Short. This means the power source is being connected straight to ground most likely resulting in zero load conditions. Depend on if the source has over-current protection, it will either shut off the source or it will destroy it.

#### coupe

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Quote:
 Originally Posted by RallyMaster When I said inverting circuit, I mean it takes positive voltage and makes it negative and makes negative voltage positive. In other words, instead of pushing the speaker in the positive direction, it pushes in the negative. Frequency response and audio produced should theoretically stay the same, if a bit out of phase. Are you talking about the negative terminal? If you are, which circuit are you referring to? Terminology: Closed circuit. This means the switch is connected and the circuit is on. Open circuit. This means the switch is not connected and the circuit is off. Short. This means the power source is being connected straight to ground most likely resulting in zero load conditions. Depend on if the source has over-current protection, it will either shut off the source or it will destroy it.

The way I'm used to thinking is of electricity as water. Positive is the mountain water or water source. Negative is the mouth of the river into the ocean.

So when I look at the op amp. I get all confused for some reason. Why all the multiple positive inputs? What do the resistors do? I guess I'm trying to get a fundamental detail of how it works in the audio sense. I like to understand these things so instead of just saying: "Ah ya this op amp is better than this op amp"; You can look at the op amp and understand why it would be better.

Why would you invert the circuit?

#### RallyMaster

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I'm not fond of the "Positive is the mountain water or water source. Negative is the mouth of the river into the ocean." analogy.

I see top of the waterfall as the source only if you define the bottom of the waterfall as ground (potential of zero). You can also define the top of the waterfall as ground, but in that case, the bottom of the waterfall will be a negative source with the same magnitude (absolute value) as if you defined the top of the waterfall as +V and bottom of the waterfall as 0. Electricity is all about defining where your reference point is.

In an opamp, you have the power pins and signal pins. Power pins actually allow the opamp to power on and function. Signal pins (+/- signal terminals) in an audio application is where your audio signal, in analog form, are found. There are two signal input terminals and a single signal output terminal. Output is V_in x Gain (NOTE: x is used in this case for multiplication to avoid confusion with *, which is used in electrical engineering for convolution).

The opamp is most closely modeled as a voltage-controlled voltage source. Your output is dependent on two things: the gain you adjusted via resistors and the maximum output capability of the opamp (the saturation voltage, dependent on the biasing voltages on the power pins). Theoretically, an ideal opamp can have infinite gain. In practice though, an opamp circuit biased with +15V and -15V typically has a range of -13V to +13V no matter how high of a gain you set based on those resistors.

In theory, operational amplifiers (single opamp configuration in a DIP8 package) work the same way. You have five useful pins on the 8 pin package. Two pins are power input. Two pins are signal input. One pin is signal output. Rest of them usually are disregarded (offset trims and one that is simply not connected). In practice, depending on how the opamp is manufactured, how much capacitance and internal resistance there is inside the opamp circuitry, the output sound signature could vary. I have yet to hear an opamp that convinced me there is a substantial difference between opamps unless it's a cheap laboratory opamp (for educational purposes) versus an opamp specifically built for audio applications with low signal to noise ratio and total harmonic distortion. The internal capacitance and resistances as well as the surrounding circuit define the frequency response of the amplifier. Most audio opamps are manufactured with a flat frequency response in mind but this FR does vary based on the surrounding components.

The inverting circuit is just one of the ways you can build an opamp circuit. Some applications call for inversion, others do not. It's typically a design decision that the engineering makes either to cut costs or simplify the circuit board.

EDIT: Kudos to whoever pointed out that I mislabeled R1's value in the non-inverting diagram. It is now corrected to 1k.

Wikipedia's link doesn't really explain that much. You need to have worked with opamps in the lab to really know what any of it means.

#### coupe

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Quote:
 Originally Posted by RallyMaster When I said inverting circuit, I mean it takes positive voltage and makes it negative and makes negative voltage positive. In other words, instead of pushing the speaker in the positive direction, it pushes in the negative. Frequency response and audio produced should theoretically stay the same, if a bit out of phase. Are you talking about the negative terminal? If you are, which circuit are you referring to? Terminology: Closed circuit. This means the switch is connected and the circuit is on. Open circuit. This means the switch is not connected and the circuit is off. Short. This means the power source is being connected straight to ground most likely resulting in zero load conditions. Depend on if the source has over-current protection, it will either shut off the source or it will destroy it.

#### jacobthellamer

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Quote:
 Originally Posted by coupe
Not negative -> just inverted

The diagram is on an inverted amplifier.

#### coupe

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Argh confusion back up!

What inverted it? How was it inverted?

#### RallyMaster

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The positive (+) on VG1 just means that it's the output side of the source. The other side is ground, which remains 0 at all times. This is like the positive side of a battery. If you use a voltmeter to measure the potential between + and -, you'll get a positive value. The negative (-) on the opamp means that whatever input placed at that location becomes inverted (+ goes to -; - goes to +; 0 stays 0) and is multiplied by the gain determined by R2/R1. I think at this point you're not only having issues understanding what an opamp does but also how circuits are labeled in general. Buy an beginner's electronics book, which is about the best thing you can do if you don't understand circuit diagrams.

#### coupe

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Quote:
 Originally Posted by RallyMaster The positive (+) on VG1 just means that it's the output side of the source. The other side is ground, which remains 0 at all times. This is like the positive side of a battery. If you use a voltmeter to measure the potential between + and -, you'll get a positive value. The negative (-) on the opamp means that whatever input placed at that location becomes inverted (+ goes to -; - goes to +; 0 stays 0) and is multiplied by the gain determined by R2/R1. I think at this point you're not only having issues understanding what an opamp does but also how circuits are labeled in general. Buy an beginner's electronics book, which is about the best thing you can do if you don't understand circuit diagrams.
I think your right man. I need to get such a book.... You have any recommendations or online sources?

#### KoolGuy

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Check This one out

#### coupe

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Quote:
 Originally Posted by KoolGuy Check This one out

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