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What Is Amplifier Slew Rate? (Answered)

As audio equipment becomes more advanced, it’s important to have an understanding of what an amplifier slew rate is. This term is typically used in conjunction with high-end audio equipment and defines the maximum frequency at which an amplifier can output power.

Unfortunately, not knowing about the amp slew rate can lead to not knowing the right frequency at which an amplifier can go.

Image of someone holding a black portable amplifier. Source: andrey matveev, pexels
Image of someone holding a black portable amplifier. Source: Andrey Matveev, Pexels

This article covered all about slew amplifiers. So, if you’re in the market for an amplifier, it’s important to know the maximum frequency that the amplifier can handle. This information can help you make an informed decision about which amplifier is right for you.

What is the amplifier slew rate? The slew rate of an op amp is the greatest rate at which its output voltage may fluctuate, and it is measured in volts per microsecond. The slew rate of an operational amplifier is determined by introducing a big signal step, say one volt, to its input and then observing how quickly the output signal’s amplitude changes from 10% to 90%.

What is an amplifier slew rate?

“Slew rate” refers to the rate at which an electrical quantity, such as voltage or current, changes over a certain period. For example, the slew rate of an amplifier (or another signal processor) is the rate at which the signal is changed (distorted). As a result, some lag may be seen between input voltage changes (both slow and rapid) and their manifestation at the output.

The dynamics (and especially the transients) of the audio waveform are negatively impacted by this distortion, which is, in fact, the case. However, slew rate really has a greater impact on high-frequency clarity in practice.

How can you measure the amplifier slew rate of your audio equipment?

The slew rate can be calculated by providing a step signal to the op-input amp’s stage and monitoring the rate at which the output signal changes from 10% to 90% of its amplitude. The applied step signal is typically about 1 V in magnitude.

Using the output voltage waveform, we can calculate the slew rate. The slew rate may be determined using an oscilloscope and a function generator.

What causes the slew rate?

In general, the phenomenon of slew rate derives from two properties of op-amp dynamic response; however, a detailed explanation of slew rate at the transistor level is beyond the scope of this paper (and my competence).

First, the output amplifiers will not immediately reflect a shift in the input. Accordingly, there will always be a lag between modifying the input and seeing the resulting effect.

Second, this delay may cause a significant discrepancy between the voltages delivered to the inverting input terminal and the non-inverting input terminal when an op-amp is coupled in a negative-feedback setup.

The behavior of the differential-pair input stage is altered by such a huge differential voltage, leading to linear growth (or decay) in the output voltage, as shown by VOUT(t) = SRt. The quantity of compensating capacitance significantly impacts the slew rate (SR).

Practical amplifier slew rates

It is well known that an amplifier’s slew rate significantly impacts signal distortion above a certain frequency. Even budget amplifiers should have a slew rate greater than 6.3 V/s.

The high slew rates often seen in amplifiers are the result of careful design. In order to effectively remove any possible mistakes and undesired distortion, the slew rate should produce a maximum frequency beyond the hearing range.

Remember that there are many additional potential sources of distortion. A slow slew rate should not be one of them. To get rid of the high-end frequencies that aren’t audible to humans, many amplifiers apply a low-pass filter to the audio stream. Why bother amplifying them if we can’t hear them?

Even if it’s debatable to do so, we may further protect ourselves from distortion caused by slew rate by lowering or eliminating the ultrasonic frequencies in the stream.

In addition, the output at high frequencies is optional for actual audio transmissions for our listening experience. In a well-balanced audio mix, the brightness range (arguably 6 kHz to 20 kHz) actually needs less power than the lower frequencies.

Image of a black amplifier on top of a wooden surface. Source: akshar dave, pexels
Image of a black amplifier on top of a wooden surface. Source: Akshar Dave, Pexels

If you want even more tips and insights, watch this video called “Operational Amplifier Slew Rate | Op Amp Slew Rate” from the ElectronicsNotes YouTube channel.

A video called “Operational Amplifier Slew Rate | Op Amp Slew Rate” from the ElectronicsNotes YouTube channel.
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Frequently asked questions (FAQ)

Do you still have questions? Below are some of the most commonly asked questions about amplifier slew rate.

What happens if the slew rate is high?

When an operational amplifier (op-amp) is used beyond its slew rate limit, signal distortion occurs. Consider a sine wave as an example. At the zero crossing point, the rate of change in voltage is at its greatest. The highest frequency or voltage that may be supported can be determined.

What causes the slew rate in op-amp?

When a signal with a high frequency and large amplitude is applied, the slew rate is created by the compensating capacitor’s slow charging rate, as well as current limiting and saturation in the op-amp’s internal stages.

What happens if the slew rate is low?

Distortion will occur at high output frequencies and amplitudes due to slew rate restrictions. Inputting a periodic waveform (sine, square, etc.) into an amplifier with a low slew rate will produce an output that resembles a sawtooth wave.

How do you control the slew rate?

An extra capacitor may be used with the slew rate control feature to limit the increase in output voltage. The CdVdT external capacitor is shown in the left figure, within the red border. Changing this value modifies the output voltage’s slew rate as it rises.

Conclusion

There you have it, the basics of what an amplifier slew rate means. This term is used to ensure that your speakers are not damaged due to too much power being pumped into them. Therefore, before purchasing any new audio equipment, make sure you know what slew rate your amps have!

However, just as you can’t become an expert cyclist by reading a book, you can’t become a great music producer by reading articles alone. It’s time to take action! Go and put what you have learned into practice.

This article covered what an amplifier slew rate is, how it is measured, and the causes of amp slew rate. Here are some key takeaways:

Key takeaways

  • “Slew rate” refers to the rate at which an electrical quantity, such as voltage or current, changes over a certain period of time.
  • By providing a step signal to the op-input amp’s stage and monitoring the rate at which the output signal changes from 10% to 90% of its amplitude, the slew rate can be calculated.
  • In general, the phenomena of slew rate derives from two properties of op-amp dynamic response.
  • Increasing the bandwidth may help with closing the feedback loop without inducing instability for larger slew rates.
  • As an essential feature in a variety of a/d driver implementations, this specification sets bounds on the maximum bandwidth that may be used without distortion.
  • Keeping distortion and other factors under control while yet maintaining a healthy sr makes sense when considering the impedance fluctuations of real-world speakers.
  • The slew rate of an amplifier is the greatest rate at which its output may vary in response to an input signal that rapidly steps from a low to a maximum level.
  • Slew-rate limitation is a key feature of op-amps for ensuring reliable operation.

So, does your amplifier respond quickly? And did I cover everything you wanted to know? Let me know in the comments section below (I read and reply to every comment). If you found this article helpful, share it with a friend, and check out my full blog for more tips and tricks on music production. Thanks for reading, and never stop making music.

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Audio Apartment Author
Written By Andrew Ash
Hey there! My name is Andrew, and I've been making music since I was a kid. I now run this blog all about home studios and music production. If you want to improve your home studio setup, this is the place for you!

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