The performance of an audio amplifier can be significantly affected by its power supply design. The power supply’s design can have an audible effect in listening tests and a quantifiable effect in bench measurement results. The type of power supply used can impact the audio performance, with unregulated supplies being the most common for audio power amplifiers due to their simplicity, good performance, and reasonable cost. However, unregulated supplies can have voltage fluctuations with load and power mains fluctuations, which can affect the audio performance.
Understanding Unregulated Power Supplies for Audio Amplifiers
The Texas Instruments application report SNAA057C provides a detailed analysis of the design of a ±72-V unregulated power supply specifically for audio amplifiers. The report includes schematics, board layer views, and a bill of materials for the power supply design. The power supply provides a ±70 V to ±73 V supply under quiescent conditions with full load voltage dropping to ±59 V to ±62 V. This voltage drop under load is a characteristic of unregulated power supplies and can affect the amplifier’s performance.
The report also discusses the importance of safety testing for the power supply design. Unregulated power supplies can pose a safety risk due to the high voltages involved, and proper design and testing are crucial to ensure the safety of the amplifier and its users.
Efficiency and its Impact on Amplifier Performance
The efficiency of a power amplifier is another critical factor that can affect its performance. High RF power amplifier (PA) efficiency is particularly important in modern wireless communication systems because the PA is often the dominant single-block energy dissipater.
The efficiency of a power amplifier can be improved by using switch mode power supplies (SMPS), which have become very popular, common, inexpensive, and readily available. SMPS are well-suited for use in computer hardware, providing good regulation with high efficiency in a small physical size. However, a drawback to SMPS is the switching nature of the power supply, which can introduce noise and affect the audio performance.
According to a study published in the IEEE Transactions on Microwave Theory and Techniques, the efficiency of a power amplifier can be as high as 80-90% when using a properly designed SMPS [1]. This high efficiency can lead to reduced heat dissipation and improved overall system performance.
Amplifier Parameters that Affect Sound Quality
The Sound of Audio Amplifiers article by Audioholics explores the technical reasons why audio amplifiers can sound different. The article discusses various amplifier parameters that can affect the sound quality, including:
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Input Sensitivity: The input sensitivity of an amplifier determines the amount of input signal required to achieve full output power. Differences in input sensitivity can lead to perceived differences in sound quality.
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Total Harmonic Distortion (THD): THD is a measure of the distortion introduced by the amplifier. Higher THD can result in a “harsher” or “muddier” sound.
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Intermodulation Distortion: Intermodulation distortion occurs when two or more input signals interact and produce unwanted frequency components. This can also affect the perceived sound quality.
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Frequency Response: The frequency response of an amplifier determines how it handles different frequency ranges. Variations in frequency response can lead to differences in the perceived tonal balance of the audio.
The article also highlights the importance of considering the speaker cables and loudspeakers themselves when evaluating the sound quality of an amplifier. The power supply’s impact on these parameters can be significant and should not be overlooked.
Quantifying the Power Supply’s Impact
To quantify the impact of the power supply on an amplifier’s performance, various measurements and tests can be conducted. Some key metrics to consider include:
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Output Power: Measure the maximum output power of the amplifier under different load conditions and power supply voltages. This can reveal the impact of voltage fluctuations on the amplifier’s capabilities.
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Distortion Measurements: Measure the THD and intermodulation distortion of the amplifier at different output levels and power supply voltages. This can help identify the power supply’s contribution to distortion.
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Frequency Response: Measure the amplifier’s frequency response under different power supply conditions. This can reveal any changes in the tonal balance due to the power supply.
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Noise and Interference: Measure the noise floor and any interference introduced by the power supply, such as switching noise from an SMPS. This can impact the perceived clarity and dynamics of the audio.
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Transient Response: Evaluate the amplifier’s ability to handle rapid changes in output demand, which can be affected by the power supply’s regulation and response time.
By conducting these measurements and tests, you can gain a deeper understanding of how the power supply design affects the overall performance and sound quality of the audio amplifier.
Conclusion
In conclusion, the performance of an audio amplifier can be significantly affected by its power supply design. Unregulated supplies are the most common for audio power amplifiers due to their simplicity, good performance, and reasonable cost, but they can be susceptible to voltage fluctuations that can impact the audio performance.
The efficiency of a power amplifier is also a critical factor, and SMPS can improve efficiency, but the switching nature of the power supply can introduce noise and affect the audio performance. Understanding the various amplifier parameters that can be influenced by the power supply, such as input sensitivity, distortion, frequency response, and transient response, is crucial for optimizing the overall sound quality of the audio system.
By conducting thorough measurements and testing, engineers and audiophiles can gain valuable insights into the power supply’s impact on an amplifier’s performance and make informed decisions when designing or selecting audio equipment.
References:
[1] Cripps, S. C. (2006). RF Power Amplifiers for Wireless Communications. Artech House.
[2] Texas Instruments, AN-1849 An Audio Amplifier Power Supply Design, June 2008, Revised June 2019, https://www.ti.com/lit/an/snaa057c/snaa057c.pdf?ts=1705643074731
[3] ScienceDirect, Amplifier Efficiency – an overview, https://www.sciencedirect.com/topics/engineering/amplifier-efficiency
[4] Audioholics, The Sound of Audio Amplifiers: Can you hear a difference between them?, February 18, 2015, https://www.audioholics.com/audio-amplifier/the-sound-of-an-amplifier
[5] AudiophileStyle, Is it possible for a power supply to affect sound quality?, June 18, 2020, https://audiophilestyle.com/forums/topic/59669-is-it-possible-for-a-power-supply-to-affect-sound-quality/
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