Why is Power Supply so Important for Amplifiers?

An amplifier (also known as an amp) is a simple electronic device that receives an input signal and enlarges it for a larger output. This process is called amplification. Typically, on an amplifier, there are three important sections: an input for the small signal, an output for the amplified signal, and a power supply. While many people intuitively think the first two sections are the most significant part for sound quality – a good input signal and a good output from the amplifier – the power supply, which is equally important, is often overlooked. Yet, it is crucial for the sound quality and performance of the amplifier.

The power supply must provide a stable and continuous voltage and current to ensure that the amplifier can amplify the input signal accurately and consistently. During sections of music with high dynamics, the demand on the power supply spikes. If the power supply is not ample or responsive enough, it might result in a distorted output signal, affecting the sound quality.

The power supply dictates the amplifier's output limits.

It's essential to understand that the transistors or vacuum tubes inside an amplifier don't act like transformers. They don't create or increase energy. The amplifying circuit merely acts like a valve, controlling the flow and consistency of energy. The key element we hear during amplification is the power supply. Differences in the amplifying circuit can be likened to varying water flow rates, flow smoothness, or valve switching speeds. However, all they do is transform the power supply into output in various ways. The output of an amplifier is limited by its power supply. In other words, the power supply capacity determined the maximum power output of an amplifier.

Why do lower ohm loads challenge an amplifier's output?

To understand the relationship between an amplifier and a speaker, we need to realize that speakers are passive components. They rely on the amplifier's voltage and current output to produce sound. Thus, connecting a challenging speaker to drive is like giving the amplifier a tough load. While a low-efficiency speaker can be considered challenging due to needing more power to achieve the same volume as a high-efficiency speaker, the more significant factor is the speaker's impedance fluctuations when playing music. Though speakers have a nominal impedance, their actual impedance varies with frequency. For instance, Speaker A with an impedance range between 7-9 ohms and Speaker B, which varies between 2-14 ohms, may both be labeled as 8 ohms. However, Speaker B can be more challenging due to its potential to drop to 2 ohms.

According to Ohm's law, when the voltage remains unchanged, a halved impedance will double the current. For an amplifier, the ability to maintain adequate current output when the speaker's impedance drops is crucial. This is even more important than the written specification of how many watts it can output at 8 ohms. For instance, if Speaker B's impedance drops to a low of 2 ohms during demanding music passages, the power consumption may quadruple. This presents a stern test for the amplifier. Some budget amplifiers might not be designed with a generous power supply, leading to a lack of power during these critical moments, causing subpar performance, less accurate representation of dynamics, reduced headroom, and narrower bandwidth – what's colloquially referred to as "weak sound." 

How to know if an amp has a good power supply?

Therefore, when choosing an amplifier, one shouldn't just look at fancy product title. It's essential to check the spec sheet and the actual power output at low impedances. If an amplifier can nearly double its output from 8 ohms to 4 ohms and then to 2 ohms, it indicates a robust power supply. For example, the K221 amplifier from DA&T Audio offers 150 watts at 8 ohms, 300 watts at 4 ohms, and 500 watts at 2 ohms, showcasing a well-designed power supply. On the other hand, if an amplifier's specified wattage drops significantly at lower ohms or deliberately avoids mentioning its capability at these levels in the spec sheet, it suggests a less capable power supply.

In conclusion, a sufficient power supply is crucial for an amplifier's performance and greatly impacts the sound quality. A good power supply ensures the amp to provide enough power, reduce noise and interference, and allow the internal circuits to perform at their best.