Home stereo - There's a "thump" when I turn off my system
This is not a Halloween scary-tale. In fact this thumping does happen with some regularity.
There are usually two reasons for this: The amp has a large power supply and its design doesn't shunt energy in a path that is outside the speaker output circuit. Let's look a bit more closely at both.
First, a power supply's job is to filter and store energy until the amplifier circuitry needs it. Most good amps have power supplies that store several thousand microfarads or even Joules of electrical power in capacitors. Thats a whole lot of stored electrons!! And its part of the reason that these amps sound as good as they do. But when you turn the system off, that energy has to go somewhere. The "thump" you occasionally hear is the power supply capacitors dissipating the energy.
While its sometimes annoying, it's not dangerous at all. In fact, it's just another sign that the amp won't run out of steam when you really want to reproduce loud transient sounds.
Sometimes amp designers employ what are known as output relays that shunt and dissipate the excess energy as soon as the power is turned off. Many other designers think that these relays degrade the purity of the audio signal so they don't include them. Thus, the excess energy is passed to the speaker outputs in one big burst.
As one high-end equipment manufacturer puts it: "Look at it this way: The "thump" is the same thing as a high performance automobile's rumbling exhaust. The sound alone tells you there's something serious under the hood, right?"
From Anthony Armstrong
There are usually two reasons for this: The amp has a large power supply and its design doesn't shunt energy in a path that is outside the speaker output circuit. Let's look a bit more closely at both.
First, a power supply's job is to filter and store energy until the amplifier circuitry needs it. Most good amps have power supplies that store several thousand microfarads or even Joules of electrical power in capacitors. Thats a whole lot of stored electrons!! And its part of the reason that these amps sound as good as they do. But when you turn the system off, that energy has to go somewhere. The "thump" you occasionally hear is the power supply capacitors dissipating the energy.
While its sometimes annoying, it's not dangerous at all. In fact, it's just another sign that the amp won't run out of steam when you really want to reproduce loud transient sounds.
Sometimes amp designers employ what are known as output relays that shunt and dissipate the excess energy as soon as the power is turned off. Many other designers think that these relays degrade the purity of the audio signal so they don't include them. Thus, the excess energy is passed to the speaker outputs in one big burst.
As one high-end equipment manufacturer puts it: "Look at it this way: The "thump" is the same thing as a high performance automobile's rumbling exhaust. The sound alone tells you there's something serious under the hood, right?"
From Anthony Armstrong
