DIY Karaoke Machine

2017-04-24 | By All About Circuits

License: See Original Project

Courtesy of All About Circuits

The origins of Karaoke, which translates roughly to “empty orchestra” in Japanese are shrouded in mystery. It was originally developed to help musicians practice without having to assemble the entire band. Now, Karaoke is often the centerpiece of both dive bars and family fun nights. The common consensus is that the karaoke machine was invented by the Japanese businessman and musician Daisuke Inoue. However, since he never filed a patent, he didn’t profit on the device’s sales. The first Karaoke machine sold commercially by the company Clarion, which is also credited often for the invention. Clarion didn’t file a patent either, so we may never know the true origins.

Daisuke Inoue with his Karaoke Machine. Courtesy of Daisuke Inoue.

Karaoke systems can be a ton of fun, but they also tend to be pricey. Luckily, with a few potentiometers and an op-amp, you can make your own Karaoke machine! At the heart of a mixing circuit is a basic summing circuit. One cool thing about this circuit is that there’s no limit to the number of channels you can add. Just because you can add 50 channels for you and 48 of your closest friends to sing karaoke, doesn't mean that you should. If you were to freeze an AC signal in time, it would look like a DC value. If we summed all 50 DC values together, you’ll probably saturate your amplifier.Let's say that you want to have 4 singers and 1 song mixed together for a party. This is a total of 5 channels, so you’ll need 1 op-amp and 5 potentiometers. An op-amp is not well suited for directly driving a speaker, so a power amp is usually added to drive the speaker. It’s also common to add a pre-amp to normalize all signal inputs.

A little info about microphone pre-amps and power amps. Many microphones may require "phantom power" depending on the type, and some microphones can be damaged by phantom power. Other microphones may use battery power. This design doesn’t include a microphone pre-amp that provides phantom power. If you add microphones, look into the type of power your microphone requires. Common specs for phantom power are 12, 24, or 48 volts. Many digital microphones often use 10 volts for phantom power.

Most stereos and computer speakers include built-in power amps. If you choose to build your own power amp, be sure to pay careful attention to the speaker’s power requirements and the power that your amp is capable of delivering. For large power amps, take precautions to ensure sufficient cooling is provided. The schematic below does not have a power amp because prebuilt speakers were used.

Schematic and BOM

You’ll probably notice that the system has the same setup in the first four channels: a microphone followed by the optional pre-amp then by the potentiometer, capacitor, resistor, and a switch. The capacitor blocks any DC signal that may be coming from one of your sources. This isn’t necessary, but if all of your sources have a DC bias of 1 volt, you may quickly approach your positive rail, which can cause significant distortion. As a result, it is very strongly recommended to include the capacitor. The series resistor in each channel keeps the op-amp from functioning like a differentiator. In the fifth channel, the microphone input is replaced by the music sources. This can be a computer, phone, tablet, or mp3 player. If you want your system to have master volume, you can build a second inverting stage for a master volume using the same design used for an individual channel.

An important note on potentiometers: they come in linear and logarithmic varieties. Although either variety works, the logarithmic taper is preferable. This is because human hearing is logarithmic in nature. This is why use the decibel system to measure volume. The logarithmic taper allows you to make one channel twice as loud by turning the potentiometer twice as high. If you use a linear potentiometer, it won’t be twice the volume; it will be twice the voltage.

There are a lot of variables that can change based on the microphone input and speakers that you use. You can find a more in depth explanation on how to balance the power flow in your own circuit design on All About Circuits.

It’s most common to use a standard 3.5mm stereo audio jack for the system input. If you choose to use one, it helps to understand which wires correspond to the jack's connections. The tip is the left channel, the middle section is the right, and the bottom section is ground. The white should be your right channel, and the other color is the left channel. As there are many variations of the 3.5mm jack, it’s a good practice to test your cable. If your source uses a mono audio jack, the left and right channels will be joined.

Below is a video of the audio mixer in action (it's difficult to hear the microphone in the video). In this system, the microphone runs on battery power and has a set of computer speakers with a built-in power amp. Now you can get your party started!

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