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Mix-It: An Easy-To Build 4-Channel Mixer

Anyone can build this high performance four-channel audio mixer...

By Nicholas Vinen

This mixer is something of a reprise of two very popular 4-Channel Guitar Mixers featured in SILICON CHIP – the first in our January 1992 issue and a more recent version in June 2007.

Click for larger image
An early prototype of the Mix-It! 4-channel mixer - some components have been moved or changed since this photo was taken. PCBs purchased from SILICON CHIP will also be double-sided, eliminating the need for the wire links shown on this board.

While this one has several similar features, (it is an audio mixer, after all!) it also has a number of improvements – for example, performance, cost, easy to build – and as a bonus, the PCB is actually smaller than either so you can fit it into a smaller case.

It features four inputs which can be configured for a wide variety of signal sources, from very low level (eg, microphone or guitar) right through to quite high (eg iPODs/MP3 players, CD/cassette decks [Gad, what are they?] ) and the like.

It has bass, midrange and treble controls, individual channel level controls along with a master volume control and an on-board power supply. You can build it as a stand-alone unit or incorporate it into a PA or guitar amplifier.

In fact, it doesn’t even need to be a PA/guitar amplifier: with almost 800mV output, this mixer could be used with virtually any amplifier with a “line in” or similar input.

Other features include a variety of power supplies – it could use a low voltage AC supply – say around 15V – or it could use a split DC supply such as that commonly found in amplifiers (eg, ±15V).

We’ll have more to say on the supply shortly.

Features

Four unbalanced inputs with 1MΩ || 100pF input impedance (see text)

Gain of 0-36dB per channel (depending on feedback components)

Bass, mid and treble controls (±10dB)

Master volume control

Input radio signal filtering

Flat frequency response

Low distortion and noise

Four supply options: 15VAC, 12-30V DC, ±15V or unregulated split supply

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