This is a universal 4 channel DJ audio mixer project that may be customized and upgraded to 5 channel or even 10 channel level as desired by the user.

5 Stage DJ Mixer

Five stages are employed within the layout; DJ mixer stage; Mono headphone amplifier stage; Balanced-microphone preamplifier stage; Stereo VU circuit stage, and General purpose preamplifier stage.

A basic ceramic cartridge preamp is displayed that looks so straightforward that it could be constructed on the input sockets itself!

When using the stages outlined above practically any audio options could be mixed or blended by the user to get a stereo transmission specifically suited for driving power amplifiers straight away.

The mixed signals may also obviously be applied to feed headphones etc. The inputs from CD players, microphones, Ipods, cellphones etc should be appropriately matched up to the inputs of the mixer board. To get this done the proper preamplifiers needs to be determined and built.

Even so, the audio mixing range could be practically endless. Before you start building consider which preamplifiers you might need, consider which kind of sockets you would like to work with, and the number of channels you would like (although demonstrated as 4 channel, the mixer could be extended with the addition of further control pots and mixer resistors).


The best thing about this balanced microphone circuit is that it gets rid of a pricey line transformer.

Even though intended for 600 ohm input and 40dB gain, various other impedances and gains could be dealt with by using R1 = R4 input impedance divided by two R5 = R11 voltage gain multiplied by the value of R3. The very first equation functions for impedances of approximately about 5k.

Over this figure R2 + R3 need to be incorporated in the computation. Even though we all posses just one mouth, the output from this circuit makes it possible to griddle the output through stereo by utilizing a couple of 10k resistors or a 20k linear pot using the wiper attached to the output enables you to pan the output via left to right.

In case a balanced MIC is applied R2 values will be as follows microphone R2 = 4k7 (limiting R2 47k) if employed with balanced preamp as input to restrict R2 = 15k


Due to the excellent feature of excessive ripple rejection ability by the incorporated integrated circuits across different segments, the power supply specifications actually tend to be quite straightforward. A simple bridge rectifier, large smoothing capacitors having a RF bypass capacitor and you own a good power reference.

Courtesy: ETI Circuits

The inputs through cellphones, SD cards, USB microphones etc has to be amplified or possibly equalized with a pre-amplifier prior to any kind of controls positioned to process them.

The output of each of such preamps is variable using a volume control or fader, previous to being added to lC1. The total gain of the mixer stage could be modified through RV1.

If various preamps possess largely varying output voltages the value of Rl-R4 could be improved in order to match them.

The output of lCl is connected subsequently to the tone control stage. lC2 typically features a unity gain when the pots are moved at the center of the dial.

However, this gain is actually variable, with regard to frequency, when the tone controls are not around the center the output of the tone control stage specifically toggles the main power amplifiers.

This output is additionally rectified by Dl to run the meter circuitry. The mixer provides stereo outputs which is accomplished by replicating the circuitry for the second channel.

The exemption may be the tone controls that are dual gang potentiometers.

Remember that the volume controls are separate units.

The power supply is actually a full wave rectified supply using a centre tap offering about 1 VDC

How it Works

The resistors linking Left and Right channel outputs are positioned to get a composite mono signal, without severely deteriorating the main mixer stereo separation.

The signal is actually picked by SW2-SW5 and raised on to a buffer having adjustable gain (IC3). The output can now be given to a LM380 power amplifier that runs the monitor headsets. Just like the mixer the input resistors may be made higher, to minimize high signals towards the other channels.

The mixer is actually a standard summing amplifier using adjustable feedback (ie gain), accompanied by a Baxandall tone-control system.

In case input ranges aren't of the identical value, the 27k input resistors could be modified to decrease the highest signal by increasing resistor value. Avoid lowering under 27k because this may decrease overall level of sensitivity of the mixer.


How it Works

Very little can probably be said about
how exactly the LM382 operates since many of the circuitry is comprised inside the IC. The majority of the frequency determining elements are
on the chip just the capacitors tend to be attached outside the body.

The LM382 has got the handy feature of obstructing ripple on the supply
path around 10 dB. Hence significantly lowering the high quality
dependence on the power supply.


The output through each preamplifier could be applied into this headphone amplifier circuit. To be able to cue signals prior to mixing them into the output it is strongly recommended that if headsets are used, include a 100 ohm 1 watt resistor which may be installed in series with the output.

This is primarily to safeguard your ears and decrease the power dissipation of the LM 380 or else a little heatsink could be needed. The volume control could be attached to the trunk of the mixer since it is not necessarily tweaked frequently.


The VU meter circuit utilized in the mixer board is quite fundamental, yet well suited for several similar audio level indicator purposes, distortion presented into the output signal can be as much as 2% THD, therefore we highly recommend the VU board.

Possibly you may leave out RV4 and D1 from the mixer board and hook up point X to the input of the VU panel. Calibration set up is performed through the preset on the VU board, give a signal input via the mixer until eventually the output is merely distorting the amplifier, and fine-tune the preset to signify +3VU.


Construct the boards using the overlay sketches, to save your time we have placed all the PCB layouts collectively, here.

The picture exhibits the general layout we made use of, however this is universally adaptable, ours had been constructed into a wooden box along with metal front side and bottom nevertheless a metallic container could be a lot more ideal within an electrically raucous atmosphere.

Inter-board cable connections could be figured out from the specific circuits and overlays.

All contacts needs to be as small as you possibly can and retained far from the mains wiring. We actually relocated the power button directly to the backside of the panel to minimize hum pickup and grounded to the metal box, having an light weight aluminum shield round the mains transformer to guarantee minimal hum pickup) If this is carried out unscreened cable connection may be used without issues.

How it Works

This VU circuit comes with an input impedance approximately 1M and consequently will never load the mixer output by virtually any visible level.

The IC features a gain of 43dB, the signal can now be amplified through Ql to attain sufficient level and push the VU meter needle.

With no signal circumstances the voltage in the penetration of D1, D2 drops to 0V due to R8. Each time a negative proceeding signal shows up at collector of Q1, C3 tends to discharge within the negative peaks. Difference between negative and positive highs is shifted via D2 to C4 and therefore is indicated on the VU meter reading.

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