The explained 5 circuits below are universal simple audio mixer circuits, that may be customized and upgraded to 5 channel or even 10 channel mixers, as desired by the user. Contributed by: Anil Rao.
Stereo Audio Mixer
The operation stereo audio mixer circuit shown below is straightforward: If a mic is "being used," its output is applied to the MIC input port of the circuit.
The signal is subsequently applied to R1 or R2 (which are utilized as faders). The signal is after that divided into a couple of diverse routes through resistors R3 and R4 using which it is possible to alter the location of the MIC inputs within the stereo range.
The stereo line inputs are simply built for this. Connecting the MIC inputs with the output of any different source, like a mobile phone or PC USB or CD player, etc., all of the signals are supplied to the inverting input of an op amp. The output extends to the master-fade potentiometers, that handle the output power.
This stereo mixer circuit is additionally simple to customize. For instance, We replaced low-noise amplifiers for the 741's, and employed 1% metal - film resistors.
We furthermore made use of slide potentiometers for the faders and line -level controls. We modified the quantity of in puts also. Rather than just a couple of MIC inputs and a single line input, We expected to get a total of 8 MIC inputs and 4 LINE inputs.
4 Channel Audio Mixer using a Single Op Amp
The next image shows a 4 channel mixer, in which 4 different audio signals can be fed to the indicated relevant inputs IN1----IN4 ports, the opamp will mix them all to produce a common mixed output at the port indicated as OUT.
4 Channel Mixer with Tone Control
Pats List for 4 Channel Audio Mixer
The signal supplied by means of a sensor involving audio frequencies, for example a microphone, a guitar-string sensor, etc all require a signal boosting before the output can be used to drive a main amplifier.
The 4 channel preamplifier displayed above can work with signals as low as 2 mV levels, comes with an input impedance of 1 k, offers a gain of around 1600, and provides an output swing as high as 3.2 V for 2 mV input.
It exhibits relatively small distortion and is built to accept four external inputs, all featuring their own level control.
An exclusive tone control system is integrated that allows bass and treble signal frequencies to be adjusted through a range of ±10 dB (at 100 Hz and 10 kHz respectively).
Even though largely designed for mixing audio signals in leisure purposes, the circuit could also be applied as a single-input, adjustable -gain unit in just about any application where gain and frequency modification are essential.
PCB Designs
Single Transistor Audio Mixer
An audio signal mixer can be actually as simple as the one indicated in the below diagram. This circuit uses just a single transistor and can be used for mixing 3 input signals or even more than this number.
Although only 3 inputs are shown that doesn't restrict it from incerasing the inputs, which may incerased to any higher desired inputs.
Each of the mixer inputs can be seen having their individual level control pots for adjusting the amount of signal that can enter through the inputs, independently.
This single transistor mixer circuit is designed for amplifying the any input signal with a 50 mV, to an output signal of around 500 mV, which is more than enough for most power amplifiers configured at the output.
The above design can be further improved, as shown in the following diagram:
MIC Mixer Circuit
This uncomplicated mic mixer circuit enables you to blend a high-level source with a low-level microphone input for amplification purposes.
Within this setup, the high-level input maintains a one-to-one unity gain from input to output, while the low-level input experiences a substantial gain boost of 100.
To eliminate the need for split supply rails, the non-inverting input of IC1 is artfully biased to a voltage level precisely halfway between the supply rail's positive and negative potentials, and this bias point is effectively filtered by C3.
Capacitors C1, C2, and C6 perform AC coupling, permitting the desired signal components to pass through. C4 serves the vital role of compensating IC1, ensuring signal fidelity, while C5 efficiently bypasses any supply rail noise.
This circuit can be efficiently powered by a single 9 V transistor radio battery, and it's advisable to include an on/off switch for convenient operation.
With this straightforward design, you can easily blend and amplify high-level and low-level signals with precision and efficiency.
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).
BALANCED MICROPHONE PREAMPLIFIER
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 input, 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
MIXER AND POWER SUPPLY
Due to the excellent feature of excessive ripple rejection ablity 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.
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 center 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.
UNIVERSAL PREAMPLIFIER
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.
Parts List for Universal Preamplifier
4 CHANNEL STEREO HEADPHONE AMPLIFIER
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.
VU CIRCUIT
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.
CONSTRUCTION
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.
Questions and Answers
Hi Swagatam,
I’m the designer of the TEC-1G which currently has only a bit-banged output from a 74HCT273 going to a speaker. I want to make a Sound Card for it that takes the output from the onboard bit-banged data line, and has two other outputs on the card, one being the SP0256-AL2 speech processor, and the other a SN76489AN noise generator. I need to mix all three inputs and amplify them to an onboard 8ohm mini speaker. Could you recommend which of the above circuits would be best suited to the task, considering all three inputs have different and varying voltages? I’m quite proficient with PCB design, but if there are any tips you can pass on, I’d gladly take your suggestions on. (Eg,. Should I go 4 layer and try to shield the inputs as best I can?)
Hi Mark, for your application the following active transistorized mixer stage would probably be the best choice among the circuits discussed.
You can feed the mixed output into an LM386 or PAM8403 amplifier stage for driving the 8Ω speaker.
A good 2-layer PCB with solid ground plane should be sufficient. I would mainly recommend keeping the digital bit-banged traces away from the analog audio section and perhaps adding a simple RC low-pass filter at the bit-banged input to reduce switching noise.
Thanks for the speedy reply! I have two problems using those circuits:
1) I don’t have 9v power. Only 5v. 😢
2) Maybe I’ m not following, but that circuit you linked has two outputs? Or is the lower one connected to ground?
I know it’s alway a bastard to look over other people’s circuits, but I’d be happy to pay for your time to take a look over mine and give any feedback. I’ve also included some screenshots of the 4 layer PCB to show how I’ve laid it out. The physical aspects of it I can’t change (size, location of connectors and volume control) but if you have suggestions for moving around other parts, I would gladly welcome. As you can see I’ve gone to some lengths to keep the noisy digital parts separated from the audio section.
(I might re-arrange the Schematic to more cleanly delineate between the digital and audio sections. I know it looks like spaghetti compared to your clean circuit diagrams. Sorry!)
Here is the link to my GitHub page for the Sound Card:
https://github.com/MarkJelic/TEC-1G/blob/main/TEC-Deck/SoundTalker/Readme.md
No problems, your comment was actually sent to the spam folder because of the link, now I restored it back.
Since I am not a professional PCB designer, assessing your PCB can be difficult for me, although overall it looks good to me from outside.
Surely, you can rearrange the schematic as you want, just make sure to keep the connections as short as possible.
Yes, the output is only one, from the transistor collector…the other one is the common ground rail…
5V DC should also work for the above BJT schematic.