# 4 input Microphone Audio mixer

Discussion in 'The Projects Forum' started by Aish_Zaleha, Mar 21, 2012.

1. ### Aish_Zaleha Thread Starter New Member

Mar 21, 2012
14
0
I am not that familiar with this kind of circuit but i highly need an expert critique and help on it.

To start with, I'm going to use 4 ordinary microphones (ones used in computers), with 3.5mm TRS plug, as inputs. I need to mix/sum the signal coming from these microphones. Then the summed audio will then be distributed/split into each of the four equivalent signals.

I have consulted my professor about it and he gave me a rough sketch of the diagram. What i need to know is how am i going to determine the appropriate values for the capacitors and the resistors. I have researched some circuits but i am not sure if they are correct. The capacitors having a value of 0.1μF, the potentiometer having a value of 10KΩ, resistors having 100KΩ and a 1MΩ value?? I'm really not sure about it. He also pointed out that we could use any usual op-amp used for audio. Do you have any suggestions about it? Will an NE5532 fit the job? or should i use something like TL084?

Another thing, is it really all right to distribute the summed audio signals by a parallel connection? Wouldn't that degrade the signal? The main purpose of this project is to produce a nice quality audio after passing through this audio mixer and splitter circuit.
Any small help would be highly appreciated. Thank you very much.

2. ### #12 Expert

Nov 30, 2010
16,705
7,358
Xc=1/(2PiFC)
Set the capacitor size so that its impedance equals the resistance at the lowest frequency of interest.

The TL071 is a singe op-amp with lower noise than the TL081/82/84

The number of parallel loads depends on whether the amplifier chip can supply enough current to drive the loads. You haven't said what the loads are, so I can't do the math.

3. ### Aish_Zaleha Thread Starter New Member

Mar 21, 2012
14
0
Ummm... I'll just show you the whole system. We plan to build a very simple language (speech) laboratory at a very low price. Our university is not that interested in providing such expensive equipments. so we thought of making something cheap and simple to operate but is still capable of the main features of the modern language laboratories.

all we did was like extending the microphone cables. the Audio mixer represents the circuit i showed on the first post. also, please know that only one person uses microphone1 and headphone1, same with the rest. the receivers of the audio will be one PC and 3 MCU-based student consoles. the PC and student consoles will then output the signal to the headphones. i'm not sure about the loading part, but i would like to know how the calculation works. I hope this doesn't confuse you.