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Problem with diy audio mixer - high frequency sound

D K

Dec 12, 2016
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Hi,
i have just build my own audio mixer that is buit of potentiometer and switch to mute ( i didnt use any pcb, only solder wires ). There is one big problem, it add too the audio some high frequency sound.

Where can i have problem? Or how can i repair it or prevent this problem?
 

Audioguru

Sep 24, 2016
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A potentiometer plus a switch is not an audio mixer circuit. If you have a [real[/b] circuit then if it oscillates the frequency would be so high that you would not hear it.

I think you have acoustical feedback howling where the microphone can hear the speaker and the sound goes around and around. Record with the mic without the speaker turned on then play it back later.
 

D K

Dec 12, 2016
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It is actually high frequent sound that I don't hear but my ears hurts if I have my headphones longer time. if I connect it directly to my PC, it is okay.
 

Audioguru

Sep 24, 2016
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Please show the schematic and a photo of your simple audio mixer and what is connected to it.
 

D K

Dec 12, 2016
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There are some pisctures. I know that it is quite messy :D
 

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Audioguru

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The capacitance of your messy wires might cause oscillation of the circuit near them.
 

(*steve*)

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If your ears hurt, either turn down the volume or get a pair of headphones that don't squeeze your ears so hard (or both).

Your circuit is poor for a number of reasons, but given your construction it would be hard to fix. If it kinda works, it is probably better than nothing.
 

D K

Dec 12, 2016
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Can you suggest some schematic that would improve it? I don't want to use integrated circuits.
I am quite beginner in building circuits.
 

(*steve*)

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You could improve it by using shielded cabling, and connecting the variable resistor as a potentiometer rather than a rheostat, and by adding a buffer amplifier to the output. I would recommend an emitter follower.
 

davenn

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Sep 5, 2009
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I don't want to use integrated circuits.

Why ?

some Op-amps and some simple circuitry around them would give you a very effective mixer

this one I built 20 odd yrs ago uses a single quad op amp

upload_2016-12-14_21-39-42.png
 

D K

Dec 12, 2016
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Why ?

some Op-amps and some simple circuitry around them would give you a very effective mixer

this one I built 20 odd yrs ago uses a single quad op amp

View attachment 30890
If i use this circuit, should i power it via usb? There is -4.5V, so can i convert 5V from usb to 4.5V and -4.5V? What about stereo? Do i have to do one more circuit?
Or should it be powered by ac adapter?
I would prefer the usb supply.
 
Last edited:

Audioguru

Sep 24, 2016
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An opamp can be simply biased so that it does not need a negative supply voltage.
A single opamp is usually used as a mixer, the circuit uses 4 opamps because each of its inputs is amplified.
Some opamps will operate from a 5V USB supply.
 

davenn

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If i use this circuit, should i power it via usb? There is -4.5V, so can i convert 5V from usb to 4.5V and -4.5V? What about stereo?

don't think you can produce + - 4.5 V from a 5V rail, you would need a higher voltage others may know a way

for stereo, you would have to double what you see for a 3 channel input


EDIT: AG has offered some ideas on the supply
 
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