Audio Mixer Circuit

Thread Starter

Sepereta

Joined Aug 26, 2023
7
Hi Friends ,

I am trying to make a simple gain circuit followed by a unity gain / voltage follower.so the circuit have two opAmps ics .the function of 1st IC is to gain the low volume audio coming from pre amp.

And the function for 2nd IC is to input the gained output of 1and summing mix with another signal and output it to the channels (using TL074 here for dual output , eg. Lin ---> L1out + L2out)

For powering the board ,I am using single supply PS and connected it ic by virtual ground method.

The problem i am facing is , i am getting high pitch noise on the output playing with the audio.

Following is my circuit (please ignore the drawing mistakes ):
20230826_162242.jpg



Following is the image I took reference from (i have altered the pin 2 with 3 and vice versa) as it was wrong in diagram.

20230826_041619.jpg



Thanks in advance for answering and your time
 

Hymie

Joined Mar 30, 2018
1,272
Your audio input 0V should be referenced (connected) to the 0V of the circuit, and not the mid-biased voltage (6V).
 

Thread Starter

Sepereta

Joined Aug 26, 2023
7
Your audio input 0V should be referenced (connected) to the 0V of the circuit, and not the mid-biased voltage (6V).
Thanks for replying. I did as u said .
But now i am getting this hissing sound when i play audio in low / mid volume or when i disconnect the audio in source(audio file attached as zip).

my updated circuit is also attached.

please let me know what more components i have to add to remove this noise and to improve the quality output .

PS i cant add another transformer supply due to lack of space.
 

Attachments

Thread Starter

Sepereta

Joined Aug 26, 2023
7
Where did you get that circuit? Make an note: next time you need a circuit, look elsewhere.
I tried to search it on google but cant find the right one for my application.

What i need is simple a mixer with 2 inputs (L+R) and three voltage following outputs (L1,L2&L3 + R1,R2&R3).
 

Ian0

Joined Aug 7, 2020
9,498
I tried to search it on google but cant find the right one for my application.

What i need is simple a mixer with 2 inputs (L+R) and three voltage following outputs (L1,L2&L3 + R1,R2&R3).
First you need to know how to write a specification. Even if you are just designing something for yourself, have a clear idea exactly what it should do.
Input levels?
Input impedance?
Equalisation?
Output levels?
Frequency response?
A good place to start is a book like Horowitz & Hill The Art of Electronics
TI's OpAmps for Everyone
or Analog Devices' Basic Linear Design
 

LowQCab

Joined Nov 6, 2012
3,937
Why do You need 3-Outputs ?
Isn't this project supposed to create a single-Sub-Woofer-Output from
a pair of standard Stereo Left & Right Line-Level-Outputs ?

Does your Sub-Bass Amplifier(s) have a Level-Control on it's Input ?
Having a Level-Control for each Output of the Pre-Amp is highly recommended.

If exactly what You want is clearly described,
I'll make You a Schematic-Drawing,
but so far this post is kinda confusing.

Do You actually have a working Dual or Quad TL072 Op-Amp ?, or 2-Dual-Op-Amps ?
This is a very good, classic, Op-Amp for Audio applications,
but probably somewhat over-kill for a Sub-Bass application.
Or, do You need a suggestion for an appropriate Op-Amp ?

Do You actually have a ~12-Volt, well filtered Power-Supply ?, please describe it in detail,
Or, is this an Automotive application ?, ( ~12 to ~14.5-Volts ).

Please describe the Amplifiers, Speakers, and Speaker-Cabinets that You will be
using for your Sub-Bass Frequencies.
Knowing this can help with designing the Filters to better suit the capabilities of your Speakers.
Pictures, or Specification-Sheets, ( PDFs ), would be very helpful for this.
.
.
.
 

Thread Starter

Sepereta

Joined Aug 26, 2023
7
Why do You need 3-Outputs ?
Isn't this project supposed to create a single-Sub-Woofer-Output from
a pair of standard Stereo Left & Right Line-Level-Outputs ?

Does your Sub-Bass Amplifier(s) have a Level-Control on it's Input ?
Having a Level-Control for each Output of the Pre-Amp is highly recommended.

If exactly what You want is clearly described,
I'll make You a Schematic-Drawing,
but so far this post is kinda confusing.

Do You actually have a working Dual or Quad TL072 Op-Amp ?, or 2-Dual-Op-Amps ?
This is a very good, classic, Op-Amp for Audio applications,
but probably somewhat over-kill for a Sub-Bass application.
Or, do You need a suggestion for an appropriate Op-Amp ?

Do You actually have a ~12-Volt, well filtered Power-Supply ?, please describe it in detail,
Or, is this an Automotive application ?, ( ~12 to ~14.5-Volts ).

Please describe the Amplifiers, Speakers, and Speaker-Cabinets that You will be
using for your Sub-Bass Frequencies.
Knowing this can help with designing the Filters to better suit the capabilities of your Speakers.
Pictures, or Specification-Sheets, ( PDFs ), would be very helpful for this.
.
.
.
Not the subwoofer out .

What i am trying to make is a simple karaoke setup . I already have a wireless karoke reciever with mics which have 3.5mm audio out and a Bluetooth decoder board.

so i want to mix audio from both this device and output it to 3 different line out so i can use this 3 outputs for following functions:

1nd output to amplifier
2nd output to live mix listening on normal earphones (not requiring high power)
3rd output to stereo audio recorder (for recording purpose).
 

Thread Starter

Sepereta

Joined Aug 26, 2023
7
First you need to know how to write a specification. Even if you are just designing something for yourself, have a clear idea exactly what it should do.
Input levels?
Input impedance?
Equalisation?
Output levels?
Frequency response?
A good place to start is a book like Horowitz & Hill The Art of Electronics
TI's OpAmps for Everyone
or Analog Devices' Basic Linear Design
I do have clear idea but i am still learning and dont have full knowledge, maybe that why i am here.
 

LowQCab

Joined Nov 6, 2012
3,937
OK, now that we have a better idea of what You want ...........

You say that You have a "" wireless karaoke receiver with mics which have 3.5mm audio out ""
Are the Mics and the Music all on one 3.5mm Jack ?,
Is this Jack in Stereo, or Mono ?,
Are the Mics separate from the Music source ?, ( 1, 2 or 3 Outputs ? ).

This is why Pictures,
and/or PDF-Files,
and/or Part/Numbers with manufacturers names,
and/or, Block-Diagram-Drawings,
are absolutely necessary.
There could be a hundred different configurations that You are trying to work with.
.
.
.
 

AnalogKid

Joined Aug 1, 2013
10,944
In case no one has made this explicitly clear yet, the "Audio Preamp Circuit" schematic in post #1 has two critical errors, and cannot work as shown. If you haven't already, you might search for another preamp circuit that actually works. For example, something like this. Other than missing two decoupling capacitors (the only thing that other schematic got right), it is a better starting point. The LM358 is very poor for audio applications, but just about any opamp can be dropped into this circuit with the appropriate pin number changes.

ak


1693161309521.png
 

Audioguru again

Joined Oct 21, 2019
6,608
In post #16, the capacitance of C1 is so low that it cuts low frequencies causing a man's voice to sound like a chipmunk.
Texas Instruments use a transimpedance design that is the same but replaces R2 with a piece of wire.
The 9V battery needs a decoupling capacitor to ground.

I have always used a non-inverting opamp as an electret mic preamp.
 

Ian0

Joined Aug 7, 2020
9,498
In post #16, the capacitance of C1 is so low that it cuts low frequencies causing a man's voice to sound like a chipmunk.
Texas Instruments use a transimpedance design that is the same but replaces R2 with a piece of wire.
The 9V battery needs a decoupling capacitor to ground.

I have always used a non-inverting opamp as an electret mic preamp.
I've always used that circuit with R2=0, because the microphone output* is the drain of a JFET, so it has a very high impedance, so a transimpedance design is appropriate.

*Not all microphones may be made to that design - on some the output is the source of a JFET, and that would require a different preamplifier design. I always used the Panasonic WM series, and they all have the output on the JFET drain.
 
Top