[Disclaimer] I am not an engineer and have little to no knowledge in circuits / electroncics

Hi everyone, I build an audio mixer from the topic here based on the following schematics

Works well, but my goal is to improve that step by step. 1st modification would be to add headphone output to allow me to listen to either channel 1 or 2 before it goes to the master volume (before the 10K variable resistance that controls the volume output, variable being represented by the arrows). I tried to add headphones based on indication of the famous DJR400 DJ Mixer (attached PDF page 4)



My question is would what I have drawn above (I drawn it in mono and without ground to simplify the schematic) theoretically work?

Would I need OpAmps at some point to prevent signal loss (I am currently learning how they work)?

Apologize if this is not in the right section / rightly schematized, I'm only starting

Thanks a lot in advance
T

 

The general rule is you want the impedance of the source to be lower than that of the load.

Here you are showing a source impedance of at least 1kΩ and as high as 11kΩ. Meanwhile your headphones will have much lower impedance, 32Ω or lower. So you have it backwards. That is why you need amplification.

 

I will explain why you need amplification.


The source and load impedances create the equivalent of a voltage divider as shown in the circuit diagram above.

The voltage at the LOAD = V1 x R2 / (R1 + R2)

If R1 = R2, you get half the voltage of V1.

If R1 is much greater than R2 there is little voltage remaining to drive R2.
The best you can do in order for the voltage to be 100% at R2, R1 must be substantially lower than R2, i.e. R1 must be zero.

Since you are most likely using LINE levels, there is not enough voltage to drive headphones.

Hence you need amplifiers, not just op-amps but amplifiers capable of providing enough power to drive headphones.

 

Thanks a lot, really greatful for the help.

I'm currently watching videos / reading about how OpAmp works and schematics of other DJ mixer to see how other do it before drawing another circuit and post it here to see if that is any better.

I guess that marks by my entry in the world of active (powered) circuits vs. pure passive!

 

I will explain why you need amplification.
View attachment 204680

The source and load impedances create the equivalent of a voltage divider as shown in the circuit diagram above.

The voltage at the LOAD = V1 x R2 / (R1 + R2)

If R1 = R2, you get half the voltage of V1.

If R1 is much greater than R2 there is little voltage remaining to drive R2.
The best you can do in order for the voltage to be 100% at R2, R1 must be substantially lower than R2, i.e. R1 must be zero.

Since you are most likely using LINE levels, there is not enough voltage to drive headphones.

Hence you need amplifiers, not just op-amps but amplifiers capable of providing enough power to drive headphones.

This is crystal clear thanks so much, will rework and revert, hoping that could benefit someone at some point!

 

You will need a power amp that can drive the headphone impedance.
Standard opamps can't.

 

Hello,

Have a look at the following pages for some decent mixer schematics:
https://sound-au.com/project94.htm
https://sound-au.com/project94a.htm

Bertus

 

thanks a lot all for your help, i'll look at everything before I settle on the best way to have this work.

For everyone's information, I tried plugging my headphones to the output of the "actual" schematic drawn (i.e. without the middle switch and associated path ending by the scripture "phone") and it works, I can hear the music, although there is a loss in volume.

Thanks a lot for the schematics Bertus, I'll have a look. At first glance looks like there is no "upstream monitor" headphone output, which is the thing I am trying to add for now. I'll experiment with a few things but need to get some parts first!