Manual for the audiomixer


This is a very simple 8 channel audiomixer but it works good enough for communication radio systems. It has 4 inputs and 4 outputs where you can individually adjust the levels. It also have a mastervolume. The amplifier is based on the OP, LM741.


The inputs can be connected to…

sound out from soundcard/PC speaker.
sound out from the repeater reciever.
sound out from the linkradio reciever.
sound out from the RLM interface.

The outputs can be connected to…

line in on the soundcard.
sound in (mic) on the repeater transmitter
sound in on the linkradio
sound in on the RLM interface (DTMF).

Build and adjust

Start with setting all the 8 trimpots in minimal volume (highest resistance) and set the the master volume in a middle position.

Adjust all the in- and outputs so that the soundlevel is the same from and to all sources. Remember not to use a fully zero ohm adjustment on a trimpot. This will cause a impedance problem.

Use shielded wire and a good noice-free powersource. If you use the power from the RLM interface you might catch some "data-noice" that will be heard on the radio.

Component list
Component Placement ELFA nr. Comments
100k trimpot R1-R8    
1k trimpot R13    
10k R10, R11    
100k R12    
1k R9    
C1, C3 1uF    
C2 10uF    
LM741 IC1    


© 1999 SM2UMH, Peter Hansson version 990208