I have this passive summing mixer pcb and this time around for a second build would like to up the quality of the resistors, lowering the resistance and using some audio grade stuff.
What i am unsure about is, how would i substitute each 9 pin = 8 resistor array if at all possible?
The last pin seems to be sth like a sum to the next stage.
The 9-pin device is just 8 resistors of the same value, with one side of them all tied together. If you want to replace this with discrete resistors, you’ll need to replace each bar with 8 resistors.
I’m not sure what you mean by “audio grade”. I think the only parameter to keep an eye on is tolerance because you want them all to be closely matched - go for 1%. If you use the resistor array bars - then it is very likely that the eight resistors are even more closely matched - if you use discretes, they may vary more - though within the 1% tolerance for audio mixing, you’ll never be able to tell.
Lastly, remember that if you lower the resistance significantly it will increase the interaction between the sources feeding the inputs: When you plug to outputs into this mixer, you are effectively plugging them together - which isn’t great. The resistors create impedance so that the outputs don’t “see” each other as much. 10kΩ or so is a reasonable compromise between output level and cross-input impedance. Rather than lower the resistance here - consider just bumping up the amplification where you send the output of this mixer.
Thanks for your insight. Maybe i should really keep it simple, i did order 2x15k arrays vs the 100k stock value, wich if iam not mistaken would be divided by 4 for resistance per channel.
I did not think about impedance indeed and given i am using transformers sometimes differently patched i ll have to watch for this.
Am i right to assume, i could sum to mono instead of stereo by strapping a 1k resistor/pot in parallel to the out jack?