1163 mixer cutting frequency

Hi all,
I have built the 1163 mixer. I get sounds from every channel and the knobs are working to attenuate the signal. (The intensity is a lot lower when going through the mixer though).
Problem is, it is cutting the high frequency.
I tried changing the tl072, I have triple checked all the joints… not sure where to continue? Could it be a capacitor?
Any comments is appreciated.

I found my mistake. I used wrong value for C5 and C6. Getting there… I have the correct sound but a buzzing issue due to bad grounding. But C5 is only half soldered…as while removing them, I broke the pcb connection for C6. I can’t see either of them on the schematic. Do you know where they connect to ? So I can add a wire and bypass the pcb.

There are no C5/C6 capacitors in the schematic here but the BOM has two 100 pF capacitors. I guess they might be in parallel with R9 and R11 or thereabout, but @lookmumnocomputer will know for sure.

I think C5 is in parallel with R9 so I assume C6 is with R11. I’ll give it a go. Thanks !!

Got it !!
I am wondering if R11 was not the issue from the start.

I connected with extra wires and it works great. No buzzing, no frequency cut-off, all good.
Many thanks !!!

hey glad its working!

yeah a bigger value for the feedback caps for instance you putting the 100nf there instead would definitely dull the sound somewhat! glad you found the solution thanks @fredrik no idea how they disappeared from the schematic its updated now.


Just to inform, it’s not fixed in this page :slight_smile:

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aaah yeah that’s fine! to be honest you can get away in most instances without these capacitors. just stop some instances of usually none noticeable noise, but there has been times usually inside circuits when its been a problem, so for the strip board layout it will stay the same as that is an exercise in bare minimum, and still works happy days :). to the point some of th mixers I have popped together I didnt bother adding those capacitors to the pcbs as I ran out haha.


I’ve made one without them, and work well too :slight_smile:

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100 pF and 100k give a corner frequency just under 16 kHz. Depending how young your ears are, you might prefer something more like 50 pF, raising the corner to 32 kHz.