jubin
Junior Member
Posts: 70
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Post by jubin on Oct 28, 2021 8:13:15 GMT
Hi everyone,
This is not directly related to AE stuff. I'm trying to build a kind of summing box.
I plug multiple input audio signals, and they all get mixed in 1 output signal. For this, I have no issue, it works fine.
The particularity here is that, on top of that, I'd like to have a passthru for each input. Let's take a picture :
Inputs are at the left column of the device. The grouped output is on the bottom right. Again, for this, no problem.
Passthru outputs are the right column (except the last bottom right).
But my passthru outputs have an issue. Each passthru output ends up having all signals mixed too.
By looking at the circuit I have done, it seems logical now.
Green wire : ground
Does some of you know how I could avoid that please ?
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Post by pt3r on Oct 28, 2021 8:44:29 GMT
How about putting diodes on the connections between the input connectors and the summing connector that way your signal can only go into the summing connector but no signal flows back from the summing connector into the individual input connectors which IMO is what causes the issue you describe.
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jubin
Junior Member
Posts: 70
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Post by jubin on Oct 28, 2021 8:53:25 GMT
Sounds like exactly what I need, but it's hard to do research without the proper wording.
Thanks ! I will try this.
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jubin
Junior Member
Posts: 70
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Post by jubin on Oct 28, 2021 9:54:46 GMT
Hm, it doesn't work, the summed output has now no sound, and the inputs still receive cross signals...
I putted the diodes right before the output jack socket (one for left, and one for right). So it means that the diodes receive group left and group right.
On the diode, the ring (or line) is pointing to the jack socket.
Is it right ?
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Post by pt3r on Oct 28, 2021 19:55:03 GMT
No you need to put a diode on every line going to the summing output, if you merge all the left lines into one diode you still have signals from one input that can reach another input, since the all merge before the diode.
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jubin
Junior Member
Posts: 70
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Post by jubin on Oct 29, 2021 9:20:20 GMT
Thanks for the answer. I will try that.
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Post by MikMo on Oct 29, 2021 10:08:47 GMT
Just remember that most diodes have a voltage drop around 0.7V, so the signal at the end of the diodes will be somewhat weaker.
Mikael
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Post by keurslagerkurt on Oct 29, 2021 13:40:29 GMT
Usually diodes don't work for audio: you need electricity to be able to flow both ways for audio, as its an AC signal. (you can see it as electrons pushing & pulling back. If you have eg a speaker, the speaker cone has to vibrate out & in. With diodes you cannot get this push-pull but only push.)
If you want your output not mixed in, i'm afraid the only way is an active build. Simplest for that is an opamp summer circuit, and probably a buffer opamp for each output.
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Post by keurslagerkurt on Oct 29, 2021 17:11:26 GMT
Here you can see a simple opamp summer circuit, which is the same as a mixer circuit: www.electronics-tutorials.ws/opamp/opamp_4.htmlYou could use the circuit with all resistors being the same value, somewhere between 10k or 100k ohm should be fine i reckon. If you then connect your pass through wires before this summer stage, you should get 0 bleed. I suppose this is not for AE cases, but I do of course not know which power supply you use for this use case? Because that can complicate the design. - for AE modular, and other only positive PSU's like guitar pedals, batteries, etc, you will need a bigger circuit like robert posted here: forum.aemodular.com/thread/1744/help-4-chan-audio-mixer. - For Eurorack gear, or others which feature a bipolar PSU, you can just use this circuit above directly. Classic opamp to use would be the supercheap & decent TL072. |
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jubin
Junior Member
Posts: 70
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Post by jubin on Oct 29, 2021 18:46:33 GMT
Yes I just realized that while prototyping. Thanks for the confirmation. 
Okay, that's way more complex than I thought. Because at first I thought it could be done with a passive circuit. So I have no idea on how to do that. I'll look at your tutorial.
Thanks a lot.
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Post by keurslagerkurt on Oct 29, 2021 19:22:20 GMT
I wandered along the same path as you two years ago: had a nice passive mixer box for my volca's (just Four Ins with resistors), but i wanted a dry/wet knob to send to An effect. Turned out that it was impossible to do with just a passive circuit.
Op-amps and IC's scared me back then, weird symbols that were hard to interpret with just basic ohms law & electric circuit rules. However, while you can make incredibly complex circuits with op-amps, it's basic rules & uses are actually fairly simple. They just take a little bit of time to mature in your brain.
If you're interested in learning further about it, i highly recommend watching this vid:
If you understand basic ohms law & resistors, you'll understand op-amps by the end of the video 😃
If you understand op-amps, this is a nice vid about there summing capability:
And this video explains why you have bleed with passive circuits:
Sorry for the big info dump!! Hope it can be of some use for someone, these videos certainly helped me a ton in the past.
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jubin
Junior Member
Posts: 70
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Post by jubin on Oct 29, 2021 19:47:32 GMT
Thank you so much for all these resources !
I will start by learning this concept.
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