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Old 2nd November 2013, 09:58 PM   #1
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Default Befuddled with routing

I'm building a multi-effect box and I'm still puzzled about routing. I'm trying to route signals so that each 'module' can be by-passable. Figure A is basically my current set up and the problem is the output of the reverb is feeding back in to itself via the EQ direct output line.

Someone suggested an opamp mixer. But if it's done like figure B, won't there be inverted and non inverted signals mixing together?

Or am I missing it altogether /: ?

TIA

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Old 2nd November 2013, 11:32 PM   #2
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If you are using standard Boss type effect units, they all fit in series and you choose where to place them.
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Old 2nd November 2013, 11:38 PM   #3
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Sorry I was not clear... this is a single, multi-effect unit that I am building. All the sections are within the unit as circuits. I'm hoping to mix them internally with the same type of versatility as having separate pedals though.
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Old 3rd November 2013, 02:05 AM   #4
gootee is offline gootee  United States
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Think "op amp summing amplifier", for mixer.

Here are the classic National Semi application notes with the schematics you need:

http://www.ti.com/lit/an/snoa621c/snoa621c.pdf

http://www.ti.com/lit/an/snla140b/snla140b.pdf

Just remember that the schematics don't show the mandatory decoupling capacitors from power pins to ground. Use 10 uF electrolytic in parallel with 0.1 uF X7R ceramic, from every op amp power pin to ground, with the 0.1 uF connected right at the power pin (not 3 mm away).
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Old 3rd November 2013, 04:42 AM   #5
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Thanks Gootee,

I'm thinking along those lines. My issue with the summing amplifier is, as far as I know, the inverting of the wave and rectifying that down the line.

I found this from Mr. Stevenson's site: Paul In The Lab: Buffered Y Splitter Stripboard Veroboard

I'm running a bipolar supply so I figure nix the voltage divider and add an extra opamp for a 3 way splitter. Here's my second idea.

Click the image to open in full size.

But I won't pretend... this is my first build and I've been learning as I go... I appreciate the feedback.
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Old 3rd November 2013, 05:36 AM   #6
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I went ahead and wired it up with the second idea and it seems to work pretty well! One issue is the eq switch pops when flipped... but the reverb and dry switches do not pop. Echo is just going to ground for now because that part of the circuit is not built yet.

I'm going to tweak it a bit and see what may come.
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Old 3rd November 2013, 11:44 AM   #7
gootee is offline gootee  United States
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Seems like that should work fine. No summer for OUT? It seems like you would at least need a largish resistor to ground if nothing else is connected to the output, to make a passive summer. You might also need an R to ground for the preamp outputs to sum. Or it might need an active summing circuit.
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Last edited by gootee; 3rd November 2013 at 11:51 AM.
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Old 3rd November 2013, 07:09 PM   #8
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Yes I have a 220K to gnd after the pre and a 1m to gnd at the end not shown in the drawing.
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Old 4th November 2013, 02:32 AM   #9
gootee is offline gootee  United States
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Looks like you should be golden, then.
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Old 5th November 2013, 03:34 AM   #10
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Thanks Gootee.

I'm curious... what are the benefits of an active versus passive summing mixer?
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