Saturday, July 26, 2008

DIY Multiple

This was supposed to be a splitter/passive mixer. I'll just get that out in the open right now. I'd gotten the idea from Blacet's "Mixer" and "Splitter" modules, which are sold together as a kit for $100.

Essentially, what I wanted to do was build something that would let me take a guitar signal, split it out to two sources (the "splitter" section) then, independent of that but in the same housing, have two "return" jacks with attenuation to a common output (the "passive mixer"). Sounded simple enough.

But after soldering everything together, the "mixer" section started giving me problems. No matter what I did, its dials would only act in concert-- if one was fully counter-clockwise, the other one, regardless of its position, wouldn't do anything-- I'd have to balance the two, as if they were each half of the same output knob. And, to make matters worse, the attenuators weren't independent of each other, signal-wise, either (the left dial did not control the signal coming in from the left jack exclusively, but dealt with half of the total volume from both inputs). In short, I hadn't created a passive mixer, I'd just made a return circuit with an annoying volume control.

So, frustrated, I de-soldered the pots, re-drilled their holes, dropped in a pair of jacks and wired this new configuration the same way I'd hooked up the "splitter" section (which worked just fine), taking us to the layout you see in the photo above.

The pedal now houses two multiples, one with three jacks and one with five: plug something (a signal or a control voltage) into one of the jacks on the top and send it to two places; plug it into the bottom group and send it out four ways.

It's nothing fancy, but it works! Plus, it's passive and is a cinch to whip up.

If you want to build your own, connect the Ground lug on each jack in a cascade, and connect the Tip lugs in the same way. Viola! I'm sure there's a limit to the amount of times the signal can be split, though the old Doepfer Multiple had eight jacks!

P.S. If anyone reading this can point me to a simple passive mixer circuit (mono, pref) or pass over some pointers, please do!

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Blogger felix said...

Hmm, it sounds like at least one of the pots might be messed up.

Normally, you'd have the #1 lug of each pot wired to the input tip, #2 would be the "output", and lug #3 would go to ground. Reverse #1 and #3 for different direction of the pot. I think you generally want to have at least a 10k resistor after each pot too, before each signal reaches the output jack.

If you don't need variable attenuators on the mixer, you can just put resistors on each input. These basically function as "static" pots. Somewhere from 50-500k should work fine.

4:00 PM  
Blogger Pete Shambler said...

Thanks for the tips, Felix! The passive mixer is going to be an ongoing project-- I'll let you know when I've got one up and running!

Looking forward to your AFG demo!!

11:23 PM  

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