Red Echo

October 5, 2017

Thoughts about audio mixers

I’ve been spending a lot of time spinning music lately, and now that I’ve basically got the sound system I want, I’m thinking about mixers.

In a nightclub environment, it makes sense for the venue to provide the equipment, since they’re going to leave it set up all the time and use it night after night. Club DJs therefore expect to show up and take turns playing their sets on the same set of decks.

Those of us who play in a festival / rave / party context, as I do, have a much more DIY attitude: everything gets set up and torn down all the time, every event comes together a little differently, and you never know what you’re going to find. We all therefore tend to be self-sufficient, bringing our own controllers and expecting nothing more than a PA hookup. So, there’s always a little fuss around patching in and out of the mixer, and it can be a little messy and complicated. At a party I went to over the weekend, there were some pretty significant disruptions to the flow of the music because the PA mixer which happened to be present worked a little differently than most of us were used to, and we had to figure it out as we went.

Beyond that, I’ve been hosting music jams at my house for a while now, where we all get together and plug in to the big PA system downstairs and take turns slinging music back and forth at each other. Normally you’re just transitioning from one DJ to the next – but in this environment there could be half a dozen of us all interacting randomly.

So I’ve been thinking about mixers. Nobody, so far as I can tell, actually makes the mixer I wish I had, so I’ve been… well, fantasizing, I guess, about the idea of building one myself. I probably won’t actually do this, more likely I’ll find an existing product which is close enough, but… I want something which is neither a standard PA mixer nor a standard DJ mixer, but something in between.

I want a six channel stereo line mixer in console format. That is, I want a box that sits on a table, with all of its plugs on top, so it’s easy to plug in and see where you’re plugged into without having to poke around in the dark.

PA mixers always have a bunch of mono channels. I don’t want any. We’re not a band, there are no instruments, there are no microphones. Everyone using this device has a fully-formed stereo signal to contribute. Most mixers also have EQs on each channel. I’d rather omit them. We already have those knobs on our controllers.

All I want, on each channel, is a pair of stereo input jacks and a volume fader, maybe also a level meter or at least a single LED to indicate that signal is present.

But! – and here’s where I get to the part I can’t just buy already – I really do want an equalizer on the master output. PA systems don’t have a flat response and they don’t always respond the same way at different volume levels. There needs to be a way I can shape the output to suit the room and the equipment, which is *separate from* the EQ control the DJ is using for their artistic purposes. That is, I want to be able to set up the EQ for the PA once, at sound check, and then each DJ can ignore that problem and use their EQs however they want for mixing.

So, this is all I want, really: six stereo inputs with volume faders, an optional “signal present” LED for each, then a master section with a master volume, a master EQ, output level meters, and – this is important – *balanced* outputs, preferably XLR. In addition, there should be a second output of the same signal, with a separate volume control, for the booth monitors.

That’s it. That’s all I need. If I had this gadget, and used it as the master PA mixer, any DJ with a controller would easily be able to step up, see what was going on, patch in, and transition over with no confusion about which inputs do what, or how to route the sound, because it would only do the one thing that we really need a mixer to do. It would also give me a way to configure the sound without having to get in the way of each performer’s creative flow or have an individual conversation with each DJ about the characteristics of the sound system and how to compensate for them… without losing the nearly-idiot-proof simplicity of the active PA gear I’m using. That is… it would work even if I weren’t there to set it up.

Notes on the basic circuits involved in an audio mixer

A simple three channel mono mixer design

Some extremely simple passive mixer designs, no power input required

A comprehensive introduction to balanced audio signals, with an approximate sketch about some of the circuitry involved

Addendum: The venerable Numark CM100 looks like a fancier version of what I want. Except… it’d be easier to patch in and out if the input jacks were mounted on the faceplate, like a PA mixer.

Second addendum: there are lots of prefab circuit modules available for cheap on eBay: 5-band stereo EQ, 10-band stereo EQ, balanced output driver, same but preassembled with XLRs

Well. I should still probably just buy something instead.