First, some necessary things...
- Thank you to those who expressed an interest, both publically and privately. While I'm more than happy to do this, time is also limited so I'm certainly happy I'm not wasting my time.
- This is offered for "informational purposes only". While I have assembled each building block (more on that as this progresses), I offer ZERO warranty and accept ZERO liability for what you do with this information. Use at your own risk.
- I am happy to discuss, and help out as is convienent for me. This might become inconvienent tomorrow, and I am not providing technical support. Use at your own risk.
- This is not a project for the meek. While it's not necessary to have a solid understanding of electronics, it definately helps. Further, if you cannot solder consistantly, and reliably, don't waste your time and money.
- Some of these building blocks are of my own design, some are from chip manufacturer reference designs, some are "leeched" off schematics in the back of instruction manuals for pro-gear, some are "leeched" off the web. I apologize up front to anyone concerned about copyrights, but alas I'm not able to make a reference for each building block simply because I don't recall where everything came from. I'm just disorganized. Since this is for educational purposes anyway, I see no real issue with this at all.
Okay, enough of the disclaimer crap. Lets build a mixing console.
First, lets look at what a mixing console is. Here is the simpliest mixing console we can make, as it's the foundation of all mixers regardless of size. Input circuitry, connected to a common buss, which drives and output. In case it's not obvious, technically a "Y" cord combining the output of two synthesizers (or other) to an input on something else, is a simple mixer. Not a good one mind you, but it illustrates the point.
So keeping this simplistic drawing in mind, we all know that a "real" mixing console will have many inputs, many busses, and many outputs, with some control "stuff" in between all three components. Buss select, Volume, Pan, EQ, and so forth. Before we design that aspect, let me point out two things that really irk me about modern day, affordable mixing consoles, things that some of the pro consoles I've had the pleasure of using in the past certainly have.
- "Flip" Switches - Pet Peeve #1
Most consumer grade analog mixing consoles force you to utilize some of your input channels as tape returns. Look at the illustration below.
In this example I've drawn the typical wiring scenario for a 32 input, 8 buss mixing console with an 8 track recorder. You can see that the recorder's eight outputs "steal" eight input channels, leaving you with only 24 input channels. The second "problem" is with the eight busses, two of them have to be output busses for monitoring, thus leaving you with six busses to feed the recorder. If you have two eight track recorders, the problem gets worse. Wait, yes, I know that most mixers also have direct outs (often used to feed recorders) as well as a stereo buss. But, wouldn't it be nice to be able to use the direct out for something else, rather than using it to feed your tape recorder? Plus what happens if you want to record input channel 1 to track 14. A patch bay will solve this problem, but so will what Neve, SSL, Amek and Trident (to name a few) did in their professional consoles - they designed in a real "flip" switch. Essentially what they do is design their input channels to be two circuits. One circuit is fed the usual mic, synth, guitar stuff, and has pan, fader, EQ, compressor (etc), and the other circuit is really a minimalistic thing - fader and pan - which feeds different busses. This way, while you're multi-tracking, you feed the tape returns to the simple circuit, adjusting fader and pan, while simultaniously recording on that input channel through the more complicated circuit, and not mixing your tape returns with the new material. Multi-tracking 101! The "flip" switch reverse the two inputs, meaning that the tape return is now fed into the complicated circuit (with compressor, EQ and so forth), and the mic/line input goes into the simple, fader/pan only circuit. There are instances where you'd want to do that, and when your console can't do it all you do is lose more input channels and spend time at the patch bay. Aggrevating. Some manufacturers (Fostex in particular - the old 450 series for example), had a cheesy version of this, where a switch selected between mic/line and tape return, to feed into the only input circuit. You'll see how this turns out and why later on. This is not a feature that is necessary by any means, but it's huge for me.
- Input Channel Compressors - Pet Peave #2
In the "old days", mixing consoles had built-in compressors in theiir input channels. Nowadays, you have to buy external outboards and attach them to your "insert" jacks. This works okay I guess for most people, however if recording a large drumkit for example, micing each drum individually, you may 12 mics and need 5-6 compressors to get the mix right. Maybe compressing the whole thing is okay with some people, but I'd much rather avoid that if I can. Might make certain drums sound better, but will "ruin" others, and cymbals, for example. So you'd either have to have a rack full of patchbays and compressors, or have them built into the console. I'm not talking very fancy, digitally controlled compressors, but rather a few parts just to take the edge off and soften, or limit, certain signals as necessary. This was one of the reasons why when I made the step into digital recording, I bought the Tascam TM-D4000 mixing console - it had assignable compressors that could be used on "all" channels (per original brochure). What they don't tell you in the brochure is that there are only eight compressors that you can assign, and only enough horsepower in the machine to run five if you have any other effects going. Six, if compression is all you are doing (no EQ). So that to me defeats the purpose. Anyway, the design here will have an individual compressor (albiet simple) for each channel. If you don't want this feature, you don't have to make it. Simply jumper across.
So now, with my two pet peeves out in the open, lets look at a diagram which somewhat represents what I've designed for. Obviously you can add or subtract to this as you wish. Each box is a "building block", and over time (more like as I have time!), we'll put the design for each "block".
Now some of my above paragraphs might make more sense. You can see there are two circuits per input channel, one for the mic/synth/whatever, and one for the tape return for the recording/multi-tracking phase. Flip switch, then the tape return goes through the main circuit and whatever is on the mic/line jacks go through the simple circuit.
In some "real" mixing consoles, the compressor "block" and the "EQ" block are reversed. This is preference. I prefer it this way, because I can then tweak the EQ to eliminate as much "huffing" from the compressor should that ever be a problem.
In the upper right I've identified some busses. These are left up to you, as to the quantity of each that you want to spend money on parts, time in soldering, and surface area in knob/switch placement. Obviously the more "stuff" you add, the more flexibility you have, but at the same time if you don't need 48 busses, why waste the time and money. Same for aux busses and so on.
Main busses are fairly obvious, and often used for two purposes. During recording, they are used to feed inputs on the recorders, and for mixing, they are used for surround sound. If you have six busses, you can mix 5.1, if you have eight busses, you can do 7.1. Generally most studios can get away with eight busses, though I've been involved in projects where 12 or 16 busses were absolutely ideal, but that isn't the common place.
Aux busses generally are used as "Aux Sends", for feeding outboards (delays, reverb, etc). On consoles that don't have more than one stereo buss for the console room, you can also use say, "Aux 6" as foldback, providing a seperate "mix" for the vocalist, musician, or whomever, seperate from the console room mix. This is useful when your vocalist needs to hear his, or her voice significantly louder than the actual music, or they wander off in pitch like a shrieking cat.
Pre Fade Listen means that you hear the signal of the selected channel alone, picked off from a point before the fader, so that the fader level has no influence on the PFL level. On some consoles, the PFL signal is routed equally to left and right speakers, on others the position of the pan control is retained. PFL is often used for setting the gain control: on each channel, one at a time, press the PFL button and set the gain so that the main meter reads a good strong level without going into the red. Solo or AFL: Solo, or After Fade Listen, is as above, but the position of the fader is taken into account. It's common for PFL and Solo busses to be mono, as they are more for troubleshooting than anything else.
Foldback Buss is what I would use to feed musicians (instead of wasting Aux sends). They are similar to the control room mix, except tailored for the musicians. The more of these busses you have (mono or stereo), the more unique simple mixes you can provide for musicians. If you record one musician at a time, you can have one of these (or a pair), or use busses if you want to "spend" them on foldback. If you record four musicians at a time through headsets (i.e., a 4 piece band, or just a rhythm section for example), this might be nice flexibility that not everyone needs.
Not shown in the diagram are some other obvious things we'd need. Like sub-mixing of the main busses to the control room busses, return aux sends to the main busses and possibly the foldback busses, and so on. I left them off the diagram intentionally to make it easier to read. As we build each building block, we'll discuss what goes where and why. And again, if you are building someting like this, you can add things, or hack off things you dislike, don't want, don't need.