Hi ! Wanabe mixer-builder from the uk here!

[blend]

Hello , great to find this board!

Been interested in getting into electronics DIY for some time, and ive recently landed a job at an electronic retailer - so im in a great position to get right into it!

My goal is to build a mixing desk from scratch , about 8 mono channels
.. each channel needs to have mic/line preamps , gain control , sweepable EQs , aux sends , foldback sends, mute + solo button, pan & volume faders.

Oh and a master volume section with 3 line outs, a monitor out and foldback outs if possible...

I know this is an extremely ambitious project for a total beginner like myself but i like to start at the deep end!!!!

Ive built a passive mixer before which was easy...was only a bunch of resistors i scavenged from a old 4 track and soldered together following a circuit diagram i found. This will be a very different story!

Anyone know where i can find really detailed documentation (in laymans terms preferabley) on how to achieve this goal??? Be it a book or website or whatever...

I want to actually build the eq section , i think you have to use capacitors and inductors in line with variable resistors.. but im really not sure! Itd be great to know how to fine tune the frequency sweep and Q settings..

Ill probably end up building something far less complex but its good to have high aspirations!

Thanks for reading, and good day to you all!

cheers



tim

[event horizon]

Hi blend/Tim, you won't need inductors as active filters can do the same trick as inductors or capacitors It all depends on the configuration as to what they'll do.

Good luck with your project, i'd suggest seeing as you want things variable to look up "state variable" filters though these aren't the best quality they may be fine if you are going the mono route as you maintained.

Bests, Mark Welcome to the forum.

[wakibaki]

That's quite an ambition.

I understand you want to build something substantial. It's often a difficult problem, to pick something to build that won't defeat you but will challenge you and will also provide something that will be really useful to you.

The project you are interested in involves a lot of buffer amplifiers and filters. Specifying the filters is just the first part of the problem.

I have a little Behringer mixer here, it has 4 stereo channels. It has 27 pots, 14 jack sockets, 2 XLR sockets, a power supply, active electronics, a PCB and case. It cost UKP 55 or UK pounds. I doubt that I could source the parts for that much in any currency, plus it would take me hours to draw up the circuit, lay it out (and make it fit in a box) stuff and solder the boards and assemble the whole thing. And then I might discover an 'undocumented feature', even after simulation.

The large majority of qualified engineers do not really need to understand filter design. It can be a difficult and intensely mathematical subject. Fortunately there are large numbers of prototype designs which can be 'designed' by selecting values from a nomogram or by substituting values in a formula. This can still require considerable expertise and there remains the question of the selection of an appropriate prototype.

In the case of the mixer the EQ section can be expected to have at least high, middle and low boost and cut. Have a look at the wikipedia article Tone control circuit - Wikipedia, the free encyclopedia

Try and get hold of a schematic for an existing mixer and try to identify what parts of the circuit are doing what functions. Obviously there is a lot of repetition from channel to channel. See if you can calculate how to change the rollover points of the filters. Get hold of a circuit simulator and simulate the originals and then verify your changes.

There will be numerous opamp circuits and not many inductors. You can learn to design inverting, non-inverting and differential opamp circuits online.

I would be more inclined to pick something that had 1 or 2 identical elements to build, with an element of luxury, or value-for-money. Speakers or an amplifier. A mixer, you could have a lot of repeated mistakes...

w

[Cal Weldon]

Hello Tim and welcome to the forums.