SDIY Class # 10 - Building a dual Mixer with Otto's DIY

[Music] hi I'm King cos and I'm a synth DIY guy today we're following up on last week's video about op-amps we're gonna actually build a dual mixer module based on the mixer circuit I showed you and for that we'll be using a prototyping kit called Otto's DIY from the wonderful people of in tech studio in Budapest thanks guys in the envelope they sent me came a few op amps two of their larger proto boards the power conditioning PCB some spacers and pots they were out of the jacks so I told them I wouldn't use my own but you surely get jacks with your kit if you order one this brings me back to hardcore DIY before I got into building full kits I have to devise my own routing paths and user interface which is challenging and fun now let's build that mixer this is the schematics right here I redrawn them we have three inputs going into three 10k potentiometers as voltage dividers which will be our level controls for each channel each one goes through a 100k input resistor onto a common node which goes into an inverting unity gain amplifier op amp circuit with 100k feedback resistor that's why it's unity gain because it's the same value for feedback resistor as input resistor and then we have another unity gain inverting amp just to get the output back to the same phase as the input so 100k input 100k feedback 100 divided by 100 times minus 1 is 1 times minus 1 which is minus 1 so you're just changing the sign of the operation and then I'm using a 1 K output resistor here just to protect the op-amp output and to set an output impedance that's somewhat compatible with analog synthesizers and the output so that's it's a very simple circuit it's a good example of what you can do with op amps and it's also a good example of what you can do with the auto slab prototyping system which is really cool if these guys in Hungary they had this idea which comes from just using normal run-of-the-mill proto boards but they have a few modifications that make it really interesting really cool let's remove the knobs from the pots and we're gonna create a layout for a dual mixer yeah this is the other components that we're going to need to make this solve the 100k resistors the 1k resistors there are six knobs because there are three inputs for each one of our two mixers and the reason I'm doing two mixers is because the proto board is a little bit big it would be a waste of space to make a single three input mixer with this big of proto board so I've already started laying it out I'll show you guys what this is later this is a power protection circuit it's really handy the way that gets mounted onto the back of these boards with these standoffs the standoffs also let us use one of the protocols as a panel and the other one as a circuit and you can detach from the circuit one you can detach this part which is what the part that goes mounted onto the panel so that you can have one of these pores dedicated as a circuit board and the other one is a panel first I want to just play around with laying it out this is what I'm thinking we're gonna have the inputs at the bottom of the PCB which is a good idea because it keeps the cables out of the way of the knobs it's a good way to lay out a mixer in my opinion and we'll have the outputs off to one side so that it's clear which ones are the outputs and you don't even necessarily have to label anything which is good because these proto boards aren't super great for labeling you know so here we go these are the inputs and the outputs of our two mixers make it do a mixer which you can use as one stereo mix or two now we need to allocate space for the circuit it's a very simple circuit with just a few resistors and capacitors we don't need to leave too much space for it this is probably enough and then up here is where the potentiometers are gonna go so let's prep the potentiometers the way we do that is this few steps one of them is removed the washer and dryer no I mean the washer and nut from each one of the potentiometers next we will once we've done that with all of them next we'll take a these needle nose pliers and straighten out the mounting lugs so that they go in straight and don't get bent underneath the potentiometer when you stick them into the little holes of the proto board see these are 10k potentiometer which is a good value for your iraq mixers now the other thing that we do to prep these is we take wire cutters and we remove the position tab from each one of these potentiometers they come with a little position tab which in industrial products the panel would have a little hole where this tab gets inserted and it ensures that the potentiometer won't rotate but in DIY we don't do that we just tighten the nut real good and that's enough also the fact that this will be soldered onto the circuit board helps ensure that it doesn't rotate so we don't need these position tabs cut them off in fact not only then we need them there will be a problem if you don't have the little hole on the panel the potentiometers will be sort of diagonal will be sort of crooked in there if you don't cut these off so do cut them off wear our protection goggles I wear glasses so I don't worry too much but if you don't wear glasses wear protection goggles because these things can fly into your eye and also make sure your pets and children are safe before you do this there we go so now all the shiners are prepped let's place them where we think looks like a good position since these are D shaft and my knobs our D shaft so there's only one way that can go that makes sense as far as the knob indicator goes let's put one in sort of just to see and that's basically with the three terminals facing down so that the minimum position is 7 o'clock and maximum position is what's that 5 o'clock right ok so let's start with the three volume controls so I left like two rows on this side so I'll do the same here and this is a grid so it's really easy to line them up you know you just make sure you make everything symmetrical yeah I think I'll probably just move one of these guys off to the side a little bit so they won't actually be symmetrically positioned according to the sides but they will be equidistant to each other so one two three four five six seven eight one two three four five six seven eight so yeah now they're equidistant and let's put the other three which will be the three volumes for the bottom mixer we want these to be far enough from the top ones so that your fingers can go through comfortably so that's a nice ergonomic tweakable module just line them up with the top ones make sure they're in the same row and column so does that look pretty symmetrical I think it does all right so now we need to calculate where we're gonna drill the panel so we need to sort of figure out exactly where the holes are gonna go you need to be very accurate with how you drill these holes otherwise they will not line up properly let's see how I can do that I think what I'll do is I'll actually use this board as the panel I'll remove each pot in mark or the very center of each one of these is and immediately transfer them to this other board and that will be our actual circuit board that seems to be the more accurate way than to just try to line up visually so I'll use a marker just a little pink marker right here probably do it looks like the sinner is bb3 so I'll move this guy to here just make sure that it's in the same position as you had it on the other board and that b3 looks like it's the sinner so okay I set this aside and Mark the b3 hole is where we're gonna drill for the first thing she ometer now this one looks like it's gonna be m3 so m3 for this one and we'll go ahead and place it on here whatever happened to the MCS m3s times then change for the trees that's a little dealer so for ya anyway this one looks like X is the mid also x3 yes the where we want to drill so that's that's the three top potentiometers right there good now this makes it really easy for these guys all we have to see is which line which looks like 13 is the place now we need to mark the jacks I can look inside the hole and see exactly which little square represents the middle that's 34 why there you go now go ahead and put it on here so that I see 34 Y through the little hole and looks like I nailed it so good this is very visual and manual way of prototyping things I didn't need to use any sort of computer-aided design I like to do things like this very visually and manually so good so this is already part of our circuit board with all of the panel components all set and we've already marked our panel where all the holes are going to go now let's go and drill them [Music] [Music] [Music] I've made my horse and I'm lining up the panel with the circuit PCB and everything looks good like my markings are centered in the holes I did hurt myself a little bit do use protection when you're drilling stuff so now we're gonna set up the panel components in their respective spaces and solder them up would be the first thing we're gonna do pull the smell of fresh blood [Music] let's see if our panel lines up with our circuit board and it's like it does perfectly so now let's put on some washers and nuts tighten it all up and the solder from behind the reason we tighten these up before we sawed out of them is just to make sure that everything is fitting nicely because if you solder them and they're a little bit crooked they won't go through the panel holes and then you have a problem so this goes for pretty much any kit not just prototypes but any kit you build you don't want to tighten them too much right now because after soldering them we will remove them let's just sort of this up now right now we don't worry about the circuit too much just securing the components to the circuit board just a tiny bit of solder is all you need try not to use more than necessary so you don't risk making bridges all of the jack spots and let's just do the position lugs for the pots no now we don't want any shorts simply use a multimeter in continuity mode so it actually beeps if there's a connection here beeps here it doesn't hear it doesn't these should beep hot body ground same here so it looks like I didn't make any bridges these two actually do connect because the switch connects to the tip on these jacks if nothing's plugged in so you actually want to hear a beep here but you don't want to hear between this and this cuz that's ground and tip this already feels like a module just like a pretty sturdy construction here now we get to think about making connections and with our schematics I'm gonna put them right in front of me you should draw your own copy and take a look so we need to solder some ground connections so the first ground connections we're gonna solder will be the potentiometer clockwise so when with all the potentiometers to the left we want to measure and see which two legs short each other and that's these two so middle and right then the middle is the wiper so we know that the right leg is the one that has to be placed a little ground we can use a little marker to point out all of our ground connections so we want this to be ground all of these right wants to be ground we want the position lugs to be ground so we ground the pot bodies that helps keep them from picking up interference so this is all ground stuff right here marking on the jacks where you see two pins very close together the outermost pin is the ground one right the little one that goes outside of the of the jack so why not mark those two and these ones are inverted relative to these ones so that's actually this one here this one here this one here this one here this one here and this one here so those are all ground connections so I'm gonna shut up for a while and just solder up all my ground I used some solid core wire for most of the ground connections it's a good idea to keep your multimeter handy to check continuity and make sure all of the grounds are connected together this is also a good time to solder on the IC socket for the op amp as well as the two decoupling capacitors while assembling the power conditioning PCB I screwed up and soldered the power head around backwards so I had to remove it and replace it with a bear connector make sure you install the header correctly this little PCB is not necessary but it's a good idea for prototyping because it protects your system from any mistakes you may have made such as shorts or inverted power connections it mounts onto the rest of the module quite nicely with included spacers [Music] next just start making the connections as you see them in the schematics each person will have their own strategies for doing this and you get better at it with practice I like using the component leads themselves to make connections as much as possible that way I avoid too many wires going everywhere and creating a rat's nest so don't cut off your resist early it's too soon make sure they're not useful for making circuit connections first again use your meter a lot to check that your connections are solid I made an annoying mistake I connected the inputs straight into the circuit forgetting all about the volume pots so I had to remove all those cables and route them correctly through the six pots on top [Music] when you're done just check your power connector for shorts place the panel back on tighten all the nuts place the knobs on the pots and turn it on since this isn't a ready-made kid it's likely that not everything will work right away I had to do about 15 minutes of troubleshooting before mine worked as expected now let's see it do its thing [Music] all right so let's come up with a quick demo batch to make sure this mixer is working as it should so what I'll do is I'll use the top mixer to mix audio so I'll throw in three oscillators let's get the pulse wave from the ether oscillator we'll put a lizard to this old version of the lizard to us in oscillator mode and send that to input two and my even VCO will take this saw wave from that and plug it into input three and we'll take the output into my leapfrog filter and we'll send that out to record so let's take off for resonance there let's open up the filter for now and here we go that's one oscillator another oscillator and another oscillator wow they seem to be in tune [Music] [Music] there you go [Music] so great the audio chuckling sir how is working for audio perfectly now let's send now I send three modulation sources to that filter and see what happens so we'll send that into the exponential FM input of the filter and the first source will be an LFO like that the other one will be a sequencer which and we'll need to send the clock to so let's grab our clock to the sequencer and that's [Music] [Music] all right and the other one can be simple and hold maybe one hold here from the artisan sample and hold so that's this thing right here so that's the sample and hold the sequencer and the other phone let's make it a sine wave or [Music] less see a little bit of that template halt and there we go looks like our mixer is working perfectly [Music] cool that's it have fun stay noisy and see you next week

Channel: Synth Diy Guy

Views: 16,414

Rating: 4.9707494 out of 5

Keywords: Modular Synthesizer, Mixer, Eurorack, Otto's DIY, Intech Studio, Quincas Moreira

Id: 0kC-33YV7oM

Length: 22min 59sec (1379 seconds)

Published: Wed May 16 2018