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THE 

SAW-TO-TRI 

Of course we’ll need a suitable signal to fold –

 

which, traditionally, has been either a sine 

or a triangle wave. And since the mki x es.edu VCO provides neither of those, we needed 
to do some extra work here. So I designed this super e

ffi

cient little sawtooth-to-triangle 

converter that uses the same basic working principle as the main wavefolding circuit. 

 

3

Содержание EDU DIY Wavefolder

Страница 1: ...tes which will direct you to an instance that already has example circuits set up for you We strongly encourage you to fi ddle with the component values and general structure of those circuits to get...

Страница 2: ...it s a great addition to the otherwise very east coast mki x es edu DIY system Why Because it can provide a ton of unusual timbres for your patches from a slight dash of brightness to harsh metallic...

Страница 3: ...been either a sine or a triangle wave And since the mki x es edu VCO provides neither of those we needed to do some extra work here So I designed this super e ffi cient little sawtooth to triangle co...

Страница 4: ...should check for with a multimeter are 220k x1 100k x3 51k x1 22k x1 20k x4 10k x4 1k x5 10 x2 A bunch of capacitors The speci fi c values which are printed onto their bodies are 47 F electrolytic x2...

Страница 5: ...s body is 10k B103 x1 A trimmer potentiometer The speci fi c value which is encoded printed on top is 10k W103 x1 A few jack sockets The speci fi c models which you can identify by their color are Swi...

Страница 6: ...V battery clips which are 3 cheap widely available in every electronics shop By connecting the batteries like this the row on the left side labeled becomes your positive rail the row on the right side...

Страница 7: ...above the folding threshold is folded inward so that the tip of the original triangle now points down In practice this would create a bunch of additional overtones that give the resulting output an al...

Страница 8: ...call this a wavefolder Because it is if you abuse it To understand why and how let s dissect this circuit step by step Functionally we can split it into two sections the resistor up top and the trans...

Страница 9: ...That resistor serves the exact opposite purpose convert current into voltage It works like this the more current we pull through the resistor the more the voltage below it will drop If we put this to...

Страница 10: ...ecause as we said earlier the transistor eats up a bit of current while active But second and more importantly this mechanism only works as long as the transistor can pull enough current into its coll...

Страница 11: ...of it like this If we d remove the transistor from our circuit we d see 600 A fl ow through both resistors And we can t increase that current without bumping the voltage or reducing the resistance So...

Страница 12: ...oltage at the collector with an oscilloscope you should see some folding happening 8 To make the e ff ect easier to understand I recommend you route the input through a mixer before sending it into th...

Страница 13: ...g threshold This would give us a symmetrical clean triangle at the output Unfortunately there isn t enough space on the module s PCB to pull this o ff since it would require us to add another op amp I...

Страница 14: ...onably make So next let s think about the resistance value we re going to add at the transistor s collector You might be tempted to just try a few di ff erent values here until you ve found the correc...

Страница 15: ...ve set this up send a sawtooth wave into the jack socket while monitoring the collector voltage on your oscilloscope Next play with the trimmer until the gap between the rising and falling slopes disa...

Страница 16: ...the lead of our VCO and use AC coupling again So after the low pass fi lter we ll set up a 1 F capacitor followed by a 100k resistor to ground Then we want to bu ff er boost the signal to avoid loadin...

Страница 17: ...For the op amp we ll be using a TL074 IC which is four op amps in a single chip Make sure that you set it up exactly as shown here if you reverse the power connections it will heat up and die To check...

Страница 18: ...he top of the output waveform As you can see the only real di ff erence here is in the type of transistor we re using I ve simply replaced the NPN with a PNP transistor And since the PNP transistor is...

Страница 19: ...the volume of the input we ll also set up a simple temporary attenuator using the 10k potentiometer from your kit Once you ve set this up try fi ddling with the potentiometer You should see the shape...

Страница 20: ...a current de fi cit at the collectors This forces us to pull more current from the positive rail through the 20k resistor which in turn will cause the voltage at the collectors to drop At least until...

Страница 21: ...output socket to the transistors collectors since that would mess with the core mechanism by pulling more current through it Okay so we ll simply route the voltage through a non inverting op amp bu f...

Страница 22: ...l node sits at 0 V At least until we start drawing current from it Then the voltage will drop by 100 mV for every additional 10 A we pull through the top resistor Interestingly we can get exactly the...

Страница 23: ...ually being one So connecting the collectors to the op amp s inverting input through a 10k is functionally the same as connecting them straight to ground here 17 With this change you can fi nally list...

Страница 24: ...he thresholds while the maximum should be just shy of crossing them a second time Ideally we would use a fi xed 100k input resistance followed by a 10k potentiometer and a 4k7 baseline resistance to g...

Страница 25: ...t it needs to So we ll simply replace the 100k input resistor with a 51k and the 4k7 baseline resistor with a 2k This roughly doubles the attenuator s range while keeping the minimum volume the same a...

Страница 26: ...attenuator s range Because otherwise the second stage will fold the signal even at minimum intensity To avoid that we ll halve the baseline resistance in the attenuator That way at minimum intensity t...

Страница 27: ...d get additional spikes in the output that make it sound even more harsh and metallic And with this our wavefolder is done Once you re done experimenting dig out the panel and PCB from the kit heat up...

Страница 28: ...e less abstract we can use a common beginner s metaphor and compare the fl ow of electrons to the fl ow of water through a pipe In that metaphor resistance would be the width of a pipe The wider it is...

Страница 29: ...use 9 V battery clips which are cheap widely available in every electronics shop By connecting the batteries like this the positive terminal of the left battery becomes your 9 V while the negative te...

Страница 30: ...that its value is not printed on the outside like it is with other components Instead it is indicated by colored stripes along with 24 the resistor s tolerance rating In addition to that the resistor...

Страница 31: ...with a maximum operating voltage Be extra careful here That voltage rating is important Your capacitors can actually explode if you exceed it So they should be able to withstand the maximum voltage us...

Страница 32: ...al usage scenarios but usually a generic 1N4148 small signal diode will get the job done SCHMITT TRIGGER INVERTERS You can think of a Schmitt trigger inverter as two separate things On the left there...

Страница 33: ...e right hand pipe First think about what would happen if R2 was completely sealed o ff Our sensor would tell us that the pressure on the right side is exactly the same as the pressure on the left Beca...

Страница 34: ...the total resistance between each track connector and the wiper From here you can move it in either direction and thereby shift the ratio between the two resistances to be whatever you want it to be...

Страница 35: ...have it the excess water can drain out of the system Until the pressure is neutralized and no water is actively fl owing anymore Okay so now imagine that the voltage on the left hand side starts osci...

Страница 36: ...reading 8 V from somewhere The other sensor called the inverting input reads 5 V Then as a fi rst step the op amp will subtract the inverting input s value from the non inverting input s value Leaving...

Страница 37: ...lly this doesn t matter much because the gain is so large As the voltage at the inverting input gets closer to 5 V though the di ff erence will shrink so much that in relation the gain suddenly isn t...

Страница 38: ...gh both resistors and into the output Now as long as the pushing voltage on the left is stronger than the pulling voltage on the right some potential e g a non zero voltage will remain at the invertin...

Страница 39: ...ween collector and emitter by applying a small voltage to the base The 29 relation is simple more base voltage equals more collector current Drop it down to 0 V and the transistor will be completely c...

Страница 40: ...r s temperature The more it heats up the more current will fl ow Now for the PNP transistor all of the above applies too except for two little details Unlike with the NPN the PNP transistor decreases...

Страница 41: ...ally straightforward Simply attach two probes to your device the one with a black cable traditionally plugs into the middle while the red one goes into the right connector Next fi nd whatever you want...

Страница 42: ...nd a smaller one which is usually a standard alligator clip The latter needs to be connected to your circuit s ground rail while you probe your oscillation with the former Now what the oscilloscope wi...

Страница 43: ...BUILD GUIDE 43...

Страница 44: ...sses through The same goes for VD2 which is connected to 12 V Because schottky diodes have a low forward voltage drop they are the most efficient choice for applications like this Next we have two 10...

Страница 45: ...xt to each IC Like the others their job is to simply compensate for any unwanted noise in the supply rails If the input voltage drops then these capacitors will be able to bridge the gap to keep the v...

Страница 46: ...46...

Страница 47: ...dering we highly recommend printing out the following part placement diagrams with designators and values Because some of our PCBs are rather densely populated this will help you to avoid mistakes in...

Страница 48: ...he PCB indicates the cathode of a diode match it with the stripe on the component Flip the PCB over and solder all components Then use pliers to cut off the excess leads Next insert the DIP socket hol...

Страница 49: ...esistor s value use a multimeter to double check Bend a resistor s legs so that its body is aligned with both legs and insert it in its designated spot Then solder the longer lead from the top side of...

Страница 50: ...n insert and solder the transistors Make sure you place correct transistors in relevant places we use both NPN BC548 and PNP BC558 and align them with the marked outline on the silkscreen orientation...

Страница 51: ...and solder them Then insert the potentiometer but don t solder it yet Fit the front panel and make sure that the potentiometer shaft is aligned with the holes in the panel and that they re able to rot...

Страница 52: ...good sign that your build was successful Patch the sawtooth signal from the DIY EDU VCO to the SAW TRI input of the module and connect the OUT of the module to a mixer You should hear some sound whic...

Страница 53: ...re areas So you need to make sure you apply equal heat to the component you are soldering and the solder pad on the PCB The pad will typically absorb more heat especially ground connected pads which h...

Страница 54: ...r DIY electronics are flat 2mm wide tips When heated up the tips of soldering irons tend to oxidize As a result solder won t stick to them so you ll need to clean your tip frequently Most soldering st...

Страница 55: ...soldering your PCB it s recommended to remove excess flux from the solder joints A PCB cleaner is the best way to go All of these tools can be found on major electronic components retailer websites l...

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