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SETTING THE BIAS

In setting the bias of your Cortado MKII, you are simply adjusting the amount of nominal current that 
is passing through the FETs, Q1 and Q2. The more current that passes through the FETs, the more gain 
the circuitry will have on the signal from the piezo disc. But on the other hand, the more gain the circuit 
has, the more the small differences in the matched FETs will be magnified. The result is less common-
mode rejection and thus a higher noise floor. So we are seeking a balance between output volume and 
noise rejection. We found these FETs work well with the bias set in the range of .1mA to .5mA through 
each FET.  

Follow these steps to set the bias on your Cortado MKII:

1.  First, you need to supply power to the Cortado by plugging the XLR jack into a mixing console or 

other phantom power source (such as the Espresso, by Zeppelin Design Labs).

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2.  With phantom power applied to the circuit, use your multimeter to measure the DC voltage 

across TP (test point, marked red on Figure 3) and ground (98.99). Make sure that the solder 
joints on the PCB don’t short against the tin container. A convenient ground point to put your 
meter probe is through the hole in the bottom of the container (100).  

 

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Содержание cortado mkII

Страница 1: ...ZEPPELINDESIGNLABS COM 2950 N WESTERN CHICAGO IL 60618 BALANCED PIEZO CONTACT MIC Assembly Instructions thE CORTADO MKII...

Страница 2: ...AUTHOR ZEPPELIN DESIGN LABS TAKES NO RESPONSIBILITY FOR ANY DAMAGE OR HARM THAT MAY COME TO ANYONE OR ANYTHING THROUGH THEIR PRODUCTS THE CORTADO IS UNDER THE CREATIVE COMMONS SHARE ALIKE LICENSE WHIC...

Страница 3: ...the recording studio or on stage the Cortado can be used on pianos percussion guitars or other stringed instruments It can be used for a variety of mic and sensor applications such as a plate reverb...

Страница 4: ...ing pad 8 Wire strippers 9 Flush cutters or small diagonal cutters 10 Needle nose pliers 11 Clamp or vise to hold the printed circuit board while soldering optional but handy 12 Solder sucker or solde...

Страница 5: ...red directly from us contact support zeppelindesignlabs com For more common parts like resistors caps or screws you may just want to go to a local electronics or hardware store Table 1 The Cortado Bal...

Страница 6: ...6 EN 30 01 PL 10 42 PL 10 90 HD 20 02 PC 41 01 VR1 R3 R4 R5 R8 R1 R2 R6 R7 C1 C2 C3 Q1 Q2 Q3 HD 40 30 TD 10 22 CB 20 18 CB 01 30 CB 01 69 TP 30 11 TP 20 14 HD 08 01 ST 10 23 FA 60 37...

Страница 7: ...nt cover if you don t have a utility work bench Solder fumes are not healthy for you The fumes consist of vaporized flux which can irritate your nose lungs and even your skin You MUST work in a space...

Страница 8: ...ep the component from falling out of its holes 4 Install all of one type of component bending each of the leads as they are installed 5 Flip the board over solder side up and solder all of the compone...

Страница 9: ...with the 150 ohm 150R resistors R3 R6 R7 R8 The body of these resistors are blue and are labeled BROWN GREEN BLACK BLACK BROWN R7 and R8 stand upright on the PCB so bend one lead nearly parallel with...

Страница 10: ...are three film capacitors of two different values in this circuit Both values of capacitors look very similar so please make sure you look closely at their markings and compare them to the photos in t...

Страница 11: ...likely be damaged to the point of not being usable Unfortunately humans are not sensitive to static electricity at such low levels in fact most people can t even feel a static discharge less than 1000...

Страница 12: ...ized meaning it is important which way they fit into the holes The component side of the circuit board shows an outline of the transistor body in the correct orientation a Place the silver painted FET...

Страница 13: ...wire 20 Place one of the ends of the wire in one of the holes in the corner of the board note the picture 21 22 Solder the wire in place 20 21 22 6 Use one of the black M3 screws to screw the standoff...

Страница 14: ...in Can Mic you will only need one piece of mic cable b Strip off about 1 2 13 mm of outer insulation from one cable end When stripping the outer insulation be careful not to cut too deep or you will c...

Страница 15: ...D 40 30 a Unscrew the tailpiece remove the strain relief and push the pins out of the housing 32 b Place the tailpiece and the strain relief onto the 12 30cm cable 33 32 33 3 Solder the wires to the p...

Страница 16: ...lly line up the keys on the insert and relief with the slot in the housing it is opposite the rectangular hole Gently press the pin insert and strain relief into the housing 38 Be very careful not to...

Страница 17: ...Tin Can Mic In this case you attach the piezo to a fine wire with no further shielding Now drop down to the section appropriate to your project STANDARD CONTACT MIC INSTRUMENT PICKUP Follow this sect...

Страница 18: ...sc When we make Cortados in the lab we use Plasti Dip tool handle coating but you can use electrical tape a Wrap the piezo disc in electrical tape 43 44 Keep the tape only one layer thick especially o...

Страница 19: ...o wrap the disc in a similar way as with the electrical tape 48 49 Once again keep the tape only one layer thick on the back of the disc b Trim off some of the excess copper tape around the disc 50 bu...

Страница 20: ...ING CONTAINER If you are building a ZDL Tin Can Mic you should follow our Instructable from here on out Follow this section if you have your own Tin Can Mic design in mind or if you are going to incor...

Страница 21: ...cohol and a rag or paper towel 57 Make sure you don t touch the surface you just cleaned 57 4 Place the double sided tape on the bottom of the piezo disc 58 59 Make sure it covers the entire bottom su...

Страница 22: ...hole on both ends of the metal tin 17 64 7mm up from the bottom 62 63 This is more likely to be successful if you start with a smaller bit and re drill a few times with progressively larger bits 62 6...

Страница 23: ...tiny patch in the corner of the can With your soldering iron tin this area 67 67 b Solder the ground wire to the tinned area 68 69 68 69 3 Attach the cables to the PCB a Pinch together all three wires...

Страница 24: ...ugh the other grommet 73 Solder the red wire to the hole labeled PZ1 Solder the white wire to PZ2 Solder the shield of the cable to ground use a pad from either R2 or R7 in the corner of the PCB Use w...

Страница 25: ...bles on the inside of the tin 78 This acts as a strain relief and protects the solder connections Press the tie snug against the can interior and pull the tail as tight as it will go 78 Trim off the t...

Страница 26: ...ed shielding container like a tin can or garbage pail or steel sculpture it does not require additional shielding 1 Solder the piezo disc wires to the PCB Use a multimeter continuity tester to identif...

Страница 27: ...copper tape instead of the metal can to shield the PCB This will keep the over all size of the Cortado small and easy to tuck inside a sound hole or instrument body Unscrew the standoff from the PCB...

Страница 28: ...5 Very carefully remove the backing from the remaining piece of copper tape Very carefully wrap the copper tape around the circuit board The goal is to encase as much of the circuit board as possible...

Страница 29: ...e instrument with Velcro The disc should be mounted to a flat resonating surface inside the instrument such as the sound board of an acoustic guitar Experiment with placement by using a temporary adhe...

Страница 30: ...output volume and noise rejection We found these FETs work well with the bias set in the range of 1mA to 5mA through each FET Follow these steps to set the bias on your Cortado MKII 1 First you need...

Страница 31: ...his current because that seems to give a good balance of output volume and common mode rejection 101 4 Now you just need to listen to how it sounds Stick the piezo to something and lend an ear If you...

Страница 32: ...to bend at all this will damage the disc The disc is rather fragile and the ceramic element can crack if it is not handled carefully The circuit board is intended to be mounted inside a shielded enclo...

Страница 33: ...experiencing signal degradation will depend on the quality of cable used but in most cases it should easily be over 100 feet The length of the XLR cable could also be extended theoretically even furth...

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Страница 35: ...R1 3 3M R2 3 3M R3 150R 1 R7 150R 1 R6 150R 1 R4 3 3M R5 3 3M R8 150R 1 GND XLR PIN 2 XLR PIN 3 PIEZO IN 1 PIEZO IN 2 C1 2 2nF FILM C2 680pF C3 2 2nF FILM Q1 AND Q2 NEED TO BE CLOSELY MATCHED XLR PIN...

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