nw2s::b Main Board Assembly Guide – Step 2

Overview

The following steps should guide you through the main board assembly process. This is the harder of the two boards to assemble. It makes sense to start with the panel board first to get into the swing of things. If you’ve done that, congrats! Be ready to calm your nerves and steady your hands.

This kit is not intended for beginners. While the circuits are not individually complicated, the volume of work is significant and requires concentration and attention to detail throughout the process. With other kits, if you accidentally swap a 1k resistor for a 10k, you just have to undo them and move on. With this kit, you’ll be 16 or 32 resistors in before you realize you’re in trouble!

I’ve purposely priced the assembled units cheap enough on top of the kit price so that if you doubt your abilities at all, you should consider if it’s worth your time and trouble to use this as a learning experience.

Click here to download the schematics and bill of materials in PDF format.

Tools

Required:

  • Nice soldering setup and the skills to use it!
  • Lead-free solder – make the switch – for the kids!
  • Quality multi-meter
  • Lead bender
  • Small flat screwdriver for tuning
  • Diagonal cutters
  • CV generator (ideally something bipolar)
  • 2.5mm hex driver
  • 5/16″ socket driver
  • Cynaoacrylate glue (super glue, aka kragle)

Recommended:

  • Panavise PCB holder
  • Nut driver
  • Oscilloscope
  • Small square file

Note that some of the pads may be closer than you are used to dealing with. USE ONLY AS MUCH SOLDER AS NECESSARY! As long as you get good flow, a little less solder than optimal is better than a lot more solder than optimal. Go easy with it. Use a very small gauge solder and a relatively fine tipped soldering iron.

Pay close attention to which side of the board the different components go on. Specifically some of the board-to-wire connectors go on one side, and some go on the other.

Bill of Materials

First, read through the instructions. Every time I mess up, it’s because I didn’t read the instructions first.

Second, gather your materials. The following table is the bill of materials for the panel portion of the build.

PART QTY DESCRIPTION IDENTIFIER
1 main pcb P55889
RIN1A – RIN12A 12 100kΩ 1% 250mW resistor Multicomp brown black black orange brown (blue body)
RIN1B – RIN12B 12 33kΩ 1% 400mW resistor Welwyn orange orange black red brown (small green body)
RO1 – RO16 16 220Ω 1% 400mW resistor Vishay red red black black brown (light blue body)
RN1, RN4 2 4.7kΩ 5% 250mW resistor Multicomp yellow purple red gold (tan body)
RN2 1 1.5MΩ 5% 250mW resistor Multicomp brown green green gold (tan body)
RN3, RN6, RN7 3 10kΩ 1% 250mW resistor Multicomp brown black black red brown (blue body)
RN5, RA1, RA2 3 2kΩ 1% 400mW resistor Vishay red black black brown brown (light blue body)
D1 1 3.3V zener 1N 52 26B
RA3, RA4 2 220Ω 1% 400mW resistor Vishay red red black black brown (light blue body)
DAC1 – DAC8 8 8 pin DIP socket
74541, LVC0, LVC1 3 20 pin DIP socket
TL074_0 – TL074_4 5 14 pin DIP socket
BUFFER1 – BUFFER3 3 14 pin DIP socket
74HC4515 1 24 pin DIP socket
CP1 – CP18 18 0.1µF ceramic capacitor tan body, IIC 104
CD1 – CD3, CD13 4 47µF electrolytic capacitor black body
Q0 – Q2 3 2N3904 transistor 2N3904-D30
CO1 – CO16, CN1, CA5, CA6 19 0.1µF poly capacitor blue square body, 1124 370
DAC1_GAIN, DAC2_GAIN, NOISE_GAIN, TUNE_RNG 4 25kΩ trimmer X253
CN2, CA1, CA2 3 4.7µF tantalum capacitor tan body, 4µ7
C2, C3 2 10µF electrolytic capacitor black body
OUTPUT_BIAS, BIAS 2 100kΩ trimmer H 104
TUNE0 – TUNE15 16 25kΩ trimmer X253
POWER_IN 1 shrouded 10 pin header (2 x 5)
POWER_OUT 1 10 pin header (2 x 5)
AUDIO 1 6 pin header
JP1 1 6 pin header
JP2 1 10 pin header
GATE 1 16 pin header
DIGITAL_IN 1 8 pin header
SDCARD 1 6 pin header
TWI 1 4 pin header
DUE 1 36 pin header (2 x 18)
DUE 5 8 pin headers
DUE 1 6 pin receptacle (2 x 3)
DUE 1 10 pin header
ANALOG_IN 1 12 pin header
BEATCLOCK 1 16 pin header
PROGRAM 1 8 pin receptacle
C1 1 1µF electrolytic capacitor black body
DUE 1 Arduino microprocessor assembly
DAC1 – DAC8 8 2 channel SPI DAC MCP4822
74541 1 digital input buffer 74HC541N
LVC0, LVC1 2 digital output driver
TL074_0 – TL074_4 5 analog output driver and filter TL074BCN
BUFFER1 – BUFFER3 3 analog input buffer TL074BCN
74HC4515 1 4-to-16 decoder CD74HC4514EN

Assembly

Analog In Resistors

The analog inputs have two resistors per channel. The A resistor is a 100kΩ resistor and the B is a 33kΩ. The A’s are RIN1A – RIN12A.

a001 - RIN

Noise/DAC

The noise and DAC circuit resistors are next. These are a little tougher only because they aren’t all the same, so you’ll need to pay a little more attention. Note that some of the resistors marked as 5% are sourced as 1%, that is not a problem.

  • RN1: 4.7kΩ 5%
  • RN2: 1.5MΩ 5%
  • RN3: 10kΩ 1%
  • RN4: 4.7kΩ 5%
  • RN5: 2kΩ 1%
  • RN6: 10kΩ 1%
  • RN7: 10kΩ 1%
  • RA1: 2kΩ 1%
  • RA2: 2kΩ 1%
  • RA3: 510Ω 1%
  • RA4: 510Ω 1%

a002 - noise1

CV Out

The CV outputs have a 3dB low-pass filter on the outputs for stability and to smooth out any imaging that may take place. The resistors are 220Ω.

a003 - ROUT

IC Sockets


When placing the sockets, note that the notch on the socket should match the notch on the silkscreen. The DAC chip silkscreen contains an asterisk (*) at pin 1 and pin 1 uses a square pad. For those sockets, ensure the notch is on the same side as the asterisk and square pad.

a004 - sockets

Transistors and Power Rail Filters

The power rails are filtered to help keep noise and signals from leaking onto the power bus and to help keep out any signal that may be leaking in. The filter network consists of four 47µF electrolytics and a bunch of 0.1µF ceramic caps strategically placed near the analog chips.

  • CD1, CD2, CD3, CD13: 47 µF electrolytic
  • CP1 – CP18 0.1µF ceramic
  • Q0 – Q2 2N3904 transistor

The transistors are part of the noise circuit and are located near the power filters. Pay attention that they are oriented correctly.


There are 0.1µF ceramics and 0.1µF polys included in the kit. Note that the ceramics are small tan blobs and the polys are blue or gray rectangular boxes. The ceramics are for power and the polys are for signal.

The stripes on electrolytic capacitors go AWAY from the positive marking on the silkscreen

a005 - transistor power cap

Decoupling Caps

Each of the op amps and DACs has its own decoupling cap. These are the 0.1µF ceramic caps. Note that the 4.7µF tantalum caps may look similar, but they are not the same!

a006 - decouple

Signal and Bias Filters

The next set of capacitors are some of the output signal filters as well as a couple of bias filters and a capacitor on the reset circuit.

  • CO1 – CO16 0.1µF poly
  • C1 1µF electrolytic
  • C2, C3 10µF electrolytic

06 signal bias

Audio filters and Trimmers

To finish off the audio and noise circuit, we will add the DC-blocking caps. These are 4.7µF tantalum capacitors. Tantalums are polarized, so it’s important to put them in the correctly. When used in a DC-blocking capacity, the positive lead always goes on the side which has the DC. This is marked on the circuitboard with a series of ‘+’ signs next to where the tantalums are placed.

In addition to the DC-blocking (high-pass filter), the audio outputs have a gentle 3dB low-pass filter whose corner frequency is about 10kHz. These use a 0.1µF poly cap.

Finally, there are four trimmers. The TUNE_RNG trimmer adjusts the gain of the noise circuit going into one of the arduino digital pins. NOISE_GAIN adjusts the gain of the noise output. DAC1_GAIN and DAC2_GAIN both adjust the output gain of the audio circuits.

  • CN2, CA1, CA2 4.7µF tantalum capacitor
  • CN1, CA5, CA6 0.1µF poly capacitor
  • DAC1_GAIN, DAC2_GAIN, NOISE_GAIN, TUNE_RNG 25k 25-turn trimmer

a007 - more caps trimmers

Arduino Headers

The Arduino headers are fairly simple to put on, but there’s a bunch of them. The best way to accomplish this is to put all of the headers in the Arduino sockets and the one receptacle onto the arduino headers.

There is one set of 2 x 18 headers which is include in the in headers. There are 5 1 x 8 headers, and one 1 x 10 header. The last arduino header is a 2 x 6 receptacle that goes on the SPI headers.

There will be one 1 x 4 header that needs to remain empty. That will not be used.

Place the Arduino with the headers on the bottom of the PCB. It may take a little fiddling to get all of the pins to line up, but once they are in place, you can use a rubber band to hold it in place. Afterwards, begin soldering. The single-row pins are fairly easy, but the dual row pins are a little close, so be careful, go slow, and make sure your soldering iron is clean as you progress.

This photo highlights the headers that will be occupied by the Arduino:

arduino-headers

Once you complete the headers, you will need to carefully remove the Arduino so that we can continue placing components. I do this by working each of the four corners a bit at a time with needle nose pliers (pushing, in reverse) until the Arduino pops off.

arduino header

Remaining Bottom Headers

The remaining bottom-facing headers are as follows:

  • BEATCLOCK
  • ANALOG_IN
  • POWER_OUT
  • POWER_IN (This used the shrouded 2 x 5 header)
  • TWI
  • SDCARD
  • JP1 (CV OUT)
  • JP2 (CV OUT)

bottom-pins

The following image shows those headers highlighted:

bottomheaders


The shrouded header is notched so that your power connector will always face the correct direction. The notch should face AWAY from the electrolytic capacitors. It should face towards the op amps directly ‘below’ it.

NOT ALL EURO MANUFACTURERS ORIENT THEIR RIBBON CONNECTORS CORRECTLY! Learn which way they should go!

power connector1

power cable1

Top Headers

The top headers face upwards. They are listed below:

  • PROGRAM (NOTE!!! This uses an 8-pin receptacle!)
  • DIGITAL_IN
  • Audio Out (this is the 1 x 6 header between DAC2_GAIN and DAC1 GAIN
  • GATE

Program

program 2b

Digital In

digital in1

Digital Out

digital out1


Don’t forget that the PROGRAM header uses an 8-pin receptacle header (female) rather than a pin header (male)! In the next set of steps, you will assemble the bluetooth board using pin headers that will slot into the receptacle.

topheaders

Unpopulated Headers


Not all of the headers will be populated when you’re done. I’ve highlighted the empty ones below. They are available for expansion.

unpopulated

CV Trimmers

There is one input offset trimmer and 16 gain trimmers. With this configuration, you can bias your op amps to run at any voltage from 0V-5V to -10V to +10V. Step three will explain how to set this up. For now, we just need to get them in place.

The input offset trimmers are both 100kΩ trimmers while the gain trimmers are 25kΩ.

bottom-pins

Assemble, Test, and Tune

The next step is to assemble, test and tune. Almost there! (Or that’s what I tell myself every time I get to this point in the build)

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