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.
- 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)
- Panavise PCB holder
- Nut driver
- 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.
|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|
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.
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%
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.
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.
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
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!
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
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
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:
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.
Remaining Bottom Headers
The remaining bottom-facing headers are as follows:
- POWER_IN (This used the shrouded 2 x 5 header)
- JP1 (CV OUT)
- JP2 (CV OUT)
The following image shows those headers highlighted:
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!
The top headers face upwards. They are listed below:
- PROGRAM (NOTE!!! This uses an 8-pin receptacle!)
- Audio Out (this is the 1 x 6 header between DAC2_GAIN and DAC1 GAIN
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.
Not all of the headers will be populated when you’re done. I’ve highlighted the empty ones below. They are available for expansion.
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.
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)