by Janne Isotalo - published 2021-05-02
An article about the key steps of building the PROGUE synthesizer
Progue is a semi-large-scale DIY project, consisting of over 500 components, mostly SMDs. There are two available starting points for the builder: the "PCB-only" and the "PCB-A" (pre-soldered SMDs). It is fair to rank the "PCB only" version as an advanced-level project, while the relatively easy-to-complete "PCB-A" (pre-soldered SMDs) version is for those who want to skip the SMD soldering. The right choice for you can depend on factors like your comfortability with working with small-sized SMDs, the access to the tools required, or maybe simply the available free time at hand. Therefore, I advise scrolling through this article before purchasing.
This article has tips for a successful build, but it is not intended to be a complete step-by-step "Build Guide". The first part of this article is SMD-related, the latter has to do with the PCB-A starting point.
Most of the SMD components are SOIC and 0603 or bigger, but there are 9 even smaller components which we will address first.
Due to their minimal size, it is highly recommended to use magnification ie. USB microscope camera. With SMDs, a professional-level optical stereo microscope can be your new best friend. And flux... always apply lots of flux!
The trickiest ICs to solder with the soldering iron are the two LDO regulators due to their mandatory powerpad under the IC case. This powerpad also functions as a ground connection and needs to be soldered under the IC. Using hot air for these components is the recommended approach. If you don't have a hot air rework station available, you can apply heat with the soldering iron via the pad on the opposite side, which is connected with four via's to the top side. After both thermal pad and IC pins are soldered, you will need a hot air rework station to unsolder the IC, so take your time with this and do it right.
The LDO regulators hand-soldering steps:
The MCU needs to be oriented correctly and placed precisely. At first, solder one corner pin only and adjust the component until it is as centered as possible. Then solder one pin on the opposite side and if all looks good, continue to solder the rest.
There are several tutorials on various techniques for soldering LQFP-48 IC packages on the internet. If you are not familiar with soldering techniques used with these types of packages, it might be a good idea to practice with cheap SMD practicing boards found at eBay/etc.
The same methods applies to soldering the DAC.
One of the most common issues with SMD soldering is an excess amount of solder used. Generally, with SMDs, it is a good idea to use solder wire which diameter is smaller than 0.4mm. It can be surprising how little solder is needed.
The LDO regulators and the DAC are the only ICs on the PCB that is rotated 180 degrees, making the pin-1 bottom-right. All other ICs have pin-1 at the top-left.
The 5 matched transistor pairs come in the TSSOP-6 package. The pin-1 can be hard to see without magnification.
If you are running a tight budget, the solution might be to check out the cheap USB microscope cameras on eBay. While they are nowhere near the quality and the ease of use of the professional level stereo optical microscopes, they still can provide a good enough video feed to your tablet/computer. Most of the cheap USB microscopes have lousy stands, so you can get more out of them by developing a custom DIY stand for them.
Follow the BOM and RefDes PDFs for all the other SMDs and make sure to finish them properly before advancing to the through-hole components. Mind the orientation with SMD LEDs and diodes. Make sure that all the SMD trimmers are centered nicely for them to match the panel holes. Once the through-hole components have been soldered, it can be hard to access the SMDs between the switches and the potentiometers. Also, some of the THT components (e.g. MHS233K switches) don't withstand high temperatures, so be careful with hot air if you need to do SMD rework afterward. Don't forget the bottom side 100nF bypass capacitors!
Once all the SMDs are soldered, your board should look like the PCB-A version.
With DIY builds in general, it is a good idea to do a continuity test between different power rails and ground on a regular basis. For example, a short between positive power rail and ground will most probably cause malfunction or even permanently damage the build. Getting accustomed to this will help diminish the time spent on troubleshooting.
Progue has many test points and numerous ground pads. Put your multimeter on continuity mode and make sure that you don't have continuity between TP11, TP12, TP13, TP14, TP15, and GND. After the power supply unit section has been built, you can also use these points to measure the power rail voltages.
Progues exponential converter uses two temperature coefficient SMD resistors ("tempco"). For good 1V per octave tracking, it is important to have them in thermal contact with the 3046 transistor array DIP-14.
First, make sure that both SMD resistors are properly soldered by measuring the resistance with your multimeter between U3 pin-2 and U3 pin-9 (or any other GND pad) and U3 pin-4 and U3 pin-9. For both measurements, your multimeter should read ~100ohms. Do NOT skip this!
The 3046 transistor array IC (DIP-14) needs to be mounted directly on top of those SMD resistors. This means that you cannot use an IC socket for it. Apply a thermal compound between the SMD resistors and the 3046 IC for sufficient thermal conductivity.
Solder the 3046 DIP minding the orientation and make sure it sits tightly on top of the SMD resistors.
It is very inconvenient to desolder DIP-14 IC, so in case of having tracking issues with the oscillator tuning, you don't want to question if the SMD resistors (tempco) under this IC were properly soldered. You did measure them, right? Good!
Bend both TO-220 regulators at a 90-degree angle and solder them accordingly. It's possible but not necessary to tighten them with a screw to the PCB.
Place all the through-hole capacitors to the bottom side. Electrolytic capacitors are polarized, meaning that their orientation must be correct. Polyester capacitors are non-polarized, their orientation doesn't matter.
Place and solder the DC-DC converter.
Place the male IDC 2x17 connector and make sure it's oriented correctly. Solder one pin and check that it's flat on the PCB. Solder the rest of the pins.
Place the Electricdruids "Noise1B" IC minding the orientation. For this IC it is ok to use an IC socket, your choice!
Place the DIP switch and make sure that it's flat on the PCB and facing out. Solder one pin, check, solder the rest of the pins.
At this point, it is possible to power up the main PCB without the Connector PCB by applying +12VDC and Ground to the Bridge rectifier (D17) pins marked with ~. Polarity doesn't matter.
Or, you can move on to finishing the connector PCB and use it to test the main PCB.
Place and solder all the resistors, capacitor and the fuse. You can use a socket for the fuse for easier replacement procedures.
Place all six 1/4" / 6,35mm jacks and two DINs, solder one pin, check, solder the rest of the pins. Repeat the same for the DC jack and power switch. Mind the orientation of the IDC connector.
If you have purchased the Progue custom enclosure, it's a good idea to mount the board while jacks are still unsoldered, tighten the screws for the jacks and then solder them. This helps to diminish the mechanical stress on the components. This is even more important for the front panel potentiometers.
Connect the ribbon and power up. If all is good, the power rail SMD LEDs will light up. Now is a good idea to verify the power rail voltages:
The reason for verifying the voltages before soldering all the tall potentiometers and switches is the easier access to the SMD components if you need to troubleshoot.
Next, unplug the ribbon cable from main PCB. Place all the front panel switches and make sure that they are seated flat on the PCB. Don't solder them yet.
Alpha 9mm potentiometers usually have one small anti-rotation tag. This must be clipped off with pliers before placing the potentiometer to the PCB.
After placing all the 24 potentiometers according to the BOM, place the two through-hole LEDs, minding the orientation. Do NOT solder any of the switches, potentiometers, or LEDs yet. Instead, place the panel PCB and tighten all the potentiometer screws. If you have purchased the metal enclosure, use that instead of the panel PCB.
Check that all the switches and potentiometers are still aligned correctly and then solder them all. This is a highly recommended procedure since it will diminish the mechanical stress to the PCB.
Make sure that the through-hole LEDs are mounted to their holes before soldering them. These LEDs are not mandatory, but as a user, it is nice to see when the unit is powered and when midi information has been received.
Connect the boards with the ribbon cable, power on, and use the line out or the headphones to test the unit. The easiest way to get sound out of Progue is to use the Gate mode at the "AUTO" -setting. Make sure to open OSC VOL, filter CUTOFF, vca env SUSTAIN, and MASTER VOL potentiometers.
If your board didn't have pre-installed firmware, you can solder pin headers for J16 and J14 and follow the firmware upload procedures. It is possible to control Progue with the CV/GATE jacks even without the firmware.
Then the unit needs to be calibrated, so follow the calibration procedure.