Monday, 19 June 2017

New Modular Case

My reasons for this were two-fold:
  1. Usability - It's a little difficult to easily see and handle a surface that is below eye level and vertical.
  2. Modifiability - Because the previous case had rails made of a very soft wood, there was no ability to "fine tune" the position of modules, and once I used a hole once, it would very quickly strip and be useless.
I began with a design in SketchUp. I wanted the classic look of an angled surface with wooden cheeks and an aluminum body.


I looked around and found that the rails most modulars use are T-Struts. Going for fairly ridiculous prices online, I had the idea to search for them on Digikey, and I found what I was looking for!

What makes these rails great is the ability to add a square or hexagonal nut inside, which can then slide freely, allowing me to position modules exactly against each other.
I had to figure out how I'd mount them to the wooden cheeks. Again, some very overpriced options exist, consisting of a metal plate and two screws. So I modified this for my own applications. I used a self-tapping metal screw to go into the central channel of the rail, to pull it against the cheek. This is not optimal, as with a sufficient amount of pulling it could eventually strip the rail, but this won't happen easily. Cutting the wooden cheeks was easy, and then it was onto sanding, staining, and lacquering, which took several days but has a great look now! (Plus stickers)


I still need to add the aluminum body, but that involves bending sheet metal, which I need to practice first.

I'm posting for now, but will be adding a discussion on the power bus.

Thank you!

Thursday, 27 April 2017

It's been 2 years?! (ie. I'm back)

Wow, this is why I should make myself more reminders!

So, a lot has happened since I last posted.

First off, I moved back home, then moved again! You'll see a change of scenery in my pictures from before.

More significantly though, I:
  1. Built a new case, complete with a standard power bus
  2. Built/fixed my VCF
  3. Built a noise generator
  4. Made a MIDI splitter box
  5. Started a few other modules by myself
All of these will be discussed in separate posts, otherwise this one would be far too long.

Monday, 6 July 2015

I'm back with a VCA!

Hey everyone,

Sorry for the long delay between posts, I was thinking of more content to put up besides just photos. Turns out I'm doing alright, so I'm posting again.

First off: the schematic (basically right from MFOS, as usual) and the board (my own design, as usual).


Since this is a "dual" module, I took the opportunity to make the board layout as symmetric as I could.

Here are the board and front panel, mounted up in my case.
 

Not much to say about it, I have an oscilloscope now so I can show you what it does with waveforms, but that will take a bit of set up. Coming soon then?

Thursday, 30 April 2015

Mixer module

Hello everyone,

It's been slow recently as my friend and I touch up on the last boards and BOMs, but I've got some building done. My mixer PCB came in a little while back. It's a 5-channel simple summing amplifier with individual and master volume control.

 

I had to do some work on the potentiometers, as I needed them to be logarithmic (audio taper) but I couldn't find any with solder eyelets. As you can see below, I bent each leg downward, then awkwardly hooked the wire onto it. This is non-ideal but should hold in a mostly vibration-free environment a synthesizer would expect. If this were to play live on a loud stage, I'd consider looking for pots with solder eyelets.

 

I have some testing to do, as well as drilling the front panel this weekend when I get back to a drill press, at which point I will post some photos of the module completed and installed in the case.

Monday, 6 April 2015

Long weekend update: Building the case

Hey everyone,

I spent my long weekend back home with my parents, meaning I had access to all the tools I needed. My dad had borrowed a friend's drill press for me, so I got to making the panels for three VCOs, a mixer, a VCA. Unfortunately only one VCO panel was finished, but this is because the whole weekend was spent building a case with my dad. We got some old floorboards as they were solid and light enough. I won't document this much because it was tight for time and has its imperfections, but I have some photos here to show the results.

Here's a shot of the floorboards. They seem to be pressed wood, topped by a thin metal layer for protection (which made some drilling and cutting a tad more arduous), and then the top layer is just this black plastic/wood stuff. I don't understand floorboard construction, sorry.


The bottom layer is also plastic, so we needed to sand off the edges of it for gluing later. Once we cut and sanded, here's the height of the side panel, with two module panels overlayed for sizing. That gap at the bottom is 1/8", giving each module an extra 1/16" at either the top or bottom. Now to install the mounting rails.



 Here it was nearly done after some staining...

And here it is back at my apartment with the PSU (sloppily) installed, as well as my VCO, which has no jacks yet (they're on the slow boat from China). Please see a doctor if your VCO shows signs of radical hair growth as pictured.


I'm glad I finished the enclosure now, since I have very little working space and just calibrating the VCO while connected to my PSU was unwieldy. I have ordered 3.5mm cables and jacks in bulk, as well as potentiometer knobs, but I would have done so earlier if I were to redo this project. Also having this physically laid out showed me some things I need to address in my front panel designs, so I'll be fixing those now.

Thank you, and have fun!

Sunday, 22 March 2015

VCO post

Hey everyone,

It's time to build my first synthesizer module! A Voltage Controlled Oscillator (VCO for short) is the heart of any synthesizer; it's usually what makes the sound that gets modulated by the rest of the system. I've already done some work on my first VCO but I'm building 2 more, so I'm able to go back a bit in the building process here.

First off, the schematic and board layout are below.


At this point in the building process, everything is "theory". Once I got the boards in and got to solder them up, the actual "practice" introduced some expected discrepancies. Here's the board as it came to me, and the board once I had soldered all the components and wires (minus jacks, I just ordered those yesterday).



As you can see in the second photo, the trimpots were quite a bit larger than the footprint in the default Eagle libraries. I should have double-checked this, but thankfully they all fit in okay.

I used Ray Wilson's instructions to calibrate all the waveforms properly, but had an issue with the very first step. The instructions call for using a trimpot to center the sawtooth wave around ground, but I couldn't get rid of a bit of offset, which in turn messed with the triangle and sine waves. I don't have any pictures of this so you'll have to understand that it worked, but not right.

So, let's debug! The circuitry around that trimpot is pictured here.


When I used my multimeter to measure resistance across my trimpot wiper, turns out I was shorted to the top pin (referenced to the above picture). This means that the 100k resistor was too large, so it was simply a matter of removing the trimpot and replacing the resistor. Unfortunately, I wasn't able to remove all the solder from the trimpot, so I was forced to take another route: lower the resistance by adding something in parallel. Shorting out the resistor would have worked as well, but drawn slightly more current and I figured I had resistors on hand anyway so why not? So here's the fix.


Not pretty, but I connected the resistors together and was able to properly calibrate the whole circuit!

Here is the VCO with all the jacks and pots installed, missing some tuning and a picture overlay.

I currently need to build Ray's tuner so I can properly calibrate the 1V/oct tracking, but that is coming in the future as this is nowhere near musical yet.

Saturday, 21 March 2015

Power Supply post

Hey everyone,

So as my first blog post mentioned, the PSU for my synthesizer has already been built but I would like to capture some information about it here.

A linear power supply is neither a novel design, nor is it complex, so the schematic below will be fairly generic.


This is actually "V2" for me; my current version has smaller pads and no LED spot. Because of this, I may swap out the power supply I currently have for a V2 if I ever order one. I have annotated this schematic for my own use and forgone the use of one of the protection diodes, so I recommend that if you want to build this yourself, look at the application notes for the 7800 and 7900 series voltage regulators so you can understand if you require something I do not have here.

Remember that you require "extras" for this power supply: mains-grade wiring, and mains power cable, and mains plug, a switch, and a fuse for safety. The datasheet for the transformer you use might recommend a fuse, otherwise look at what similar transformer datasheets recommend.

Here is my board laid out and the front panel design, done in Front Panel Designer. The spacing across standoff holes is important for the front panel design.


After buying the aluminum sheet from Metal Supermarkets, I went to work drilling and filing (square holes are a pain; note to self: get a nibbler or dremel cutoff discs) and ended up with this.

It's not perfect, but I definitely like it! The picture is of the Homunculus nebula, a picture I have always seen as powerful. I plan to use a relevant astronomical photo for each of my modules.

Next up, my 3 VCOs!

UPDATE: I ordered my "V2" power supply when I realized the first would not provide enough current for the entire synthesizer. Main differences are larger caps, replacement of components on the board for better heatsinking capabilities, and a larger transformer. I've also mounted the board with all components except the LEDs facing away from the aluminum panel. I plan to do this for all my modules, since it allows easier access to trimpots, defective components, etc.