Saturday, June 18, 2011

Not Quite Quad Slope

Like most modular synthesizer users and builders, I suffer from Serge envy. Thankfully for all of us, Ken Stone licensed some of Serge's designs to sell as CGS PCBs.

Here is my first module using these Serge designs:

Obviously, this module is influenced a bit by this lovely little beast. Once I panel up the Attenuverting Mixers I have, I will pretty much have the same capability. I am looking forward to checking out the other Serge PCBs, but first I have to panel up some of my backlog.

Build breakdown:

The front panel is 42 hp. It was the first panel that I ordered from Front Panel Express. I've since ordered another and have about ten designs in various states of completion that I'm working on in Front Panel Designer. They are a great company to deal with and I find it quite fun. Total cost of the panel with shipping was $105. I will share the FPD file if anyone is interested. If you are thinking of using them and are a first time customer, hit me up for a discount code.

The PCBs are attached to the panel with nylon standoffs that are JB Welded to the panel. I had originally planned on using a homemade bracket to mount them, but my bracket making skills are non-existent. The bracket I tried to make looked like a badger chewed on a license plate. The new panels I am working on all have holes for mounting standoffs directly to the panel. With some tidier wiring I could easily cut the module depth in half. The nice thing about this, is that I will be able to use use my DIY modules in most commercially available cases.

Here you can see the little power filtering daughter board that I modeled after the filtering (electro + ferrite) that Ken usually has on his boards.

When I fired it up for the first time, I noticed almost right away that the negative power rail was not being regulated properly. My surplus power supply now needs repair. Hopefully it wasn't doing this before when I had some of my other modules plugged in. Luckily, I have another power supply that I can try. This one is working fine, but I no longer have a +5V rail, so I have to remove that wiring. I also have to drill new mounting holes for the power supply since it is a different size.

Once the power was sorted, it was time to test the module. Only half of it worked fully right away. Not coincidentally, it was the second board that I stuffed. I was a bit clumsy and out of practice when I stuffed the first one and lifted a few pads, which broke continuity in few different parts of the circuit. While chasing these problems down I fried a 3900 chip. Man, I forgot how BAD the magic smoke smells when you let it out! The working pcb, schematic, and continuity tester helped me track down and repair the damaged traces. There is absolutely nothing wrong with CGS boards, they are just a little more delicate than some other PCBs. Build carefully and methodically and you will experience none of what I went through above. Also, don't blame the semiconductors (or any other parts) right away! They may need replacing in some cases, but make sure everything else is right first.

I had a great time testing the module last night. I did notice that my 256K BBD module doesn't seem to be working right. I'm not sure when that happened, but I guess I know what my next project is. (edit: was/is working fine, brain fart)

Welcome to the fun and exciting world of DIY!

Here's a picture of the project supervisor: