Friday, November 21, 2008

x0xb0x SS#01: Day 2. VCO

Since the PSU went relatively quickly, I went ahead and started on the VCO as well. Overall this was a much bigger task. While I'm not entirely new to electronics, I also don't have expert ... or even real intermediate skills doing this. A good chunk of my time in this phase involved troubleshooting, trying to get my homemade probe to work with the software scope (unsuccessfully), and trying to follow the steps and instructions really carefully. Total time spent was about 10 hours, four of which involved the above. I also socketed all the ICs and 'rare parts' and made my own cabling as per subatomic's x0xl0g. That also added to my overall time.

Because the scope never did fully work, I had to go the headphone route to test the VCOs. Again - a bit more time was spent on that. Thankfully I got to hear a saw wave before calling it quits for the night. I was quite thankful for that :) I slept better for sure! One unfortunate aspect in this is that the 2SA733Ps I have are all really low hFE. The highest ones I have are 225 so q8 has one of them in there now. I'll certainly be replacing these. It'll be interesting to hear what such low hFE will sound like though. So just as a note:

  • q8: 225 hFE
  • q27: 198 hFE

Day 2 was spent troubleshooting some more and filling out the rest (i.e. majority) of the VCO section. I continued to use the headphones as my 'scope' but I don't entirely trust the results. It really would be nice to see it on the scope just to be sure it's working as it should and that the frequencies are set just so. My multimeter and variable PSU have been quite good but I will need to get the scope up and running to really get the results I want.

One thing that baffled me was that the instructions for the VCO section are also not entirely complete. I had to double check the last round of resistors, caps, and ICs that would have to be added. I learned that I've been relying too heavily on the images at the site. I was a good exercise to have to track things down on my own and place the components correctly. These first two section taught me to have a clearer strategy before embarking on upcoming sections. I can see where I can be more efficient in this process.

All in all it was really nice to hear both the square and saw running. They're tuned quite well so far. Once the scope is up and running I can fine tune them some more.

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