this must be the place....goin strong , yeah baby!!!

Saturday, September 25, 2010

x0xb0x Etudes - pt. 2

Power Supply completed last round.
VCO section is what I am working on now, and glory be, I got a sawtooth.

It didn't come without a bit of pain though.

First problem, in my attempts to be overly organised to make the process smoother, I made a mistake and put all the schematic part numbers for a couple of similar looking transistors under the wrong batch. This was not a huge problem once I realised that a set of 10 transistors probably didn't go in 24 different places. Anyway, thought I'd mention it as it could have completely derailed the project.

The second problem was a total new one to me: CONTROL VOLTAGE. How did I miss the part of the prep guide that said I would need a variable power supply to test the thing?!
Anyway, I got my sawtooth generator all put together, and when I went to test, I was getting very strange results. Weird waveforms, a lot of incorrect DC offset, on and on. I figured, incorrectly, that you could test this stage WITHOUT the variable power supply (supplying control voltage) applied. Boy was I wrong.
So, a quick trip to 'The Shack', as they are very obviously trying to rebrand to now, picked up a voltage regulator, and using parts I had lying around I managed to build a working variable power supply running off a 9 volt. It supplies between 1.25 and 7 volts.
Once I got that in place per the fabrication manual, things started to look exactly right. That saw wave is beautiful, and the tuning pot and the PS adjustment all change the frequency of what I see on the scope.
So I learned that you really shouldn't try to skip steps. I thought, CV, who cares? I won't be messing with it anyway. What I failed to realise is that the CV circuit seems to be integral to the proper functioning of the saw tooth generator.
I was hoping to have the entire VCO finished last night, but a lack of adjustable power supply and a wicked case of allergies has left me OVERLY pleased with my little, buzzy waveform.

Next time, the square wave + VCO completion.

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