Friday, January 20, 2012

VC Oscillator complete!

I've now completed one of my two initial VCOs.

As you can see, there's a lot of wiring! I've added the HF compensation board, which gets wired down to three points on the main PCB. It is indicated on the schematic, and some good quality photos that David has on his site. (Of course, ground can go to many places, but I just chose one that was easy.)

The calibration is pretty extensive for this module. First the waveforms need to be calibrated: first the saw, followed by the pulse, triangle, and sine.  Then the 1V/Oct tracking, and then the frequency range.  This is documented on the build pages.  I've done all on this module, but will go over it again just to get things as precise as possible - I just did a quick setup of the tracking, for instance.  One thing to note on the waveform calibration is that if you see truncated waveforms, be sure to check the DC offset for that waveform.

Unfortunately, my second VCO isn't going so well, at least where the sine wave is concerned.  There's two settings of the trimmer where you get a sine wave, and only one is correct.  (The incorrect one has a very high point-to-point voltage!)  I've managed to get to both of them, but haven't managed to get the trimmer settings right.  (Or there's something wrong!)  A bit frustrating staring at a scope and holding the module awkwardly and turning the trimpots.  (I really ought to power this on my bench, rather than out of my Dotcom modular...)

Once I have it working, though, I'll share any further tips... plus oscilloscope shots!  Hopefully I'll have some time this weekend, though all of Sunday I'll be up in Anaheim at NAMM.

In the meantime, I've been working on the power supply & distribution panel, which I'll share shortly.  Additionally, I've ordered PCBs for the Noise, Peak Selector, Ring Modulator, Phase Shifter, Triple EG, and Frequency Dividers.  All the board parts are on-hand, so putting those together should go rather smoothly!

1 comment:

  1. EXCELLENT! Kyle, you are doing a wonderful job with this. Thanks for sharing