My Mini Moog Voyager. Click to go to my web site...

Tuesday, February 15, 2011

VCO High Frequency Tracking modification

Hi everyone.

Well, I thought I was done, but when I finally got to playing with the few modules I actually have racked, I found out first hand that the original Steiner VCO was not immune to the dreaded high frequency tracking problem in exponential converters. I approached Nyle to see if he had any ideas and he had actually explored this problem, and had added a correction circuit to the Microcon. He drew a couple of ways to add the correction and I undertook to investigate. I ended up using the one which was the most direct to implement and did not require cutting PCB tracks. I also have built a very small PCB which can be added as a modification to the VCO if the HF tracking error bothers you.

I'm not going to re-issue the VCO PCB with this correction modification on the PCB. The original did not have it, so mine won't either. This is an easy modification and only requires you to solder three wires to the main VCO PCB. The best thing is it works. I get excellent tracking from 50 to 3200 Hz.

I should also note, using a Polystyrene capacitor for the VCO timing capacitor, and good metal film resistors with a low temperature coefficient makes this a very stable VCO. I left mine on in an open rack for a couple of days and had a drift of under 1 %.

I also updated the calibration section of the VCO page, in particular the Sine shaping section. I'm planning a video for the YOuTube channel going through the calibration procedure, so stay tuned.

Anyway, see the web site on the VCO and in particular the HF tracking page.

If you bought a VCO PCB from me and I haven't written you, please PM or email me. I'll send you a PCB when I get them. Probably two weeks.


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