MFOS 16-step sequencer rate is too fast

vitamineli · Joined: Jul 26, 2014 Posts: 4 Location: West Hurley, NY

Hi everybody, hoping I can find the help I need in this forum.

I assembled the MFOS 16-step sequencer, and it's mostly working, and I'm already getting great sounds out of my synths connected to it. However, it does have a few kinks that I'm trying to iron out.

Most of them have to do with the gates, and seem to be covered by this post (http://electro-music.com/forum/post-401288.html), even though that is for the 10-step sequencer. In short, it recommends trying a new, non-TI 40106 chip, which I have on order from Jameco. If that doesn't work, I'll repost with more specifics.

However, there is an issue that I don't foresee a new 40106 chip solving: at the very lowest position, my 1M potentiometer for the sequence rate still has the sequence flying by, somewhere around 16th notes at 130 BPM. At the highest position, it's actually cycling at frequencies well up into the audio spectrum, which is kinda cool, but not super-useful as far as meaningful sequencing goes. So the question is, does anyone know how to slow the sequencer rate down to a more useful range, perhaps by swapping out the rate potentiometer or a resistor somewhere else?

Thanks in advance, I look forward to learning more and more about this stuff on this forum, as I'm relatively new to synth-assembling.

Eli

prgdeltablues · Posted: Mon Jul 28, 2014 4:59 am Post subject:

I'd check whether you've got the correct value for C10 (1uf = 1000nF). The clock rate should simply be determined by C10 and R19 (R18 and R23 also contribute, but really only serve to limit the minimum rate) At 1M and 1uF, you should get in the region of 1 Hz - sounds as if you're at least 1000 times that, which rather suggests the wrong value cap, 1nF perhaps?

Peter

vitamineli · Joined: Jul 26, 2014 Posts: 4 Location: West Hurley, NY

Peter, thanks so much! I had accidentally put a .1uF tantalum cap in there, I have the 1uF on order now and will report if that fixes it, which I imagine it will.

For those paying attention, the new 40106 chip didn't help my gating situation, so I metered the output of my gate jack and saw it was giving negative voltage (which I should have done in the first place). I had wired the 3.5mm jacks backwards, since they were a type I hadn't used before. Oops! At least it was an easy fix to rewire them all. That also explains why my fine and coarse pots were operating backwards, which was going to be my next question! Now all gates and CV pots are working beautifully.

Back to the rate issue, I'm now contemplating putting a switch in to choose between the "proper" 1uF C10 and the "wrong" .1uF one I have in there. Some pretty cool sounds start emanating at the extreme cycle rate which I don't think I want to lose access to...

Thanks again,
Eli