After nine months of patiently sourcing components from around the world and several nights of soldering (and desoldering), I’m happy to say my MB-6582 is more or less finished. It’s my first (working) diy synth, and I’m very satisfied with the results. Big thanks to TK, Wilba, and Smash TV for making this possible. It’s populated with six 8580 R5s and two more are on their way. Things still left to do are:
install the feedback pots and expansion port connector
drill holes for the bottom vents and the 6.5mm audio jack
eventually upgrade the cheap plasticky knobs
install a display window
install low profile heatsinks (can anyone point me to a source for these?)
I also have one small issue - the filter cutoff value seems to jump around a bit when I change it, especially if I make slow adjustments. I’ve kept the detention on all my encoders. Is this behaviour normal?
Thanks Jaytee. Like you, I also had the problem that my LCD backlight wasn’t dimming, but thanks to your thread earlier this year I learnt about the workaround with jumping B+ and B- with an LED. I’m already thinking about upgrading to an OLED.
In addition to my question about the jumping filter cutoff values, I’m also wondering what exactly are the feedback pots supposed to do? I’ve used dual-gang 100K pots, but as far as I can tell all they do is mute the channel when turned hard one way. Am I missing something obvious here?
If you turn on the external input and route it to the filter, the feedback pots should introduce overdrive and additional resonance, especially in bandpass mode. I don’t think it should ever go mute. Check your wiring, you can’t go directly from the three pins of the pots to the three header pins.
Check your wiring, you can’t go directly from the three pins of the pots to the three header pins.
Now I’m really confused. In all the pics I’ve seen it looks like the three pins of the pots are wired directly to the three header pins. Is something further necessary? Apologies for the noob questions, I’m just trying to understand how it works.
