OK dudes, here it is!
A fellow contestant was graceful enough to put up with my bellyaching, so I'll save us all the excuse-making and indignation. That being said, I hope I'm not wasting the judges' time with my terse video, lack of fidelity-conscious recording, crappy schematic, and even worse layout.
Honestly, I enjoy using what I've built and I'm proud of it, just a little embarrassed of my presentation. This pedal can go from 'stuck wah', to pheux phasor, to Leslie rotating speaker sounds, to MFOS style ray gun weirdness, to subtle blooming. I'm looking forward to tweaking further in the future, improving the PCB, and doing a full-blown build thread. I'm also planning on doing a simple op amp HP/LP version.Folie à Deux
Dual bandpass filters with LFO controlled modulation.
I got hopelessly hooked on filters recently after spending some time noodling with Cliff Schecht's MS-20 schematic, from a thread started by Strategy and expanded by Jordan A, along with Cliff. Being a noob to this, designing a PCB for a dual LM13700 project was a little out of my league, at least if the PCB was expected to be something that would fit in anything smaller than a suitcase. So I decided to work my way up to it by making a few simpler filter circuits. The 'tunability' of a multiple feedback BP filter with a single pot seemed like a good reason to try that out first. Because the MS-20 is actually 2 filters in series, I decided to make a circuit with 2 filters, switchable between series and parallel, thanks to Rick Holt's elegant switching schematic (posted in the MS-20 thread). Of course, BP filters in series are almost painful to listen to, at least without significant post-processing, so I ended up ditching that for hard-wired parallel filters.
Each filter has it's own standard op amp LFO, with controls for rate, ramping, and depth.
There is a 'blend' knob to mix wet and dry signals, and a 'tune' knob to adjust the resonant frequency of each filter. The tunability is limited. Also, because the LFOs are controlling LEDs affecting the LDRs in parallel with the 'tune' variable resistor, the 'depth' affects the frequency, too.
I used white LEDs for the roll-your-own vactrol because to my ears, they worked the best, and in conjunction with the display LEDs, other types did not light up both. I know there's a smarter way to wire up the indicator LEDs, but I was been pinched for noodle time.
I messed with the final op amp stage for a while, and the component values are chosen strictly by ear. Again, I'm sure there's a better way to do it, but I'm still learning the basics, so for now all I have are my ears to guide me.
I wasn't sure how to deal with the input impedance.
The power supply took some big caps to filter: 470uF and 220uF, again, chosen by ear.
Figured it's a current hog, so I didn't bother with the battery.
I whine a little bit, only play one damn chord the whole time, and leave out a few key examples of cool sounds this pedal is capable of, but I think y'all will get the idea
can't believe I called it a 'bypass filter', ha!
You can see my improvised fixes for a few basic layout mistakes if you look close, but other than those, it turned out great.
Thanks to Aron and everyone on the forum, especially the veterans throwing their wisdom around for free; you're beautiful people!!!