The four PCBs work!

    I ordered the four projects and wrote about it in my previous post here, and of course the PCBs arrived on the first day of my 4-day weekend, so I couldn't test them out until yesterday.

    Here's the rundown.

    One of the orders was for my MS-20ish business card PCB, which is unchanged from the prototype I ordered, and works great. Not exactly unchanged, this version is lead-free, which is nice if you are giving people things they may put in their pocket and handle a lot. I hope JLCPCB is actually sending out lead-free PCBs and it's not just marketing. There's lead tests out there maybe I should get one.

    I'm planning to offer a limited project for Knobcon 11. One of the candidates is the ZV.HP module, which I wrote about in my previous post. It's a two-pole high-pass filter based on half of a Polyfusion design. It works wonderfully, with this weird quirk that I forgot to include an audio out... pretty dumb to be honest... I suppose I was excited to get it designed. The good news is that it performs very very well, with the same stable predictable self-oscillation I get from my tin-can version. Even when set to a very very low cutoff frequency. It'll be able to rumble warehouses and blow subwoofers.

    The DumpsterDelay works pretty well with a strange thing happening with the input stage. I'm going to have to do at least one more prototype of that one. Maybe I'll just hurl another op amp buffer for the input stage. I have a bad habit of just adding op amps even places there might be a more elegant solution. They're so useful though, and so so cheap as to be nearly free!

    HA!!!! Storytime. Last Friday we watched Descendants, a Disney TV Original Movie with some of the most delightful performances from some talented youngsters, singing dubsteppy musical numbers. Lots of over-the-top acting, Dove Cameron and Kristin Chenoweth my work, what a silly great movie. Anyway, our anti-heroes break into a museum, the alarm sounds, and the kid who mutes the alarm has to answer the phone call from the alarm company (one would assume) assuring them things are okay. He says something like "There was a malfunction in the TL714 microchip." He said that and I hollered HHEEYYYYYY he got that wrong!!! The script most likely said TL741, not 714 because while the TL714 is a microchip out there (it's a comparator) it's much much much less common than the 741. An alarm system is likely to have dozens of 741 chips (or compatible) so the writer must have asked an engineer "hey, name a chip" and they went "okay, TL741" but the kid misread it anyway I wonder if that really is an error and if it's been caught by anyone else.....

    meh, I looked up the script, and sure enough, the script says TL714. Oh well.

    My NyquistNightmare works so well, I'm absolutely thrilled with it. I yoinked the VCF CV input (who's gonna be enveloping the VCF? Not me that's for sure) and added two CV to control the cross-modulation. This will allow really weird signal mixing if you plug audio-rate signals into the CV inputs. Or you can put an LFO signal into them and get AM/FM tuning sounds, or maybe modem sounds... I love this module so much. So anyway, I guess I need to make another video about the NyquistNightmare. And that one is READY TO ORDER!!! WHEE!

Four PCBs ordered!

    

 

    The first time I went to Knobcon (synthesizer convention in Chicago) I met Constantine, who was representing Tip-Top. He was making techno beats with his little modular, which was filled with TipTop modules, obviously, including the wonderful ZDSP reverb and several of those little sample playback ONE modules.

    As Knobcon was winding up, I screwed up my courage and was like "hey wanna go get lunch" and he was like..... okay......... I guess that was a weird American thing to do. But anyway, we had a hamburger in that extremely loud heavy-metal themed restaurant near the hotel, and Constantine (artist name Zvuko) told me about the subtle differences between kick drums, and how best to process them.

    "The 808 kick," said my buddy, "can be tweaked to sound great live. You can adjust the frequency and decay to match the acoustics of the space. The 909 kick," he continued, "will sound great in any room, but won't have the same adjustability." Of course, with mods, the 909 can be just as tweakable as the 808 but I didn't know that at the time.

    "You should put your kick drum signal through a high-pass filter first, then a low-pass filter." What????? I said. 

    So anyway, I went home, thinking about what he'd said, and searched everywhere for a good high-pass filter design. I found one drawn by Ron Folkman for Polyfusion, which was a four-pole filter. I built it point-to-point (using a bit of stiff paper to hold the components as I did back then) and it sounded great, but the cutoff was a bit too steep for my liking.

    I cut the filter in half, studying the schematic carefully, building another example as I went, not as comfortable with the functions of all the components as I am now. Well, when I finished the high-pass filter, and put it in a can, it performed amazingly well, and thus the ZV.HP was born.

    Here's what's going on with that particular signal path: the ZV.HP filter can self-oscillate at very very low frequencies. Probably lower than 10Hz. When you hit a filter that's near self-oscillation, it will "ring" at the cutoff frequency (like I said, down lower than 10Hz if you want!), so you can open a high-pass filter up nearly all the way, so the cutoff is at a frequency that matches the pitch of your kick drum or not (more on that next!) and use the filter as a way to bring even more boom to your kicks.

    Some of the ways I love using my ZV.HP filter: setting the cutoff to a frequency that's really working with my kick drum... so much bass goodness. Tuning the filter slightly higher or lower than the kick frequency will let the kick bounce up or sag down in the decay section of the sound. I'll plug a separate knob into the filter's CV port, and use that to close the filter up when I want to lose some (all!) of the bass frequencies. House and techno producers and DJs use this trick all the time. Many mixers have a bass-cut switch built in. With the separate knob turned up to cut some of the bass, but leaving the cutoff knob on the module alone, you can bring the bass all the way back to your set frequency with a quick flick of the knob.

    All that to say: one of the four PCB projects I just ordered is a 2HP version of that filter. I hope it works because it's a great little filter! Also, my tin-can ZV.HP broke a while ago and I've been using the steep-cutoff Polyfusion one in my kick chain, and it's still okay but not as good.