To say that I’ve been eagerly awaiting the F3DB in my mailbox is an understatement. I love filterbanks in general, but I was so excited to see Zlob’s take on the classic Moog 914 that when I finally was able to put the F3DB in my rack, it was a momentous occasion that I promptly celebrated by absolutely destroying a drum track with.
Taking its initial cues from the aforementioned Moog’s 914 Fixed Filter Bank, along with some inspiration taken from YuSynth.net [a great DIY site for those who aren’t familiar with it], F3DB does the filter-bank thing and has many Zlob features that you just won't find on another module like this. Actually, is there another module like this? I don't think so, which is why there's been excitement around this module that's been building since its release. Don’t believe me? Try finding a pre-built one for sale. Sure, F3DB is an all through-hole build and not for DIYers who are faint of heart, but know that its scarcity has nothing to do with the ongoing parts shortage; this gem is all analog. Speaking of gems, F3DB might actually be Zlob’s crown jewel, and that’s saying something as they’ve got a long list of excellent modules.
F3DB is an impressive module to be sure, beautiful on its facade as well as the component PCBs. Zlob always has an interesting take on the physical design and build of its modules in terms of the PCBs; how they fit together, where the power header is located, how they connect to expanders, etc., and I’m sure this is due to the fact that there are no surface mount components to be seen and therefore space is at a premium. Having designed enough component PCBs myself to understand the thought and planning that goes into building a module like this, I get that it’s no small undertaking. F3DB is dense, filled with components of all shapes, colors, and sizes, with circuit boards coming out of everywhere possible, reminiscent of the way a shark's teeth populate its mouth. It’s actually a shame that you can’t see its makeup once it’s mounted in a case.
Going through its features via its signal flow, there are two inputs which are then routed to a clipping feedback circuit with switchable HARD or SOFT clipping. There’s a GAIN level knob and the option via the GFB [Gain Feedback] to add some GFB and dial in the desired amount via a GAIN FEEDBACK level control. From there the signal is finally routed to the bank of filters.
There are six frequency bands, with the middle four [250Hz, 750Hz, 1kHz and 2.8kHz] being band-pass and the two extremes [88Hz and 7kHz] being a low-pass and a high-pass filter, respectively. Each of the six bands has a dedicated VCA with an illuminated slider to control its level, and a CV IN for modulation purposes. There’s also a toggle switch above each band for muting the given frequency. After the VCA section, there are envelope followers for each band as well as individual outputs for each. There is also a summed output and an ODD and EVEN output [referencing the band numbers]. The summed output is fed back into the input for some feedback, which can be dialed in with the FEEDBACK control knob. This feedback also has a CV in and an external FEEDBACK IN.
With the option to clip the signal at the input or at each individual band, there are so many tonal possibilities. Running my Drumbute through F3DB with some random LFOs coming out of Xaoc Device’s Batumi and into the CV in for each band’s VCA—with some bands clipping and some not—F3DB got crazy with the sound and beat. The ever-changing sonic percussive storm that ran out, with varying degrees of modulated feedback destroying the sound, was something totally unique. Using a few of the envelope followers to add melodic bursts to my rhythmic patch, by running one through some long-tailed reverb, and patching others for more percussive accentuation purposes, turned out really interesting results with a beastly sound, and self-patching one of the envelope outputs back into the FEEDBACK IN helped accent the rhythm even further. Continuing with this, patching multiple envelope outputs into a mixer, and patching that summed output into the FEEDBACK IN brought in even crazier dynamics, with the end result being a rhythm that breathed, panted really, and came to life in a bizarre and unpredictable way.
Wanting to dirty up the sound as much as possible, cranking the GFB completely destroyed the sound altogether, so I backed off a bit to where the rhythm became a staggering, sputtering shell of itself, yet still recognizable. This of course all depends on what level each band is at, if some bands are clipped, etc., but if you love distortion, and perhaps even more—if you love shaping your distortion—F3DB needs to be in your rack.
On top of the functions already mentioned, F3DB can self-oscillate and with so many variables—clipping, feedback, envelope following—the sonic possibilities are endless, especially if you like distorted chaos, and who doesn’t like that? F3DB can be used sparingly, and in fact works great to really hone in on a specific sound frequency-wise that you may be going after. Honestly though, that seems like a waste of F3DB's talents. It’s a sound-sculpting delight, think filter-bank on dirty steroids.
I think one thing most of us can agree on about modular is the obsessive desire for supreme controllability. Strange, how it’s the unpredictable, unrepeatable noises and moments that I love the most with F3DB. I mean, I might be a control freak, but it’s the unmistakable randomness that makes modular synths feel so special and exciting, and with F3DB there are a LOT of potential moments like that.
I always like Zlob’s modules. Entropy, Diode Chaos, Vnicursal…I find myself using those modules constantly in my patches, but with F3DB, it’s a bit of a different story. This module has become more of a focal point in all of my recent patches. I've found that before I start a new patch I'll be thinking, planning, wondering, where in the chain, and on what part of the patch I want to use F3DB in and in what fashion. I can’t say that having more than one in my rig—it's equal parts utility and effects module—wouldn’t be supremely cool, but I’m not a glutton. At least, I profess to not be one.
I’m constantly finding myself in such surprising territory with F3DB; it’s such a fun module to explore, that even running something simple like just a high-hat through it, with only a few audible frequencies being used and minor additions of modulation, has proven to be a fun. It's a really effective way to muss up the rhythms, to bring something new to a patch.
As said before, F3DB is 100% through-hole [as are all of Zlob Modular’s offerings], meaning that building one can be a somewhat time-consuming affair. It’s definitely one of their more complicated builds and since all of Zlob’s pre-built modules are made by hand, as mentioned, finding a F3DB for sale isn’t always easy. But be persistent…it’s worth it. If you’re inclined to skip the lines and build it yourself, let me share this warning, as seen on the Zlob Modular website:

“THIS IS NOT A BEGINNER OR INTERMEDIATE PROJECT. This is a highly involved DIY all through-hole project. It is a long build with 5 different pcbs to solder and assemble.”

My F3DB came assembled, so I can’t make any claims on this, but it’s something to keep in mind if you’re planning on building it yourself. Another thing to be mindful of is that this is a deep module at 45mm from faceplate to ribbon cable, so make sure you have enough room in your case to handle it. Otherwise, do whatever you must to grab one, you’ll be glad you did.

16 HP +12v 75mA -12v 75mA
Depth 45mm
Price: $100 - $420

zlobmodular.com