Maybe this is best admitted in private, Maybe this is best admitted in private, but I’ve never read the Lewis Carroll classic Alice’s Adventures in Wonderland. I bring this up because Apollo View’s Rabbit Hole makes reference to the Carroll book in a few ways, aside from just the name, and from what I’m guessing by my hazy knowledge of the book, it’s an apt title.
Rabbit Hole is a module of many faces; it’s a 16HP summing mixer, a dual VCA, a dual-filter tone control, and a saturation/distortion unit with an all analogue signal path. And it has a tube. Right smack dab in the middle. Were there tubes in Alice’s Wonderland? If so, her adventures wouldn’t have taken her very far if she’s anything like the tube-loving music crowd. I mean, the first thing I did when I got this into my rack was blast some acid bass lines through it, going down a tubular-shaped rabbit hole, as with a big fat 12AU7 [OK, so not that big or fat] sticking out of it; Rabbit Hole is made to distort, right? Why else have that tube? But oh, how deep that journey to the center of the earth can go.
As it is, Rabbit Hole is well-named, as it provides a plethora of goodies—not just a pretty glowing tube—and going deep with it is a call to arms, an invitation to an investment of time and [head] space, where staying hydrated and bringing a reliable GPS tracker is advisable.
Rabbit Hole has an elegant aesthetic. The matte black faceplate lights up in a very cool way, with red LEDs glowing through PCB lookouts in a fun circular pattern that flashes in time with your input [setting dependent], and there is small, but legible gold text throughout, which looks classy. There are solid knobs for the seven main parameters that encircle the tube, and mini-pots for the CV controls and main output. It even has those cool black circle nuts around all the jacks. Points!
There are two input channels [A and B] available, each with its own VCA, and you have the ability to add two [or more] channels via the expander, Curiouser. Curiouser is another two VCAs that can be chained together and summed, mixed in with the signals of Rabbit Hole, or used by itself for dual VCA implementation. What’s cool is that you can add multiple Curiousers to have more channels, making this a potentially never-ending mixing setup. I settled on just one expander, so four total channels [albeit with three outputs as the two on RH are summed].
Back to Rabbit Hole, there are GAIN controls for each input, and CV inputs for each of the channels VCAs as well, where the CV A is normalled into CV B. There’s a solid-state DRIVE circuit that can clip the signal if hit hard enough, and of course, the tube circuit, where it can go from smooth and subtle to not-smooth or not-so-subtle. There’s a TUBE control for the bias amount and an L8 toggle switch that determines the routing of pin 8 of the tube. This can change the sound and tonality in various ways, and overall it seemed to decrease the volume while cleaning up the sound a little, though it depended on my other settings. A tone circuit sees the signal split and go through both low-pass and high-pass [2 pole] filters to join back together where it routes through the TONE control that has a CV input and attenuverter—that blends between the two filters.
As if two tone shaping circuits weren’t enough, there’s also a diode LED clipping circuit, as signified with a mysteriously labeled “OWTH” toggle. OWTH stands for “Off With Their Heads,” if that gives any indication of what to expect from it. There’s also a MIX control to blend between the wet and dry signal, with a CV input and attenuverter as well. The feedback circuit, controlled by the FB knob—again, with a CV input and attenuverter—and an on/off FB toggle, finishes off the list of controls.
With a basic input, just a triangle wave running through Input A, Rabbit Hole is capable of bringing some nice tube saturation, as well as complete annihilation of your sound. One thing to note is that all of the potentiometers are attenuverters, not just attenuators, and as such, the GAIN knobs are attenuverters, with what I found at times, to have a particular sweet spot in a pretty small range. Add to that the interactivity between the various stages and circuits and sometimes RH would go from self-oscillation to nasty distortion [nasty=good] with just a fraction of a knob twist. I wasn’t really able to tweak with much predictability—not too surprising in a module with stacked distortion/feedback options—that’s par for the course, but it really made it that much more obvious that this is an experimental hands-on module where you need to get dirty and do the work. A um…wonderland of sorts. And since many/most/all of the pots are dual functions, turning it to 11 might not be nearly as effective as turning it to -3, even if it’s not quite as catchy to say in a quotable cult movie sort of way. If there’s ever a modular synth version of Spinal Tap, maybe that’ll be the line. Either way, even the output control is an attenuverter, so flipping it towards the negative can give you completely different sounding results than its positive voltage counterpart.
There’s a lot you can do with Rabbit Hole and Curiouser. Processing drums to add some saturation or distortion, clean mixing of a melody line, using them as VCAs with character, or pitting the channels against each other using some alternating envelope/clocking techniques. You can even get some pretty nice self-oscillation going on and throw some sequenced voltage into the inputs for some brute force V/Oct melodic action. I’ve enjoyed my time experimenting with it and getting to know it. It’s quite versatile and it was really fun running speech/audio through it as well. It sometimes took some fiddling to adjust things just so, you sort of have to muscle your way in there a bit, but the exercise will do you well, and it’s a great escape while it lasts. Once you enter and set foot on this journey, it will make you curiouser, and curiouser, and curiouser, and…

Rabbit Hole
16 HP +12v 260mA -12v 95mA
Price: $389
Curiouser
6 HP +12v 60mA -12v 12mA
Price: $169

apolloviewmodular.com