Acid house has a debated history, from the purported derivations of the term itself (a drug reference/homage? An anti-political term?) to its origins, usually tied to Chicago, but in some circles to India and a man named Charanjit Singh. There may never be 100% agreement on origination, but there’s no debate as to its influence and what its signature sound is—the wompy, squelchy sound attributed to the Roland TB-303, a sound cemented in acid house music history, and as identifiable as it is ubiquitous.
From its birthplace of Chicago or India, to its popularity in the 80s/90s in the UK, to, well…just outside of Lisbon, Portuguese outfit ADDAC Systems have taken the inspiration and the sound for their new Acid Source 107, a complete single voice Eurorack module that brings all of the melted smiley faces and lollies to your modular rig. I decided to write the bulk of this review while listening only to Sleezy D’s “I’m losing Control, Phuture’s “Acid Track”, and Singh’s “Synthesizing: Ten Ragas to a Disco Beat,” on a loop, and while I had to do some muting and pausing here and there to gather my thoughts together, the tracks still sounded pretty fresh to these ears, and it definitely brought back some hazy memories of late nights/early morns in the 90s.
Conceived as a source for complex percussion, that use was shelved when the folks at ADDAC started using 107 as an acid synth voice and realized that’s where it excelled. And does it ever. It’s got everything you need in its 9 HP frame. It starts with a VCO (either saw or triangle) that’s tunable to four octaves and has Frequency and Fine Tune controls and a CV Input with attenuation. The signal is then mixed with a square wave en route to the filter, a mutli-mode type that’s switchable between Lowpass, Bandpass, and Highpass, and which has controls for Cutoff and Resonance and a CV input/attenuator for Cutoff. From there it’s onto the VCA, and this is where 107 gets interesting. The VCA has a small Gain knob that can go past unity gain up to double the amplification, lending the sound a some not-so-subtle distortion when pushed. Depending on the mix of the signal (saw/triangle + square), the instant I passed unity gain on the Gain Input I quickly found myself in distortion territory, so you don’t have to work hard to get there. The Input can take any signal, whether it be Gate, Trigger, or CV, and whatever signal is patched in goes through the VCA, which is an AD (attack and decay) type with a toggle to determine the Decay length (the attack length is a short fixed length), that being short/off/long. The Decay is CVable and has an attenuverting control, and the slew signal at the VCA output is copied to the CV Out for use as a way to add modulation from 107 to other modules in your setup. There is a CV Out, which is a combination of the Frequency CV and Cutoff CV, and there are jumpers beneath the faceplate on the side of the module that will take the normalizations of these particulates out of the signal for the CV Out if you just want only one of those. Even though this would be better served if it was accessed on the top of the module, it’s completely understandable why ADDAC designed this the way they did, and I think it’s to their credit that they give the option; they could have just as easily hardwired the normalizations in there.
There’s also an Accent Input which can add some dynamic juice to the VCO by patching in CV, and this input can also be used as an external input for another VCO or sound source by removing a jumper that’s in between the VCO and the filter, which takes the internal VCO out of the signal path. The jumper is placed in a circuit-bendy kind of way on the front of the module, and it’s a little odd—you don’t see jumpers on the front much—but it works fine and is an interesting way to add options without taking up too much space, but for the most part I found no need to un-jump/unhitch the VCO as the onboard VCO section is fine, and most of us have other synth voices for other sound sources. Another thing that’s interesting about this section of 107 is that the Input allows for more than the usual +5V and won’t clip at above that, which is what most modules do at this point. Patching in CV over +5V can send the sound into saturation via the Gain, and as such, amounts to a sort of a CVable distortion/boost, kind of a two-in-one deal, and it brings more animation and movement to a patch. It wasn’t hard to get the acidy sound this was designed for, a bit of patching here and tweaking there, and I can see why ADDAC changed their tune on this, but I thought I’d give 107 a whirl as a percussion source, since this what it was originally created to be. While I got decent enough kicks and some other percussive sounds, there’s no question that I wouldn’t use this module as anything but an acid source as it’s really quite enjoyable to easily pump out the squelch and twist a few knobs to bring out its full potential. I found that while mixing in another sound source obviously added to the impact on the resulting filter, I preferred 107 solo; adding more seemed to hide the essence of what makes it work so well.
107 has got some quirky flexibility options (the jumpers, that unmarked toggle), but it also highlights ADDAC’s working sensibilities; focused , somewhat whimsical, but always musical. There’s a sense of humor to this, they even put the ubiquitous smiley face on the bottom, but nothing lacking in the seriousness of sound and possibilities it delivers. This is also available as a full DIY kit, so if you like dropping acid—music, that is—the ADDAC107 has got you covered.

9 HP +12v 80mA -12v 80mA
Price: $249

addacsystem.com