Review: Mystic Circuits 0hp Vactrol LPG

Before we talk about this little Vactrol LPG module, I want to talk about the concept of 0hp modules, because I absolutely adore them. For me, this goes back to my earliest experiences with synthesis. *Cue Flashback*

Early on it was just me and a couple semi-modular synths. Sometimes, I needed attenuation where there was none to be had, but I didn’t have a rack. Somehow, I ran across the Pulp Logic Atten-B module (passive, linear attenuator). It’s a tiny, 6hp, tile-format module. It’s never been in a rack. Even after I moved to modular and got Blinds, it still came to the rescue at times. To me, that Atten-B is the “original” 0hp module. It doesn’t always get used, but it is always there when needed. It still shows up here and there. I consider it an essential utility.

Because of this, the idea of the Mystic Circuits 0hp modules resonates with me. That little Atten-B made patches and sounds possible, that I couldn’t have otherwise made. And now, here come these new, inexpensive, and capable 0hp utilities. SIGN ME UP!!!

Ok, so… I like them. I guess it’s time we get to the 0hp Vactrol LPG.

The vactrol LPG is simple and handy. If you don’t know what a vactrol is, it’s a LED coupled to a photoresistor. An incoming voltage illuminates the led, which opens up the photo-resistor so a signal can pass. This tends to create a sort of signature attack-decay response. Though the precise response varies a bit between individual vactrols. An LPG is a combination of low-pass filter and voltage controlled amplifier. Vactrol LPG’s are a classic piece of West Coast synthesis. They have a unique and wonderful sound to them.

It doesn’t just do audio. This module is AC and DC coupled. This means it can pass both audio and control voltages. So, whether you want a vactrol sound, or to put some vactrol smoothing on your control voltages, you can do that. It can also do VCA type work on your control voltages. Though, I do have to say, I particularly love it for audio.

Lastly, it has a passive mixer. As Eli notes, you will experience a bit of signal loss, but nothing major. The mixed signal does not go through the vactrol LPG (as you will hear in audio above). I found this particularly wonderful with my Make Noise STO oscillator. I plugged the Shape output into the IN and the Sub output into the MIX. (I used my little Atten-B module on the Sub to dial it back a bit.) The result was a lovely vactrol LPG plucking away while the sub backed it up nicely.

The Mystic Circuits 0hp Vactrol LPG is a lot of fun and utility for $23 USD (kit) or $33 USD (assembled). It is has an excellent set of features for such an inexpensive module. It’s an excellent way to try out a vactrol LPG if you’re curious, but aren’t ready to commit too much money or rack-space just yet. And, it’s a perfect companion for a small system, to extend your capabilities or to keep for utility.


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Honorable Mentions
Mystic Circuits 0hp Modules
Blog: Mystic Circuits 0hp Builds
Pulp Logic Atten-B