Winterbloom - Castor & Pollux II Review
A Juno-inspired dual oscillator that can be the heart of your system.
After starting my modular journey, I’ve been trying to find a great oscillator. And that’s how I came across the Castor & Pollux II by Winterbloom. Winterbloom is a small, independent, woman-owned music technology company from Atlanta, US that makes a few very cool modules that are also open source actively contributing to the synth community! Their most famous module is by far Castor & Pollux which recently got a version II. This is a Dual Oscillator that’s heavily inspired by the oscillator on the legendary Roland Juno 106 and expands it into new sonic realms.
A thing I love about some products is how they are based on a story or concept that you can see all over the product and Castor & Pollux II is exactly that. And since I’m Greek, let’s do a quick mythology lesson. According to mythology the Queen of Sparta has given birth to two sets of twins. One set from Zeus and one from her husband. All four kids were raised together and the two boys, Castor who was a mortal, and Pollux who was immortal were best friends and loved each other so much. But during a fight, Castor got killed. Pollux was devastated for the loss of his half-brother and best friend so he asked Zeus to allow him to be with his brother. Zeus agreed and the two brothers met again and since then they spent half of their time in the underworld and the other half in the sky on what we now called the stars of Gemini.
Castor & Pollux II is a module with a lot of stars that light up with different colors representing the Gemini stars on it and the two oscillators represent the two brothers, Castor and Pollux, who are now together intertwined on a Digital Dual Oscillator module. And if you look closely you’ll see that a few of the knobs have a Greek letter below them. How cool is that?
So after talking to Thea Flowers from Winterbloom (what a cool name btw), we got our hands on the Castor & Pollux II and its Expander and I’ve been using it quite a lot in the past few weeks to understand what it can do and tell you about all the different ways I’ve been using it to make patches!
Design & Specs
Castor & Pollux II is a 14HP Eurorack module and its Expander is 2HP. The Expander module is included with the main module and gives you individual outputs for each oscillators’ waveforms. That’s actually the main difference between version I and version II. In version I the individual outputs were already on the module but in the second version, mainly due to the new & bigger knobs, they decided to add them to a separate expander module. To be honest, I really love the feel of the new knobs and I much prefer them from version’s I knobs which were very small knobs. Plus, if you don’t find yourself using the expander, you can take it off your case and make some more room.
The first thing that I noticed when I got this module was its looks and design. It’s one of the most beautiful modules I’ve seen and once you plug it in and all the lights start to play with different colors it’s a joy to watch. Yeah I know, design and looks may not matter to most people but I always say that an inviting and beautiful design makes me use something more. It’s something that’s often overlooked but I believe that psychologically it makes a big difference.
The new layout is much cleaner since you can see all the knobs on the top and the inputs and outputs on the bottom of the module. The two big knobs on the top control each oscillator’s pitch, the Φ knob controls the internal LFO, there are two Pulse Width knobs for each oscillator, and lastly the Σ knob is a crossfader between the two oscillators. Below that, you’ll find individual knobs to control the volume of each waveform for each oscillator. The button that’s below the Σ knob is a mode selector that we’ll get to it later!
As far as inputs and outputs, Castor and Pollux II has two V/Oct inputs (α & β), two inputs for Pulse Width, two individual outputs for each oscillator (the ones with the star signs), and the main output that outputs the mixed signal of both oscillators (ΙΙ). If you add the expander, you’ll also get individual outputs with Saw, Pulse, and Sub outputs for each oscillator.
Modes
Castor & Pollux II has 4 different modes that you can choose by tapping on the button that’s in the middle. This button also works for changing additional parameters while holding it depending on the mode you’re at. One minor thing that got me confused a few times is that it’s not really obvious on which mode you are in. Once you tap on the Mode button a light animation is happening to show that you’ve switched modes but once you do you’ll have to figure out which mode you’re in. I may have misunderstood something but I can’t seem to find a clear indication of each mode. So let’s go through all the modes and see what they can do!
Chorus: This wouldn’t be a Juno-inspired oscillator without the iconic Juno chorus. But since the Juno has only one oscillator the Chorus was applied after the sound was generated while in Castor & Pollux, the module is using its internal LFO to modulate the Frequency of the second oscillator. To hear this effect you must use both oscillators and has no effect if you use the individual oscillator outputs. By using the Φ and Σ knobs you control the intensity of the effect. This is a very good-sounding chorus that’s not quite similar to the Juno chorus. If you are used to that specific chorus sound, you might not find them identical but it definitely gets the job done.
LFO PWM: In this mode, by using the internal LFO you can modulate the Pulse Width of each oscillator. As expected, you have to use the Pulse waveform to actually hear the modulation happening. The Φ knob controls the frequency of the LFO and the Pulse Width knobs the Depth of the modulation which is summed with any signal patched into the pulse inputs. By holding the button, you can also tweak the Pulse Width center as an additional parameter of the Pulse Width knobs.
LFO FM: Here, you can use the internal LFO to modulate the frequency of each oscillator. This is an effect I use all the time at very low rates to add just a tiny vibrato to my sounds and it’s really cool that I can do it directly on the module.
Hard Sync: Last but not least, Castor and Pollux II has a Hard Sync mode. This of course could be possible if it didn’t have two oscillators so it’s something you wouldn’t find on a Juno since it only has a single oscillator. In this mode, Pollux is synced to Castor’s frequency. The effect is only audible when you use Pollux as a sound source either by its output or by setting the crossfader all the way to the right. By using the Pitch knob of Pollux that’s hard synced to Castor’s frequency, you can get that distinctive hard sync sound!
Overall Experience
As you probably can already tell, Castor & Pollux can be used as a Dual Oscillator where you treat each oscillator separately or as a two-oscillator voice. Both oscillators are digital or to be more accurate DCOs (Digitally Controlled Oscillators) just like the Juno. Quick note, I never really cared about the whole analog versus digital thing that’s all around the synth community. This module’s oscillators sound amazing and even better than some analog oscillators I have in my Eurorack case. And for a modular synth specifically, I tend to prefer the flexibility that digital oscillators provide. I’m lucky to have a few analog synths for when I want the basic analog sound so in my Eurorack synth, I’m all about weird sounds and flexible modules.
Overall, I’m really excited about this module. Most of the time, I just use the oscillators separately since I want those extra voices and it sounds great. I’ve even used them alongside my trusty OXI ONE as a pseudo duo phonic synth by programming different pitch sequences for each oscillator and that also worked great! I’m much more of a Saw type of guy and I heavily use the Saw waveforms on the Castor & Pollux for leads and bass sounds and I can honestly say it sounded massive!
It certainly takes some time to get used to the different modes and what every knob does in each mode but once you get a hold of it it’s not that big of a deal. Maybe if the button lit up with a different color for each mode it would make things a bit easier. As I said before, I mostly use the LFO FM mode for some pitch fluctuations, and the Chorus mode when I want a more mellow sound. The only thing that I feel it’s missing in this module is an input to control the Crossfader with CV. I would love to have different sounds on each oscillator and be able to modulate the crossfader to go back and forth on each one. I think that this would be a very nice addition!
Since this is a 14HP module and when you add the expander, it goes to 16HP. Some may say that you can get a couple of oscillators for that HP give or take. While this is true, Castor & Pollux II is much more than just two oscillators in one module. The fact that you can use the summed output and add the Chorus is a big plus while the module still offers you the flexibility of using Castor & Pollux as two individual and fully-featured oscillators. And with no hidden menus or shared functions which is another huge plus.
Castor and Pollux II alongside another very cool Dual Oscillator that we are going to feature in a later post, have become the heart of my modular. It just sounds good, it has hands-on controls and it’s very versatile. If you just need a single voice you can use the main output, detune the oscillators, or hard sync them and get , massive sounds and if, on the other hand, you need more voices you can treat them as individual voices with different characteristics and sounds.
By the way, the whole Juno-inspired thing might sound promotional (which of course it is and there’s nothing wrong about it) but in reality, Winterbloom took their inspiration and made something new, more versatile, and with more features out of it. After all, there’s nothing that special about the Juno in 2023, but there is something quite special about Castor & Pollux II. But it also reminded me of how cool modular synthesizers are. I currently run a Juno-106-inspired Oscillator into a Jupiter-6-inspired filter (System80 - 860 MK2 review coming soon) and can modulate everything to my liking. That’s the beauty of modular and the endless possibilities that all these amazing modules offer!
Conclusion
Winterbloom’s Castor & Pollux II is a solid oscillator module and it’s staying indefinitely on my Eurorack case. The things that I like the most are the core sound of the oscillators which is loud and thick, the versatility of using two oscillators separately or stacked, and the multiple outputs you get. The four Modes help you do things within the module itself without the need for additional modules like a chorus effect, or an LFO for Pulse Width modulation.
Regarding its price, it’s also very well priced at 289$ which is very reasonable for a dual oscillator with all these features. If you’re starting out with modular synths getting a dual oscillator is a very wise choice since you’ll probably save space and money and still have a couple of voices to play with. But even if you have a ton of modules, Castor & Pollux II certainly won’t disappoint you. You can get a lot of sounds out of it and by pairing them with the internal Modes you’ll have even more interesting results.
To sum up, Castor & Pollux II is hands down a killer choice for your next oscillator. Another thing that I love about it (and many other modules) is that it’s coming from a tiny, indie company like Winterbloom. Thea & Maggie who run Winterbloom are showing us that it’s possible to make music gear that’s affordable and great without being a huge corporation and at the same time trying to do it with responsibility to our environment. And as a bonus, these modules are open source to spread the knowledge and expertise with other aspiring gear makers!
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