I love the EHX Stereo Pulsar tremolo for drone work: goes from very slow and subtle undulation to crazy chopping and buzzing. It’s awesome but has one drawback: mono input.
I thought the EHX Super Pulsar would alleviate that and got one. Alas, it has one critical flaw: instead of just 1 rate knob it also has a button that selects the rate range. This makes continuously fading the rate from slow to fast impossible without evident jumps. Not good for the drone ambiance.
I tried clocking it externally but the tracking is too coarse. Jumps are also audible, and it doesn’t track very slow rates.
So I’m considering building an alternative in modular. I thought I’d ask you folks for advice before digging into the zillions of LFO, VCA and other modules.
What I must have:
stereo line level in/out (or 2 separate channels)
wide freq range LFO with multiple waveforms, something like 0.05-30Hz minimally and at least triangle and square waves
2 LFO channels 180deg out of phase / one is the invert of the other
modulation depth control
What is nice to have:
phase control of the 2 LFO channels (so not fixed at 180 deg)
LFO shape control (like on the Pulsars)
continuous LFO waveform selection (fading from one to the next)
the Stereo Pulsar starts adding a nice phasing effect when pushing the depth past 3 o’ clock or so
Bonus question: what are the coolest LFO modules around?
In my very uneducated opinion, the smart thing to do would be to avoid the long walk around recreating something in eurorack that already exists in reality and which you will constantly compare the results against and just buy a used or perhaps “new old stock” EHX stereo pulsar when one becomes available.
It will undoubtedly be the same or less expensive than any modular alternative.
I don’t have a specific answer, but some thoughts…
You don’t really need “stereo” or two lfos. All you should need is 2 vcas, any should do, and some way to invert the LFO cv. So one lfo feeds both vcas, one regular, one inverted. There might be some lfos that offer an inverted output or you could just buy a small module that does that.
You might be able to find a vca that has an attenuverter on the cv input so you could invert the lfo signal directly on the vca.
So then that leaves you to just search for an lfo with these features. I would just look at all of the ones on perfect circuit or whatever until you find what you need.
For the modulation part, I reckon you can do all of this with just a Xaoc Batumi II + Samara II. The continuous waveform selection you may struggle with in the traditional sense but you’ve got either stepped/smooth random modes, or with the Poti expander you can modulate each of your LFOs to get something.
Line in/out not really sure tbh but there’s no shortage of modules. I have that 1u trs thing on my befaco case which serves as either/both.
I’m not one to read manuals, but Xaoc ones are straight to the point and a cmd+f with the keywords should hopefully answer some questions (in case I have partly misunderstood what you’re after).
The Batumi is a very good recommendation indeed. So far I’ve found only one other LFO module that is a good contender for my needs:
It’s also digital with a little fewer features but I think I like it more because of the fat knobs. My system 's meant for live performance and I’d prefer big knobs over sliders for the LFO frequency. It also allows to select sync mode for each LFO channel separately, giving me 2 extra LFO’s to use elsewhere. Expensive though…
I’ve been looking into the signal processing driven by the LFO CV output. I made a little Max patch to model it out (just one of the two channels):
I haven’t modeled the whole LFO part, just took a sine generator as placeholder. For controls I’ve got a volume control that sets the maximum output amplitude of the channel, and a depth control that sets the amount of modulation. The resulting CV would feed exponential 2 VCA’s that regulate the output volume.
And then I made a VCV rack patch (only hooked up 1 channel) (I noticed I didn’t really need the volume control that the Max patch has)(VCO is placeholder for my actual input)(the Vermona LFO is not available in VCV):
This is missing the exponential VCA at output stage. I’m using the 3rd A*B+C instead of a VCA because it 's multiplication is bipolar. I think that phasing effect that the EHX Stereo Pulsar displays at high depth settings is due to the modulation going partly negative and this might approximate it.
Any thoughts/recommendations?
I’m looking for a big and chunky control knob for the depth parameter. What do you folks do when you need a knob to send a CV elsewhere? Is that a VCA module with knob that you give a 5V input to attenuate?
Not a knob but the Lapsus Os by Noise Engineering is excellent for dispatching CV in a system. You can even flip the range on the sliders with switches at the back. So, you can mount the patch points at the top or the bottom:
@dtr since it’s not been mentioned already, take a look at the 4MS Meta Module. You’re already building your setup on VCV Rack so why not use the Meta Module to host it for you? I don’t have one but it’s a brilliant idea:
I finally landed on the Metamodule indeed. Compared to the other options (building it in eurorack and Max/Rnbo on a micro-computer with somekind of audio interface) it offers a really good value proposition with its 8 i/o’s and 12 knobs. When I found out Rnbo patches can be compiled to run on it it was a no brainer.
My stereo tremolo on steroids is running nicely, and now got stereo filter and eq on top. Nearly maxing out the cpu at 48khz but gonna see if I can optimize some elements and add some more goodies.
