4ms Quad Pingable LFO (2013–2020)

A tap-tempo LFO that turns pulses into living, breathing modulation—four channels of ping-driven rhythm that sync, skew, and surprise.

Overview

You don’t so much set the tempo on a 4ms Quad Pingable LFO as invite it in. Plug in a clock, tap the button, send a burst of pulses—any rhythmic signal becomes its heartbeat. That’s the magic of the QPLFO: it doesn’t just follow time, it interprets it. The result is an LFO that feels less like a machine and more like a collaborator, especially when you start pinging it with jagged envelopes or erratic gate patterns. It’s not the flashiest module in a Eurorack case, but in a system short on modulation sources or tight on space, it’s a quiet powerhouse—four independent LFOs in just 12 HP, each capable of morphing from plucky transients to smooth triangle waves and everything in between.

The “pingable” concept isn’t just marketing fluff. It means the frequency is determined by the time between incoming pulses, making it inherently musical when synced to a sequence or drum pattern. But what really sets it apart is how it handles those pings. Unlike some LFOs that demand clean clock signals, the QPLFO uses comparators on its Ping and Reset inputs, so it’ll accept anything—noisy waveforms, audio-rate bursts, even feedback from other modules. That makes it unusually flexible in chaotic patches, where clock sources might be irregular or creatively mangled. The tap tempo button is tactile and responsive, glowing with each press, and it runs freely when tapped manually—handy for jamming—but stops when an external clock cuts out, preventing runaway modulation.

And then there’s the skew. Not just a shape knob, but a full CV-controllable parameter that lets you stretch the waveform from a sharp, plucky attack to a slow ramp-up, with a triangle dead center. At extremes, you get near-exponential curves that feel more like envelope generators than traditional LFOs. Pair that with the ability to reset each channel externally—or have one channel reset another—and you’re deep in generative territory. Cross-modulating the skew inputs between channels creates evolving, almost organic shifts in rhythm and contour, perfect for ambient drones or unpredictable rhythmic textures. It’s not a sound generator, but it makes everything else in your system sound more alive.

Specifications

Key Features

Four LFOs That Listen

Most quad LFOs are just space-saving conveniences—four copies of the same circuit. The QPLFO is different. Each channel is a full-featured, independent unit with its own tap button, skew control, CV input, reset, and output. That means you can run one channel synced to a drum clock, another pinging off a sequencer’s reset pulse, a third modulating the skew of the fourth, and all of it interacting in real time. The ability to use any signal as a clock—no need for clean square waves—opens up wild possibilities. Feedback patches where an envelope triggers a ping, which then modulates a filter, which in turn alters the envelope’s decay, become not just possible but intuitive. It’s rare for a modulation source to feel this responsive, but the QPLFO pulls it off by treating timing as a fluid, dynamic parameter rather than a fixed rate.

Skew as Expression

The skew control is where the QPLFO stops being just a utility and starts sounding musical. At 0%, you get a fast, plucky rise and a slow exponential fall—perfect for percussive accents or pseudo-envelope effects. Turn it up, and the wave flattens into a ramp-down, then a triangle, then a ramp-up. Because skew is CV-controllable, you can sweep through these shapes in real time, or let another LFO modulate it for evolving textures. One favorite trick: patch a slow sine wave into the skew CV of a channel running at audio rate, and you’ll hear the waveform morph from buzzy to smooth and back, creating a kind of harmonic drift that feels more like a synth voice than an LFO. And because the skew knob adds an offset to the CV, you can use any control voltage range—no need for precise 0–10V scaling.

Sync, Reset, Repeat—On Your Terms

The reset input isn’t just for restarting the cycle—it’s a creative tool. Hold a high gate on the reset jack, and the LFO enters “floating reset” mode, where it runs freely without re-syncing to the ping clock. That’s huge for generative patches where you want temporary independence from the master tempo. The reset can also trigger a one-shot envelope if the ping clock stops, effectively turning the LFO into a quasi-ADSR. And with the “fire-on-unmute” jumper (solderable on the PCB), you can make the LFO reset every time you unmute it—great for live performance when you want consistent timing on activation. These aren’t gimmicks; they’re thoughtful design choices that reflect how modular users actually patch.

Historical Context

When the QPLFO launched in 2013, Eurorack was growing fast, but many systems were still space-constrained. Most LFO modules offered one or two channels, and tap tempo was still a luxury feature. 4ms, already known for clever, compact designs like the Dual Looping ADSR and the Spectral Multiband Resonator, saw a gap: a need for a dense, performance-ready LFO that could handle both precise sync and expressive timing. The QPLFO answered that with a design philosophy rooted in playability. It wasn’t just about fitting more in less space—it was about making modulation tactile. The glowing tap button, the immediate response to pings, the ability to mute and reset on the fly—all of it catered to live use.

At the time, competitors like Doepfer’s LFO and Intellijel’s uLFO offered solid performance but lacked the QPLFO’s ping-driven flexibility. The idea of using any signal as a clock was still niche, and the ability to cross-modulate four channels in such a small footprint was nearly unmatched. Paired with the 4ms Quad Clock Distributor (QCD), it became part of a tightly integrated timing ecosystem—modules that spoke the same language. That synergy made it a favorite in portable and travel systems, where every HP counts. By 2020, when 4ms discontinued the pre-built version (focusing on kits), the QPLFO had already cemented its place as a cult favorite—less a replacement for traditional LFOs than a new category of modulation source.

Collectibility & Value

The 4ms Quad Pingable LFO is no longer in production as a built module, but it remains highly sought after—especially in fully assembled form. Used prices vary widely based on condition and whether it’s a kit build or factory module. Factory-built units typically sell between $350 and $450 on the secondary market, while DIY kits (still available from 4ms) go for around $225. Boards and faceplates alone can fetch $100–$150, reflecting the demand for complete builds.

One caveat: the QPLFO is generally reliable, but service technicians observe that the comparator threshold can drift over time, especially in units exposed to voltage spikes or poor power regulation. A trim-pot on the PCB allows adjustment, but it requires opening the module—fine for experienced users, less so for buyers who just want to plug and play. The jumpers for +5V source and bipolar/unipolar output are also critical: misconfiguring them can lead to power issues or unexpected signal levels. Collectors note that units with the “fire-on-unmute” jumper installed are slightly more desirable for live performance use.

Common failures are rare but include flickering LEDs (usually a loose connection) or unresponsive tap buttons (wear from heavy use). The real risk isn’t hardware failure—it’s misunderstanding the module’s behavior. Forum reports confirm that if the ping rate changes rapidly, the LFO may lag slightly before catching up, especially at extreme frequencies. This isn’t a defect, but a consequence of how it measures time between pulses; it expects relatively stable clock sources. For users expecting instant tracking like a PLL, this can be frustrating. But for those who embrace its organic response, that slight delay becomes part of the character.

When buying used, check that all four channels respond to pings, that the skew knob sweeps smoothly, and that the mute buttons latch correctly. Verify the jumper settings match your system’s needs—especially the +5V selection, since some power supplies don’t provide +5V. And if possible, test with both internal tap and external clock to ensure the auto-stop behavior works as expected. A working QPLFO is a joy; a misconfigured one can feel erratic.

eBay Listings

4MS QPLFO Quad Pingable LFO Eurorack Module w/ Manual & CV P

$189

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