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What is Jet Holt?
Jet Holt is the personal website of Jet "Jetroid" Holt: a developer and hardware tinkerer who writes about his projects and interests, including synthesiser modules, video games, running and photography. The site presents him through his work rather than a formal biography, with a short introduction and a project gallery.
What the site shows
The clearest picture of his work comes from his collaboration with Frequency Central, a synthesiser company. The page describes several modules he programmed and co-designed:
- Bartos Flur — an "esoteric sequencer/trigger generator" whose step is set by input voltage, created for his A-level Electronics course at 17.
- Deep Thought — a logic-gate learning tool with switches and LEDs, including a section that can act as any gate.
- Polygraf — a programmable drum sequencer that grew from an experiment; seven-segment displays and a reworked record mode made it more usable.
- Chronograf — a start/stoppable low-frequency oscillator intended to control Polygraf and similar modules, notable for its range of waveforms.
He notes that he uses PIC microcontrollers and writes in assembly code. The page also lists interests such as video games, running, photo editing and SVG creation.
Who it is for
The site suits readers curious about small-scale synth hardware design, embedded programming, or the person behind those modules. It is a personal portfolio rather than a tutorial archive or shop; the module entries link out to Frequency Central for product details. If you want to understand his design approach, start with the Bartos Flur and Polygraf entries, which explain how each module came about and what problem it solves.
What synthesizer modules has Jet Holt created with Frequency Central?
Jet Holt has co-designed and programmed several Eurorack-style synthesizer modules with Frequency Central, working in PIC assembly code. The projects listed on his site are:
- Bartos Flur — an esoteric sequencer/trigger generator where the step is chosen by the incoming voltage level rather than a conventional clock-and-knob setup. Holt describes it as "weird... but fun," and it was his first synth module, made at 17 for an A-level Electronics course.
- Deep Thought — an all-in-one boolean logic module containing the standard logic gates plus a section that can be configured to act as any gate. It grew out of a joke about building a teaching tool with gates, switches and LEDs.
- Polygraf — a programmable drum sequencer. It began as an experiment that produced a sequencer "normal people" would struggle with (binary entry), so seven-segment displays and a reworked record mode were added to make it usable.
- Chronograf — a start/stoppable low-frequency oscillator intended as a controller for Polygraf and similar modules: it tells them when to start, stop and which sequences to play. Holt highlights its wide range of waveforms as making it a strong modulation source.
How to use this list
If you are deciding which one to look into, the split is roughly by role: Bartos Flur and Polygraf generate sequences, Deep Thought processes logic signals, and Chronograf provides control and modulation for the others. Someone building a small generative or rhythmic patch would typically pair Polygraf with Chronograf; someone exploring gate-based patching would start with Deep Thought. Check Frequency Central's own product pages for current availability, since Holt's descriptions are project write-ups rather than shop listings.
How does the Bartos Flur sequencer determine its step from input voltage?
The Bartos Flur is a sequencer whose active step is set by the voltage level present at its input, rather than by an internal clock advancing through steps in order. Jet Holt describes it as "a sequencer whose step is determined by the input voltage level" and calls it "a quirky creature… weird… but fun." That means the input voltage acts as a position selector: different voltage levels map to different steps, so changing the voltage jumps the sequence to a different point. The site does not publish the exact voltage-to-step mapping, so treat any specific scaling as unconfirmed.
What that means in practice
- Voltage as position, not timing. Instead of a clock pushing the sequence forward, an external control voltage parks the sequencer on a chosen step. Feed it a slowly rising voltage and the sequence sweeps through its steps; hold a steady voltage and it stays put.
- Useful for addressing patterns. A keyboard, a CV source or another sequencer can steer which step is active, letting you select events by voltage rather than by count.
- Less predictable for clocked patterns. If you want a steady, tempo-locked run of steps, a voltage-addressed design needs a suitably stepped or ramped input; a plain clock won't do the job on its own.
A concrete scenario
A player wants a short melodic or trigger figure that changes shape depending on which note is held. Sending the held note's CV into Bartos Flur selects a step tied to that pitch, so each note addresses a different point in the sequence—an approach closer to a voltage-addressed switch than to a conventional step sequencer.
Decision criterion
Choose this kind of sequencer if you want voltage to choose where you are in a pattern and are comfortable with its quirks. If your priority is a straight, clock-driven sequence, a conventional step sequencer will be easier to predict. For the module's own documentation, see Frequency Central, and for the designer's write-up, Jet Holt.
What makes the Polygraf drum sequencer difficult for non-experts to use?
The Polygraf is hard for non-experts because its core interaction is binary: steps and patterns are read and entered as on/off bits rather than as an obvious grid of numbered steps. Jet Holt describes it as an experiment that "inadvertently created a powerful sequencer that 'normal people' would struggle with," and adds that only "nerds" can read binary. The fix in the design was to add seven-segment displays and rework record mode, which suggests the original difficulty was as much about feedback—seeing where you are and what you've entered—as about the underlying logic.
What that means in practice
- Reading state takes translation. A musician used to a row of step buttons with a moving playhead has to decode a binary representation to know which steps are active.
- Entering patterns is less direct. Without clear per-step feedback, recording a rhythm becomes a mental conversion task rather than tapping out a beat.
- Power and accessibility trade off. The same compact, logic-driven design that makes the module capable also raises the entry cost for anyone who wants a quick drum pattern.
A useful test if you're considering one: try to program a simple four-on-the-floor kick and a snare on the backbeat using only the panel's displays and record mode. If you can do that without counting bits on your fingers, the learning curve is probably manageable. If not, a sequencer with a visible step grid will get you to a playable pattern faster.
For context on the module and the rest of the collaboration, see Jet Holt.
What waveforms can the Chronograf low frequency oscillator produce?
The page does not list the specific waveforms the Chronograf can produce. Jet Holt's description highlights waveform variety as his favorite feature, calling the module "a powerful modulation source," but names no individual shapes (sine, triangle, square, etc.).
What the page does establish
- Chronograf is a start/stoppable low frequency oscillator built to control Polygraf and similar sequencer modules — telling them when to go, when to stop, and which sequences to play.
- Its value is as a modulation and control source, not just a clock: the range of waveforms is what makes it flexible.
- It is a collaboration with Frequency Central, so the definitive waveform list sits with the manufacturer's own documentation.
Next step
Check Frequency Central's product page or manual for Chronograf to confirm the exact waveform set and ranges before planning a patch. If you are comparing it with other modulation sources, list the shapes you actually need (for example, a ramp for sweeps versus a pulse for rhythmic gating) and verify each against the manual rather than assuming variety covers them.
What is Deep Thought and how can it be used as a learning tool?
Deep Thought is a synthesizer module Jet Holt co-designed with Frequency Central: an all-in-one boolean logic unit that combines the standard logic gates with switches and LEDs, plus a section that can be configured to act as any gate. Holt has described it as growing out of a joke about building a hands-on circuit to explain logic gates to a teacher, so its purpose is as much pedagogical as musical.
How it works as a learning tool
- See the gate, not just the symbol. Switches set the inputs; the LEDs show the output, so the truth table becomes something you observe rather than memorize.
- Compare gates side by side. Because the common gates sit on one module, a learner can feed the same input combination into AND, OR, XOR and the rest and watch how the outputs differ.
- Use the configurable section to test understanding. Ask a learner to predict the output for a given input pair, then set the flexible gate to match and check. That predict-then-verify loop is where the actual learning happens.
- Bridge to patching. In a Eurorack-style setup, logic outputs can drive triggers, clocks and sequencers, which turns abstract boolean results into audible rhythm changes.
Practical scenario
A teacher or synth hobbyist working with a small group could set up two input switches, walk through each gate's truth table, then hand the switches to a student and ask them to produce a specific output pattern. The LEDs give immediate feedback without needing a scope or meter. Holt's own framing—that the module should work as a teaching aid—suggests this kind of classroom or workshop use is the intended one.
Decision criteria
Choose Deep Thought if you want a single panel that covers many gates and rewards experimentation. If you only need one fixed logic function in a performance rack, a simpler dedicated gate may be less to learn. For background on the designer and his other modules, see Jet Holt.
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