The Yellowcake Psychotropia is a sample and hold filter pedal from Yellowcake Pedals, first shown at Summer NAMM in July 2019 and launched that August1. Where a regular autowah sweeps a filter up and down on a smooth curve, a sample and hold circuit grabs values at intervals and jumps the filter between them, producing the random, stepped, "talking" filter motion heard on vintage synths. Delicious Audio notes this kind of circuit was used in filters on some vintage synths and later adopted in filter pedals like the Subdecay Proteus, ZVex Ooh Wah and Xotic Robotalk1.
At its heart, Delicious Audio describes the Psychotropia as a tap tempo enabled autowah-style filter using "weirder" LFO waves, with controllable resonance and CV ins and outs1. MusicRadar framed its range broadly: useful "for adding some disco funk to your tone, pitching you headlong into off-grid, experimental prog, or for simply inspiring the odd flashback with the sci-fi weirdness at its outer limits"2. The pedal ships in a neon pink enclosure3.
How the filter works
The Psychotropia's LFO can be set to three different wave shapes, more complex than a regular autowah sine wave, selected through the left toggle1. Pedal of the Day breaks the positions down: Up gives a rising edge, Middle gives both a rising and falling edge, and Down gives a strictly falling edge3. MusicRadar describes the same three modes as rising, rising and falling, and falling waveforms2.
The steps themselves can be reshaped two ways. The Glide knob sets how much slide happens between them, and the Log/Lin toggle changes the character of the square wave pattern: Lin is a hard-edged square wave, while Log softens and rounds the edges1. Gearnews adds that the Log toggle activates a function to soften or round the edges of the random pattern5.
"The 'angularity' of the steps can be tamed by raising the value of the Glide knob."
The controls
The pedal keeps its control set compact: a few knobs, a tap tempo footswitch and three toggles. Here is what each one does, drawn from the press coverage and Pedal of the Day's review.
| Control | What it does |
|---|---|
| Rate | Sets the speed of the filter movement5 |
| Tap tempo | Adjusts rate on the fly instead of using the Rate knob, so you can change the effect's tempo mid-song12 |
| Glide | Sets the amount of up and down slide between the sample and hold steps; higher settings tame the angularity of the steps13 |
| Res | Controls the amount of self-oscillation, or resonant feedback, of the filter side of the circuit53 |
| Level | Controls the overall output volume3 |
| Left toggle | Selects the waveform: rising, rising and falling, or falling3 |
| Middle toggle (Log/Lin) | Chooses Logarithmic, which rounds and softens the edges of the waveform, or Linear, a more traditional hard-edged waveform13 |
| Hi/Low toggle | A Hi/Low EQ cut that gives a brighter or darker tone option; Gearnews notes it seems to interact with the sample and hold pattern15 |
The tap tempo is one of the pedal's practical strengths. Guitar World highlighted it for on-the-fly rate adjustments4, and MusicRadar pointed out that it lets you bypass the Rate control entirely and change tempo mid-song2, which matters for locking the stepped filter motion to a groove rather than chasing a knob.
CV connections and synth use
The Psychotropia has a CV input and output for external triggering5. Delicious Audio notes the CV In/Outs make it compatible with synths supporting that format, specifically Eurorack gear1. On the output side, Pedal of the Day reports that CV Out sends the Rate and Glide knob functions along with the Up, Mid, Down and Lin/Log toggle positions3, so a modular system can follow the pedal's settings. This is the feature that separates the Psychotropia from most autowah-style filter pedals: it can sit in a synth or modular rig as well as on a pedalboard.
Where it came from
The Psychotropia continues Yellowcake's interest in creative stompboxes1. The maker's earlier filter work includes the Yellowcake Lida Machine. The Psychotropia was first noticed at Summer NAMM 2019 in July, and the first official videos appeared in September 20191.
What reviewers said
Coverage at launch was positive. Gearnews wrote:
"I'm a huge fan of Yellowcake Pedals and I think they make some truly sumptuous effects. This one seems well worth checking out."
Pedal of the Day's 2020 review walked through the controls, toggles and CV jacks and concluded there was "a lot to explore in this neon pink gem"3.
Videos
Premier Guitar
Eirik Stordrange
Eric Merrow
Questions
Is the Yellowcake Psychotropia true bypass?
Yes. Gearnews reported that the Psychotropia is true bypass, so it leaves your dry guitar signal alone when the effect is switched off. That makes it a safe fit on a larger pedalboard where you want other pedals to hear an uncolored signal.
How much does the Psychotropia cost?
The Psychotropia was priced at $229 when it launched in August 2019, according to both Guitar World and MusicRadar. It was available to order direct from Yellowcake Pedals and through select dealers.
What does the Glide knob do on the Psychotropia?
Glide sets how much slide there is between the steps of the sample and hold waveform. Delicious Audio describes it as taming the angularity of the LFO steps, so low settings give sharp, stepped jumps and higher settings smooth the transitions into a more sweeping motion.
What is the difference between the Log and Lin settings?
The Log/Lin toggle changes the shape of the square wave pattern. Lin is a hard-edged square wave, while Log softens and rounds the edges of the waveform, giving the filter a less abrupt, more fluid character.
Can the Psychotropia sync to a synth?
Yes. The pedal has CV input and output jacks, and Delicious Audio notes the CV format is compatible with Eurorack gear. CV Out sends the Rate and Glide knob functions along with the Up, Mid, Down and Lin/Log toggle positions, so it can integrate with a modular or synth setup.
Sources (5)
- Yellowcake Psychotropia, Delicious Audio, 2019-09-24
- Yellowcake Pedals unveil the mind-expanding Psychotropia, MusicRadar, 2019-08-12
- Yellowcake Pedals Psychotropia Sample/Hold Filter, Pedal of the Day, 2020-08-01
- Yellowcake's Psychotropia takes waveforms into new realms of weird, Guitar World, 2019-08-13
- Yellowcake Pedals induces Psychotropia, a trippy kaleidoscope of sound, gearnews.com, 2019-08-12
