A stereo lamp phaser
Guilt Complex 'A' Lamp Phaser
The phaser you leave on (because you couldn't live without it.)
A 1970s German lamp phaser, solved from a photograph of its schematic: eight all-pass stages whose resistors are light-dependent cells, two incandescent lamps that light them, a feedback loop and a blend. Nothing draws the sweep. The filaments heat and cool, and the cells follow them, slowly in the dark.
VST®3 effect · Windows 64-bit No activationmacOS VST3 and Audio Unit are in development.
Listen
The same sixteen seconds, dry and twice through Guilt Complex 'A'. The three play together, so switching keeps your place: listen to WET 1 or WET 2 for a while, then press DRY.
Where it came from
Most phasers sweep along a shape: something draws a curve, and the notches follow it. A lamp phaser has no curve to follow. Its LFO swings the voltage on two small incandescent lamps, the lamps light eight cells whose resistance falls as the light rises, and the cells move the notches. So the sweep is a temperature. A filament heats in about 60 ms and cools over about 200, and a cell keeps darkening for 300 to 700 ms after its lamp has settled.
That is what makes it lean and breathe instead of wobble, and why you put it on a track and never take it off. Guilt Complex 'A' is a 1970s German lamp phaser solved from a photograph of its schematic: the eight stages, the feedback loop, the blend, the LFO, and the lamps and cells as the physics they are.
What is in the netlist
Nothing in the signal path is told where to sweep. The LFO warms the lamps, the lamps light the cells, and the cells are the stages' resistors, all solved together with the feedback around them.
THE LAMPS AND THE CELLS Two small 7 V lamps in series, one lighting four of the cells and the other the other four. Each filament heats and cools by its own heat balance, and each cell answers its lamp's light, quickly as it brightens and slowly, over hundreds of milliseconds, as it fades.
Read from one photograph
The source is a single photograph of the unit's schematic: no service notes, no parts list, no voltages. It prints two figures, the lamp line's top and the floor of its trim, and the sweep is calibrated to exactly those two.
| WHAT | THE SHEET | THE NETLIST |
|---|---|---|
| The sweep's floor | 50 Hz | F MIN solved to it: the lamp line at 3.95 V |
| The lamp line's top | 12.5 V | AMPLITUDE at full: the lowest notch at 4.8 kHz |
| One notch, two ways | the lamp line at 7.124 V | 750 Hz solved, 751 Hz calculated |
WHAT THE PHOTOGRAPH COULD NOT SETTLE
The lamp driver's front end is too faint to read, so the follower that is legible is fed the triangle mapped onto the sheet's range. The jacks' and the footswitch socket's switching are not modeled beyond the line path. One resistor in the LFO would, as read, stop it from running, so it is left out, and a third lamp is read as a panel light.
HOW THE NOTCH WAS CHECKED
With FEEDBACK off and the lamp line held at 7.124 V, the netlist's lowest notch lands at 750 Hz, 51 dB under the dry signal. A separate calculation from the filaments' heat balance, the cells' law and the stages' corners, with no circuit solved, puts it at 751 Hz.
Playback and bounce
The circuit cannot promise real time on every kind of material, so Guilt Complex 'A' keeps two engines and tells you which one you are hearing. The panel prints it along its foot:
LIVE PLAYBACK / CIRCUIT ENGINE ON BOUNCE
LIVE PLAYBACK
While you play, the eight stages and the feedback loop are solved exactly each sample with ideal op-amps, the LFO is a triangle between the circuit's own turning points, and the lamps' heat and the cells' response are integrated as the circuit's are. It takes a few percent of one core. Through a sweep its lamps stay within 20 K of the circuit's and its cells within 5 to 10 percent. It leaves out the op-amps' finite bandwidth and the lamp follower's own law.
BOUNCE ENGINE: CIRCUIT
When your DAW renders offline, Guilt Complex 'A' solves the netlist in three blocks: the LFO, the lamps and their follower, and the eight stages, whose cells read the filaments' temperatures. The knobs move their parts as it goes, so the bounce follows your automation (CAP, the eight stage capacitors, from the next bounce), and both engines have the same delay, so a bounce lines up with playback to the sample.
| BOUNCE ENGINE | THE PANEL SAYS | A BOUNCE RUNS | HOW LONG IT TAKES |
|---|---|---|---|
| LIVE | LIVE ENGINE / PLAYBACK + BOUNCE | The live engine, exactly as it plays. | Faster than the song |
| CIRCUIT | LIVE PLAYBACK / CIRCUIT ENGINE ON BOUNCE | The netlist: the eight stages, the feedback, the LFO, and the lamps and cells as heat and light. | From about the length of the song to a few times longer on bright, busy material |
The panel
FRONT is the unit, with a window on LAMP 1 and LAMP 2 glowing at the engine's own filament temperature. INSIDE is what a technician would reach: the TRIMS, the SELECTED PARTS a unit was built with, and the LINE.
FEEDBACK
How much of the phased signal returns to the input: deeper, sharper notches, up to just short of oscillation.
MODULATION
The blend, from DRY through EVEN to WET. EVEN gives the deepest notches.
AMPLITUDE
How far the lamps swing above their floor, up to the sheet's 12.5 V at full.
PERIOD
The LFO's timing resistor; it shows the period, 4 seconds by default.
SPEED
FAST, or SLOW: the footswitch's slow contact.
SWEEP
ON, or HELD: the triangle stops where it is, and the lamps settle there.
BOUNCE ENGINE
CIRCUIT, an offline render solves the netlist; or LIVE, it renders the live engine, as fast as playback.
INSIDE / FRONT
The key at the top right turns the panel round: FRONT is the unit, INSIDE its trims and selected parts.
F MIN
TRIMS. The trim that sets the lamps' floor, so the sweep's lowest notch at its bottom, 10 to 400 Hz; the sheet's 50 Hz by default.
FB ADJ
TRIMS. The trimmer beside FEEDBACK, 10k to 220k: the most feedback FEEDBACK gives.
CAP
SELECTED PARTS. The eight stage capacitors, 15 to 33 nF, the range the sheet allows; in a bounce, from the next one.
SPREAD
SELECTED PARTS. How unevenly the eight cells answer their lamps, up to 50 percent.
LAMP
SELECTED PARTS. The filaments' thermal time, half to twice.
CELL
SELECTED PARTS. The cells' speed, a quarter to four times.
DRIVE
LINE. The level in, from -12 to +18 dB, and back out, so it changes how hard the circuit works rather than how loud it is.
What it is, and what it is not
Guilt Complex 'A' is not a replica of any one unit, and we do not claim it sounds like one. It is what the circuit on that sheet does, with the parts the sheet left open chosen inside the ranges it gives and the rest estimated and marked.
SOLVED
The eight stages and their op-amps, the feedback loop, the blend, the LFO, the lamp follower, the two filaments by their heat balance and the eight cells by their own physics, quick to brighten and slow in the dark.
NOT MODELED
The power supply: the rails are ideal. The jacks' and the footswitch socket's switching, beyond the line path and the two footswitch contacts. In live playback, also the op-amps' finite bandwidth, which is why the circuit has the final word.
ESTIMATED
The cells' sensitivity, their slope and dark resistance, and their speed; the lamps' thermal time; one transistor's gain. Each is bracketed in the netlist. The cells' sensitivity sets the top of the sweep, so its 4.8 kHz at full AMPLITUDE is our best estimate.
The lamp phaser, solved
Guilt Complex 'A' Lamp Phaser
The phaser you leave on (because you couldn't live without it.)
VST®3 effect · Windows 64-bit No activationmacOS VST3 and Audio Unit are in development.
At a glance
| Format | VST®3 effect · Windows 64-bit |
|---|---|
| In development | macOS VST3 and Audio Unit |
| Requires | 64-bit Windows 11, in any version Microsoft still supports. When the Mac version ships: macOS 15 or later, on Apple silicon or Intel. |
| Channels | Stereo |
| The netlist | Eight all-pass stages, the feedback loop, the blend, the LFO, the lamp follower and the two lamps |
| Read from | One photograph of the schematic sheet · its 12.5 V lamp line and 50 Hz floor |
| Playback | The live engine, from the same parts · a few percent of one core |
| Bounce | BOUNCE ENGINE CIRCUIT: the netlist · LIVE: the live engine |
| Bounce time | From about the length of the song to a few times longer |
| FRONT | FEEDBACK, MODULATION, AMPLITUDE, PERIOD · SPEED FAST or SLOW · SWEEP ON or OFF · BOUNCE ENGINE |
| INSIDE | F MIN and FB ADJ · CAP, SPREAD, LAMP and CELL · DRIVE |
| Latency | The same in playback and the bounce, so a bounce lines up to the sample |
| The panel | 1200 by 480 · two faces |
| Validation | 47 of 47 validator tests · host-tested |
| Activation | None. No license server, no phone-home |
| Security updates | Until November 2031 |
| License | License agreement · Facts sheet |
VST is a registered trademark of Steinberg Media Technologies GmbH.
