Struct PowerSupply 

pub struct PowerSupply { /* private fields */ }

Power supply sag model for tube amp B+ rail behavior.

Models the real electrical phenomenon where the B+ supply voltage drops (“sags”) when the output stage draws more current than the supply can deliver instantly. The power supply has output impedance from:

• Rectifier forward voltage drop (tube: ~40-80V, solid-state: ~1-2V)
• Transformer winding resistance
• Filter capacitor ESR (equivalent series resistance)

The instantaneous sagged voltage is: V_sagged = V_nominal - I_draw * Z_output

The filter capacitor provides energy storage that smooths the sag, creating the characteristic “spongy” compression feel. The RC time constant (Z_output * C_filter) determines how quickly the voltage recovers after a transient.

This is what distinguishes a Marshall Plexi (tube rectifier, high sag, spongy feel) from a Mesa Boogie (solid-state rectifier, stiff response).

Implementations

impl PowerSupply

pub fn new( nominal_voltage: f64, impedance: f64, filter_cap: f64, rectifier: RectifierType, sample_rate: f64, ) -> PowerSupply

Create a new power supply sag model.

• nominal_voltage — No-load B+ voltage (e.g., 480V)
• impedance — Supply output impedance in ohms (tube rect: 50–200Ω, SS: 1–10Ω)
• filter_cap — Main filter capacitance in farads (e.g., 40µF)
• rectifier — Tube or solid-state rectifier
• sample_rate — Audio sample rate (Hz)

pub fn tick(&mut self, current_draw: f64) -> f64

Process one sample: given the instantaneous current draw (A), returns the sagged supply voltage.

The model works as follows:

1. The rectifier charges the filter cap toward V_nominal through Z_output.
2. The load draws current from the cap, discharging it.
3. The cap voltage is the actual supply voltage seen by the circuit.

The differential equation is: C * dVcap/dt = (V_nominal - Vcap) / Z_output - I_load

Discretized (forward Euler): Vcap[n+1] = Vcap[n] + dt/C * ((V_nominal - Vcap[n]) / Z_output - I_load)

pub fn set_sample_rate(&mut self, sample_rate: f64)

Update the sample rate (recomputes dt/C).

pub fn reset(&mut self)

Reset to nominal (no-load) state.

pub fn voltage(&self) -> f64

Get the current (sagged) voltage.

pub fn nominal_voltage(&self) -> f64

Get the nominal (no-load) voltage.

pub fn steady_state_voltage(&self) -> f64

Get the steady-state output voltage at no load.

This accounts for the rectifier static voltage drop that is always present, even with zero current draw. The cap charges to nominal voltage, but the output seen by the circuit is always reduced by the rectifier forward voltage drop (tube: ~10V, solid-state: ~1.4V).

Use this to initialize set_supply_voltage() so the first audio sample sees the same voltage the PSU will produce at idle.

Trait Implementations

impl Clone for PowerSupply

fn clone(&self) -> PowerSupply

Returns a duplicate of the value.

fn clone_from(&mut self, source: &Self)

Performs copy-assignment from source.

impl Debug for PowerSupply

fn fmt(&self, f: &mut Formatter<'_>) -> Result<(), Error>

Formats the value using the given formatter.