Band‑Selective Current Drive Amplifier

Clearer highs, controlled lows.

Most modern amplifiers already have extremely low measured distortion; so low that, in a real speaker system, the driver is the distortion bottleneck.
The amplifier’s distortion is typically under 0.01%, while the driver’s can be 0.1% to 10%. So adding another “zero” to THD is often an engineering flex more than a system upgrade.

I’ve been exploring a different lever: make the driver’s current more linear, because current is what creates force in the voice coil. That’s what this module does. It uses Band‑Selective Current Drive (BSCD): it behaves like a normal voltage amp at low frequencies (i.e. high damping factor), then transitions to current control through the rest of the band to clean up driver distortions (see the study). It also includes a built‑in DSP with a simple desktop app for easy active crossover and EQ design.

Why this matters

Midband/HF distortion = fatigue

Non‑linear distortion blurs vocals and cymbal detail and leads to listening fatigue. A big contributor is current distortion from inductance modulation in the driver.

We control what makes sound

Electrodynamic drivers create sound from voicecoil current (Lorentz force), not voicecoil voltage. By improving current linearity we improve sound linearity.

Clarity without pricier drivers

Reducing nonlinearity with BSCD drops offensive distortions to levels you’d expect from drivers 6x more expensive. That’s a difference you can hear.

How it works

Current control where it matters

Above the LF region, the module presents high output impedance so coil current is unaffected by the driver’s back‑EMF nonlinearity—cleaning up harmonic and intermodulation distortions that cloud detail.

Resonance stays controlled

Pure current drive removes electrical damping (Q_es), causing a resonant peak at Fs. BSCD keeps low output impedance at low frequencies so the amp behaves like a voltage amp around Fs—your woofer remains well‑damped.

Set once with a simple switch

Use the Transition Frequency switch to place your driver’s Fs inside the low‑impedance region. Choose once during setup—then forget it.

Built‑in DSP: Active XO & EQ

Active crossovers

Design flexible active crossovers in the desktop app—no passive network between amp and driver. Save and recall presets for different builds.

Powerful EQ

Shape your response with DSP‑powered EQ to fine‑tune voicing and fix room or driver quirks.

Simple programming

Once you dial your XO & EQ, send the configs to the amp through USB-C connection. Configs can be save to and loaded from the amp itself or a human readable text file.

No compromises

Quality components

Audio-grade Coilcraft output inductors for ultra-low distortion.
Signal-path capacitors are Nichicon electrolytic, film, or Class-I (C0G/NP0) ceramics.
Thin-film resistors throughout to minimize noise and distortion.

Meticulous design

Reverse polarity and in-rush current protection.
Low-jitter clocking with careful noise control.
Differential audio routing with matched, interference-resistant pairs.
Low-noise power network for clean, stable power delivery.

In Short

What you’ll get

Hybrid current‑control Class‑D amplifier module
Desktop app for configuring DSP active crossover & EQ
Guides, presets, and build examples

Who it’s for

Boutique speaker manufacturers
DIY speaker builders & modders
Makers who value clarity over color

Specs

2 x 120W into 4Ω @ 1% THD+N
0.005% THD+N @ 1W
15V - 36V supply
2 flexible balanced analog inputs
I2S input and output
Exposes I2C, SPI, ADC, GIPOs
6” L x 2.5” W x 1.75” H

FAQ

Does it work with passive crossovers?

For current control to be effective, the amplifier should connect directly to the driver. Use the built‑in DSP to implement your crossover and EQ actively. However, the amp can be set to operate in voltage drive mode to work with a passive crossover.

Do I need to be “super technical” to use it?

The desktop app exposes a friendly UI and simple controls. If you are familiar with EQs and crossovers, you are good to go.

Curious how/where current drive helps?

Technical appendix (optional reading)

An electrodynamic driver’s back‑EMF can be modeled as including a distorting voltage source that is produced by modulation of its inductance as a function of current i.e. Le(i) and Le(x). Both distortions tent to be dominant at low displacement regimes (e.g. mid and high frequencies) - even at low volumes.
By keeping output impedance low at low frequencies, the amplifier preserves Qes‑linked damping around resonance. Above that region it presents high output impedance (i.e. transitions into current drive), making current unaffected by the distortion voltages produced by Le(i) and Le(x) thereby reducing harmonic and intermodulation distortion products.