ARP 4023 (1972–1975)

Name: ARP 4023
Brand: ARP

The raw, unvarnished voice of the original whiteface Odyssey—less polished than a Moog, more aggressive than a Prophet, and utterly alive in a way only ARP’s 2-pole design could be.

Overview

Plug in a whiteface ARP Odyssey from 1972 and twist the filter cutoff just past 12 o’clock—you’ll hear it: a growl that starts in the chest and climbs into the skull, thick with harmonics and just shy of oscillation. That’s the 4023 talking. Not the later 4035 or the 4075, but the original 2-pole voltage-controlled filter that defined the early Odyssey’s character before ARP smoothed out the edges. It doesn’t purr like a Minimoog; it snarls. It doesn’t emulate anything. It just *is*—a dual OTA (operational transconductance amplifier) bi-quad design that trades the 24dB/oct slope of its successors for a looser, more organic 12dB/oct roll-off. The result? A filter that breathes, wobbles, and bites when pushed, with a resonance that doesn’t just peak—it howls.

Found exclusively in the first run of ARP Odyssey Mk I units (Model 2800), the 4023 was ARP’s answer to the need for a compact, stable, and sonically distinct filter that could handle the aggressive output of the Odyssey’s dual oscillators. Where Moog went for the deep, rounded ladder, ARP went for speed and attitude. The 4023 responds to modulation with a nervous energy—slap on some keyboard tracking, crank the envelope, and you’re not just shaping sound, you’re wrestling with it. It’s not the most precise filter ever made, but precision wasn’t the point. This was a gigging synth in the early '70s, built to cut through a mix with sawtooth waves, ring modulation, and that signature PWM. The 4023 gave it the teeth.

Later revisions of the Odyssey would swap in the 4035 (a 24dB/oct ladder) and eventually the 4075, both of which tamed the wildness in favor of smoother sweeps and better bass response. But collectors and tone hounds still chase the 4023 for what it *doesn’t* do: play it safe. It’s the filter that made Herbie Hancock’s “Chameleon” lead sound like a laser ricocheting through a steel mill, the one that gave Jan Hammer his early fusion bite. It’s also the reason why a well-maintained whiteface Odyssey commands a premium today—because no other ARP filter sounds quite like it.

Specifications

Manufacturer	ARP Instruments, Inc.
Production Years	1972–1975
Original Price	Not available
Filter Type	2-pole voltage-controlled bi-quad
Filter Slope	12 dB/octave
Topology	Dual OTA (CA3080 or equivalent)
Resonance	Voltage-controlled, self-oscillating
Frequency Range	Approx. 20 Hz – 20 kHz
Control Voltage Input	Exponential, temperature-compensated
Signal Path	DC-coupled
Key Components	CA3080 OTAs, 2N5459 FETs, matched TO-92 transistors, temperature compensation resistor
Potentiometers	Six 20mm Alpha slide pots (on original module)
Module Designator	4023
Used In	ARP Odyssey Mk I (Model 2800), whiteface and early grey/gold variants
Replaced By	4035 (in Odyssey Mk II), 4075 (in later models)
Dimensions	Not available
Weight	Not available
Power Requirements	±15 VDC (via host synthesizer)

Key Features

A 2-Pole Rebellion in a 4-Pole World

In an era where 24dB/oct filters were becoming the standard—Moog, Oberheim, even ARP’s own later designs—the 4023’s 12dB/oct slope was a deliberate act of sonic defiance. It doesn’t scoop the mids as dramatically, doesn’t tighten the bass as aggressively, and doesn’t give you that “locked-in” sweep some players crave. But what it *does* give you is movement. The transition from open to closed feels more like a slow sunrise than a slamming door. This makes it exceptional for evolving pads, squelchy leads, and anything that needs to feel unstable in just the right way. The bi-quad topology means it can be patched for multiple outputs (low-pass, band-pass, even high-pass with external circuitry), though in the Odyssey it’s hardwired to low-pass only. Still, that secondary band-pass output lurking on pin 9 of the module has become legend among modders—some quietly tap it for an extra flavor of grit.

OTA Grit, Not Ladder Warmth

The heart of the 4023 is its dual CA3080 OTAs, running in a transconductance configuration that gives it a faster, more dynamic response than the integrator-based ladder filters ARP would later adopt. OTAs are inherently noisier and less linear, but they’re also more immediate—there’s no lag between your envelope and the filter’s reaction. That’s why the 4023 feels so “present,” even at low resonance settings. It doesn’t just filter; it modulates, distorts, and interacts with the input signal in ways that ladder filters avoid. The trade-off? Higher noise floor, especially as the module ages and the OTAs drift. But many argue that noise is part of the charm—the slight hiss under a sawtooth lead is like tape saturation on a vintage console. It’s not clean. It’s *real*.

Drop-In Legacy, Still Alive Today

The 4023 wasn’t just a circuit—it was a module, a self-contained black box designed for easy replacement and service. That modularity has kept it alive decades later. Today, boutique builders like Synthchaser, Frequency Central, and G-Storm Electro offer faithful recreations, often with modern reliability tweaks like temperature compensation resistors and matched transistors. Eurorack users can drop a 4023 clone into a 5U or 3U case and patch it like a standalone processor. And because the original schematics are well-documented (thanks to ARPtech and the DIY community), even failed modules can be rebuilt from scratch. It’s rare for a 50-year-old filter to have an active clone ecosystem—but then again, most filters don’t sound like they’re trying to eat your speakers.

Historical Context

The 4023 emerged at a pivotal moment: 1972, when ARP was racing to capitalize on the Odyssey’s surprise success while fending off cheaper competition from Roland and Korg. The original whiteface Odyssey wasn’t just a scaled-down 2600—it was a statement. Where Moog emphasized stability and musicality, ARP leaned into aggression and versatility. The 4023 was central to that identity. It wasn’t trying to imitate anyone. It wasn’t even trying to be “better.” It was trying to be *different*. And it succeeded.

By 1975, ARP had shifted course. The Mk II Odyssey introduced the 4035—a 24dB/oct ladder filter that brought the synth closer in tone to the Minimoog, likely to broaden its appeal. The move made commercial sense, but it alienated purists who missed the 4023’s raw edge. Later models like the Omni and Pro Soloist would use the 4075, a cost-reduced version of the same ladder design, cementing ARP’s pivot toward smoother, more predictable tones. The 4023, meanwhile, became a footnote—except among those who remembered how good it felt to lose control.

Today, the 4023 is revered not just for its sound, but for what it represents: a brief window when ARP prioritized character over conformity. It’s the filter that refused to grow up, even as the rest of the company moved on.

Collectibility & Value

If you’re hunting for a 4023, you’re not just buying a filter—you’re buying a piece of a whiteface or early grey/gold Odyssey (Model 2800). These synths are rare, and the ones with original, unmodded 4023 modules command serious money. A fully serviced whiteface Odyssey with its original filter intact can fetch $2,000–$3,000, sometimes more if it’s in exceptional condition. But beware: many have been recapped, slider-upgraded, or even retrofitted with 4035 modules. A “whiteface” with a 4035 isn’t a whiteface in spirit, no matter what the case says.

The 4023 itself is prone to a few failure points. The CA3080 OTAs degrade over time, leading to loss of resonance, instability, or complete cutoff failure. The 2N5459 FETs can drift, causing tuning issues in the filter’s response. And while the module is DC-coupled (great for CV processing), that also means any power supply ripple gets amplified straight through. Tantalum capacitors in the surrounding circuitry are notorious for leaking or shorting, so a full recap of the host synth is strongly advised—even if the 4023 module itself is sealed and untouched.

For the budget-conscious, standalone 4023 modules on Reverb or eBay offer a way in. Expect to pay $250–$400 for a tested, working unit—less if it’s untested or cosmetically worn. Clones from Synthchaser or Frequency Central run $180–$280 and often outperform originals in stability, though some argue they lack the “magic.” Either way, the 4023 is no longer just a repair part. It’s a cult object.