ARP 1006 FILTAMP

Four signals in, one filtered roar out. This 2500-series board has a dual-analog design.

Overview

The ARP 1006 FILTAMP isn't a synth, a keyboard, or a standalone module. It's a circuit board. Built as a module for the ARP 2500 modular synthesizer, it combines a transistor ladder filter and a voltage-controlled amplifier (VCA) on a single densely packed board of through-hole components. It has no front panel of its own and sits in the chassis like a utility player. The same board is shared with the 1045 Voltage Controlled Voice module, so ARP trusted the design enough to reuse it.

What makes the 1006 stand out, at least to those who’ve poked around in the guts of a 2500, is its signal flow: four inputs feeding into one filter, then summed through a single VCA to a pair of outputs. That’s unusual. Most modular thinking leans toward one signal path per module, but here you’ve got a mini-mixer baked into the architecture — four sources, one filter sweep, one dynamic envelope. Imagine running two detuned oscillators, a noise source, and an external input all through that same ladder filter, tightening the cutoff until everything compresses into a pulsing, breathing mass. That’s the fantasy one user voiced online, and honestly, it’s a tempting one. The 1006 doesn’t just process sound — it homogenizes it, smearing distinct sources into a unified analog voice.

Specifications

Key Features

Transistor Ladder Filter + VCA: One Board, Two Jobs

ARP didn't waste real estate. The 1006 puts both a filter and a VCA on one shared circuit board. The signal path is fixed: all four inputs hit the filter first, get shaped by the ladder topology (the same one behind the character of the 2500 and 2600), then pass into the VCA for amplitude control. There's no bypass and no alternate routing. That might seem limiting today, but in the 2500's ecosystem the modules were building blocks, and the 1006 was a self-contained voice processor.

Four Inputs, One Voice

Four inputs on a single filter stage is rare, even in modular. Most filters expect one primary signal. The 1006 lets you feed it multiple oscillators, noise, and modulation sources, all filtered together. That creates phase interactions and subtle cancellations that are hard to replicate with discrete filtering. Since the board is used in the 1045 Voltage Controlled Voice module, ARP was probably repurposing a proven, compact design for a more complete voice solution.

Matched Transistors & Exponential Control

The 1006 includes multiple matched transistor pairs - NPN, PNP, and a complementary NPN/PNP assembly (Q18 and Q19) - which matter for stable, temperature-resistant performance in analog filters and VCAs. They are hand-paired during manufacturing to keep current handling and response symmetrical. The 4001-003 exponential converter module is on the board too, which means it expects control voltage input for filter cutoff. It translates linear CV into the logarithmic response our ears prefer.

Collectibility & Value

There's no current market data on the ARP 1006 FILTAMP as a standalone unit. It wasn't sold separately to consumers, so it rarely appears on its own in the used market. Most surviving examples are still embedded in 2500 systems or pulled for repair and restoration. One user noted appreciation for the four-input design, and another imagined using it with detuned VCOs and extra waveforms. Anyone hunting one is likely doing it for a restore, a DIY project, or a deep system mod, not as a collectible. Failure points and maintenance needs aren't documented in available sources, but given the transistor-heavy design and reliance on matched pairs, drift over time or after servicing would be expected.

eBay Listings

Behringer 1006 FILTAMP MODULE 24 dB Low-Pass VCF and VCA Mod

$46.90

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Related Models

• ARP 1004-T
• ARP 1004
• ARP 1005 ModAmp (1970–1981)
• ARP 1006 (early 1970s)
• ARP 1023 Dual VCO