AMSynths AM1013 (2024)
Eight fixed bandpass filters spaced an octave apart, bringing back a lost ARP 2500 concept with modern precision and WIMA caps.
Overview
Patch in a sawtooth wave, flick the bypass switch, and the modular starts speaking in vowels. These are real formant textures, somewhere between a choir and a vintage sci-fi laser blast. That's the AM1013: eight parallel 12dB/octave bandpass filters, each tuned a full octave from its neighbor, spanning 63Hz to 8kHz. It's not a resonant ladder and not a sweeping multimode. It's a fixed filter bank that carves broadband sound into harmonic islands. The module never existed in ARP's original 2500 lineup, though Tonus teased it in 1970 as the 1013. AMSynths dusted it off and rebuilt it with modern components and a sonic upgrade.
The AM1013 uses an op-amp-based topology. Each bandpass filter is a 12dB high-pass and a 12dB low-pass in series, both with a Q of 5.0. That's tighter than the Yusynth FFB (Q=2.7) and less wild than the Behringer FFB's Q of 7.0, which leans on ceramic SMD caps. AMSynths went with WIMA polypropylene capacitors, known for clarity and warmth, so the response is clean but not clinical, with a rounded presence that suits both noise and pitched sources. The frequency range is broader than Moog-style fixed banks, which typically start at 125Hz, so you get deeper lows and airier highs. Each of the eight bands also has its own output, so you can route individual slices to VCAs, delays, or other filters.
The module is 14HP. The front panel is a clean, anodized aluminum slab with twelve 3.5mm jacks: two inputs (with level control), two mixed outputs (also level-adjustable), and eight individual band outputs. The blue ARP 2500-style knobs set each band's contribution to the mix, while green knobs handle input and output gain. A momentary push-button toggles the bypass, with a green LED indicating when the effect is off. Early units had the LED logic reversed, a quirk AMSynths acknowledged and promised to fix in later runs. It ships with a Doepfer-style power cable and mounting hardware.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2024–present |
| Original Price | £195 / €225 / $249 |
| Format | Eurorack |
| Width | 14 HP |
| Depth | 40 mm |
| Current Draw | 120 mA on +12V, 30 mA on -12V |
| Filter Type | Fixed bandpass filter bank |
| Number of Filters | 8 |
| Filter Spacing | One octave apart |
| Frequency Range | 63 Hz to 8 kHz |
| Filter Slope | 12 dB/octave high-pass + 12 dB/octave low-pass (24 dB/octave effective bandpass) |
| Q Factor | 5.0 |
| Capacitors | WIMA polypropylene |
| Inputs | 2 x 3.5mm (with level control) |
| Outputs | 2 x 3.5mm mixed output (with level control), 8 x 3.5mm individual filter outputs |
| Controls | 8 x level pots (individual bands), 2 x level pots (input/output), 1 x bypass switch |
| Power Connector | 10–16 way Doepfer standard |
Key Features
Op-Amp Precision with Vintage Character
The AM1013 doesn't emulate the discrete transistor guts of old filter banks. It uses modern op-amp circuitry to keep all eight bands tight and consistent. Each filter is a cascade of a 12dB high-pass and 12dB low-pass, both with a Q of 5.0, so each band is narrow enough to isolate specific harmonics but wide enough to avoid sounding pinched. The WIMA polypropylene capacitors, known for low distortion and smooth high-end, give the module a polished but organic tone. It doesn't chase a "vintage" sound through component scarcity. It aims for clarity.
Individual Outputs Unlock Creative Routing
Most fixed filter banks give you a single mixed output and maybe a bypass. The AM1013 breaks each of its eight bands out to its own jack. You can feed each filtered slice into a separate VCA (like the AM1042 Triple VCA), then modulate their levels over time with envelopes or LFOs. You could patch the 1kHz band into a delay, the 2kHz into a ring mod, and the 4kHz into a reverb, each treated differently, then recombined. It also works with the AM1032 Mixer & Distributor for complex, time-variant formant sweeps. Feedback patches work too: route the mixed output through a delay, then bring the repeats back into the AM1013 to be filtered again.
Bypass Switch with Level Trim
The bypass is part of the workflow. The momentary switch toggles the effect in or out, with a green LED showing bypass status (early units had this inverted, but AMSynths confirmed a fix for later production). The input and output level controls are more useful still. Filter banks can load down sources or output unexpectedly hot signals, so front-panel trim pots let you match levels without repatching. That helps when A/B'ing processed against dry sound, or when feeding the AM1013 different sources - noise, drums, vocals, or complex FM tones - which might each need different gain staging.
Historical Context
The AM1013 isn't a clone. In 1970, ARP announced a 2500 system expansion that included a module called the 1013 Octave Filter Bank, designed by Tonus. It never made it to production, lost to the shifting priorities of a company racing to keep up with Moog and Buchla. The idea lived on elsewhere, most notably in the EMS Synthi 100's Eight Octave Filter Bank from 1971, which used a similar concept for formant synthesis and spatial effects. AMSynths' version draws direct inspiration from that EMS design but puts it in the ARP 2500 style with modern Eurorack usability. It's part of a "lost modules" series from AMSynths - recreations of ARP concepts that never shipped, like the AM1026 Preset Voltages and AM1028 Sequential Volts.
It arrives while Eurorack users are rediscovering static spectral shaping. Most modules chase movement, like sweeping filters, modulated waveforms and sequenced effects. The fixed filter bank holds a single moment of harmonic selection. It works for sound design and for experimental processing. You don't need CV to make it musical; patch in a source and the sound is pulled apart into its component frequencies.
Collectibility & Value
As a 2024 release, the AM1013 isn't vintage in the traditional sense, but it's already finding a niche among ARP 2500 rebuilders and formant enthusiasts. New units sell for around £195 / €225 / $249 directly from AMSynths, and they tend to sell out quickly, especially in batches tied to synth shows like Synth East or Machina Bristronica. Secondhand prices on the modular market hover near MSRP, with few discounts unless the seller is clearing space. There are no known failure points yet, with no batch issues with power draw or capacitor leaks. Given the through-hole WIMA caps and Alpha pots, long-term reliability looks strong. The only reported quirk is the LED polarity on early units, which indicates "bypass active" when lit. AMSynths acknowledged this and committed to reversing it in future runs, so collectors may want to verify production date if the LED behavior matters.
For buyers, the real value isn’t just in the module itself but in what it enables. Pair it with the AM1032 Mixer & Distributor, and you’ve got a full-featured formant processor. Stack two AM1013s for stereo filtering. Use it to process external audio—field recordings, vocals, drum machines—and you’ll find it excels at turning mundane sources into evolving pads or rhythmic textures. It’s not a “must-have” for every rack, but for anyone chasing the ARP 2500’s unrealized potential or exploring spectral synthesis, it’s becoming a cornerstone. Watch for used units with bent jacks or scratched panels—otherwise, it’s a low-risk, high-reward addition to any Eurorack system.
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