AMSynths AM1035 (2024–)
A Eurorack revival of ARP's triple modulator - 54 years in the making.
Overview
The original AM1035 was supposed to be part of the 2500's lineup, priced at a hefty $820, but it vanished before full production. It existed only in ARP's 1970 catalogs and prototype photos. For decades it lived in schematics and speculation. Now AMSynths has brought it back as a Eurorack module.
This isn't a clone in the strictest sense. It's a reimagining, built from ARP's original 4014 multiplier circuit but adapted for modern use. Each of the three channels is a four-quadrant analog multiplier, capable of ring modulation, voltage-controlled amplification, and clean mixing, all switchable on the fly. Most ring modulators only do one thing, but here you can go from metallic bell tones to smooth amplitude modulation to simple summing without repatching. The MOD/MIX switch on each channel does the work. Flick it to MIX and you hear the unprocessed blend of your two inputs. Flip it to MOD and everything collides in a mess of sidebands.
The layout mirrors the original ARP look, clean and functional. The front panel uses ARP 2500-style Rogan knobs in silver, yellow, and blue to tell the three channels apart. The orange LEDs, a modern upgrade from the original's incandescent bulbs, glow when you push past ±10V, a warning that your signal is clipping. It's 14HP, which is tight but not cramped. Channels 2 and 3 are normalized to channel 1, so you can run multiple modulators in parallel with minimal cabling.
Specifications
| Manufacturer | AMSynths |
| Production Years | 2024– |
| Original Price | £149.00 (inc. tax) |
| Format | Eurorack |
| HP | 14 |
| Depth | 40mm |
| Power | 16-pin Doepfer |
| Current Draw | ±12V: 100mA / +5V: 0mA |
| Channels | 3 independent four-quadrant analog multipliers |
| Inputs per Channel | 2 (X and Y, DC/AC switchable) |
| Outputs per Channel | 1 (audio) |
| Input Coupling | Switchable AC or DC per input |
| Operating Mode | MOD (ring mod/VCA) or MIX (summing) |
| Gain Control | Level potentiometer per input (X and Y) |
| Overload Indication | 3 orange LEDs (per channel, ±10V threshold) |
| Normalization | Channels 2 and 3 inputs normal to channel 1 |
| Knobs | Rogan ARP 2500 style |
| Potentiometers | Alpha high-quality |
| Weight | 350g |
| Mounting | M3 screws and washers included |
Key Features
Four-Quadrant Multipliers with Real Switching Flexibility
The heart of the AM1035 is its trio of discrete four-quadrant multipliers, based on ARP's 4014 circuit, the same topology used in the 1005 Mod Amp. That means true analog multiplication, not digital approximation or diode-ring trickery. Each channel can multiply two signals, whether audio or control voltage, and the result depends on how you patch it. Feed two audio signals in AC mode and you get classic ring modulation - metallic, atonal, and full of sidebands. Patch a CV into Y and an audio signal into X, and it becomes a VCA with exponential response. The MOD/MIX switch lets you blend the raw mix with the modulated output, so you can compare pre- and post-modulation states directly.
AC/DC Coupling Per Input—No Compromises
Most multipliers force you to choose between audio and CV use, but the AM1035 doesn't. Each input has a dedicated AC/DC switch, so you can mix and match. You can modulate a slow LFO with an envelope, or ring mod two oscillators and then use the output to modulate a filter cutoff. The AC path includes a gain stage adjustable from unity to 10x. DC bypasses the amp and feeds straight into the multiplier via a unity-gain buffer. This separation is crucial for clean CV processing and avoids the low-frequency roll-off that plagues many AC-coupled designs.
Overload LEDs That Actually Help
The orange LEDs are functional. Each one lights up when the output exceeds ±10V, a sign that you're hitting the rails and introducing distortion. Some clipping can be musical, but uncontrolled clipping in a multiplier chain can create unpredictable artifacts. The LEDs let you back off the gain or attenuate inputs before things get messy. Unlike the original's slow incandescent bulbs, these respond instantly.
Historical Context
In 1970, ARP teased the AM1035 in their Tonus announcement and early 2500 catalogs as a high-end, multifunctional processor. At $820, it was one of the most expensive modules in the system. But for reasons lost to time, it never went into production. The rack space it would have occupied often held a second dual envelope generator instead. For decades it was a footnote for synth historians.
In 2024, AMSynths, led by Rob Keeble, an engineer with deep ARP restoration experience, decided to finish what ARP started. Keeble had already worked with Behringer on their 2600 and 2500 reissues, which gave him rare access to ARP's design language. The AM1035 is part of a larger "lost modules" series. Other companies reissue classics, but AMSynths is building something ARP never shipped.
Collectibility & Value
The AM1035 isn't vintage in the traditional sense, since it's brand new, but it's already collectible. Limited production runs (around 500 units per year) and high demand mean it sells out quickly. At £149, it's not cheap for a 14HP module. There's no secondhand markup yet. Condition is straightforward: since it's new, there's no wear, but check that the LEDs respond correctly and that the pots turn smoothly. There are no known failure points. AMSynths uses SMD components and matched transistor pairs, and the build quality is consistent. If you're buying used, verify that the Doepfer power cable is included and that the module isn't DOA from a power surge.
The MOD/MIX switch should click cleanly between positions. If it feels loose, the internal connection might be weak. Test both AC and DC coupling too. Some users report slight noise in DC mode if the op amps are mismatched, though this is rare. Maintenance is minimal: occasional contact cleaner on the jacks and knobs, and no recapping or alignment needed.
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