API 550A

API 529 The API 529 is a powerful stereo bus compressor for the API 500-series format, bringing many features of the legendary API 2500 compressor into a compact dual-slot module. It is designed for professional mixing and mastering environments where analog bus compression and punch are essential. The compressor uses API’s classic discrete circuitry including 2520 and 2510 op-amps with transformer-balanced output, delivering the signature API sound known for punch, clarity and musical saturation. A key feature is API’s patented THRUST® sidechain circuit, which shapes the detector response to maintain a tight and powerful low end while compressing the rest of the mix more transparently. The Old/New switch allows users to choose between vintage-style feedback compression and modern feed-forward compression, offering different dynamic behaviors and tonal characters. Sound Character The API 529 delivers the classic fast, punchy and musical API compression sound. Its discrete design reacts quickly to transients and works exceptionally well on stereo buses, drum groups and mix processing. The THRUST® circuit helps maintain strong low-frequency energy while keeping the mix tight and controlled. Highlights ✔ stereo bus compressor in API 500-series format ✔ occupies two slots in a 500-series rack ✔ derived from the API 2500 compressor design ✔ discrete 2520 and 2510 op-amps ✔ THRUST® sidechain filter for punchy low end ✔ Old/New compression modes ✔ auto or manual makeup gain ✔ three selectable knee curves ✔ hard-relay bypass ✔ 10-segment LED metering Technical Specifications ✔ device type: stereo VCA compressor (500-series) ✔ format: dual-slot API 500 module ✔ attack time: <1 ms – 50 ms ✔ release time: 0.05 s – 4 s ✔ ratio: 1.5:1 – ∞:1 ✔ threshold: -20 dBu to +10 dBu ✔ frequency response: 20 Hz – 20 kHz (±0.25 dB) ✔ maximum level: +26 dBu input / output ✔ power: +16 V via 500-series rack

API 525A The API 525A is a modern discrete FET compressor/limiter for the API 500-series format, based on the classic API 525 compressor originally introduced in the early 1970s. The new model expands the original design with additional control options for greater flexibility in modern studio workflows. Like the original unit, the 525A uses a feedback compression topology, known for its musical response and natural dynamic behavior. The discrete audio path features API 2510 and 2520 op-amps with a proprietary output transformer, delivering the signature API tone with strong midrange punch and excellent transient detail. Compared to the vintage design, the 525A introduces a variable attack control, seven selectable release times, and the classic Ceiling control, which simultaneously adjusts threshold and make-up gain for consistent output levels while changing compression depth. Sound Character The API 525A delivers the classic fast, punchy and musical API compression character. Its FET-based dynamics control responds quickly to transients and can range from subtle dynamic control to aggressive limiting. It is especially effective on drums, guitars, bass and vocals, adding punch and analog density to recordings. Highlights ✔ discrete FET compressor/limiter (500-series module) ✔ based on the classic API 525 compressor ✔ variable attack control (15 µs – 15 ms) ✔ 7 selectable release times ✔ Ceiling control for simultaneous threshold/output adjustment ✔ compression or limiter mode (2:1 / 20:1) ✔ discrete circuit with API 2510 and 2520 op-amps ✔ API transformer-balanced output stage ✔ analog gain-reduction VU meter ✔ hardware bypass Technical Specifications ✔ device type: FET compressor / limiter (500-series) ✔ ratio: 2:1 / 20:1 ✔ attack: 15 µs – 15 ms ✔ release: 0.05 – 2 s (7 modes) ✔ maximum gain reduction: 25 dB ✔ frequency response: 20 Hz – 40 kHz ±0.5 dB ✔ max input level: +27 dBu ✔ max output level: +28 dBu ✔ format: API 500-series module

API 512c The API 512c is a legendary discrete microphone, line and instrument preamp in API 500-series format, based directly on the classic API-312 preamp design. It has become one of the most widely used API modules in professional recording studios worldwide. The module uses API’s classic signal architecture with discrete Class-A circuitry, API 2520 op-amp and proprietary transformers, delivering the recognizable API sound with strong transient response, powerful midrange and high headroom. The 512c provides a microphone input, balanced line input and front-panel Hi-Z instrument input, allowing flexible use with microphones, instruments or line-level sources. A dedicated output level control makes it possible to drive the input stage harder for API transformer coloration while controlling final output level. Sound Character The API 512c delivers the classic fast, punchy and direct API preamp sound. Its discrete circuitry responds extremely quickly to transients and produces a clear, powerful signal with strong midrange definition. It is especially popular on drums, vocals, guitars, bass and percussion. Highlights ✔ microphone, line and instrument preamp in API 500-series format ✔ classic API 312 circuit design ✔ discrete Class-A circuit with API 2520 op-amp ✔ proprietary API output transformer ✔ up to 65 dB gain ✔ output level control for variable saturation ✔ front-panel Hi-Z instrument input ✔ 48 V phantom power ✔ 20 dB pad ✔ polarity reverse ✔ peak LED

API 312 Mic Pre The API 312 Mic Pre is a legendary discrete microphone preamplifier in the 500-series format, based on the original design created by Saul Walker in the early 1970s. The 312 became one of the first API mic preamps and formed the foundation for many of the company’s console designs and later rack units. The circuit combines API’s famous 2520 discrete op-amp with a proprietary AP2516 input transformer and transformer-balanced output stage. This architecture produces the unmistakable API sound characterized by high headroom, fast transient response and powerful midrange punch. With up to 69 dB of gain, the 312 can drive everything from dynamic microphones to low-output ribbon microphones. Features such as a 20 dB pad, phantom power, polarity switch and transformer output tap selection make it highly versatile in modern recording environments. Sound Character The API 312 delivers a fast, punchy and forward-sounding tone that has become a staple of countless professional recordings. Its discrete circuitry and transformer design provide excellent transient response, strong midrange presence and tight low-frequency control. For drums, electric guitars and rock vocals in particular, the 312 is widely associated with the classic “American console sound.” Driving the input stage can also introduce subtle analog saturation, adding harmonic richness and character. Highlights ✔ classic API microphone preamp in 500-series format ✔ based on the original 1970s API 312 circuit ✔ discrete design featuring the API 2520 op-amp ✔ proprietary AP2516 input transformer ✔ up to 69 dB of gain ✔ -20 dB pad switch ✔ 48 V phantom power ✔ polarity reverse switch ✔ 3:1 output transformer tap selection ✔ integrated VU meter and peak indicator Typical Studio Applications ✔ drum recording (kick, snare, overheads) ✔ electric guitar amplifiers ✔ rock and pop vocals ✔ bass DI recording ✔ synthesizers and drum machines ✔ general recording front-end in API-based studios Technical Specifications ✔ device type: microphone preamplifier (500-series module) ✔ gain range: +34 dB to +69 dB ✔ frequency response: 20 Hz – 40 kHz (±0.5 dB) ✔ maximum output level: +31 dBu ✔ signal-to-noise ratio: approx. 120 dB ✔ pad: -20 dB ✔ phantom power: 48 V switchable ✔ output impedance: < 75 Ω transformer balanced ✔ format: API 500-series module

API 560 The API 560 is a classic 10-band graphic equalizer in API 500-series format, widely regarded as one of the most iconic analog EQ modules in professional studio environments. It is based on traditional API circuitry and delivers the recognizable API sound with precision, musicality and immediate hands-on control. At the heart of the API 560 is the legendary API 2520 discrete op-amp, combined with a fully discrete analog signal path. This design provides excellent headroom, clarity and strong analog punch. Its ten fixed frequency bands allow precise control across the full audio spectrum. Each band offers ±12 dB boost and cut, making both subtle corrections and strong tonal shaping possible. The graphic layout allows very fast decision-making during recording, mixing and bus processing. Sound Character The API 560 delivers the classic precise yet musical API EQ character. Adjustments sound direct and controlled without becoming harsh. Midrange shaping is particularly effective, while lows stay tight and highs remain open and detailed. It works exceptionally well on drums, vocals, guitars, bass and stereo buses. Highlights ✔ 10-band graphic equalizer in API 500-series format ✔ discrete API 2520 op-amp design ✔ classic API graphic EQ architecture ✔ ±12 dB boost/cut per band ✔ extremely fast hands-on workflow ✔ musical shaping across the full spectrum ✔ high headroom ✔ hard bypass ✔ ideal for recording, mixing and bus processing

API 550B The API 550B is a classic 4-band equalizer in API 500-series format, widely regarded as one of the most iconic analog EQ modules in professional recording studios. It is based on the legendary API discrete circuit design and delivers the recognizable API sound with musicality, punch and exceptional clarity. At the core of the module is the classic API 2520 op-amp design, combined with a fully discrete analog signal path. The four EQ bands feature fixed selectable frequency points for fast and intuitive operation during recording and mixing. A defining feature of the API 550B is its proportional-Q circuit: as boost or cut increases, the filter automatically becomes narrower, resulting in highly musical yet precise tonal shaping. The 550B is equally suited for individual tracks and stereo bus processing and remains one of the most widely used API EQ modules. Sound Character The API 550B delivers the classic musical, punchy and direct API EQ sound. Midrange remains present and focused, lows stay tight and highs sound open and natural. Boosts especially retain a very organic musical character. It performs exceptionally well on vocals, drums, guitars, bass, synthesizers and stereo buses. Highlights ✔ 4-band equalizer in API 500-series format ✔ discrete API 2520 op-amp design ✔ classic proportional-Q circuit ✔ 7 selectable frequencies per band ✔ ±12 dB gain per band ✔ switchable high and low band filter behavior ✔ highly musical tonal shaping ✔ hard bypass ✔ ideal for recording, mixing and summing

API 525 The API 525 is a classic discrete compressor/limiter module for the API 500-series format, originally introduced in the early 1970s and now reissued using the original design documents from the API archives. It uses a feedback compression topology, which produces a smoother and more musical response compared with modern feed-forward designs. The module features API’s discrete 2510 and 2520 op-amps with transformer-balanced output, delivering the signature API sound characterized by punchy transients and strong midrange presence. A unique feature is the Ceiling control, which simultaneously adjusts threshold and make-up gain so engineers can change the amount of compression without altering the overall output level. Sound Character The API 525 provides the classic fast, punchy and musical API compression sound. Its feedback design responds naturally to transients, making it ideal for dynamic sources such as drums, guitars and vocals while adding analog character and density. Highlights ✔ classic API 500-series compressor/limiter ✔ faithful reissue of the original 1970s design ✔ feedback compression topology ✔ discrete API 2510 and 2520 op-amps ✔ unique Ceiling control ✔ 2:1 compression / 20:1 limiter mode ✔ integrated de-esser detector filter ✔ four automatic release modes ✔ analog gain-reduction VU meter ✔ hardware relay bypass Technical Specifications ✔ device type: compressor / limiter (500-series) ✔ ratio: 2:1 / 20:1 ✔ attack time: approx. 15 µs ✔ release times: 0.1 – 2 s automatic modes ✔ frequency response: 20 Hz – 40 kHz (±0.5 dB) ✔ max input level: +27 dBu ✔ max output level: +28 dBu ✔ signal-to-noise ratio: approx. 112 dB ✔ format: API 500-series module

API 512V The API 512V is a professional microphone, line and instrument preamp in standalone rack format, based on the classic API 512c / API 312 circuit design and delivering the legendary API sound in a flexible outboard format. It combines the traditional API discrete signal path with additional gain and output control features for modern recording workflows. At its core is the classic API 2520 op-amp circuit combined with proprietary API transformers, producing the recognizable API sound with fast transient response, punchy midrange and strong headroom. Unlike the 512c, the 512V adds variable output control, allowing engineers to drive the input stage harder for API saturation while independently adjusting output level. The preamp also includes switchable microphone, line and Hi-Z instrument inputs, along with standard studio features such as pad, polarity reverse and phantom power. Sound Character The API 512V delivers the classic fast, direct and punchy API preamp sound. Transients remain precise, mids stay forward and low frequencies sound tight and energetic. It performs exceptionally well on drums, vocals, guitars, bass and synthesizers. Highlights ✔ microphone, line and instrument preamp in standalone rack format ✔ classic API 312 / 512 circuit design ✔ discrete API 2520 op-amp design ✔ proprietary API transformer stage ✔ variable output control for saturation shaping ✔ up to 65 dB gain ✔ front-panel Hi-Z instrument input ✔ 48 V phantom power ✔ 20 dB pad ✔ polarity reverse ✔ peak LED metering ✔ 19-inch rack / 1U

API 527A The API 527A Compressor/Limiter is a versatile VCA compressor/limiter for the API 500-series format, designed for modern recording and mixing workflows while retaining the classic API analog sound. The module belongs to API’s family of VCA-based compressors (including the 225L, 2500 and 529) and features discrete API 2510 and 2520 op-amps with transformer-balanced output, delivering the signature API tone with punchy transients and strong midrange presence. A defining feature is the switchable feed-forward (“NEW”) and feedback (“OLD”) compression topology, allowing engineers to choose between modern precision or vintage-style dynamics behavior. The compressor also includes API’s patented THRUST® sidechain circuit, which reduces low-frequency influence on the detector circuit to maintain a punchy and stable low end during compression. Sound Character The 527A delivers the classic fast, punchy and versatile API compression character. The selectable compression topology allows it to operate as either a transparent modern compressor or a smoother vintage-style dynamics processor. Combined with the THRUST® circuit, it maintains strong low-frequency energy while controlling overall dynamics effectively. Highlights ✔ VCA compressor/limiter for API 500-series racks ✔ switchable feed-forward and feedback compression modes ✔ hard or soft knee compression ✔ THRUST® sidechain filter for enhanced low-end punch ✔ discrete API 2510 / 2520 op-amps ✔ adjustable threshold, ratio, attack, release and output ✔ stereo-link capability ✔ 10-segment LED meter for gain reduction or output level ✔ overload indicator ✔ relay-based hard bypass Technical Specifications ✔ device type: VCA compressor / limiter (500-series module) ✔ ratio: approx. 1.5:1 – ∞:1 ✔ attack: 0.03 ms – 30 ms ✔ release: 50 ms – 3 s ✔ threshold range: -20 dBu to +10 dBu ✔ maximum input level: +26 dBu ✔ maximum output level: +30 dBu ✔ format: API 500-series module (VPR Alliance compatible)