API 550b 500 Series 4-band Equalizer

A detailed overview of the API 550b 500 Series Modular 4-band Equalizer. This equalizer is designed to be a modern version of a classic music recording tool that played a significant role in the music industry during the 1960s and 70s. Here’s a summary of the key points you mentioned:

Historical Significance:

The API 550 EQ was important in the history of music recording in the USA in the 60s and 70s. The API 550b is a modern version that continues the legacy of the original 1967 550 model.

“Proportional-Q” Control:

The API 550b uses API’s “Proportional-Q” design, introduced in the 60s. This control intuitively widens the filter bandwidth at low settings and narrows it at higher settings. This helps minimize the “phase-shift” sound that can be present in many equalizers.

Tonal Modifications:

The API 550b excels at affecting or reversing tonal modifications. It offers a wide range of tonal variations with just a few knob adjustments. The use of API’s 2520 op-amp provides predictable and gentle “analog” performance even when major tonal restructuring is needed.

500 Series Modular Format:

The API 550b is part of the API 500 Series, a modular format that provides long-term flexibility and lasting value. The modular design allows you to easily adapt your studio setup to changing needs. The 550b can be mounted in various frames compatible with the 500 Series, ensuring it remains a valuable asset in evolving studio rigs.

Rugged Design and Sound Quality:

The API 550b is designed to be rugged and enduring, offering sound quality that will stand the test of time. It’s crafted to remain a reliable sonic partner year after year.

Overall, the API 550b 500 Series Modular 4-band Equalizer is a modern iteration of a classic EQ with a rich history in the music industry. Its unique features and design make it a versatile tool for shaping and enhancing audio in a studio environment.

API 550b 500 Series Modular 4-band Equalizer Features:

• 4 bands of their famous-sounding equalization
• Each band offers 7 API-selected frequency centers
• Reciprocal and repeatable filtering
• 12dB of boost/cut per band
• EQ Band 1 and 4 offer shelf/peak switching
• “Proportional Q” narrows filter Q at extremes
• Traditional API fully discrete circuit design
• High-headroom +30dB clip level
• Reissue of 1967 API 550 EQ with an extra band

API 550B 500 Series Modular 4-band Equalizer Specifications:

• Modular 4-band Equalizer
• Filter Type:”Low” and “High” bands are Peak/Shelf switchable. Low-Mid and Mid-High are peaking type
• Low Filter Frequency Center: 30, 40, 50, 100, 200, 300, 400Hz
• Low-Mid Filter Frequency Center: 75, 150, 180, 240, 500, 700, 1Khz
• Mid-High Filter Frequency Center: 800, 1.5K, 3K, 5K, 8K, 10K, 12.5K
• High Filter Frequency Center: 2.5K, 5K, 7K, 10K, 12.5K, 15K, 20K
• Filter Boost/Cut: +/- 12dB
• Filter Slope: 12dB per Octave
• Nominal Levels: -15 to +15 dBu
• Clipping Level: +30 dBu at +/-16 V
• Noise:Actual, unw noise, <-98 dBu, 20-20 kHz
• Distortion:.07% max, at +18 dBu Output
• Connectors:15 position .156sp edge connector
• Size: 1.5″ X 5.25″ X 6″ Deep