The beginnings of the 5500 circuit can be traced back to the original 550 equalizer designed by Saul Walker, the founder of Automated Processes Inc. The 550 was designed as a console equalizer, which uses an unbalanced input due to the architecture of the recording console. As the ergonomics of a console dictate that the controls take up little space, sometimes the number of functions included may be limited. The 5500 was specifically designed to address these limitations; it has a balanced input, a true direct bypass, an integrated power supply with quiet muting, and a range control that expands its versatility for mastering applications.

Typical of API products, the 5500 contains no integrated circuits in its signal path. Gain comes from two handcrafted 2520 op amps on each channel. The balanced input is controlled by a 2510 discrete op amp, which is similar to the 2520 but without the high current output stage. A key component of API sound, the 2520 coupled to the API 2503 output transformer, is capable of delivering +30dBm before clipping.

An extremely useful feature on the 5500 is range control. The range of the amplitude controls can be reduced to 1/2 or 1/4 of their stated scale, providing a means of adjusting tonal balance with finer resolution in an even smoother manner. This is especially useful for complex program material contained in stems or submixes and is ideal for mastering purposes.

The API 5500 also features a true hard wire bypass that connects the output connector directly to the input. Shortly after power is first applied, or immediately after it is lost, a special circuit activates “bypass mode” so that shocks of power are never heard.

The 5500's XLR input is connected to an active balanced circuit. The unit's XLR output is driven from a transformer-coupled output and can drive any load of 600 ohms or more to full output capacity. There is no change from input to output in the polarity of the unit, so it is suitable in studios using pin 2 or pin 3 as the “warm” connection. Additionally, the 5500 has a 1/4-inch input jack. which interrupts any signal present at the XLR input. It is balanced and can be driven by balanced or unbalanced sources. A positive signal at the tip will provide a positive signal at pin 2 of the XLR output. Using the 1/4 in. does not bypass any internal circuitry and does not alter gain or operating levels.

The 5500 features API's industry-exclusive five-year parts warranty and exhibits the reliability and long-life characteristics of all API products.

Characteristics

• Classic 550b equalizer design;
• Two range switches to individually change gain steps;
• Usable as 550b, 550D or 550M;
• Peak/shelf switch on Hi and Lo bands;
• True wire bypass;
• Balanced in and out on XLR;
• 1/4 inch balanced input;
• EQ In/Out switch.

Specifications

• Type: Solid state;
• Number of channels: 2;
• Bypass: yes;
• Number of bands: 4;
• Type Q: Fixed (12dB/octave);
• Boost/cut range: ±12dB;
• High frequency range: 2.5kHz–20kHz;
• Hi-Mid Freq Range: 800Hz–12.5kHz;
• Lo-Mid Freq Range: 75Hz–1kHz;
• Low frequency range: 30Hz–400Hz;
• Inputs: 2 x XLR, 2 x 1/4 inch TRS;
• Outputs: 2 x XLR;
• Frequency response: 10Hz–30kHz;
• Rack Spaces: 1U;
• Power source: standard IEC AC cable.