API 215L Discrete HP/LP Sweep Filter

• Wide range 6 dB per octave LOPASS control
• Wide range 12 dB per octave HIPASS control
• Balanced input stage
• Passive filter design for smooth tone
• Unity gain throughout
• Hard Wire BYPASS switch
• Transformer Coupled Output to +28 dBu
• All Discrete Design

The API 215L is a unique passive, sweepable filter, designed specifically to contour the sound to preserve the natural tone of the signal. Its extreme flexibility, repeatable settings and superb sound make it ideal for all studio, live sound and broadcast applications.

The 215L design is a passive low pass filter with a slope of only 6 dB per octave, and a passive dual high pass filter with a slope of 12 dB per octave. The filters are isolated from each other with the same discrete transistor buffer used in the famous 550 series equalizers. This minimizes interaction between the filters, as well as providing a low impedance source for the filter following the buffer.

The input section is a balanced circuit using the API 2510 all discrete op-amp, minimizing the loading effect on any device plugged into it. The output stage is a transformer balanced output, driven by the all discrete API 2520 op-amp.

The filters are both continuously adjustable, with a range from 20 Hz to 20 kHz in two bands. The low pass filter has a range from 500 Hz to 20 kHz, and the high pass filter has a range from 20 Hz to 600 Hz. This covers a broad range of frequencies throughout the entire audio spectrum.

Because of the subtle nature of the 215L filter, it finds a home with uses like rolling off the low end of a hi-hat, where a natural sound is desired, not the usual “phase-shifter” sound of a 18 to 24 dB per octave filter found on most consoles. It can also be used to thin out room mics, without the complete loss of low end which again usually results from steep filter circuits.

The 215L can be used in the Legacy, Legacy Plus or Vision Series Consoles, or in the L200 Rack. The 215L Filter makes use of the 2520 and 2510 op-amps and therefore exhibits the reliability, long life and uniformity which are characteristic of API products.