The 215L design is a passive low pass filter with a slope of only 6 dB per octave, and a passive dual hgh 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 eintire 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 a complete loss of low end, again, resulting from steep filter circuits.
The 215L can be used in the Legacy 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.
