In all of our amplification products such as power amps and preamps we work hard at extending their bandwidth to way outside the limits of human hearing.
And, on the flip side of this design choice, we restrict the upper limits of frequencies that can pass through to the ultra high bandwidth amp.
The BHK preamplifier, for example, extends out to 200kHz—10 times higher frequency than humans can hear—yet its input is limited to 50kHz.
This might seem a bit contradictory to design an ultra high bandwidth device only to limit what it is able to reproduce.
There is a method to our seeming madness.
Let's start with the input low pass filter. Here, we know there's no value in passing ultrasonics to the amplifier. In fact, we're better off gently limiting these frequencies because what is there is nothing but noise and garbage. The trick is to roll off gently so that there's zero phase shift in the audio band. A trade-off (if you will) between letting everything we want pass unimpeded, while limiting that which we don't want to pass on to the power amplifier.
Next, we have found that the higher the native bandwidth of the amplifying device, the more open and transparent the sound within the audible band.
Combine the two: gently limiting the input ultrasonic content and making sure the device has enough bandwidth to handle that which gets through, results in an openness and transparency that is breathtaking.
Sometimes, what seems a contradiction can be the key to making great music.