PS Audio: So the next time you’re looking for no-compromise bass, look towards equipment with servos – you’ll be well served.

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Paul McGowan writes: If the high-end designer really wants thunderous bass response in his equipment, a servo is perhaps the very best way to go.  You’ve probably heard of servo bass before but servo controlling the low end response of an amplifier is a technique perhaps buried in the details of some designs and rarely implemented in most.

If you’ll remember from a few days ago I suggested that in order to make direct coupling possible – eliminating any of the components in the signal path – we’d have to rolloff the amplifier’s bass response.  We usually do this with our old friend the capacitor, but that technique has major limitations – you are rather limited in how low the amplifier can go – and the lower the better if you want stunning bass.  Using a DC servo, instead of a capacitor, is the answer.

A DC servo is an electronic circuit that magnifies the effect of a capacitor by several magnitudes, allowing designers to set the low frequency rolloff of their circuits at well below 1Hz.  For example, in our circuits we roll off at about 1/10th of a Hertz using a servo.

Why does this matter if we have amplifier response below one cycle, vs. a capacitor set 10 or 100 times higher?  Simply put the lower you go the less you hear its impact.  Using a capacitor to rolloff the bass has phase shift damage into the audible regions of the music and, even if you’re able to minimize this shift, the capacitor still intrudes into the music.

I’ve run multiple tests over the years demonstrating the difference between servo controlled bass and capacitor controlled bass and I am here to tell you there’s simply no comparison between the two.  Servo bass is rock solid, with no end to where it seems to go – while capacitor rolled bass certainly goes deep but seems to be missing something.  It also loses pacing and rhythm compared to the servo.

So the next time you’re looking for no-compromise bass, look towards equipment with servos – you’ll be well served.

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