Originally Posted by dmusoke
How do you explain the excessive switching noise seen on the amps output when Stereophile tested with a 10kHz square wave? How would you explain their statement below? Did they get two bad samples for review?
"Without the AP filter, the Anthem's wideband, unweighted signal/noise ratio, ref. 2.83V into 8 ohms with the input shorted, was miserable: 10.4dB, due to the ultrasonic noise"
Since our amps don't have AP filters to limits their bandwidths to 20kHz only, this switching noise(@400kHz) could damage tweeters and/or be picked up by speaker cables turning them into an antennas. A concern shared by the magazines reviewers...
It only looks excessive because an 8-ohm resistive load is one thing and a real-world speaker load is another.
At 400,000 Hz, tweeter impedance is so high that the switching noise has a hard if not practically impossible time getting in. Taking the report at face value regardless, 2.83V reference into 8 ohms amounts to 1 watt and noise was 10.4 dB lower than this, which means its power into stated load was under a tenth of a watt. It's hard to imagine a tweeter that gets blown by a tenth of a watt let alone one that's a mere 8 ohms at 400,000 Hz.
As for the speculation over potential emissions via speaker cable, FCC certification which the M1 has suggests otherwise. For safety certification, the Statement M1 amp is classified as a commercial product due to the amount of power it's capable of putting out yet for FCC certificaton we went for its more stringent domestic spec even though we didn't have to.
Note that in your last paragraph you're paraphrasing inaccurately because nobody said the ultrasonic noise could damage tweeters - the statement in the review was about wondering
whether it could happen and for that matter, I've never heard of tweeters being blown by M1s, which have been on the market for three years and counting. I'd be a lot more worried about clipping distortion from underpowered amps leading to blown tweeters.