SMSL A100 class D amplifier test

[pma]

To me, it is enough that internet DSL modem stops working if the amp is on and with speakers connected by 3m wires. It is also enough to see that the amp manufacturer did not follow Infineon recommendations on output filtering vs. speaker wire length. It is also enough to hear FM radio interferences. It is enough to see that the added LC filter fixes the problem. The filter made according to Infineon datasheets. I do not have instruments to measure according to FCC. But I want the amp to be compatible with other devices. Show me the protocol that it passed FCC test with 3m speaker wires as is, filterless, without additional filters. Not the protocol with 40 cm speaker wires.
BTW, I measure behind the speaker cable. So, the mere cable inductance does not help.

 

[pma]

I see measurements connected to outputs. Where is the single loop antenna at 1, 3, and 10m distance while amp is connected to speakers to support claims it emits compliance-breaking levels of radio power? It is useless to speculate on CFR Title 47 Chapter 1 Subchapter A Part 15 compliance if you do not measure it in the manner specified by the FCC. Which is at 3m, non-contact, single loop antenna.

I do not have instrumentation to provide valid FCC EMI test. However, I have prepared a test with a single-loop antenna with 25cm diameter, placed 1m from the resistive load. Same speaker cable of 3m length, once used "as is" connected to SMSL-A100 output, then with the LC filter at the amp output (2x33uH, 2x470nF). Below the measurements of loop induced voltage. From the frequency and amplitude it is easy to calculate B and H of the EM field. The amp was working at idle.

1. Filterless operation as is normal with SMSL-A100

2. With LC filter

3. Maths

From firsthand experience with wifi and MA12070 (I still run 2x PA3s as biamp for stereo speakers)... signal strength never changes. And since my teardowns of the PA3s PCBs, I have added a wifi video doorbell (Reolink) which has both amps and speakers flanking the transmission path to either side.

Now, you are speaking about PA3s, I do speak about SMSL-A100. Do they have same circuit schematics? Especially output circuit? Do they share same modulation scheme of MA12070? I do not know. And, the amp operation (without added LC and with long speaker wires) paralyzes my ZXHN H267A VDSL modem/router. We probably speak about two absolutely different configurations, right?

 

[MaxwellsEq]

Bench tests with dummy loads often use short cables, so it's possible that this unacceptable behaviour doesn't get spotted. Perhaps bench tests should always use a realistic length for speaker cables, e.g. 3m of 12AWG.