Was this instruction part of the amps manual?
No, but to be fair I have not yet seen an amplifier user manual saying "if you want to test this amplifier on a test bench you need to add X or do Y".
Those are operation manual not test manual.
The datasheet for the Merus MA12070 does clearly states this requirements for testing.
Again if you connect a set of regular speakers(with woofer, tweeter and crossover) to the amplifier this issue does not happen. The only issue I'm aware of it's when you try to bi-amp or connect to tweeter directly. In that case the tweeter coil inductance might not be enough, therefore noise and distortion is present.
Big screw up from SMSL just to save some cents on the amplifier. But is not the end of the world.
I'm just trying to let people know the truth about this amp, and then it's up to them decided based on facts if this amplifier is adequate to them or not. And not based on a inadequate test which does not tell the whole story about this amp.
But you know what, let's invite people to try another very similar amplifier, the Sabaj A10a. It is an hybrid between the SA300 and the A100. Internal high quality Power Supply, nice film capacitors on output filter, nice power supply bypass capacitors, Digital Volume control and I believe it also uses the OPA1678 opamp. No BT of USB inputs. All for $136, or its big brother Sabaj A20a for $205 The only problem for me it's the form factor and the blue LED display.
Is it worth the extra $46 for the A10a,or the extra $115 on the A20a? well it's up to the people to decide.
The SMSL DA-9 for $250 is another option (better form factor) and the same performance and features as the A20a, but more expensive. There is always a trade off.
If you want something better then be ready to pay more. I'm just highlighting those rare exceptions (amplifiers with a low price but performance comparable to more expensive amps).
Right know I'm enjoying my favorite music (Classic Rock) on my budget system: SMSL SU-6, SMSL SH-6, FX Audio Tube 01 (heavily modified with new resistors, capacitors, tubes and power supply), SMSL A100 with replaced voltage supply bypass capacitor, it comes with a 1000uF Panasonic capacitor and I replaced with a 3000uF Nichicon UBY, on the heavily modified Jamo C93 II (with new polycaps, resistors, and modified port tubes, speaker basket damping with duct seal and felt pads, and cabinet damping with cotton bathing sheets) and a Mirage S8 sub connected from the A100 sub out.
Yesterday I was listening with my heavily modified Aiyima A04 (all capacitors, inductors, OPA1656 and NP0/C0G MLCC Murata and TDK Ceramic Bypass capacitors on all capacitors and on the opamp voltage pins as well, and a modified 36V power supplied dialed down to 33V and multiple bypass capacitor to smooth the voltage to a 5mV P-P ripple)
I simply enjoy modding, it's on my blood.
I'm planning on doing an A/B test using a Speaker Selector Switch but used backwards. Instead of one input and multiple outputs I can wire it to be multiple inputs and one output to speakers.