MPS-1 Measurement and Analysis - Part 2

Damping factor was greater than 50 and remained linear for full audio bandwidth.

The true test is how well an amp will hold up into low impedance loads. Ideally an amplifier should act like an ideal voltage source, meaning power will double as load impedance halves since output voltage will remain constant. In order to do this, the amplifier output impedance must maintain a low enough level to not be the limiting factor.

As you can see, the output impedance is very similar (actually better) to the 8 ohm 1 watt test! Perhaps what's most impressive about the MPS-1's drive capability is its output impedance composure when driven at full power. Many lesser designed amps fall apart here, especially into 4 ohm loads. The MPS-1 sails by with vanishingly low output impedance, very similar for 4 and 8 ohm load impedances.

There is no substitute for good old fashion amplifier design with plenty of power devices to maintain a low output impedance, an ample power supply to keep the source resistance low and in the Emotiva case, a well executed switching topology to ensure high efficiency to minimize heat dissipation and maximize power transfer to the loudspeaker.

Amplifier Damping Factor 8/4 ohm Full Power

Damping factor remained stable and uniform at full unclipped power into an 8 ohm and 4 ohm load. Based on the principle of voltage divider, we see roughly ½ the damping factor for the 4 ohm load, but this was close to our minimum recommendation of 50. For more information on this topic, read our article on Damping Factor: Effects on System Response .

Signal to Noise Ratio (SNR) Measurements
Measuring the Signal to Noise ratio of this amplifier proved to be quite challenging due to the lack of proper LPF for limiting the bandwidth to below the switching frequency.

By applying A-weighting response curve, I was able to achieve partially reasonable measurements of 82dBA (A-wt) at 1 watt or about 102dBA at 270wpc.

From Emotiva Engineering Labs: We perform my signal to noise ratio test a little different than you do. We base our measurement strictly on the rms voltage as measured on the AP with a < 10Hz to 30Hz bandwidth selected. No other weighting is applied. The amplifier is connecting to a purely resistive load, in this case 4 ohms. We measured a noise floor voltage of 268uV using the balanced output of the AP with a 50 ohm output impedance - generator selected to off to terminate the input to the amplifier. From this starting point we let the AP do all the work. We select the output level from which I want the S/N ratio to be referenced at and call that the 0dB point. Below are some measurements we have taken:

• 102dB ref 300W
• 101dB ref 270W
• 87 dB ref 10W
• 77dB ref 1W

These numbers should be more consistent with what you are hearing from the amplifier. Also, we believe these numbers represent a best case scenario because we are using the balanced input. The key to this test is the noise floor of the amplifier. This can change significantly if power cables are inducing 60Hz into signal, other equipment could be radiating noise, etc.

In any event, the 77dB @ 1 watt number isn't flattering to say the least, but given the unique amplifier topology, I suspect the out of band switching noise is producing a non representative number since noise was never an audible issue in real world listening tests. When using the Yamaha RX-V2500 as the preamp for the Emotiva MPS-1, the set-up was dead quiet and sounded as silent as other amps I have measured with significantly lower noise floors.