By Gene DellaSala
I did some quick spot-checking on the RPA-1 amplifier gain structure to ensure it could be properly driven with a wide assortment of preamps or receivers. My personal criteria for amplifier gain structure is that it should be able to hit full power when driven with 2Vrms. The RPA-1 fell well within this criteria.

Amplifier Power & Efficiency

Due to the inherent multi rail switching scheme of the RPA-1, my efficiency measurements are much lower than actual for this amplifier design since I use continuous sine wave testing. My measurements indicated how efficient the amp is when driven continuously at full power (0.1% THD + N), hence when the amplifier is operating in linear A/B mode. During normal music listening, expect to see around 65-67% efficiency which is about the best you can get from a linear amplifier design.

As you can see, I measured the RPA-1 to deliver about 210wpc into 8-ohms and 320 watts into 4-ohms at 0.1% THD + N using my APC S-15 and SBATT to ensure the line stayed at 120V +- 2V.    Keep in mind most review publications test at clipping and don’t do continuous power measurements so our power numbers are usually a lot more conservative than what you typically find from other reviewers. This amp hit its power rating of 200wpc into 8 ohms. Their 350wpc rating isn’t specified at any particular distortion level, but rest assured it can do it at 1& THD + N.

For more info, see: The All Channels Driven (ACD) Test

I asked Emotiva to furnish their power measurements vs. distortion to see if their ratings jived with my findings and they did.

Emotiva Power Measurements

Figure 1. RPA Power vs. Distortion

As you can see, the true continuous power rating of this amplifier (Audioholics style at least) is in excess of 200 wpc into 8-ohms.

Frequency Response

Figure 2.  RPA-1 Frequency Response

The frequency response was smooth and extended to a -3dB point of 65KHz which is more than enough bandwidth, but a bit puzzling since all of the other Emotiva amps we reviewed had about double the bandwidth. In any event, bandwidth uniformity was excellent at low or high power indicating that this roll off was intentional to ensure the best SNR performance.

FFT Distortion Analysis

Figure 3.  FFT Distortion Analysis at One Watt

At 1 watt, the RPA-1 FFT distortion test resulted in nearly immeasurable harmonics, a scenario I rarely run into. This amp is super clean at low power which in my book is one of the most important virtues of quality amplification for a controlled listening space concerned with high fidelity playback.

Figure 4.  FFT Distortion Analysis at Full Power

At near full rated power (200wpc) into 8-ohms, the RPA-1 exhibited impressively low distortion (31.6+58.3)dBv = 89.9dBv or 100*alog^-1(-89.9/20) = 0.003%. This figure is even lower than what I measured on the MPS-1 (.008%) under similar load conditions. I suspect the removal of the soft clipping circuit has paid dividends in this regard (lower noise floor, lower distortion).

As many amps approach their full power rating, their power supplies tend to run out of gas and show large harmonic nasties of the fundamental test tone. The RPA-1 maintained its composure commendably demonstrating perhaps why it also sounded so good.

Output Impedance and Damping Factor

Figure 5.  Amplifier Output Impedance vs Frequency

Amplifier output impedance when the RPA-1 was driving an 8-ohm load at 1 watt and full rated power 200wpc was well below 100 mohm for the entire audio bandwidth with a gradual rise above 20kHz. We like to see amplifier maintain 150 mohm output impedance or less so that it will sound consistently good for a larger variety of speaker and cable loads with rather complex impedance profiles. This is a very good measurement and one of the primary design attributes that will ensure this amplifier will sound consistently good on a wide variety of speakers.

Figure 6.  Amplifier Damping Factor vs Frequency

Again the RPA-1 did NOT disappoint. An amplifier with a low output impedance will also maintain excellent damping characteristics since these are related metrics. The RPA-1 maintained a damping factor of around > 150 for 8 ohm loads. This exceeded our benchmark criteria with flying colors.

Signal to Noise Ratio

Using balanced inputs, I measured 79dB (unweighted) with 145mVrms driving an 8 ohm load.  With unbalanced inputs the SNR dropped about 2.6dB as expected. Both measurements were very good, confirming that this amplifier was dead quite at very low power levels where it matters most.

Av (BAL) = 25.9dB
Av (unBal) = 27dB (THX standard is 29dB)

Editorial Note on Amplifier Voltage Gain
With most amps, the voltage gain difference between balanced vs unbalanced is 6dB with the unbalanced connection being the hotter of the two.   This is a standard practice in most consumer and pro audio. The preamp therefore usually has a +6dB boost via the balanced outputs to compensate. Emotiva didn’t seem to be following this convention but considering the unbalanced input was a mere 2dB shy of THX standard, it shouldn’t be an issue at all as long as your preamp can deliver at least 1.5Vrms of clean output to hit the rated power of this amplifier.

Recommendations

Are you kidding? It is hard to NOT sound like a fanboy when you are dealing with a company that sells quality components at rock bottom prices.  Our bench tests also support our listening evaluation.  This amp is a golden nugget at twice its price.

Conclusion

I'll repeat myself for people that skip to the end of the review - It is hard to NOT sound like a fanboy when you are dealing with a company that sells quality components at rock bottom prices. The RPA-1 offers one of the best values in reference quality amplifiers out there. Beautiful, powerful, and bulletproof, if this amp isn't on your father's day/mother's day/birthday/Christmas wish list, it should be. You may not need an amp this powerful, but don't lie to yourself, you want it. You know you do.

Emotiva Audio Corporation
106 Mission Court
Suite 101
Franklin, TN 37067

615-771-1224

877-EMO-TECH
Fax: 615-771-1128

RPA-1 Review
MSRP: $699

About Emotiva Audio
Emotiva engineers believe that the experience of enjoying home audio and home theater components begins with thoughtful design, robust engineering, superior quality materials and a deep understanding of what the audio/video enthusiast wants and needs. It occurs all too often; designers and manufacturers consider technology and ease of use to be mutually exclusive qualities in a product. Emotiva engineers think differently. Technologically superior and user friendly products are paramount to the Emotiva design philosophy and are qualities that allow Emotiva users to appreciate their purchase in the future as much as they do today. We utilize only premium components with proven, critically evaluated circuitry in the audio and video paths to preserve the original quality of the sound and vision experience. Emotiva products compliment the entertainment experience and bring it up to a level rarely experienced with other mass produced products.