- Written by Chris Groppi
- Published on 05 January 2009
On the Bench
I measured the XPA-1 using SpectraPlus FFT analysis software with a Roland Edirol UA-101 24 bit/192 kHz sound card. I measured the amp into an 8 Ohm, 300W load resistor. Unfortunately, while trying to measure THD vs. frequency, I managed to set the generator level of the sound card too high, and blew out the input on the sound card. I was unable to make any measurements into 4 ohms. In addition, I could not measure output power as the power resistors I have are only rated to 300 W. Emotiva provided me with THD versus power output plots measured with an Audio Precision system, which I also include here.
THD was measured at 1 kHz and 10 kHz at 20V p-p output level into 8 ohms. Measured THD is well under 0.1% at both frequencies. The THD+N measurements are much worse, but this is an issue with my sound interface, and do not reflect reality. The 60 Hz signal is a ground loop caused by an interaction with the amp and the sound card. This noise is completely gone when disconnected from the UA-101 at the input, as measured with a Tektronix oscilloscope.
Emotiva XPA-1 THD spectrum of a 1 kHz sine wave at 20V p-p output amplitude.
Intermodulation products were over 60 dB down from the fundamental tones at 1 kHz and 500 Hz, which is very good performance. Here is the Emotiva XPA-1 intermodulation spectrum of a 500 Hz and 1 kHz sine wave each at 20V p-p output amplitude.
Frequency response was flat as a board from 20 Hz to 48 kHz, the limit of the SpectraPlus software. The slight linear rise towards higher frequency is the response of the sound card input, not the amplifier itself. The same slope is present running the UA-101 output directly into the input. Shown below is the Emotiva XPA-1 frequency response at -30 dBV RMS level into an 8 Ohm load.
THD at 1.535V RMS input voltage (maximum rated output power level) stays at around 0.003% until about 1 kHz, and then rises gently to about 0.02% at 20 kHz. At 0.1V input voltage level (about 5V output voltage), THD is flat as a pancake at around 0.002% over the full frequency range. Results were slightly worse (a bit less than a factor of 2) into 4 Ohms (not shown). Here is the THD+N vs. Frequency graph for the Emotiva XPA-1 at 500W output power into an 8 Ohm load. (Measurement provided by Emotiva.)
THD+N vs. Frequency for the Emotiva XPA-1 at 5W output power into an 8 Ohm load. (Measurement provided by Emotiva.)
Power output into 8 Ohms and 4 Ohms is incredibly impressive. At the rated powers of 500W and 1000W, the THD levels are a very low 0.003% and 0.05%. At the 1% THD spec for output power, the XPA-1 puts out 680W into 8 ohms (37% higher than spec) and 1100W into 4 Ohms (10% over spec). Below is the THD+N vs. output power level for the Emotiva XPA-1 into an 8 Ohm load. (Measurement provided by Emotiva.)
"THD+N vs. Output Power for the Emotiva XPA-1 into a 4 Ohm load. (Measurement provided by Emotiva.)
Overall, the bench results for the XPA-1 are excellent, and prove you are getting even more than advertised. Quite amazing, given the low cost of these amps!
Addendum from the Editor 4/1/09:
I (JEJ) was so impressed with Chris' review of the XPA-1, I asked Emotiva to send me one so I could run some of my own tests. I borrowed a different power amplifier from a friend that cost more than 6 times the price of the XPA-1, which I will call Amplifier "X" here. I ran the same tests on both amplifiers. Here are the results.
With the XPA-1 and a 1 kHz sine wave at 40 volts output into 8 ohms, THD+N was 0.017%. For Amplifier "X", it was 0.023%.
IMD for the XPA-1 was 0.007%, while for Amplifier "X", it was 0.013%.
The frequency response also differed. The XPA-1 was flat to 50 kHz, and Amplifier "X" started rolling off above 20 kHz.
Now, I have to say that I have listened to Amplifier "X" many times over at my friend's house when we get together, and I consider it a fine amp. However, these tests show that, at least within the 200 watt tests (40 volts into 8 ohms) that I ran for this comparison, the XPA-1 comes out ahead. It is a surprisingly good amplifier for its price. A set of three XPA-1's across the front, with their smaller amplifiers for the sides and rear, would be a dynamite home theater setup. JEJ