- Written by John E. Johnson, Jr.
- Published on 02 October 2013
On the Bench
All distortion tests were made within an 80 kHz bandwidth. Tests were with an 8 ohms load, unless otherwise specified.
Now, what I suggest you do is open another window in your browser and go to the bench test page for the INT-150. Then you can scroll down the page to see the same tests for both amplifiers, side-by-side.
At 1 kHz and 5 volts output, distortion was 0.008%. There are only two harmonics, the second and third ordered, with the third being the largest. With the INT-150, there were second, third, and fourth ordered harmonics, but the second harmonic was the largest.
At 10 volts output, there are multiple harmonics, with the third being the largest, and the smallest being the thirteenth. Overall, the harmonics present in the INT-30A are lower in height than in the INT-150, even though the measured number is higher. This higher measurement reflects some noise around the 1 kHz region, and that increases the numeric value.
The 19 kHz, 20 kHz test results are shown below. There is a visible B-A peak (1 kHz) that is 84 dB below the fundamentals. Not significantly different from the INT-150. There is one more side peak to the left of the fundamentals in the INT-150. Again, not significant, in my opinion.
IMD at 10 volts was 0.02%. This is less than half that measured in the INT-150 and may be part of the reason I found the INT-30A sound to have more detail.
The following graph shows THD+N vs. Frequency with a 10 volts output into 8 ohms and 4 ohms. With the INT-30A, distortion begins to rise at 200 Hz (8 ohms), while with the INT-150, it begins rising at 1 kHz. This is where having more power makes a difference, because 10 volts is a smaller percentage of the output in the INT-150 than in the INT-30A.
THD+N vs. Output Voltage is shown below. The first graph is with an 8 ohms load. The soft knee is at 4 watts output, and the hard knee is at 80 watts, with clipping at 90 watts. So, for a 30 watt spec, that is pretty fine performance. (The INT-30A leaves Class A operation at 60 watts output, and goes into Class AB operation.)
With a 4 ohms load, the soft knee is at 7 watts, and the hard knee is at 130 watts. Clipping occurred at 150 watts output. This is SOME 30 watt amplifier ! !
The measured Frequency Response was down 0.5 dB at 30 kHz. There was a bit more attenuation with a 4 ohms load.