Integrated Amplifiers

Pass Labs INT-30A Pure Class A Integrated Stereo Amplifier

ARTICLE INDEX

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.

INT-30

 

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.

INT-30

 

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.

INT-30

 

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.

INT-30

 

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.

INT-30

 

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.)

INT-30

 

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 ! !

INT-30

 

The measured Frequency Response was down 0.5 dB at 30 kHz. There was a bit more attenuation with a 4 ohms load.

INT-30