RESULTS

Acoustic Monster (A.M.)

DIY and Custom Built High-End Audio Equipment

Designed and Developed in Singapore

Technical Review and Specifications of Audio Note 211 Ongako Monoblock Parallel Single Ended Tube Power Amplifier.

RESULTS & DISCUSSION OF 211/845 MPAs

The 211/845 MPAs measurement results will be discussed in this section. With a dummy load (a huge power resistor) connected to the amplifier’s output, we drive the power amplifier input with a reference voltage just below clipping across the output terminals. The output power is plotted against frequency from 10 Hz to 20 KHz.

This measurement allows us to look at a power amplifier’s output capability and is known as the power-bandwidth test. We are looking for widest bandwidth over which the amplifier can maintain full output power. The measured result shown in figure 10 is the power-bandwidth measurement. The frequency response is ranged from 10 Hz to 45 KHz, taken at - 3dB region.

Figure 10. 211/845 MPAs Frequency Response

The second measurement taken is the THD+N against output level of 1 Watt into 8 ohms. The result is shown in figure 11. The harmonic distortion is fairly low at the important frequency range of 100Hz to 10KHz.

Figure 11. 211/845 MPAs Harmonic Distortion

As you can see from the THD+N measurement in figure 11, the result measured is not as good as compared to transistor’s THD+N measurement. However, bear in mind that valve amplifier in clipping produces primarily second- and third-harmonic distortion, which is fairly benign sonically. A transistor amplifier when driven into clipping immediately produces a whole series of very objectionable upper-order odd harmonics (fifth, seventh, ninth). In fact, 10% second-harmonic distortion is less annoying than 0.5% seventh-harmonic distortion.

Figure 12. 211/845 MPAs Phase Response

Lastly, phase measurement is taken for the 211/845 MPAs. In figure 12, it shows that the amplifier does not have any severe phase angle swings. The phase angle swings at +/- 20 degree variation at both the extreme ends of the audio frequency range. The amplifier stays resistive at the frequency range of 60 Hz to 3 KHz. The result obtained is very healthy for music reproduction.

CONCLUSION

Considering the THD+N measurements, we can see that Valve amplifiers do not measure well on paper. However, at the end of the day, what matters most is the music and we know that valves sound more musical than our solid-state counterparts.