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Performance in RightMark Audio Analyzer Tests

Of course, I was interested in measuring the parameters of the KamaBay Amp objectively, but it was problematic with the tools I had at hand (the RightMark Audio Analyzer software and a sound card for recording signal) because of the bridge design of the main amplifier’s output cascade. There is no “ground” in the outputs and I didn’t risk measuring the output signal relative to the “ground” of the input connectors. The headphone amplifier’s characteristics could be measured easily, however. Running a little ahead, I can say that they coincided with the specs of the employed chip well enough, so I will just show you the distortion graph of the digital amplifier from that document.


Digital Amplifier, Stereo Mode


Digital Amplifier, Mono Mode

So, the level of distortions corresponds to chips like the popular TDA7265. This quality is high enough for a good TV-set, but owners of more or less decent passive speaker systems will ask for more.

Now I invite you to the most interesting part of the test. I will test the Scythe KamaBay Amp’s headphones amplifier and compare it with the line outputs of two sound cards and of a C.E.C. HD53-R80 amplifier. The level of distortions was measured for a real load (a pair of Grado SR 325i headphones) thanks to a Y-shaped splitter connecting the amplifier’s output with the headphones as well as with the line input of a Creative X-Fi Elite Pro sound card. I preferred that card to an ASUS Xonar D2 due to a trivial reason: having almost the same recording quality, the Creative card allows to easily amplify the input signal. With the ASUS card, the signal would have had to be recorded into a file and processed in a sound editor. The signal has to be amplified because the sound of my headphones is just unbearably loud at the level required for RightMark Audio Analyzer. No one will listen to music at such a high volume, so there is no point in performing any tests in such mode.

So, my objective tests were limited to the following measurements:

  1. The amplifier works without load (its output is loaded by the sound card’s line input); the calibration signal level is -1dB (at the maximum sensitivity of the sound card’s line input) as is required by the RightMark Audio Analyzer test methodology.
  2. The volume setting being the same as in the previous measurement, the headphones are plugged into the amplifier.
  3. Thanks to the program’s ability to automatically increase the signal level within 10dB (normalization), the signal level is reduced to the possible minimum.

These three variants will allow us to track changes in the distortions at different output power. I want to note that even the third variant is too loud for most of modern highly compressed musical recordings.

Before discussing the results, I have to note one peculiarity about them: poor separation of the channels. When making the splitter, I did not take into account that the rather high currents flowing through the low-impedance headphones created interference between the wires of the left and right channels that shared a common screen. Anyway, we still can get some useful information. So, let’s see.

When without load, the Scythe KamaBay Amp delivers excellent parameters for an amplifier: the frequency response deflects by less than 0.5dB from 22 to 50kHz. The signal-to-noise ratio is -100dB, even exceeding the specifications. Interestingly, this amplifier is absolutely free from ground loops that might have worsened its noise characteristics. The level of harmonic distortion is also impressive at 0.0005% whereas intermodulation is completely lost in the noise.

This idyllic situation was disrupted by the connection of 32Ohm headphones, yet the THD of 0.01% at both volume settings can be considered acceptable. The level of intermodulation is proportional to volume, but not excessive, either. Interestingly, the signal-to-noise ratio didn’t lower when I connected the headphones. It means that this amplifier has zero output resistance.

Let’s check out the individual characteristics in more detail. From here on, the first diagram shows the frequency response, the second diagram shows the harmonic distortion spectrum, and the third diagram shows the intermodulation distortion spectrum.

The lack of notable deflections in frequency response at the resonant frequency of the headphones’ dynamic heads and at high frequencies indicates again that the amplifier has zero output resistance. The slump of frequency response at low frequencies is proportional to sound volume and is due to the presence of DC-blocking capacitors at the amplifier’s output. I guess they have the right capacitance, and the 1-decibel difference at 30Hz won’t be perceptible. The nonlinear distortions – a very long and nearly not swooping spectrum of harmonics with prevailing odd-numbered ones – do not bode anything good. The reduction of sound volume doesn’t reduce the harmonics after the 20th one. The intermodulation distortions are reduced at lower volume, but the high intermodulation constituents near the higher-frequency tone (7kHz here) and its harmonics (14, 21kHz) remain unchanged.

Thus, the KamaBay Amp shows ambiguous results in my tests but I will make my final opinion after I discuss the results of the other devices.

 
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