YBA CD 1 Blue Laser CD player Measurements
Sidebar 2: Measurements
Before telling you about how the YBA CD 1 measured, I must report some serious problems with the measurement sample. First, the display flickered on and off, staying on only after I jiggled an unmarked rear-panel switch. Second, the CD 1 required repeated attempts to read the table of contents of some discs. Once the CD 1 read the ToC, it had problems searching certain tracks. The player would look for the track, not find it, then shut off. To search a later track on the disc, I had to skip just a few tracks at a time, wait for it to start reading data, then skip a few more tracks. On the CBS Test Disc, the YBA player wouldn't play through track 20; it would skip forward or start playing at 35 seconds. I suspect that the laser sled may have encountered a mechanical impediment at that disc radius.
Moreover, the CD 1 was the most ergonomically unfriendly CD player I've put my hands on. Using momentary toggle switches to control transport functions is ludicrous. The requirement that you push up a toggle switch twice to make the player read the ToC is equally annoying.
The CD 1's maximum output level was higher than specified but still low at 1.3V, a figure 3.7dB below the CD standard 2V output level. The output impedance at 17Hz was a high 750 ohms, a figure that decreased to 63 ohms across the rest of the band. At 31Hz, the output impedance measured 135 ohms. I measured a low 0.1mV of DC offset at the left channel output, 2mV at the right. Because the CD 1 wouldn't read the Japan Audio Society test disc, which has a positive-going impulse, I couldn't discover if the CD 1 inverts absolute polarity. When playing the Pierre Verany Test CD, the YBA mistracked at track 31.
When looking at the CD 1's output on an oscilloscope, I saw an unusual stairstep shape in the waveform. The waveform was also overlaid by very-high-frequency noise with a strong component at 220kHz.
Fig.1 is the CD 1's frequency response and de-emphasis response, shown using our normal scale. We can see some ripple in the frequency response, and the de-emphasis error is off the scale. Fig.2, the same data shown to different scale, shows the extent of the de-emphasis tracking error: a whopping 7dB at 10kHz, and 8.6dB at 16kHz. This suggests that the YBA doesn't actually correct for pre-emphasized discs at all! The CD 1's channel separation (fig.3) was rather low, measuring just 73dB at 1kHz and decreasing to 46dB at 16kHz.
A spectral analysis of the CD 1's output when playing a 1kHz, 90dB dithered sinewave (fig.4) shows that the player has a high noise level, particularly in the lower octaves. This noise is apparent only when the DAC is decoding a signal; a wideband spectral analysis (fig.5) made with a test signal of all zeros shows a lower noise level at low frequencies, but a higher noise level in the treble. Some DACs shut off when fed digital silence, to make their noise performance look better. The removal of DAC noise between figs.4 and 5 uncovers some power-supply noise at 60Hz, along with an odd energy peak centered at 7kHz. The latter is perhaps a DAC idle tone. It is also unusual to see such a wide disparity in noise levels between channels, along with the fact that the noise isn't "white" in character, but instead has more energy in some octaves than in others.
I was unable to measure the CD 1's linearity because it refused to play the fade-to-noise track on the CBS test disc, from which a player's linearity is derived. I did, however, play spot tones, and manually measured the CD 1's linearity at 70dB, 80dB, 90dB, and 100dB. At 70dB, the CD 1 had a positive error of 1.1dB (left channel) and 1.6dB (right). This error decreased to 0.76dB at 80dB (both channels). At 90dB, the CD 1 had a negative linearity error of just 0.3dB (left channel) and 0.05dB (right). At 100dB the negative linearity error increased to 2.15dB (left channel) and 1.7dB (right). This is relatively good linearity performance.
The CD 1's reproduction of a 1kHz, 90dB undithered sinewave (fig.6) shows an asymmetrical waveshape, a high noise level, and a negative DC shift. Fig.7 is the CD 1's intermodulation distortion spectrum, made by playing a full-scale mix of 19kHz and 20kHz. This is the worst-looking IMD spectrum I've seen, with lots of IMD products and a high noise level.
I was unable to measure the CD 1's jitter because its DAC is a surface-mount device located on the underside of the player's main circuit board. The circuit board appeared to be supplied as a whole and not specially designed for the CD 1.
Overall, the CD 1 had poor bench performance, with severe de-emphasis errors, low channel separation, high noise levels, and an alarming amount of intermodulation distortion.Robert Harley