Pre/Power Amplifiers

JBL CD350 Classic
As the digital engineering inside the CD350 and SA550 Classic is distinct – the former based on a PCM1796 DAC and the latter an ESS9038K2M – this also informs both their technical performance and sound. For the CD350 JBL has chosen a ‘slow’ linear phase digital filter as its default, offering reduced pre/post ringing (reduced time domain distortion) but traded against a poor 7dB stopband rejection and rolled-off top-end, falling steeply beyond 15kHz to –3.3dB/20kHz. The analogue line output is to a good 2.2V standard, from an equally standard 48ohm source impedance, but it’s also phase-inverted so you might want to bear this in mind before comparing the CD350 with any other ‘comparable’ player. Otherwise, the A-wtd S/N ratio is a good 106dB and stereo separation >100dB across the 20Hz-20kHz audio range. Low-level linearity holds true to within ±0.5dB over a 100dB dynamic range while distortion – mainly a simple 2nd harmonic at high signal levels – peaks at a very respectable 0.00015-0.00075% [see Graph 1, below].

Higher sample rate media, up to 96kHz/24-bit WAV/FLAC, is accommodated via the CD350’s USB-A input, but the resolution realised here is generally lower than that achieved via CD/CD-R/CD-RW discs in the same player. Distortion is higher (though not especially ‘high’) at 0.0009% but harmonics range out to the 9th, 11th, etc. Bit depth also looks to be truncated to <16-bit [red trace, Graph 1] and the A-wtd S/N is a reduced 102dB. Jitter is well suppressed in both modes [see Graph 2, below] although the ~117psec recorded for CD is simply a reflection of the residual 16-bit J-test data pattern. The 97psec pattern revealed for 24-bit USB-A data is shown via markers in Graph 2. PM

Distortion versus digital level over 120dB dynamic range (16-bit CD, 1kHz, black; 20kHz, blue; 48kHz/24-bit USB-A, red, showing truncation at –85dB)

: High res. jitter spectra (16-bit CD, red with residual pattern; 24-bit USB-A, black with markers)

JBL SA550 Classic
JBL’s blend of Class AB and Class G output configurations involves a transition point – around 10W/8ohm – that is more obvious under continuous power conditions [dashed white trace, Graph 1] than dynamic, music-like conditions, or at least until the amp is faced with very low 2 and 1ohm loads [blue and green traces, Graph 1]. There’s a useful amount of headroom too, so the 2x115W/8ohm and 2x170W/4ohm output, already comfortably exceeding the rated 90W and 150W spec., increases still further to 149W and 254W into 8/4ohm, respectively, under dynamic conditions. Protection limits this to 230W and 135W into 2/1ohm loads, respectively. Distortion transitions from 0.0007%/1W through 0.007%/10W to 0.035% between 20W and the rated 90W/8ohm (all 1kHz) while the response has a smooth HF roll-off amounting to –0.2dB/20kHz and –2.9dB/100kHz. The A-wtd S/N ratio is a very respectable 94.5dB (re. 0dBW) but overall gain, at +46dB, is very high and so full use (swing) of the volume control may not be possible with all sources.

Tested via the SA550’s preamp output, the ESS9038K2M DAC-based digital stage offers a good performance, with the option of all ESS’s seven built-in digital filters. With ‘Linear Phase Fast’ selected, the SA550 combines a low 0.00015-0.0013% peak level distortion [see Graph 2] with a wide 106dB A-wtd S/N ratio and excellent jitter suppression to, typically, <10psec over all sample rates. Responses are filter specific but, with the linear phase option, amount to –0.06dB/20kHz, –0.6dB/45kHz and –2.3dB/90kHz with 48kHz, 96kHz and 192kHz media, respectively. If you are pairing the CD350/SA550, and want to employ external digital sources, the SA550 is the way to go. PM

Continuous (dashed white, 8ohm) & dynamic output vs. distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads

Distortion versus 24-bit digital signal level over a 120dB range (1kHz, black; 20kHz, blue)