Copland CTA408 Integrated Amplifier Lab Report

Lab Report

While Copland offers two output taps from its speaker coupling transformers – 8ohm and 4ohm – its 75W power is specified, unusually, into 8ohm and 3ohm. Either way, the CTA408 readily bests this figure, delivering 2x95W/8ohm and 2x90W/4ohm via its 8ohm and 4ohm taps, respectively. Under dynamic conditions this increases to 110W and 100W into 8/4ohm loads (8/4ohm taps) up to 1% THD and 155W/160W into 2/1ohm loads (4ohm tap) with the distortion limit relaxed to 2% [see Graph 1, below]. Distortion scales with output level and frequency, and although the pairs of KT150 tubes are matched at Copland's factory, and the bias adapted accordingly, there was still a difference between L and R channels in our sample. (The fact that it's the protective shipping boxes and not the tubes themselves that are marked V103/V104, etc, is simply asking for trouble the moment a CTA408 is packed and moved from demo to demo...)


Dynamic power output versus distortion into 8ohm (black trace), 4ohm (red), 2ohm (blue) and 1ohm (green) speaker loads. Max. current is 12.7A


Distortion versus extended frequency from 5Hz-40kHz at 1W/8ohm (black) and 10W/8ohm (red)

In this instance, distortion increases from 0.022%/1W to 0.2%/10W (left) and 0.07%/10W (right) before coalescing at 0.75%/75W – all at 1kHz/8ohm. The modest 15dB overall NF also means distortion increases with frequency – 0.7%/10W/20kHz (left) and 1.5%/10W/20kHz (right) – and at low bass frequencies through transformer core saturation [a feature of every such tube amp; see Graph 2, above]. Otherwise, the 0.9-1.1ohm output impedance is well matched between channels, as is the 83.5dB A-wtd S/N ratio (re. 0dBW), but is sufficient to cause variations in system response with swings in loudspeaker load impedance. Into a 'flat' 8ohm load the response is good for –0.2dB/20kHz and –3dB/60kHz (8ohm tap) and holds firm out to 30kHz right down to 1ohm loads (via 4ohm tap). PM

Power output (<1% THD, 8/4ohm) 95W / 90W
Dynamic power (<2% THD, 8/4/2/1ohm) 110W / 100W / 155W / 160W
Output imp. (20Hz–20kHz/100kHz) 0.890–1.10ohm / 2.35ohm
Freq. resp. (20Hz–20kHz/100kHz) –0.05dB to –0.23dB/–4.75dB
Input sensitivity (for 0dBW/75W) 24mV / 218mV
A-wtd S/N ratio (re. 0dBW/75W) 83.5dB / 102.3dB
Distortion (20Hz-20kHz, 10W/8ohm) 0.05–1.2%
Power consumption (Idle/Rated o/p) 190W / 410W (2W standby)
Dimensions (WHD) / Weight 435x220x460mm / 25kg
Price £6398
Copenhagen, Denmark
Supplied by: Absolute Sounds Ltd
0208 971 3909