Musical Fidelity Titan power amplifier Measurements

Sidebar 3: Measurements

I measured the Musical Fidelity Titan using mainly Stereophile's loaner sample of the top-of-the-line Audio Precision SYS2722 system (see the January 2008 "As We See It" and www.ap.com); for some tests, I also used my vintage Audio Precision System One Dual Domain.

Before performing any tests on an amplifier, I run it for 60 minutes at one-third its specified power into 8 ohms, which is thermally the worst case for an amplifier with a class-B or -AB output stage. For the Titan, this meant operating at 300Wpc into 8 ohms, which was about the limit of my test load's thermal capacity, so I had to cut short the test after 25 minutes. An internal fan appeared to turn on after 20 minutes at this power level, venting through the amplifier's sides, and at 25 minutes the Titan's main chassis was hot, though not unduly so. The power-supply chassis remained cool.

The Titan's voltage gain was the same from its balanced and unbalanced inputs: 30.17dB, which is 4dB higher than is usual for US-made amplifiers. Both inputs preserved absolute polarity; ie, were non-inverting. The XLRs are wired with pin 2 hot, the AES convention. The input impedance was to specification at low and midrange frequencies, at a usefully high 100k ohms for the unbalanced input and twice that for the balanced. At 20kHz it dropped to 66k ohms for the unbalanced input and to 180k ohms for the balanced; neither drop will have any practical consequences.

Despite the Titan's having a bridged output stage, its output impedance was low at<0.08 ohm in the bass and midrange, rising slightly to 0.2 ohm at the top of the audioband. The modification of the amplifier's response due to the Ohm's Law interaction between this source impedance and the impedance of our simulated loudspeaker remained within±0.1dB limits (fig.1, gray trace). The amplifier offered a wide small-signal bandwidth into 8 ohms (fig.1, blue and red traces); the–3dB point lay at 125kHz, which resulted in a well-defined 10kHz squarewave with short risetimes and no overshoot or ringing (fig.2). The bandwidth decreased somewhat into low impedances, due to the increasing output impedance in this region, but the response was still just 0.5dB down at 20kHz into 2 ohms (fig.1, green trace).

Fig.1 Musical Fidelity Titan, frequency response at 2.83V into: simulated loudspeaker load (gray), 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green). (0.25dB/vertical div.)

Fig.2 Musical Fidelity Titan, small-signal 10kHz squarewave into 8 ohms.

Surprisingly, considering the Musical Fidelity's dual-mono construction, the channel separation at 10kHz was 80dB in both directions, though this did improve to 100dB at 1kHz. The amplifier was extremely quiet, the wideband, unweighted signal/noise ratio (ref. 2.83V into 8 ohms) measuring 83.5dB, and improving to 96.1dB when A-weighted. When you take its very high specified output power into consideration, the Titan has enough dynamic-range capability to cope with the demands of true high-resolution recordings.

Fig.3 plots the THD+noise percentage in the Titan's output against continuous power. The amplifier is specified at 1kWpc into 8 ohms (30dBW); I measured its power at clipping (1% THD) with one channel driven as 1050W (30.2dBW). The AC wall voltage, which had measured 125.7V with the Titan idle, at this point dropped to 122.4V. When the amplifier clipped at 1700W into 4 ohms with one channel driven (29.3dBW), the wall voltage fell to 119V. Into 2 ohms with one channel driven, the Titan clipped at 2.2kW (27.4dBW), and the wall voltage was now 116V. I had the amplifier plugged into a single 20A circuit for the tests, meaning that with both channels driven, the AC voltage would have dropped more and the amplifier's power delivery at clipping would be lower. But if you could manage it so that each of the Titan's channels was plugged into a separate AC circuit—easily done, as each has its own 20A IEC cord—you would get a maximum power delivery from each channel comparable to what I measured from just one.

Fig.3 Musical Fidelity Titan, distortion (%) vs 1kHz continuous output power into (from bottom to top): 8, 4, 2 ohms.

While fig.3 reveals that the distortion rose with reduced load impedance, the Titan is still an extremely linear amplifier. To be sure that I was looking at actual distortion rather than background noise—which, as mentioned earlier, was also very low—I had to plot the THD+N percentage against frequency (fig.4) at a high level: 29V! Into 8 ohms (blue and red traces) and 4 ohms (cyan and magenta traces), the THD+N slightly increases with increasing frequency. Only into 2 ohms (green traces) is there any noticeable rise in THD, but this is still not to any significant level. However, I am not sure why the 2-ohm trace in this graph is rather rough-looking.

Fig.4 Musical Fidelity Titan, THD+N (%) vs frequency at 29V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta), 2 ohms (green).

And even then, the predominant distortion harmonic was the subjectively innocuous third (fig.5). This graph was taken at 400W into 4 ohms, and I averaged 32 readings to drop the level of background noise enough to make clear the waveform of the harmonic spuriae. I originally performed this test with both channels driven, but the 20A circuit breaker blew after the first minute when 24 readings had been averaged, so I repeated the test with just one channel driven. As with the maximum power measurements, this test suggests that the Titan owner would be well advised to upgrade his home's electrical wiring if he is to get the maximum performance from this amplifier that he has paid for.

Fig.5 Musical Fidelity Titan, 1kHz waveform at 398W into 4 ohms (top), 0.0024% THD+N; distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.6 shows the spectrum of the Musical Fidelity's output while it drove 50Hz at 205W into 8 ohms. Again, the third harmonic dominates—if something almost 110dB down from the fundamental can be said to "dominate." This graph indicates that the left channel (blue trace) is even more linear than the right (red trace). Other than the second at around–120dB, no even-order harmonics can be seen, and the higher-order odd-order harmonics are all at or below 120dB (0.0001%). Halving the load impedance gave the spectrum shown in fig.7; the second, third, and fifth harmonics have all risen by 10dB or so, but note that, even despite the high current demand now being made on the power supply, the 120Hz components still lie at just–117dB (right) and–124B (left). This amplifier has a titanic power supply!

Fig.6 Musical Fidelity Titan, spectrum of 50Hz sinewave, DC–1kHz, at 205W into 8 ohms (left channel blue, right red; linear frequency scale).

Fig.7 Musical Fidelity Titan, spectrum of 1kHz sinewave, DC–1kHz, at 400W into 4 ohms (left channel blue, right red; linear frequency scale).

Finally, despite my driving the Titan within a couple of dB of clipping with an equal mix of 19 and 20kHz tones (fig.8), all the intermodulation products remained at or below–80dB, with the second-order or difference product at 1kHz lying at–112dB (0.00025%).

Fig.8 Musical Fidelity Titan, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 1000W peak into 4 ohms (linear frequency scale).

Despite its enormous output power and dynamic-range capability, Musical Fidelity's Titan offers measured noise and distortion more typical of a high-quality preamplifier than a power amplifier. Technically, this is an extraordinary amplifier. But I must complain about the fact that neither the amplifier nor the power-supply chassis, which weigh 99 and 150 lbs, respectively, has handles. Maneuvering the Titan into listening room or test lab was no trivial matter, even for two people. The exterior design doesn't allow for handles on the front panel, but a pair of horizontally oriented handles on the bottom of the back plate of each chassis would have helped considerably, and minimized the risk of crushed fingers.—John Atkinson

COMPANY INFO
Musical Fidelity Ltd.
US distributor: KEF America
10 Timber Lane
Marlboro, NJ 07746
(732) 683-2356
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