Arcam FMJ A19 integrated amplifier Measurements

Sidebar 3: Measurements

I measured the Arcam FMJ A19 using Stereophile's loan sample of the top-of-the-line Audio Precision SYS2722 system (see www.ap.com, and the January 2008 "As We See It"). Before performing any measurements, I ran the FMJ A19 for an hour at one-third its specified maximum power of 50Wpc into 8 ohms, thermally the worst case for an amplifier with a class-B or -AB output stage. At the end of that period, the internal heatsinks, which are shielded by the top panel, were at 140.3°F (60.2°C). The top panel had a more reasonable temperature of 102.6°F (39.3°C). The THD+noise remained at a very low 0.0054% throughout this period.

The maximum volume-control setting was "99"; it operated in accurate 0.5dB steps, meaning that an indicated "69" was 15dB below maximum. With a 1kHz tone, the A19 offered a maximum voltage gain for line-level sources of 39.1dB into 8 ohms. Measured at the Preamplifier outputs, the maximum gain was 9.7dB, sourced from an output impedance of 227 ohms at all audio frequencies. This output preserved absolute polarity for both phono and line inputs (ie, was non-inverting), as did the speaker outputs.

Looking first at the phono input, this offered a gain at 1kHz of 48.8dB measured at the Preamplifier outputs, which is appropriate for moving-magnet and high-output moving-coil cartridges. The input impedance was 44.5k ohms at low and middle frequencies, slightly lower than the specified 47k ohms, dropping further at 20kHz to 39k ohms. The error in the RIAA de-emphasis was impressively small and well matched between channels (fig.1), though this graph reveals that the A19 implements the IEC-recommended infrasonic rolloff, reaching –3dB at 21Hz. The phono input was also quiet, the wideband signal/noise ratio measuring 75dB in both channels, ref. an input signal of 1kHz at 5mV and taken with the input shorted. This improved to 83.5dB when A-weighted. Channel separation via the phono input (not shown) was excellent, at >80dB below 2kHz and still 73dB at 20kHz.

114A19fig01.jpg

Fig.1 Arcam FMJ A19, MM input, response with RIAA correction (left channel blue, right red) (0.5dB/vertical div.).

The phono-input overload margin was an even 20–21dB throughout the audioband, which is excellent. With a 1kHz signal at 5mV, the only harmonic visible in the output spectrum (fig.2) is the second, at –100dB (0.001%), just more than 20dB below the level of the highest power-supply–related spurious tone, at 60Hz. High-frequency intermodulation was also very low (fig.3).

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Fig.2 Arcam FMJ A19, MM input, spectrum of 1kHz sinewave, DC–10kHz, at 2V into 100k ohms (linear frequency scale).

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Fig.3 Arcam FMJ A19, MM input, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 2V peak into 100k ohms (linear frequency scale; left channel blue, right red).

Turning to the A19's performance via its line-level inputs and measured at the speaker terminals, these offered an input impedance of 10k ohms from 20Hz to 20kHz, as specified. The output impedance was 0.155 ohm at 20Hz and 1kHz, rising slightly to 0.19 ohm at 20kHz. The modification of the Arcam's response due to the Ohm's law interaction between this source impedance and that of our standard simulated load was ±0.2dB (fig.4, gray trace). The low frequencies in this graph roll off by a low 0.25dB at 20Hz but more rapidly above the audioband, reaching –3dB at 55kHz, which slows a little the leading edges of the A19's reproduction of a 10kHz squarewave (fig.5). A small overshoot is visible in this graph, as there is with a 1kHz squarewave (fig.6), but there is no ringing. The traces in fig.4 were taken with the volume control set to "99"; there was no change in the measured frequency response at lower settings of the volume control, which is commendable.

114A19fig04.jpg

Fig.4 Arcam FMJ A19, 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) (0.5dB/vertical div.).

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Fig.5 Arcam FMJ A19, small-signal 10kHz squarewave into 8 ohms.

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Fig.6 Arcam FMJ A19, small-signal 1kHz squarewave into 8 ohms.

Channel separation for line-level signals was good rather than great, at 70dB R–L and 87dB L–R at 2kHz, decreasing to 52 and 68dB, respectively, at 20kHz. The wideband, unweighted S/N ratio, ref. 2.83V into 8 ohms and taken with the input shorted but the volume control set to its maximum, was an okay 70.3dB in both channels, improving to 77.3dB when A-weighted. These ratios will increase at lower volume-control settings, of course.

The way the traces slope upward to the left in figs. 7 and 8, which plot the THD+noise percentage against output power into 8 and 4 ohms, respectively, means that any distortion is below the level of the noise, up to a few tens of watts. (A constant level of noise becomes an increasing percentage of the signal level as the latter drops.) We define an amplifier's clipping point as when the THD+N reaches 1%; these graphs indicate that with a 1kHz tone, the A19 clips at 61W into 8 ohms (17.7dBW) and 85Wpc into 4 ohms (16.3dBW)—slightly more and slightly less, respectively, than the specified maximum powers of 50Wpc into 8 ohms (17dBW) and 90Wpc into 4 ohms (16.5dBW).

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Fig.7 Arcam FMJ A19, distortion (%) vs 1kHz continuous output power into 8 ohms.

114A19fig08.jpg

Fig.8 Arcam FMJ A19, distortion (%) vs 1kHz continuous output power into 4 ohms.

I didn't test the A19's power delivery into 2 ohms, as it had difficulty with low impedances. For example, I had some problems when I tried to measure how the percentage of THD+N changes with frequency. Usually, I choose a level where I can be sure I am seeing actual distortion rather than noise when I look at the THD+N vs power graphs. I first tried plotting the THD+N at 9V, which is equivalent to 10W into 8 ohms or 20W into 4 ohms. However, as you can see in fig.9, the THD+N into 4 ohms (cyan and magenta traces) rises dramatically below 125Hz. This is because, with continuous drive into 4 ohms at this level, the A19's protection circuit cuts in at frequencies below the midrange. Investigating this, it appears that the amplifier will protect itself when asked to deliver a low-frequency signal at more than 15W into 4 ohms for more than 5 seconds or so. I therefore repeated this test at a level of 2.83V, equivalent to 1W into 8 ohms or 2W into 4 ohms. Now all appears well (fig.10), with the small rise in THD at the top of the audioband due to the circuit's reduced open-loop bandwidth in this region.

114A19fig09.jpg

Fig.9 Arcam FMJ A19, THD+N (%) vs frequency at 9V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

114A19fig10.jpg

Fig.10 Arcam FMJ A19, THD+N (%) vs frequency at 2.83V into: 8 ohms (left channel blue, right red), 4 ohms (left cyan, right magenta).

Not only is the Arcam A19's distortion very low at small-signal levels, it is predominantly the subjectively innocuous second harmonic in nature (figs. 11 and 12). Fig.12 reveals that the supply-related spurious tone at 120Hz is also low in level. Intermodulation distortion is also negligible, even with an equal mix of 19 and 20kHz tones driven into 4 ohms at a level a couple of dB below visible clipping on the oscilloscope screen (fig.13).

114A19fig11.jpg

Fig.11 Arcam FMJ A19, 1kHz waveform at 10W into 8 ohms, 0.004% THD+N (top); distortion and noise waveform with fundamental notched out (bottom, not to scale).

114A19fig12.jpg

Fig.12 Arcam FMJ A19, spectrum of 50Hz sinewave, DC–1kHz, at 30W into 8 ohms (linear frequency scale).

114A19fig13.jpg

Fig.13 Arcam FMJ A19, HF intermodulation spectrum, DC–24kHz, 19+20kHz at 50W peak into 4 ohms (linear frequency scale).

Arcam's FMJ A19 shouldn't be used for driving loads much below 6 ohms at high levels, but that is a sensible compromise made to keep its price affordable. Other than that caveat, the A19's measured performance is excellent.—John Atkinson

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Arcam
US distributor: American Audio & Video
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Southaven, MS 38672
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COMMENTS
low2midhifi's picture

I own the A18 predecessor model to the A19 reviewed in this article.  Thanks to Stereophile for reviewing a fine integrated amp that offers great value for the money. 

I stepped down in watts per channel from other comparably priced amplification to purchase the Arcam A18.  While the watts per channel reduction does cost a reduction in volume, the Arcam delivers in ways that more than compensate for the difference.

Stepping up to the Arcam A18 from more modest equipment, one will find a big step up in sound quality from a less expensive power amp, receiver, or integrated amp. 

Going to the Arcam from a stereo receiver, for example, one notices succinct pauses—true musical pauses—from a recording.  With lesser equipment one discovers a type of smearing of the musical notes, where the Arcam delivers the musical impulses with natural and punctuated phrasing of the music. 

The Arcam doesn't immediately seem loud (an attribute that many of us have been trained to equate with “good”) but listening to this unit requires a different approach to listening.  With the Arcam there is a subtle but room-filling expansive sound projection. It’s different than a more intensive, visceral, in-your-face sound that one may get from amplification with more wattage in a less expensive product.

The sound quality of this unit is great.  Arcam gives a budget-constrained hi-fi enthusiast a taste of the sound that is available with finer products, but is often economically unattainable for many enthusiasts. 

I would recommend that a purchaser of the A19 (or a A18 if a used one is to be had) take care with speaker pairing.   For listeners of music without many quiet passages (Rock, Country, some types of Jazz) a purchaser of an Arcam A19 or A18 can probably use speakers with sensitivity of 84db to 86db without issues.  For Classical music listeners, a person should pair this integrated amp with speakers having sensitivity of 87db or higher.  I have used this speaker with speakers of 87db and 88db sensitivity, and will have turn up the volume in some recordings, though the power source of the Arcam A18 accommodates use with its volume over ½ of the maximum range without strain or distortion.  Since this is more of a laid back sound than other comparable products, a person could pair this unit with a "brighter" pair of speakers with metallic drivers.

The machined faceplate of these Arcam integrated amp is of very high quality.  A person who has owned stereo or home theater receivers will have achieved a noticeable improvement in build quality, vibration control, and durability with the Arcam.  The green display is impressive and alluring to behold while listening to music.  The volume control moves with silky precision.  Turn on the Arcam, put your ear to the unit, and you won’t hear a thing.  The build quality is impressive throughout the unit.  It's a thin, low profile unit, though the user should put this unit where it has an unobstructed space above to allow for proper ventilation (the manual and my dealer recommended this).

I have no regrets of my purchase and ownership of my Arcam A18.  I plan on keeping it for years, and upgrading around this fine integrated amp.  A superior product can be had, but you’ll pay almost twice the amount, at the least. I don’t think—having reviewed many products in this range—that you can get a better product with comparable specifications for the same amount from a major manufacturer.

brightonrock's picture

I upgraded last month from the A18 to the Arcam A19 amp and have noticed much more detail coming through in my music. Even though the paper specs don't indicate much power differnece, the A19 seems much more gutsy than the A18, especially in the bass.

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