LaB­o­Ra­toRY test Re­sULts

Australian HIFI - - ON TEST -

Newport Test Labs tested the power out­put of the Au­dia Flight FL Three S us­ing its stan­dard test pro­ce­dures, which re­sulted in the nine mea­sure­ments that are tab­u­lated in the ac­com­pa­ny­ing test re­sult ta­ble as well as shown vis­ually in the bar graphs. You can see that the Au­dia Flight FL Three S eas­ily met its rated out­put power fig­ures (of 100-watts into 8Ω and 160-watts into 4Ω) at the 20Hz and 1kHz test fre­quen­cies, but fell around 0.7dB short at 20kHz when driv­ing 8Ω loads and 1.2dB short at 20kHz when driv­ing 4Ω loads. The slight lim­i­ta­tion at this fre­quency was not due to am­pli­fier clip­ping, but in­stead be­cause the wave­form dis­tor­tion ex­ceeded 3.0% THD.

Driven into 8Ω loads at 1kHz, the Au­dia Flight FL Three S de­liv­ered 110-watts per chan­nel with a sin­gle chan­nel driven, and 106-watts with both chan­nels driven. Driven into 4Ω loads at 1kHz, the Au­dia Flight FL Three S de­liv­ered 187-watts per chan­nel with a sin­gle chan­nel driven and 170-watts with both chan­nels driven. In prac­tise, due to the dis­tri­bu­tion of power across the au­dio spec­trum when any am­pli­fier is re­pro­duc­ing mu­sic, rather than test sig­nals, the Au­dia Flight FL Three S will al­ways de­liver high fre­quen­cies at the cor­rect lev­els, de­spite not be­ing able to de­liver its full rated power at high fre­quen­cies with con­tin­u­ous test sig­nals.

Newport Test Labs usu­ally tests power out­put into 2Ω loads as well, but in the case of the FL Three S, Au­dia Flight has built in an out­put cur­rent pro­tec­tion cir­cuit that kicks in slowly (four sec­onds) if the am­pli­fier is asked to de­liver full power into any load of less than 2.5Ω, and quickly if it de­tects a short cir­cuit. This pro­tec­tion cir­cuit pre­vented any full-power test­ing into 2Ω loads, since it takes more than four sec­onds to make a con­tin­u­ous power out­put mea­sure­ment.

Chan­nel sep­a­ra­tion was an ex­cel­lent 107dB at low fre­quen­cies and still a very good 80dB at 1kHz. The re­sult mea­sured at 20kHz (55dB) is more than suf­fi­cient to en­sure per­fect chan­nel sep­a­ra­tion and stereo imag­ing, but I am used to see­ing higher fig­ures mea­sured by Newport

Test Labs for this par­tic­u­lar test. Chan­nel bal­ance was ex­cel­lent at 0.02dB (at 1kHz) and in­ter­chan­nel phase also ex­cel­lent, mea­sur­ing just 0.01° at 20Hz, 0.05° at 1kHz and 1.11° at 20kHz. Th­ese re­sults are par­tic­u­larly good since Au­dia Flight says this am­pli­fier is es­sen­tially a ‘dual mono’ de­sign.

Dis­tor­tion at one watt was fairly high for both 8 and 4 test loads, with Newport Test Labs mea­sur­ing over­all THD+N of 0.14% for a 1kHz test sig­nal. The struc­ture for the dis­tor­tion into an 8 load is shown in Graph 1. You can see that both the sec­ond and third har­mon­ics are sit­ting at around –60dB (0.1%) with a fourth at –90dB (0.0031%) a fifth at –71dB (0.0281%) and a sixth at –88dB (0.0039%). The six higher-or­der com­po­nents vis­i­ble on this graph are all around 100dB (0.001%) or more down.

Graph 2 shows dis­tor­tion into a 4 load at an out­put of one watt. The sec­ond har­monic sticks on –60dB (0.1%) but the third har­monic com­po­nent in­creases to –54dB (0.1995%). The fifth har­monic also in­creases (to –60dB or 0.1%), with the sixth har­monic com­ing up to –70dB (0.0316%). At this lower im­ped­ance, higher-or­der har­mon­ics rise in level com­pared to into an 8 load, but with two ex­cep­tions (the 8th and 9th) all are more than 90dB down (0.0031%). Over­all dis­tor­tion gets very slightly higher at rated out­put, with Newport Test Labs mea­sur­ing to­tal THD+N at 0.15% and in­ter­est­ingly, there is al­most no dif­fer­ence be­tween the mea­sure­ments into 8 and 4 loads. The sec­ond har­monic dis­tor­tion is at –60dB (0.1%), the third and fourth are at around –70dB (0.0316%) and the sixth and sev­enth at around –77dB (0.0141%). Then, right out to the 17th har­monic, all are around –70dB (0.0316%).

In­ter­mod­u­la­tion dis­tor­tion (CCIF) fol­lowed the same pat­tern as the har­monic dis­tor­tion mea­sure­ments, in that they’re all more like the dis­tor­tion I ex­pect to see from a valve am­pli­fier than what I ex­pect from a solid-state am­pli­fier. The two test sig­nals at 19kHz and 20kHz (Graph 5) re­sult in a re­gen­er­ated sig­nal down at 1kHz that’s only 58dB down, plus the high side­bands also re­sult in ad­di­tional sig­nals at 2kHz, 3kHz and 4kHz.

The noise of the FL Three S was low, with Newport Test Labs mea­sur­ing 81dB un­weighted ref­er­enced to one watt, a fig­ure that in­creased to 88dB with A-weight­ing. Ref­er­enced to rated out­put, the over­all fig­ures mea­sured were 99dB (un­weighted) and 107dB (A-weighted). For an in­te­grated am­pli­fier to so sig­nif­i­cantly break through the 100dB bar­rier (clear­ing it by 7dB, in fact) is quite an achieve­ment. (It also ex­ceeded its man­u­fac­turer’s claim of 95dB by a long shot!) You can also see the dis­tri­bu­tion of the noise across the au­dio band from Graph 1, with the noise mostly more than 120dB down: it’s only the low-fre­quency, mostly mains-re­lated noise that is above that level.

For an in­te­grated am­pli­fier to so sig­nif­i­cantly break through the 100dB bar­rier (clear­ing it by 7dB, in fact) is quite an achieve­ment.

The fre­quency re­sponse of the Au­dia Flight FL Three S was very ex­tended, ex­tend­ing from less than 1Hz to 510kHz (–3dB) and from less than 1Hz to 251kHz (–1dB). This makes this am­pli­fier an ex­tremely wide-band­width de­sign. As you’d ex­pect from this, the fre­quency re­sponse within the au­dio band into a stan­dard 8 non-in­duc­tive lab­o­ra­tory test load is ab­so­lutely ruler-flat, as you can see from the black trace on Graph 6. The trace doesn’t start rolling off at low fre­quen­cies un­til 4Hz, and is only 0.1dB down at 5Hz, which is the graph­ing limit. The FL Three S’s fre­quency re­sponse into a load that sim­u­lates a typ­i­cal two-way loud­speaker (red trace) was al­most equally good, with Newport Test Labs mea­sur­ing an over­all re­sponse for this load as ex­tend­ing from 5Hz to 40kHz (±0.2dB).

As you’d ex­pect given the enor­mous band­width and the am­pli­fier’s lin­ear­ity, the square wave re­sponses recorded by Newport Test Labs were out­stand­ingly good, with the 100Hz and 1kHz square waves in par­tic­u­lar look­ing like they’d come straight from the sig­nal gen­er­a­tor, rather than via the Au­dia Flight FL Three S. The 10kHz square wave shows just the slight­est hint of round­ing on the lead­ing edge, but is oth­er­wise per­fect. The re­sponse into a highly re­ac­tive load (1kHz cap) was also ex­cep­tion­ally good, with ba­si­cally just a sin­gle over­shoot to barely 1/8th wave height that was damped within one cy­cle. It ap­pears this was a de­sign in­ten­tion that re­sulted from the com­pany’s de­ci­sion to use cur­rent feed­back rather than volt­age feed­back, with the re­sult that, in the com­pany’s words: ‘ the feed­back is closed be­fore the out­put stage … the re­sult­ing out­come con­sists of fast, sta­ble cir­cuits with the ut­most abil­ity to con­trol even the wildest re­ac­tive loads.’

Out­put im­ped­ance was rel­a­tively high, at 0.3 , which as a direct con­se­quence means damp­ing fac­tor was rel­a­tively low, at 26 (@1kHz), again mean­ing the Au­dia Flight FL Three S will be more valve-like in its re­la­tion­ship with the loud­speak­ers it’s driv­ing.

The Au­dia Flight FL Three S’s test re­sults show all the hall­marks of an am­pli­fier that’s been de­signed to sound good, rather than mea­sure well, yet it still per­formed very well on Newport Test Labs’ test bench, though the re­sults re­turned al­ter­nated be­tween those that would be typ­i­cal of a good valve am­pli­fier (i.e. THD, IMD, DF) and those that would be typ­i­cal of a state-of-the-art solid-state de­sign (i.e. fre­quency re­sponse, band­width, sig­nal-to-noise ra­tios, square wave per­for­mance). Steve Hold­ing

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