Amplifier Sound Quality

Do Amplifiers contribute to your systems sound quality?

You hear it all the time in hi-fi audio system reviews, phrases like:

You need a warm sounding amp to mellow out your bright speakers sound.

Audiophiles have been associating acoustic qualities to the choice in amplifier for decades. There must be some difference in sound, otherwise there wouldnt be such a wide disparity between the really exotic amplifiers that cost thousands versus the mainstream amplifiers that cost less than $500. The differences certainly arent in the specifications. Cheaper amps these days always go for the 100 Watt per channel rating on their specs sheet. It seems even a $200 Sony receiver desires to be called a 100W amp.

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What about the amps contribution to sound quality? Can an amp color your music with any acoustical qualities outside clipping? Experts in hi-fi magazines regularly write reviews on esoteric brand name amplifiers filling them with adjective-laden praise for warm sound, liquid highs or edgy bass. The question of the amplifiers contribution to sound really started when the first transistorized amplifiers appeared in the 60s. Many die-hards still claim there is positive coloration to acoustic quality from tube amplifiers. They claim tube amps have a warm, smooth sound and that transistorized amplifiers introduce a harsh sound quality.

Double blind testing (the Pepsi challenge) is where participants choose between two things but dont know which is which. Its probably the only way of applying scientific methodology to audio. High profile double blind tests have tested everything from audio cables, speaker wires and even (the old controversy) amplifier sound.

Editors of Stereo Review magazine (now called Sound and Vision) conducted a high profile test of their own, recruiting expert double blind tester David Clark of DLC Designs (who does such tests professionally for CD players and hi-fi VCRs). The test was reported in detail by Ian G. Masters and published in Stereo Review magazine. The test was designed to be as objective as possible, using the same system, speakers, playback etc. They had a panel that consisted of some 25 listeners all audio/hi-fi professionals with an equal number of hi-fi objectivists who believed there would be little to no perceptible difference between amplifiers, and audiophiles who believed there was a huge difference between expensive or tube amps and their cheaper counterparts.

Futterman Monoblock Amplifier array couldnt beat the $200 Pioneer

The array of amplifiers was laughable, from the most exotic to the most humble and everything in between. Topping off the high end was a Julius Futterman tube amp array, consisting of two $6,000 tube mono-block amps with separate power supplies, a total of four giant boxes that take up the space of a small fridge. The bottom end was represented by a $200 Pioneer receiver; it even had a cheesy five band equalizer on the face and a slide volume control. Its the kind of device that makes audiophiles cringe. The testing took place in an acoustically neutral environment that favors hi-fi listening but not one particular amp.

Middling brands included some nice NAD 2200, Hafler DH-1 120, and a Mark Levinson ML-11 $2000 50 watt per channel amp that delivers 25 volt peak power with current of 12.5 amperes. Now thats a high current amp. The A-B testing was preceded by a session where each listener got to toy with the amps and freely listen to each knowing what they were listening to. Doing the sighted listening, many of the listeners claimed to hear a distinct difference. Some of the skeptics were even admitting that they could actually hear significant differences between the sound quality of the different amps.

When it came down to the blind A-B testing of the 25 testers, only 3 participants scored 60% or greater correct when they guessed which amp was which, when comparing between two. Nobody got higher than a 63% score. Most amazing was that in testing between the Pioneer amp and the Futterman array, only 114 of 212 listeners could tell the difference -- thats a 54% correct guess! This is the most extreme example: audiophiles not able to tell the difference between a $200 Pioneer receiver and a $12,000 separate mono-block tube amp array with separate power supplies.

$200 Pioneer amp sounds like a $6,000 mono - block tube array

What does it mean? It means that people who advise you to buy expensive amplifiers because they believe amps contribute coloration to acoustic quality probably couldnt tell the difference between their favorite exotic amp and a $200 Pioneer. It doesnt mean that you should only choose the cheapest amp you can. There are other considerations not the least of which is the longevity of the unit. A $200 receiver is more likely to have a short lifespan, but a decent quality power amp could last a lifetime. There are also other considerations: the one thing that will certainly present problems is clipping. In the test they set the gain equally to all amps, so there was no difference in the power output, and the gain was set well within the specified limitations of the amp itself. This might not be the case at home; the speakers you use could be of all different efficiency ratings. You have to ensure your amp has plenty of reserve power for handling spikes in the soundtrack without clipping. Clipping is distortion, and distortion is the simple explanation for the coloration people claim to hear from certain amps. So, the weak highs or muddy bass you might hear from a cheap amp is probably clipping, or it could be a placebo.

Speakers are the device that creates the sound you hear. The room in which they produce sound is almost equally important to the speakers; room acoustics provide reflections or dampen sound, which will make or break many sound systems. The amplifier only powers the speakers to let them do their job. Beware of adjective laden descriptions of acoustic colorations from an amplifier.

Thanks to Bruce Coppola for providing the Stereo Review article in its entirety.