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The pleasures of a little HiFi distortion

5th November 2019

Bending technology can lead to some great music.

Some time ago I came across a 1991 review by Robert Deutsch of Threshold’s FET Nine/e preamplifier, in which he attributed this statement to J Gordon Holt: “accuracy in audio reproduction is the ultimate objective of an ideal sound system, which everyone claims they want but nobody likes when he has it.”

Many would say that much has improved since 1991 in the design of amplifiers with cleaner power supplies, very low levels of distortion and attention to detail when it comes to noise reduction. Yet J Gordon Holt’s assertion is as true today as it ever was.

This topic came up at last year’s Burning Amp Festival (http://www.burningamp.org/) where Nelson Pass presented a talk on second harmonic distortion and its role in ‘warming up’ an audio system’s presentation. For good measure he even gave away a little gadget to show people what it sounded like. He noted that as a practical matter, the problems of distortion had been solved but that people don’t necessarily find this gives them what they want from their sound systems.

He introduced Marshal McLuhan’s idea that we turn our mature technologies into Art and Entertainment and observed that many audiophiles want more than low distortion, something different – subjectively good sound.

His full article based on that talk can be found at http://www.firstwatt.com/pdf/art_h2_v1.pdf and the full presentation including a design for an active crossover is here: http://www.linearsystems.com/burningamp.html

But why would one fight years of technological progress to introduce distortion? Well one answer is that it can sound pretty good. You can also argue it can just be fun to explore what electronics can do for your sound system.

Nelson explained that he had explored the relationship between distortion and audio satisfaction with a design of his, the SIT-1 amplifier. This had a knob on the front of the amplifier which varied the amount and phase of the 2nd harmonic. He would then lend the amplifiers to listeners who didn't know what the knob did and gather their comments. Roughly speaking, they tended to prefer about 1% negative phase 2nd harmonic.

I experienced this myself when I built another of Nelson’s designs (the BA-3 power amp), that allowed the builder to choose between a minimum distortion point or by adjusting a small pot on the circuit board, a small amount of 2nd harmonic distortion. I wasn’t the only one to find that I preferred the latter.

Now purists may well argue that this is not what the audiophile experience is all about and that is a perfectly valid position to take, but for me at least, the musical presentation just sounded more ‘alive’.

To illustrate these acoustic properties of distortion at last year’s festival, Nelson designed an inexpensive JFET circuit that could introduce a very low level of positive or negative 2nd harmonic distortion into an audio system (his was the gadget given away at the show but if you have a few basic skills you can explore these ideas as a DIY project of your own). The findings are interesting. Negative 2nd harmonic distortion produced by this device was interpreted by listeners as giving a deeper soundstage and improved localization than otherwise. Positive phase 2nd harmonic seems to put the instruments and vocals closer and a little more in-your-face with enhanced detail.

Commercial products have always been available to produce similar effects although the audio press tends to be shy of the word ‘distortion’ instead talking about the ability of some valve amps to ‘warm up’ a system.

So, where does this leave accuracy as a goal for many audiophiles? Probably where it was before, as a prerequisite for an excellent system but the art of great listening starts when you learn how to make it work for the individual music enthusiast.

You really don’t have to be an engineer or a geek to explore your individual HiFi preferences. The DIY community is both generous and patient and if you are in San Francisco this next weekend (9th and 10th November 2019) you can take these ideas further and get close up and personal. I see that “Measurement vs. Perception” with Nelson Pass, Sean Casey and Kent English at this year’s Burning Amp Festival is just one of a host of interesting sounding presentations and equipment demonstrations.

Copyright © C J Bell 2019

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