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Published on February 27, 2008

The interesting question in this case is why does a low-current device with perhaps 20 watts of power produce a better sound than a transistor amplifier?

One of the reasons is the high working voltage through the tubes in a valve amp, without the need to pass through complicating circuitry. This makes them well suited for radio transmitters, and in fact valves remain in use today for very-high-power radio transmitters, where there is still no other technology available.

This week, I'd like to share some of my experiences with valve amps, particularly the do-it-yourself products that come from a Thai audio enthusiast.

There are some Thai audiophiles who have persisted in their appreciation of valve amplifiers, so much so that they have made them more commonly available. They make inexpensive valve amplifiers, use them to reproduce fine sound and distribute them among themselves. Some of their valve amps have become so popular that they have begun producing them for sale. The business does not make much money, but most of them don't mind, because they build these amplifiers with a great deal of love.

One Thai audio enthusiast in particular is besotted with the beauty of valve amplifiers. He is a dedicated tube collector who has gathered and played with vacuum tubes for decades. He has ancient as well as modern vacuum tubes in his collection. Most of all, he appreciates the sound produced by valves and is fascinated by the way each of them works. Each tube, he says, offers a unique sound quality. Even tubes of the same variety but from different production lots have a different quality. With his many years of experience, this audio enthusiast has created a valve amp that not only sells, but also has become popular.

He explained to me that tubes must be biased justifiably regarding the cathode. This makes it quite difficult to direct-couple the output of one valve to the input of the next, and herein lie the differences that can make a good or an indifferent valve amp. Even installing the tubes on a valve amp requires special techniques that can affect the sound quality.

This designer pioneered a type of valve amp called twin tubes, by paralleling tubes in a horizontal order, instead of the so-called vertical order found in most valve amps. He says this gives the amp a compact size, even though some people disagree and say this configuration will cause a non-linear flow, leading to high distortion. In fact, the amp produces low distortion and has the capacity to drive very large and difficult loudspeakers. The key to making valve amps, he says, is finding the point at which the performance of the tubes is optimised.

In theory, the twin-tube amp will give an output of only 10 watts. But we do not want an amplifier with a high-watt output. What we need is a high-quality output, and an amplifier delivering only 1 watt could possibly produce every audio nuance in fine detail and even give a deep bass. The twin-tube design is an attempt to match impedances in a way fundamentally different from a transformer. This is how valve amps often have a unique sound quality.

The nature of vacuum tubes, or valves, results in significant differences in circuitry and characteristics to transistor-based amplifiers. As a generalisation, valve amps tend to operate well if they have a "minimalist" design concept. There is no need for many inputs, tone controls (bass/treble adjustment), any imperative circuitry or buttons. They can be "flat" amplifiers, so as to have as little distortion as possible, offering a sound quality that is flat, warm and natural.

So perhaps you should not bother noticing the number of watts delivered by a transistor amplifier. Try a valve amp instead, and you may realise that high wattage without good quality is no quality at all.

By Wijit Boonchoo

The Nation

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