Sunday, 8 November 2009

In the Glow

Filed under: Uncategorized — Michael @ 18:04

I really don’t understand the folks in the audiophile community that claim that tube amplifiers sound better than transistor units. I mean, for some time now, solid-state audio amplifiers have been capable of reproducing the input signal with virtually perfect fidelity.
Maybe I should say ‘didn’t understand’. Let me explain.
In my home system I use a NAD C315BEE and am absolutely pleased with it. When, a few months ago, I went looking for a system, I listened to a number of amps and honestly couldn’t really hear any difference between most of them. I choose the NAD because it was relatively inexpensive and had all of the features I needed. Before then I listened with headphones using a couple of amplifiers I built myself, one with op-amps and another, class-A amp, using discrete transistors. Both sound very good with the class-A amp being, marginally, my favorite.
Anyway, I got to thinking it would be interesting to hear a tube amp and see, er, hear, if there really was something to it. I found a simple headphone amp circuit ( that many have built and given positive comments about. Here is a pic of my result.

(The whole box is 20cm (8″) wide, 30cm (12″) deep and 12cm (4.5″) high. The big tube is just under 13cm (5″) tall. The actual amp is completely built on the lower plate. That’s why the input, volume control and output jack are “on top”. The rest is the power supply. The two switches control the filament and high-voltage separately to let it warm up before applying the real juice.)

Well, I have now listened to the warm (er, hot) glow of tubes and can report that the sound is really quite pleasing. It definately has a different character than with my other semiconductor amps. So, what makes it so? I have some thoughts on that. First, no question that the fidelity of the playback is comprimised. But the odd thing is, in a somehow “good” way. The sound of a violin or soprano, e.g., is softer. And bass sounds such tympani or bassviolin roll in rather than pound in. It really does give an impression of a “rounder” sound. (But I don’t want to imply that the sound from the tubes is more accurate. It’s not. Violins can be hard and tympani really do pound.)
I have an analogy. With my class-A amp, for example, everything in the recording is reproduced with, for all intent, no loss in fidelity. I close my eyes and I am alone in the second row of the auditorium, right behind the conductor (or depending on the mastering, in the orchestra) and I can hear everything in analytic detail. With the tube amp I am in the first balcony with friends around me. I mean there is no longer the analytical precision but the sound of life is around. Or something. It is “verblüffend” (a good German word meaning baffling/intriguing/fascinating all at once).
Now, I have heard only one circuit, one tube type, etc. But I think that this “good” fidelity loss would be somewhat different with other choices. Can this be what the tube-heads are really chasing? I mean the good loss that best satisfies them?
So, will I use it regularly? Probably. It was fun to build and does, in fact, sound really nice. But it comes with some minuses. It’s heavy. No, not that way, I mean really heavy as in weighs a lot. The high-voltage supply has to deliver almost 10 watts at 150V with no ripple. That means lots of transformer, lots of capacitance and a big inductor. And the 6V supply for the heaters is cruising at over 15W. Another big transformer and more capacitors and a voltage regulator that needs a huge heatsink (and it still gets too hot to touch after a couple hours).
But it’s pretty, glowing there in a darkened room. Maybe that is the real draw.