What kind of cheap Chinese tube amp should I get?

October 8, 2007 5:51 AM

What kind of cheap Chinese tube amp should I get?

In the last few weeks, I've become obsessed with vacuum tubes, and would like to buy a tube amp and speakers. I'm currently in Hong Kong, and there is quite a variety of Chinese-made tube-based audio equipment available here. The sad truth is that I'll probably only listen to fairly low-quality AAC and MP3 files piped through an Airport Express, so the appearance of the amp is likely at least as important as the quality. I figure eight to thirteen watts per channel should be sufficient power. There are a dizzying variety of power tubes to choose from: EL34, EL84, 6V6, KT88, 6BX7, FU50. Most of the tubes are Chinese made, but a few are Russian. The amps I've gravitated to are the Image Audio SE8 (which is expensive and low-powered, but appears very well made), the Audio Space AS-3i (twice the tubes and 50% more power), and the Music Curve D-2020A (very impressive looking with lots of interestingly-shaped tubes, but but appears to be very cheaply made). Most of these amps are available with a choice of power tubes, and are all within the same price range (between USD 400-500). What should my main considerations be, and what should I be looking for?

posted by Etaoin Shrdlu to sports, hobbies, & recreation (6 answers total)

The Music Curve D-2020A doesn't look poorly made to me. That point-to-point wiring may not look fancy, but it works well.
posted by StickyCarpet at 6:36 AM on October 8, 2007 [1 favorite]

"silver 6mm after the panel drawing process. -- High Technology wrinkles from cattle enclosures, aluminum alloy wire drawing process cattle covered"

I would go for the one with the spec that sounds most like dadaist poetry.
posted by zemblamatic at 7:41 AM on October 8, 2007 [1 favorite]

Anyone know what that chinese-language alert that comes up in that Music Curve link says? It only offers an "Okay" response.
posted by Thorzdad at 7:48 AM on October 8, 2007

Yeah, you want that point-to-point wiring. Most tube amps will have it. That looks like a nice, clean internal layout.
posted by marionnette en chaussette at 7:54 AM on October 8, 2007

I'm mostly familiar with tube guitar amps, where my preference is the 6V6. A stereo amp likely isn't going to use output tubes at the rate a guitar amp does but you should keep the cost in mind. Typical cost, low to high: EL84, 6V6, EL34, 6L6, 6550, KT88.

Aesthetically, I like the Image Audio SE8 best. As has been noted, the Music Curve D-2020A doesn't appear to be cheaply made in terms of the wiring. But both it and the Audio Space AS-3i will be more expensive to retube. As an aside, typically the preamp tubes last much much longer than the output tubes (the big ones) so when it comes time to get new tubes don't replace the preamp ones unless they've actually gone bad or start sounding different (flat or dull or lifeless). I've never actually had a guitar amp preamp tube go bad or wear out, though. For people in the US I recommend getting tubes from Lord Valve in Denver. Decent prices, excellent quality control, and stands behind the tubes.

The difference between the SE8 and the AS-3i and D-2020A is that the first is single ended and the latter two are push pull (why they have two output tubes per channel). PP designs almost always have more power due to the design; typically you'll find a pair will get 3 to 4 times the power a given tube SE. Try them all, back to back through the same speakers if you can, to see if you like PP or SE better. A lot of the very highly regarded amps are SE and low powered using expensive tubes like the 300B. But others think SE is fatiguing to listen to and prefer PP or want the higher power available.

The other aspect, and it's huge, are the speakers you'll use. My stereo tastes run to 1970s/early 80s solid state (ONKYO, Pioneer, Marantz, TEAC, AKAI, Harmon/Kardon, etc) and I've found the speakers are absolutely the largest factor for a great sounding system, by an order of magnitude. It's a fairly subjective area and it's further compounded by the fact that most don't do back to back tests but whatever amp you pick out make sure you try them with various speakers at the store. Also keep in mind that power rating of the amp is only part of the perceived loudness of a system. The other factor is speaker efficiency. Very efficient speakers, which people typically use with low powered SE amps, can still sound quite loud (loud enough to get you kicked out of an apartment if you turn it up).

I really can't stress the importance of speakers enough. Try as many as you can before buying, or buy from a place that will let you exchange them if they turn out to not sound good in your apartment.
posted by 6550 at 10:37 AM on October 8, 2007

The Image Audio SE8 is a Class A amp, the other two are "push-pull" amps, either Class AB₂ (Audio Space AS-3i) or Class B (Music Curve) type amps. For sheer musicality, the Class A amp will generally be better, because Class A amps are generally built around simple triode tube output stages, biased to run in a fairly linear portion of the tube's operating envelope. Accordingly, Class A amps need less positive feedback, and have better bandpass and gain characteristics, at the expense of much worse efficiency than their generally bigger "push-pull" cousins.

Most large tube audio power amplifiers are "push-pull" devices, designed as Class B amplifiers, but generally biased for more linear Class AB operation. Thus, they sacrifice some efficiency of the pure Class B design, for better linearity in signal processing. For power ratings above a few watts, these type amps are the only practical choice, given the physical constraints of commonly available vacuum tubes.

In general, you should consider the power demands of your speakers, and the listening environment you'll be in, when considering what kind of amplifier to buy. If you buy very efficient speakers, like Klipschorns, you can be happy with very small amplifiers, perhaps even 1 watt output per channel, because the speaker wastes very little amplifier energy to create a full range of sound. But if you buy typical bookshelf speakers, you may find that they are quite inefficient, and require tens, or even hundreds, of watts of amplifier power to produce reasonable sound levels, across the full audio spectrum.

Because of the physics of sound, and non-linear response of the human ear, it takes a lot more energy to create realistic volumes of bass frequencies than it does higher frequency sounds. So, one long standing solution to the problem of providing speakers with the kinds of amplification they need, is to bi-amp, or tri-amp speakers. Basically, you buy a powerful amplifier to drive the bass speakers, and smaller, but perhaps more musical sounding amplifiers to drive the smaller treble producing loudspeaker elements, and use an electronic crossover network to seperate the bass frequencies from the treble frequencies, prior to sending the signals to the appropriate amplifier and loudspeaker elements. It doesn't so much matter if the powerful bass amplifiers distort the sound somewhat, since the human ear is not so sensitive to bass, anyway. And this strategy greatly relieves the remaining treble producing amplifiers and speakers of the work they'd otherwise have to do, making it easier for them to produce very clean music, through the majority of the audio spectrum.

So, depending on your choice of speakers, you might consider bi-amping or tri-amping, as a strategy for using smaller Class A amplifiers, if that appeals to you. One good strategy for doing this is to use a common center channel servo sub-woofer with its included servo amplifier to create bass, and then use the stereo tube amp of your choice to drive efficient speakers.
posted by paulsc at 10:41 AM on October 8, 2007