Tuesday, March 12, 2013

Pitfalls of Vacuum Tube Amplifiers

Woo Audio WA3
The vacuum tube amplifier is something that all true audiophiles yearn to own at some point, if they don't already.  There is something unique and special about the warm, rich sound produced from a vacuum tube amplifier as apposed to a solid state amp.  Even I have been eyeing vacuum tube amp's for the last few years like the Schiit Audio Valhalla and the Woo Audio WA3.  I am positive that a pair of Sennheiser HD 650's, the Valhalla vacuum tube amplifier and some sort of quality DAC (most likely the Schiit Audio Bifrost) would sound truly spectacular.  However, someone who is unacquainted with vacuum tube amplifiers should be aware of a few pitfalls associated with vacuum tube amps.

There is no doubt that if you are looking for the purest analog sound possible, the vacuum tube amplifier is the way to go.  Todays solid state amplifiers lack the rich and luscious sound that the vacuum tube amplifier provides.  However, the biggest pitfall of the vacuum tube amplifier is well... the vacuum tubes.  Vacuum tubes are an extremely antiquated technology making them relatively expensive to replace and yes, you will be replacing them.  There is also the issue of quality.  Not all vacuum tubes are created equal.  The crappy ones will often muddy the sound as well as affect the sound signature of your expensive amp in a variety of negative ways.  The better vacuum tubes obviously sound better, but they tend to be much more expensive than their low end counterparts.  There is also different types of vacuum tubes that you can select.  Each different tube produces a slightly different sound signature when paired with your amplifier, so selecting the proper tubes can sometimes be a chore.  You must also understand that almost one hundred percent of the vacuum tube manufacturing process is done by hand.  This results in vacuum tubes that are ever so slightly different from each other. Most of the differences are almost imperceptible to the regular listener, but the discerning audiophile can often pick up on the differences.

Schiit Audio Valhalla
Vacuum tubes will need to be replaced from time to time as well.  Smaller tubes tend to last anywhere from five to eight years depending on use.  Typically, the bigger the vacuum tube, the less time you can expect it to work (although this rule does not always necessarily hold true). Many big tubes will only last from one to three years.  It all depends on how hard you push your amp, for how long you use your amp and the quality of the tubes.  Because of all these factors, it is hard to definitively figure out how long your vacuum tubes will last. One last rule in vacuum tube life is that they will often burn out faster when using harder to drive headphones (because obviously the tubes are being worked harder by high impedance cans).  For example you can expect a Woo Audio WA3's power tube (the largest vacuum tube on the unit) to burn out quicker if you are driving a pair of 300Ohm Sennheiser HD 800's as apposed to the 150Ohm Sennheiser HD 700's.  Tube life is very hard to determine due to a host of effecting factors, but the main point I am trying to make is that if you have a vacuum tube headphone amplifier, you will be replacing the vacuum tubes at some point.  Replacing the tubes obviously costs money and thats why vacuum tubes can become a bit expensive to maintain over the years.  Some smaller tubes can cost around $10 to $15 dollars while the bigger tube can cost upwards of $30 to $40 dollars each.  With a vacuum tube amplifier that has say four tubes, it is probable that you will be investing an additional $60 to $100 dollars into the amplifier over a period of 3 to 5 years.  Some really expensive amplifiers have several tubes and obviously with more the more tubes you have, the more costly it becomes to replace them.

Schiit Audio Valhalla Tubes
Another, somewhat minor pitfall with vacuum tube amplifiers is vacuum tube burn in and what I like to call "vacuum tube roll-off".  When you first insert brand new vacuum tubes into your headphone amplifier, they need a chance to burn in, similar to a brand new pair headphones.  Your tube amplifier wont reach it's full sound quality potential until new tubes have been used for a few hours.  Vacuum tube roll-off occurs a few years later  when your tubes are no longer new.  As they begin to get old (nearing burning out) the sound quality tends to decrease.  It continues to decrease until eventually the tubes burn out and are need of replacing.  The primary indicator of an old and worn out vacuum tube is when the sound quality begins to decrease.  Many people replace the vacuum tubes during this point because they know that they are nearing the end of their life.  This is a common practice, as using the tubes until they burnout can, in relatively rare cases, damage the headphone amplifier. A few other vacuum tube amplifier related pitfalls are that when the amplifier is first switched on it needs a good minute or so to warm up the vacuum tubes before you begin listening and that vacuum tube amplifiers tend to produce much more heat and in some cases require more power than their solid state amplifier counterparts.

The pitfalls listed and explained above are the major possible downsides to the vacuum tube amplifier.  This post is in no way intended to dissuade people from purchasing a vacuum tube amplifier.  In fact, in my personal opinion, the benefits of the vacuum tube amplifier far outweigh the detriments as a good vacuum tube amplifier paired with quality headphones sound's truly spectacular in comparison to even some of the best solid state amplifiers.  It's really an experience that is difficult to describe, except that a good vacuum tube amplifier often makes a standard solid state amplifier sound cold and lifeless in comparison.  Tube amplifiers tend to produce a much more rich, lively and often times detailed sound signature, although keep in mind that this is not always true as there are quite a few good and expensive solid state amplifiers out there as well.  I feel like it is important for anyone on a tight budget looking at tube amplifiers to understand that you are going to have to spend more money on it in the future, and that vacuum tubes do have limited life spans.  I would highly recommend a quality tube amplifier to anyone who is serious about high end headphone audio and for someone who actually has a headphone that can benefit from it (sorry, but your ATH-M50's will most likely not benefit from a tube amp).  If you have a moderately or even extremely hard to drive audiophile class headphone, are serious about the best headphone audio has to offer and are willing to pay a pretty penny on an amplifier and some more money on the tubes in the future, then a tube amplifier is for you.

Below I have linked several companies that make quality tube amplifiers.  Some of them even sell the individual vacuum tubes as well!

CLICK HERE for Schiit Audio
CLICK HERE for Woo Audio
CLICK HERE for Eddie Current Audio
CLICK HERE for Cary Audio
CLICK HERE for Icon Audio


  1. I couldn’t agree more! A well-executed SET tube headphone amp along with a pair of audiophile-quality headphones can achieve some of the finest sound you’ll ever hear. I recently purchased a Schiit Valhalla to drive my Cardas-cabled Sennheiser HD650’s and the sound is amazing! Far more detailed, open, transparent and life-like than the headphone amp in my Carver C-1 preamp.

    The Valhalla uses soviet designed and manufactured tubes that are extremely linear, quiet, and highly detailed. They may not be as “warm” and “tube like” as some of the other tubes but they are extremely accurate. I’ve found that Russian tubes made in the 60’s and 70’s tend to sound the best. 60’s vintage tubes can be difficult to find and command a hefty premium. A matched pair of 1964 Russian 6N1P drivers (the smaller tubes) can cost in excess of $80. The later vintages are readily available on eBay for $2 to $10 per tube. If you don’t have a tube tester (and who does now days) you’re better off buying a matched pair as the sound will be more uniform between channels.

    With the Valhalla and pretty much all tube amps, the input or driver tubes are the more critical regarding sonic differences when replacing tubes. My experience is that changing to a 1960’s or 70’s matched set of 6N1P’s resulted in greater detail, openness, and transparency whereas a similar change of the output 6N6P’s had minimal effect.

    One other caveat that needs mentioning: the impedance of your headphone will determine if a tube amp is right for you. Most tube headphone amps including the Valhalla and Woo Audio WA3 couple best with higher impedance cans such as the Sennheiser 580, 650, 800, etc. and the Beyerdynamic T1. In general, headphones with impedances between 300 and 600 ohms are ideal matches for SET tube amps. Orthodynamic headphones such as the Audeze LCD-2, HiFiMan and other low-impedance, low-efficiency headphones with impedances of less than 50 ohms cannot be properly driven by pure tube amps. Solid state or hybrid amps are much better choices for these cans.

    I’m extremely pleased with my Valhalla/HD650 combination and never would have believed an amp could make such a difference in sound quality.

  2. What are the pluses and minuses in useing a hybrid amp like the Lyr 2 over the Valhalla 2.
    what would be best for the line up of LCD2 and HD800.

  3. Shame that WA1music player is just bad, WA3 was good but nothing beats PowerAMP

  4. Hi, love the circuit! I started with transistors as a child, so learning vacuum tubes in my late 30's is killing me. The resources are limited nowadays, and I am having to scrape and interpolate/extrapolate what I can. I think I can modify your circuit to broadcast on the AM band (just experimenting). I am having a difficult time finding circuit info for various designs, including calculations.
    best tube amplifier