When using our headphones with computers or iPods we hardly ever give much thought to the little jack we plug it into. After all, what could be simpler? You plug the headphones in and sound comes out of the speakers in the headphones.
Devices such as CD players, iPods, and smartphones do, however, have tiny amplifiers built into them, so that when you plug headphones in the volume will be loud enough to listen to.
If you are using a turntable and have a preamp that undoes the RIAA distortion, you have a line-level output standardized for further amplification. If you were to plug your headphones into a line-out socket you may hear something on low-impedance headphones, but the volume is likely to range from almost inaudible to something in the middle, depending on the specific headphones.
Just as you need an amplifier to sit between your preamp and loudspeaker, you need a headphone amp to get listenable volumes from your headphones. However, the amps in your computer, phone, and other small devices are usually not that great. So using a dedicated amp can really transform how good your headphones sound. Remember that an amp not only affects how loud the headphones can go, but also the quality of the sound that you get out. The tiny amps in mobile devices can introduce unwanted distortion.
The point of a headphone amp is not to have unsafe sound levels, but to have your music remain distortion-free through the peaks and valleys of its playthrough.
A good component amp can solve this problem if it has a headphone jack in addition to the normal speaker outputs, but if you are going to use headphones most of the time that’s a big waste of space and money.
A dedicated headphone amplifier gives you the ability to tap the full potential of your headphones, while being relatively affordable and small.
The next big question we have to ask is the same one we ask of big component amplifiers and preamps: to tube or not to tube?
That is indeed the question, and the answer can be a little hard to get. Tube amps provide more of that warm analog sound that vintage audio lovers crave, but they are more expensive and fragile than their solid-state counterparts.
On top of this, not all tube amps are purely analog. Some so-called “hybrid” amplifiers have some stages handled by solid-state components.
Honestly, there are good and bad examples of all these approaches. A good tube amplifier will add warmth to the sound, but a good solid-state amp is unlikely to take warmth away from a vinyl. On the other hand, if you want to add some vintage warmth to digital sound outputs from a computer, for example, a tube amp is a great way to do that.
The problem is that tube amps are much more expensive and more fragile than their solid-state friends.
Getting in Shape
Headphone amplifiers come in all shapes and sizes. You can get small battery-powered ones that are meant to come with you to improve the output from a tablet or smartphone. While these ARE better than relying on the built-in amp, they are not suitable for what we want in a home listening environment.
Instead I’d generally recommend desktop headphone amplifiers. These are not as small as the mobile versions, while being far smaller than full-sized component amplifiers.
This means that you can fit them into limited spaces (such as right next to your turntable) and move them between different devices.
Tonight’s Main Feature
Every headphone amp will give you the same basic features. There will be an input for line-level RCA or 3.5mm sources and then an output for your headphones. You’ll also find a volume and gain control.
To be honest, that’s all you need if you are going to be listening to nothing but vinyls. You may encounter some other features that could be worthwhile if you were going to do something other than just listen to your record player. But think carefully about it, since every feature comes at a cost , either in terms of money or in terms of the quality of the core amplification performance.
So what sort of additional features might you see? One that’s coming up more and more is a digital to analog converter or “DAC”. This is an onboard component that takes a digital signal directly and outputs it as an analog amplified signal to your phones. Obviously a record player is an analog source, so this feature is pretty much useless unless you also want to use the headphone amp with a digital source. The downside is that DACs add to the price and can even add unwanted interference in the amp if they are poorly shielded. So, in general, I don’t think it is worth the hassle unless you absolutely know that you need one.
What about the numbers that you should be aware of? First of all, I suggest you pick out a pair of headphones first before you buy a headphone amp. Why? Because many of the numbers are going to depend on what you headphones are designed to handle, so it makes sense to first get the headphones you want and then get an amp that you know will work with it and amplify it to unlock its full potential.
Look for the THD or IMD numbers. This should be 1% or lower. These are the harmonic and intermodulation distortion. Don’t worry too much about it, just keep that number at or under 1%
The signal to noise ratio is exactly what it says on the tin – the strength of the signal versus the noise. The higher this number the better when comparing two headphones, and keep in mind that the best record players have signal to noise ratios of over 70 dB. CD audio pushes that number to the 90s. Your amp’s SNR should at least match and preferably exceed the SNR of you audio source.
Impedance is very important and here you just have to make sure that the amp has output impedance compatible with that of your headphones. This will usually be quoted as a range in ohms; your preferred headphones should fall within that range.
The power output of the amp should also match the rated output of the headphones. The headphones will usually state how many milliwatts they are rated for.
Buying the right amp specifically from the vinyl or vintage audio enthusiast perspective can be tricky, but really it is just a matter of keeping in mind exactly what you need and ignoring any features or gimmicks that don’t fit in with that mission.