About amplifiers
Summary
A ‘DAC’ is a headphone amplifier
All discussion on these pages will call them ‘headphone amplifiers’
In general, spend your money on headphones, not a headphone amplifier
The jumps in quality and usability of headphones are large
…or try an app to alter the equalisation
That can be messy, but will cost you no more then £10 and makes a huge difference
If you fit any of the reasons below, try looking at headphone amplifiers
You may need one. Also, headphone amplifiers may not make as much difference as the headphones or equalisers, but they make a special difference
Oue experience is that headphone amplifiers often do not connect properly
Be warned. Our current experience is that there is a one in four chance—the amplifier may refuse to connect or set volumes to extemes, and you are highly unlikely to get an equaliser to work with them—it’s one or the other
Separate headphone amplifiers come in many shapes and sizes
Expensive headphone amplifiers can be less convenient. See our guide
About
The world of headphones has started to talk a lot about DACs. I find the subject is misnamed. What the commentators mean is not DACs, it is headphone amplifiers. And ‘amplifiers’ is what we say here.
Why would you plug a headphone amplifier into a smartphone or computer? I think there are a few reasons,
You expected a headphone amplifier to change sound like a headphone
The amplifier makes some unexpected behaviour in your system, like crackles or quiet sound
I cover the changes in sound below. But first,
What do you mean, plug a headphone amplifier into a mobile phone?
Computers and mobile phones have builtin amplifiers. But on a tablet/computer you can plug an amplifier into any USB socket. On smartphones you can use the charging socket (with the right adaptor for Apple/Android etc.).
You can choose the amplifier you plug in—the range of products is vast.
Reasons for plugging in a separate headphone amplifier
You may want to use a separate headphone amplifier because,
your phone or tablet has nowhere to put wired headphones
you like your headphones but want to update their replay
you want to improve the sound in ways that are not to do with headphones
you want to power difficult headphones
A warning
Tou may not get the result you hoped for. For unexpected behaviour, see the article on amplifier fixes.
General notes
So what is a DAC?
DAC stands for ‘Digital–Analogue Converter’. A DAC changes digital audio, which you get from a CD, sound files or the web, into the analogue signal used by speakers. DACs have feeble output. To power even small earphones, they must have an amplifier after them.
Everyone says the DACs (headphone amplifiers) in mobile phones are poor!
Half‐true. A smartphone contains modern audio processors. These are very good. But a phone only needs to play some speech, and make the speech audible in traffic and other busy environments. That’s nothing like listening to voices for performance, such as audiobooks, or replaying music.
How can a separate headphone amplifier make the sound better?
Not in the same way as speakers. Generally, a good quality amplifier may,
Have a good quality DAC with better clocks
The sound may be more ‘stable’ (though people argue about this one)
The DAC and amplifier will have lower or more pleasant distortion
The sound may have ‘blacker silence’, or voices and instruments sound ‘clearer’
A good quality amplifier can start and stop the sounds where the signal asks
The sound may be ‘faster’, or ‘less muddled’
May isolate outputs and bands of music better
Such as the connection between DAC and amplifier, or the left/right channels. Again, the sound may be ‘clearer’, or have a ‘better soundstage’
A powerful, low‐noise amplifier can drive a speaker over greater volume range
The sound is more ‘dramatic’, has a ‘greater dynamic range’
A powerful amplifier can better maintain a flat frequency response
The sound may have finer volume changes, better ‘detail’. It may also make instruments more ‘colourful’ or ‘present’. Bass especially can be better controlled
An amplifier that matches the headphones may drive the headphones more appropriately
That can change the way the headphones react. Sometimes irritating noises can disappear (or appear)
These changes add up.
What can go wrong? At my cost?
I’m obliged to say that you should exercise caution with separate amplifiers, because over‐driving headphones can break them, or your ears, permanently.
What can go wrong? Apple device support
Whatever a manufacturer claims, always check if a headphone amplifier is made for an Apple devices. Some examples,
At least one amplifier made for Apple phones will kill the battery of non‐Apple phones
The electronics can not detect non‐Apple phones. The electronics assume non‐Apple phones are trying to charge the amplifier battery. In half an hour your phone will be dead
At least one mid‐priced amplifier will not run on an Apple phone
The amplifier draws too much power. An Apple phone will reject it
Several HiFi review organisations only review amplifiers on Apple phones
So they don’t recommend anything under £80. This is unfair—on a non‐Apple phone, those amplifiers may be a big improvement
These are critical problems, enough to make you send an amplifier back. Which annoys you and the retailer both.
What can go wrong? Unexpected behaviour
When you plug an amplifier into a source and headphones, the system can react in unexpected ways. Some of these reactions, like reduced volume, are unwanted. Some reactions, like muting or crackles, make the system useless. Our experience is that any headphone amplifier, cheap or expensive, when given provoked can show unexpected behaviour. Try our article on amplifier fixes.
Computer connections
When you plug a new amplifier into a computer, it may prompt you to download a new ‘driver’. You need this. Apple (and Linux) devices are more reliable and erratic.
What can go wrong? My disappointment?
You will find reviews online saying, “I’m disgusted, I expected this to work, Very disappointed, returning this item!”. Because,
Of an expectation that amps change sound by “making more bass”
Of an expectation that a cheap amplifier will beat the electronics in an expensive phone
There is no output, or output is quiet/indifferent
Nasty effects emerge
Volume changes are difficult
Switches don’t work
Batteries drain
Plugging and unplugging wires and boxes is a mess
For problems with sound like crackles, try our article on amplifier fixes. As for functions not working, well, the ‘standards’ are messy, and it is difficult for manufacturers to cover them all.
How much better will a separate headphone amplifier sound?
Hard to say. An amplifier is plugged into a system, which affects it. That said, we think a £20 amplifier can improve any cheap phone. We think £80 can match, or better, an expensive phone. We think, unless you have special needs, there’s no good in spending over £120.
Refs
One reviewer, one hundred cable/dongle amplifiers,
A forum whose members believe that by measuring audio equipment, objective conclusions about performance can be reached. If you are interested in sound replay, go read,