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How do headphone amplifiers differ from speaker amps?

garbulky

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#1
What I'm really trying to ask is how do headphone amplifiers get their noise levels down to power very sensitive headphones? Is it a simple thing like a resistor or is it more complex like very high performance parts?
 

solderdude

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#2
more complex.

Different power supplies, different components, different voltage rails, different power levels, different gains, different load impedances, different currents.
The only thing they (speaker amps and headphone amps) have in common is that both amplify signals and drive voicecoil(s)
The basic design can be similar.
 

Killingbeans

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#3
One factor is probably that headphone amps runs with lower voltages and sucks up less amperage, meaning that the supply rails can be regulated way more precisely. A speaker amp does not have the luxury of linear voltage regulators.
 
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garbulky

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Thread Starter #5
So how does one get the noise levels down in a headphone amp?
 

Killingbeans

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#6
Kill noise from external sources (regulation and filtering/shielding) and minimize nonlinearities in the signal path?

There's no golden formula. I's all about careful design and compromises.
 

solderdude

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#7
So how does one get the noise levels down in a headphone amp?
When you have a headphone amp with a too high noise level for sensitive IEM's then either you need to buy another amplifier or use THIS
 
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garbulky

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Thread Starter #8
When you have a headphone amp with a too high noise level for sensitive IEM's then either you need to buy another amplifier or use THIS
I gotcha. I was just wondering about how headphone amplifiers are designed from the get-go to provide such low noise levels that it works for headphones.
 

RayDunzl

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#9
So how does one get the noise levels down in a headphone amp?
Part of the equation:

Low gain, or even attenuation of the incoming signal in normal use with headphones.

My speaker amp adds 26.4dB to whatever you feed it.
 

gvl

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#10
I have thought of using a powerful headphone amp with low output impedance to drive very efficient near field speakers. Bad idea?
 

amirm

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#13
I have thought of using a powerful headphone amp with low output impedance to drive very efficient near field speakers. Bad idea?
Speakers present a much lower impedance to the amp than headphones. So you can easily damage the headphone amp if it doesn't have appropriate current limiting. That said, I think some people were trying that with Massdrop THX 789.
 

solderdude

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#15
I gotcha. I was just wondering about how headphone amplifiers are designed from the get-go to provide such low noise levels that it works for headphones.
Low gain, low noise opamps/circuits, low noise power supply rails, circuits with a high immunity to power supply noise... careful PCB design and component choices... that kind of stuff.
 

sergeauckland

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#16
In theory, there's no difference between a headphone amplifier and a loudspeaker amplifier.

Both have to drive a certain number of volts into a defined impedance with low distortion.

However, loudspeakers have an impedance in the range of 3-16 ohms (with a few outliers) and with power requirements from a couple of watts to several hundred. Headphone amps tend to drive higher impedances, and with far greater sensitivity so need fewer volts. That makes the task of the headphone amp much easier, albeit with more emphasis on low noise.

A typical headphone amp consists of a 5532 op-amp, which provides typically somewhere around 8v (+20dBu) at vanishingly low distortion and inaudible noise into typical headphones. I know there's a lot of 'typical' in that statement, but I think it's justified for the majority of headphones and amplifiers. Where it perhaps falls down is for the very sensitive, where noise may become an issue, and the headbangers and specs merchants for whom loud is good and VERY LOUD is better.

I have several pairs of headphones, from AKG (75 ohm), KOSS (270 ohm) and a good few 'no-name' in ear types (20 ohm or so) that I use when travelling, and I've never found any of them a problem, so assume that the spread of output voltage, headphone impedance and sensitivity are all such that any headphone amplifier can cope adequately. I've never seen the need for a dedicated headphone amplifier, what comes out of my tablet pc or pre-amp has worked fine for me.

S.
 

RayDunzl

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#17
In theory, there's no difference between a headphone amplifier and a loudspeaker amplifier.
Yeah. In theory.

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But where's the headphone jack, anyway?
 

restorer-john

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#19
Very low output impedance.
Power amplifiers (speaker) have much lower output impedance than headphone amplifiers. By factors of 100 or more in many cases.

The OP asked : "How do headphone amplifiers differ from speaker amps?"

They don't really.

Headphone amplifiers are simply very low powered (and hopefully low noise) miniature power amplifiers running on low voltage rails. The fact that people the world over are suckered into expensive ones makes me smile. Look at the internals of any of them and give me a BOM cost, they are highly profitable little boxes of SMD single board creations. Hardly worth the stupid money being charged.

As Serge said above, a 5532 can swing more than enough voltage in a typical implementation to more than adequately drive my AKG-702s with a 100ohm source impedance and noise levels down to a few uV (<115dB) and distortion so low it is irrelevant. If I want more voltage swing (unlikely) or have some high impedance cans to play with, I can plug them into my preamplifiers or even run them straight from their buffer/line stage just for fun. My old Accuphase preamplifier has a 1 ohm output impedance and can deliver swings of >20V with a S/N of over 110dB.

There's nothing magical about headphone amplifiers. They are a product segment dreamed up by the 'separate everything into an individual box crowd', tell them it's so much better and charge lots for the inconvenience. First it was outboard phono 'stages', then separate D/As and transports (when there was good reason to leave them slaved together back in the day and now), outboard passive 'preamps' (what a joke), etc.
 
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