[maggotbrain]

Why are headphone amps better than speaker amps at driving phones?

Im looking at the Marantz PM4001OSE. It costs £200 and seems to be alot of kit for the money. It also comes with a remote control, tone controls and a headphone jack. When i compare that against a £200 headphone amp...

So how many times better is a headphone amp than a speaker amp?

Why are they better?

 

[chadh]

I'm no expert on these sorts of things, but my vague understanding is that this all has to do with the difference in impedance of headphones and of speakers.  Typically, speakers have an impedance of something between 2 and 8 ohms.  Sometimes you might find 16ohm speakers.  But when you get to headphones, their impedances are significantly higher.  A pair of headphones with impedance of 30ohms is extremely low (although not uncommon), and for some well respected cans the impedance can be as high as 600ohms.

While headphones don't require a great deal of gain in amplification, the output impedance of the amp needs to be appropriate to ensure the right kind of current delivery to the headphones.  I think you'll find that the importance of a specialized headphone amplifier increases as the impedance of your headphones increases.  So, for example, Grado headphones are extremely well respected and also have (relatively) low impedence (around 30 ohms), and are probably less dependent upon a good headphone amp than the high end Sennheiser cans (with impedance of around 300ohms).  To continue with that comparison, it probably makes sense to use Grado headphones with a personal digital player like an i-pod, even though the amplifier in the i-pod isn't all that great.  But you would never want to plug a pair of Sennheiser HD600s into your i-pod, as the i-pod amp couldn't drive them.

Chad
 

[maggotbrain]

I'm no expert on these sorts of things, but my vague understanding is that this all has to do with the difference in impedance of headphones and of speakers.  Typically, speakers have an impedance of something between 2 and 8 ohms.  Sometimes you might find 16ohm speakers.  But when you get to headphones, their impedances are significantly higher.  A pair of headphones with impedance of 30ohms is extremely low (although not uncommon), and for some well respected cans the impedance can be as high as 600ohms.

While headphones don't require a great deal of gain in amplification, the output impedance of the amp needs to be appropriate to ensure the right kind of current delivery to the headphones.  I think you'll find that the importance of a specialized headphone amplifier increases as the impedance of your headphones increases.  So, for example, Grado headphones are extremely well respected and also have (relatively) low impedence (around 30 ohms), and are probably less dependent upon a good headphone amp than the high end Sennheiser cans (with impedance of around 300ohms).  To continue with that comparison, it probably makes sense to use Grado headphones with a personal digital player like an i-pod, even though the amplifier in the i-pod isn't all that great.  But you would never want to plug a pair of Sennheiser HD600s into your i-pod, as the i-pod amp couldn't drive them.

Chad
 

Many many thanks chad. Very kind of you to take the time out.

Im counting the days untill i get the money together to  send my ipod of to Red Wine Audio to be imodded. Im looking to exploit the imod sound but simply cannot afford a load of expensive gear.

With the marantz amp i could kill two birds with one stone. Drive speakers & headphones.

I currently have a pair of grado sr 80's, some goldring dr 150's (in the post) and will be ordering some allesandro ms-1's in a few weeks. In the future i will hope to buy some senny hd650's.

I just did a search of impedance on wiki. WAY over my head. But there was an article on impedance matching.

Impedance matching is the practice of attempting to make the output impedance of a source equal to the input impedance of the load to which it is ultimately connected, usually in order to maximize the power transfer and minimize reflections from the load. This only applies when both are linear devices

Is there a device that could sit in between the headpone jack and headphones that would automatically adjust the impedance i.e impedance matching?

I remember reading about one headphone amp that adjusts itself to the headphones it is driving. I guess that would be impedance matching?

As opposed to having an amp that adjusts itself to the headphones, would it be possible to retrofit a device that
automatically matched the impedance?

perhaps a silly question, but i know naught about these issues!

[chadh]

I'm probably not the best person to be giving you advice here, but there are products available that assist with "impedance matching." 
Some people will use buffer circuits to assist in this area.  Paul Speltz also markets a product he refers to as the "zero autoformer", which can be used to change the impedance of your speakers, for example.

Chad

[ecramer]

check out the web sight head-fi.org but it really boils down to that the Marantz PM4001OSE might have $2 in parts dedicated to the headphone section while a good headphone amp may well have a couple of hundred $ worth of electronics.

[R_burke]

Chad nailed the basics pretty well. 

I have found most amplifiers that have a headphone out to be less than desirable, rarely do they have much of any kind of real headphone amplification.

There are some CDP sources that have decent headphone amp sections.  I have the Shanling CD T-100 in my main system and it has a separate headphone amp that is very good.  In my bedroom set up I use a Marantz CD-5001 as a stand alone unit.  It has a good headphone amp and I don't use speakers in my bedroom set up.

As to impedance, there are a few headphone amps that have two outputs with different impedances, Mapletree has one and they have their own circle here.  I've never seen a headphone amp that has an adjustable impedance, but it doesn't seem like it would be too hard to accomplish. sp they probably exist.