[copperdusk]

I'm curious because I've started to get a grasp of what the different specs on headphones actually mean. Now I'm a bit confused on how to figure out if an amp will be able to drive a certain pair.

I think an example should be in order. In said example I'll be using my Peachtree Audio Nove as the amp and a pair of AKG K701s as the example pair of headphones:

The amps specs(copy pasted from the website) :

Suitable for all electro-dynamic headphones
Frequency response: DC ~ 100 kHz +/- 0.1dB
Voltage gain: 10dB
Maximum output voltage: 7Vrms
output impedance: <30ohms
Maximum output power: 100mW into 8Ohm / 300mW into 150Ohm / 150mW into 300Ohm
Class A output stage
6922 Tube is in circuit


Now the headphone specs(only the parts that matter(according to what I've read) copy pasted from the website) :

Sensitivity (dB/mW, dB/V*) 105
Rated impedance (ohms) 62



I hope the above example isn't too horrible and doesn't make me sound like a complete idiot. So great masterminds of head-fi, how do all those numbers fit together and what do they mean?

 

[Uncle Erik]

It has more to do with the curves than the numbers. If you visit HeadRoom, you can pull up an impedance curve for the K-701.

A headphone's impedance and the output impedance tell you how well power transfers from the amp to the headphones. The K-701 is 62 Ohms at a given input, but you'll see that the curve varies depending on the frequency it is fed.

I don't know if there is a handy output impedance chart for your amp, but it certainly has a curve for output impedance.

So, if you plot those two curves over each other, you'llnotice that the power demanded and the power supplied varies depending on the music. It is a complicated dance.

However, you need to see this bigger picture to understand why two amps with similar (or even the same) output numbers can sound significantly different from each other.

There are other factors, too. The damping factor (ratio of output impedance to headphone impedance) tells you how tightly controlled the drivers will be (the higher the better, generally speaking, though there are exceptions) and you also have to keep in mind the amp's own quirks. Tubes and transformers are not entirely linear, noris every chip. Those imperfections lend a sonic signature and character to the sound.

So... maybe that's not quite the answer you're looking for, but those are what I've found to be important in figuring the sound and characteristics of an amp with a given pair of headphones.

If you're interested in amps, there are some terrific books and online information about them. And if you want to build your own, that's very possible and extremely rewarding.

 

[dishkyun]

Quote:

Originally Posted by copperdusk /img/forum/go_quote.gif I'll be using my Peachtree Audio Nove as the amp and a pair of AKG K701s as the example pair of headphones:

How do you rate the Peachtree Nova as a headphone amp? Wonder how it will stack up against tube/ss dedicated headphone amps like WA6 or GS-1.

 

[FraGGleR]

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif It has more to do with the curves than the numbers. If you visit HeadRoom, you can pull up an impedance curve for the K-701. A headphone's impedance and the output impedance tell you how well power transfers from the amp to the headphones. The K-701 is 62 Ohms at a given input, but you'll see that the curve varies depending on the frequency it is fed. I don't know if there is a handy output impedance chart for your amp, but it certainly has a curve for output impedance. So, if you plot those two curves over each other, you'llnotice that the power demanded and the power supplied varies depending on the music. It is a complicated dance. However, you need to see this bigger picture to understand why two amps with similar (or even the same) output numbers can sound significantly different from each other. There are other factors, too. The damping factor (ratio of output impedance to headphone impedance) tells you how tightly controlled the drivers will be (the higher the better, generally speaking, though there are exceptions) and you also have to keep in mind the amp's own quirks. Tubes and transformers are not entirely linear, noris every chip. Those imperfections lend a sonic signature and character to the sound. So... maybe that's not quite the answer you're looking for, but those are what I've found to be important in figuring the sound and characteristics of an amp with a given pair of headphones. If you're interested in amps, there are some terrific books and online information about them. And if you want to build your own, that's very possible and extremely rewarding.

This might be the single most useful post I have read on truly determining if an amp has "it" to handle a particular set of headphones. While it can't help me determine if I like the way an amp sounds, it has made it immensely easier to understand if it at least can provide all the power necessary. I was getting tired of asking can this amp handle these phones. So now, I will simply start approaching manufacturers for their amp output impedance charts.

Thanks!

 

[copperdusk]

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif I don't know if there is a handy output impedance chart for your amp, but it certainly has a curve for output impedance.

I'm searching for said chart, but I can't seem to findanything like it anywhere. Would it be at all possible to make the chart myself or would I just be opening up a can of worms and a massive headache?


Quote:

Originally Posted by dishkyun /img/forum/go_quote.gif How do you rate the Peachtree Nova as a headphone amp? Wonder how it will stack up against tube/ss dedicated headphone amps like WA6 or GS-1.

Frankly, I can't give you an opinon until I have a decent pair of cans to hook up to it. Once I get those and burn them in, I'll be sure to write a review for all the wonderful audiophiles here.

 

[dishkyun]

Hey did get your system setup?

 

[jcx]

amp manufacturers - especially smaller headphone amp makers are often weak on specs

I consider the I,V output limits of the amp as necessary to determine if the amp can drive a given headphones impedance with enough power for the sensitivity - I'd consider reaching 120 dB SPL without clipping necessary for a high end audiophile amp/headphone combo, less than 110 dB peak might be acceptable in a portable or if you listen to "loudness war" victim genre music or at safe background/all day long levels but not if you ever want anything near live orchestral or club jazz music peak levels

Amp output impedance is mostly assumed to be near Zero today by headphone designers - a very few may still offer designs voiced for DIN(?) 120 Ohm "standard" amp output

Zero output impedance of the amp means the headphone impedance load curve doesn't cause response changes - added amplifier output impedance makes the response more dependent on the headphone impedance curve

the K701 actually have one of the flatter impedance curves and would be expected to have less interaction with amp output impedance – excepting of course the necessity to drive the larger power required by the low sensitivity K701 through the extra loss of the amplifier’s output Z

OTL tube amp often do have large output impedance relative to many headphones and the frequency response is then strongly shaped by the headphone impedance curve, but only if the headphone impedance curve shows a large peak like the HD650 - then you’d expect a SPL peak at that frequency

Low frequency response can be compromised by a output capacitor – common in tube amps and single supply portables – like iPods
If sized too small for the load impedance a output coupling capacitor rolls off the base – some cheaper OLT tube amps may have low frequency corner frequencies >100 Hz with lo Z headphones – portable players also have (too) small output caps due to physical size limits

The Peachtree does give enough information to determine its peak I, V output - it should be fine with K701 on power and frequency response if I've read the spec correctly as long as any tube swapping doesn’t change output specs