Headphone amplifiers vs Integrated amps

[Vladimir]

I recently visited a website that has really nice headphone measurements published in english, although a russian website. I noticed the measurements show minor improvement in the FR balance of the AKG K702 with a higher output impedance amplifiers. 300 ohms looks like a minor boost of high treble and lower bass, which is something that makes these open back headphones sound a little bit better.

90dB view

24db view

I often read how AKG K701/2, Q701, K712, K7XX are recommended with powerfull headphone amplifiers to sound more balanced. One guy wrote they benefit from higher output impedance amps, which is why people like them with beefier amps and tube amps. Obviously tube amps have high Zout and more powerfull head amps need bigger resistors in the voltage potential divider, thus result in higher Zout.

Therefore, not only integrated amps headphone output can be as good as a dedicated can amp, but if you have bat hearing to notice a 1db bass/treble boost, it can make your cans sound even better. Makes me think what all the NwAvGuy craze was about. I see people still stress over amplifier output impedance as if it's the end all factor of amplification.

Technics SU-7700 integrated

✓ 330ohms output impedance

✓[/b] Gobs of clean power

✓[/b] First 1W in Class A

✓[/b] Sexy retro look

✓[/b] Dancing VU meters

SMSL sApII Pro with 24V linear PSU

✓[/b] 10 ohms output impedance

✓[/b] Texas Instruments TPA6120A2 headphone chip amp

✓[/b] Black and boring

✓[/b] Horrible and cheap feeling knob

✓[/b] Chuck it in the storage bin

 

[Vladimir]

John Dawson from Arcam gives a bit more detailed explanation about the technical execution of integrated amp headphone out.

Clicky

Each channel of the headphones output socket on the A85 is fed via a simple resistive potential divider from the output of the main power amplifiers - 330 ohms in series and 100 ohms to ground. This socket therefore has an output impedance of around 77 ohms. These values were chosen as a compromise that will work with all headphones from those with very low (say 4 ohm) impedances right up to 600 ohms ones or more, as one cannot tell in advance what will be used and we want all types to work OK and not inadvertently deafen the listener. The chosen values also ensure that the series resistors can be of a reasonable physical size as they have to dissipate heat when the amplifier is running hard.

The sound quality of the A85 is outstanding (and certainly not lousy!) with very low distortion and the amplifier's headphones feed is derived directly from the main speaker outputs. However I am prepared to accept that some headphones will work optimally when fed from a very low impedance source - in that case why not build a simple external attenuator to drive a pair of headphones, and switch it on and off with one of the front panel speaker switches? Its difficult to suggest optimum component values without knowledge of the particular headphones and some experimentation, but a series resistor of say 47 ohms (rated at 20W or so) and a resistor to ground of say 6.8 ohms (rated at 2W) would be a good starting point. It could all be built into a small die cast box. The maximum voltage swing available would be about 4 volts rms with an A85.

I am prepared to bet that driving this from the speaker outputs of an A85 or other Arcam integrated amplifier would give sound every bit as good as dedicated headphone amplifiers at a tiny fraction of the cost (all the bits from Maplins would probably cost a tenner or less).

So who wants to try this out and report back to the group?

John Dawson (Arcam)

 

[Vladimir]

A dedicated headphone amp is essentially a weak power amp with couple of resistors to attenuate the signal just like in your integrated amp.

Lehmann amp on the photo with the output resistors marked.

My Technics' main PCB, the two resistors marked in top right (photo from someone's amp restoration).

Bellow, the headphone output on a TEAC AI-2000.

Caturday

 

[nopiano]

Do you think that dedicated headphone amps - aside from the particular types needed for, say, Stax electrostatics - are a solution to a problem that doesn’t really exist? Or at least didn’t exist for many years.

I rarely listen to headphones but always had headphone sockets on my receivers and amplifiers. They were once standard, just as all had a phono input. I’m wondering if the advent of hair shirt amps with line input only, no tone controls and no headphone socket, were just an invitation to create lots of expensive add-ons!

 

[Gray]

I had an A85 on home loan from a dealer. When I tried the headphone output, the right channel was as dead as a doornail.

 

[Vladimir]

It's just a headphone jack wired to the speaker terminals in paralel via couple of resistors. Does no harm to anything in the circuitry. Those two resistors you see on the photos. That's it.

 

[Vladimir]

I had an A85 on home loan from a dealer. When I tried the headphone output, the right channel was as dead as a doornail.

Broken jack, cold solder joint or cooked resistor. Not much else to go wrong. Simple to fix.

 

[nopiano]

It's just a headphone jack wired to the speaker terminals in paralel via couple of resistors. Does no harm to anything in the circuitry. Those two resistors you see on the photos. That's it.

Exactly, yet they’re quite rare. My Primare doesn’t have one, but the CD player has a good one!

 

[dalethorn]

Do you think that dedicated headphone amps - aside from the particular types needed for, say, Stax electrostatics - are a solution to a problem that doesn’t really exist? Or at least didn’t exist for many years.

I rarely listen to headphones but always had headphone sockets on my receivers and amplifiers. They were once standard, just as all had a phono input. I’m wondering if the advent of hair shirt amps with line input only, no tone controls and no headphone socket, were just an invitation to create lots of expensive add-ons!

Creating products that need add-ons - yes - the perfect capitalist idea. But a simple headphone amp with just enough power for dynamics and planars, with a volume knob, headphone jack, and line input - that seems like an ideal product for headphone users. Theoretically at least, creating a lot of power in an integrated amp just to step it back down with resistors, wouldn't result in as good a sound as creating just the right amount of power for headphones in the first place. But there's a caveat. For some reason, a lot of headphone amps don't have enough power for dynamic transients or good bass control with some headphones, and some of the integrated amps will do much better even through the headphone jack, if the power isn't too restricted. One person who has posted here in the past, named Donunus, has experimented with integrated amps and receivers using headphones, with some surprising results. My personal experience says if you're spending big on a headphone amp, get lots of power - way more than the minimum. Some of the valve (tube) amps have plenty of power, due to the nature of the beast - the glowing bottles need lots of juice to heat their grids.

 

[Vladimir]

Buying a full sized integrated amplifier (or receiver) for powering normal headphones is indeed unpractical, especially for a desktop setup. Burning 50W of heat in Class AB just to end up using 150mW. But I use mine for powering a pair of speakers, and since I have it, I see no point adding clutter with separate head amp. Apparently the cans I have (actually most cans according to that russian websites measurements) are not that fussy about output impedance.

I posted my thoughts on the topic here at WHF because people at Head-fi are more likely to be exclusive headphones users, or have desktop setups with actives, so they do need a dedicated head amp.

What about Class D amps with switch mode PSU? They use practically no power, generate no heat, can be made in a small format. Amps like Class D Primare and NAD could be ideal for both speaker and headphone listening.

Oh wait... they all don't have... headphone... jacks...

 

[MajorFubar]

Do you think that dedicated headphone amps - aside from the particular types needed for, say, Stax electrostatics - are a solution to a problem that doesn’t really exist?   Or at least didn’t exist for many years.  

I rarely listen to headphones but always had headphone sockets on my receivers and amplifiers.  They were once standard, just as all had a phono input.  I’m wondering if the advent of hair shirt amps with line input only, no tone controls and no headphone socket, were just an invitation to create lots of expensive add-ons!

Probably not a conscious invitation by the amp manufacturer, unless they had already planned to market a headphone amp in advance. But definitely just an excuse to shave a few pence off the build price of the amp and tell us it's all about minimising unnecessary frills to improve sound quality. Complete rubbish of course.

 

[Deleted member 160668]

Interesting, particularly that the Arcam guy is bigging theirs up. I have an A29 (which has a decent headphone out according to reviews) and which sounds pretty decent to my ears with my Audio Technica ATH M50X's.

I did breifly consider buying a dedicated headphone amp to listen through, but then couldn't make my mind up so held off. I do wonder if there would be a substantial improvement, or just a minor one. Any thoughts on this?

Arcam also offer a rHead headphone amp suggesting they may offer 'better' (i'm in no way bound to use only Arcam - but as example only).

The other train of thought is to go for something like the Mojo, to use between the Chromecast and Arcam and then use the headphone out on this.

None of this is imminent though as i may end up changing amp in Nov if possible to do so.

 

[Deleted member 160668]

Whoops

 

[Deleted member 160668]

Whoops

 

[Vladimir]

Even less of a difference than my AKGs with a high output impedance amp. Worst case scenario you will get 1db less bass and 0.5db less midrange.