[oneeyedhobbit]

Hello, this is a fairly new concept to me...I've been doing some reading and discovered that headphone jacks basically come in two "settings" for lack of a better word? 0 ohm and 120 ohm. What on earth does this mean? Is one inherently sonically superior to another?

I ask because I'm going to get a PPA with a headphone jack set at 0ohms, and am told my A-T A900 might be to bright with this setting...of further consideration, down the road I might be looking at Sennheiser 600s or AKG 271s. What difference will any of these make? Can one buy an Ohm adaptor if needed, and if so, where?

 

[pedxing]

You can buy the jack from Meier-audio, one of the advertised retailers of this forum, shown on head-fi's main/home page. Or you can try constructing one for yourself.

If you really want to know what the plug really does in technical terms, please do a search on this forum, maybe with the words "output impedance". Its complicated. I think the extra impedance softens the treble and adds more emphasis towards the bass region. It does not necessarily enhance the listening experience for all headphones. For example, some people have claimed that HD600 runs best when the output impedance is at 0 Ohms while other headphones like the DT-931 may benefit from 120 Ohm impedance jack.

 

[Steve999]

It's very complicated and confusing.

Here's the best explanation I've come across at head-fi. Read PeterR's posts, it's the best explanation I've ever come across at head-fi (I was asking the same question you are.)

PeterR's terrific explanation that helped me to finally sort of understand this stuff.

Long story short, higher impedences will cause the low or mid bass and the upper treble to be emphasized to varying and relatively small degrees.

A 120 ohm jack might increase the upper treble and low bass by about 1 db for some headphones, for example. For other headphones there will be almost no effect, for others it may be a little more. Not night and day.

Most phones are designed to be driven near 0 ohms so most will sound best out of a near-0-ohm jack. (There's no such thing as an absolutely 0-ohm jack.)

A few phones are designed to be driven at 120 ohms, so they will sound as intended out of a 120 ohm jack. Most modern component headphone outs are 32 ohms, pretty close to a 0 ohm jack. Older high-end receivers or amps may have higher impedence jacks. I have an old NAD receiver with a 220 ohm headphone jack.

If there are any rocket scientists or the like out there and my lay interpretation is wrong again, please correct me.

BTW, what you typically read at head-fi about this can be a little far from the truth, as it is tough going technically.

 

[3lusiv3]

My headphones plug into the headphone jack of a 10 year old Technics SA-GX170 amp/receiver, the instruction manual of which says: headphone output level & impedence 430 mV / 330 ohms.

Would the A-T A900's sound fine plugged in there?

My current Sennheiser HD 590's sound great, but I haven't plugged then in anywhere else yet.

 

[Steve999]

I'm sure they'll sound good. As to whether the sound will be altered a little, that will depend on how the impedence chacteresticis of the headphones change at the high and low frequencies. It varies significantly from headphone to headphone. It could make virtually no difference or it could make a moderate difference, depending on the impedence characteristics of the headphone's drivers. You'd need graphs of the impedence characteristics and someone who really know What they are doing to give you a solid idea of the impact. Both are pretty hard to come by. Trust your ears, if you like the sound, then good.

If it makes a difference, it'll emphasize the upper (and perhaps barely audible) treble and/or the mid or low bass. Again, I really don't think it's going to be night and day by any means. If you are just into enjoying the music it may be best not to worry about it.

A near-0-ohm headphone amp, or a component or amp or receiver with a 32 ohm (or less) headphone jack is pretty nice to have if you are into this hobby and you want be confident you are hearing most headphones at their best or at least as intended, IMHO.

Now, keep in mind, four days ago I had no idea what I was talking about.

Quote:

Originally posted by 3lusiv3 My headphones plug into the headphone jack of a 10 year old Technics SA-GX170 amp/receiver, the instruction manual of which says: headphone output level & impedence 430 mV / 330 ohms. Would the A-T A900's sound fine plugged in there? My current Sennheiser HD 590's sound great, but I haven't plugged then in anywhere else yet.

 

[oneeyedhobbit]

Thank you for your responses, especailly Steve999. I had never heard of this before, or knew it made a difference. The PPA i'm looking at has a 0ohm output Jack. I'll be (initally, at least) using it with low impedance (32) cans, the AT A900, as I said. This combination will be ok? What about future phones. For example, I recall reading a thread which stated that the higher end Senns (580, 600, 650) were designed for a 120 ohm jack. Is this accurate?

 

[Steve999]

The HD580 and HD600 (and I assume the HD650) were designed for a 0 ohm jack, so worry not. Jan Meier verified this at the Sennheiser plant. They design their phones for 0 ohm jacks as a matter of design philosophy.

The 32-ohm A900s from a 0 ohm jack should be just perfect.

 

[audiopile]

O.K. - I find this entire subject real world confusing. My Grado SR-60 definetly sounds better driven off the headphone jack of my Marantz DR-700 cd burners (8-2Kohm @0-5V RMS). Sony CD-3000's are definetly best driven direct off my EAD 9000's output (50 ohm output impedance). Both are 32ohm? phones.
My understanding of this issue is old - but I was brought up to always drive higher impedances with a lower impedance source. Most pre-amps have a output impedance somewhere in the 50 ohm to 1Kohm area. Most SS power amps have a input impdeance between 10K ohm to 50 Kohms.
Driving devices outside of this low feed ing to high relationship has always led to odd problems - frequency aberations , clipping , etc.
I continue to look for a plot of frequency v. impedance for my Sony CD-3000's.
It would also be interesting to see the actual output impedance of various heaPHONE AMPS?

 

[lini]

Quote:

Originally posted by audiopile I continue to look for a plot of frequency v. impedance for my Sony CD-3000's.

Well, in the meantime you could refer to this one: http://www.headphone.com/headphonege...ts04-02-21.pdf - provided by HeadRoom as "A Gift for the Group" in the according forum here...

Greetings from Hannover!

Manfred / lini