Picked up an Objective2 Headphone Amp

Porter_

Porter_

[H]F Junkie
Joined
Sep 10, 2007
Messages
8,467
last night i bought a used JDS Labs O2 Headphone Amp from a head-fi'er that lives local to me. my DT770 Pro 80's aren't particularly hard to drive but after reading NwAvGuy's Headphone & Amp Impedance article i became curious about the theory behind the 1/8th rule. for the lazy:

NwAvGuy said:
All you really need to know is most headphones work best when the output impedance is less than 1/8th the headphone impedance. So, for example, with 32 ohm Grados the output impedance can be, at most, 32/8 = 4 ohms. The Etymotic HF5s are 16 ohms so the max output impedance is 16/8 = 2 ohms. If you want to be assured a source will work well with just about any headphone, simply make sure the output impedance is under 2 ohms.
Click to expand...

this is a new concept for me, i started reading about it a couple days ago. according to goldenears.net the titanium HD has an output impedance of 35.6 ohms:

73c27e548c0a2d3bfbcd4bb7f4e6cc70.png


my DT770's are rated at 80 ohms and verified by NwAvGuy (measured at a low of 83 ohms) so going by the 1/8th rule i'd need a source with an output impedance of 10 ohms or less. with my DT770's connected directly to my Titanium HD i have a damping factor of 2.33 instead of the desired 8 or more. the O2 is measured at an output impedance of 0.54 ohms so that gives a damping factor of 153.7. i was lucky enough to find a used O2 local to me at a reasonable price so i took the plunge to see for myself.

IMG_4069.jpg


IMG_4098.jpg


IMG_4099.jpg


the previous chain was: Titanium HD headphone out -> DT770
the new chain is: Titanium HD RCA out -> O2 -> DT770

I want to make that distinction before i start gushing about the O2; i swapped from the headphone out on the Titanium HD to the RCA out. i don't know what effect this has if any. also i'm just a guy sitting at my desk comparing. i haven't performed a blind level-matched ABX test or anything like that.

gushing: very surprised to hear an audible difference! the bass is very controlled and responsive now. i didn't realize how muddy it was. treble sounds nice and smooth but really i notice the difference in the lower frequencies the most. i don't hear anything crazy like the soundstage opening up (some have said this), that sounds exactly the same to my ears. after reading NwAvGuy's impedance article i had my doubts about the theory behind damping factor and if it would actually come to fruition for me (my hearing wouldn't be good enough to notice it, etc.). i read the impedance article before i picked up the O2 so the idea of 'expectation bias' comes into play (also a good NwAvGuy article). and it's still a new shiny toy. regardless, there is a very audible and real difference.

wanted to share my still-new-to-me experience with the O2 amp :)
 
Last edited:
I think the DT 770s are probably along the lines of a best case scenario for electrical damping considering they emphasize bass so heavily AND you came from a source with an inordinately high output impedance.

That said, good to hear.
 
Output impedance is one of those dirty little amp secrets. For speaker amps, it usually isn't a problem. Speakers are normally 8 ohms, which means you need a low impedance amp with good negative feed back. That stat has become a marketing term "damping factor" and most amps are plenty low.

Not the case in the headphone market. For various reasons, designing an amp with higher output impedance is easy to do and fixes several potential issues. So most do. They figure, rightly so, it is something few know about and thus won't care.

However low impedance is all the rage with headphones these days, due to portables and so on, so as such it DOES matter in most cases.

I got one since I have Denon D2000 headphones which are quite low impedance, and have good bass, and it does help for sure.

I really wish headphone outputs were better designed since it really doesn't take a ton of money/effort to get a pretty good output (TI makes a little chip solution that is good). However it is generally just phoned in, and output impedance is one thing that is often a problem.
 
32 ohm output impedance on the Ti HD sounds really really high, is that on the line out or headphone out? And here I thought my STX's 10 ohm output impedance was a bit of a nuisance.... If that's accurate, I would think the Ti HD would make almost every single popular headphone out there very loose on the low end.
 
Impulse said:
32 ohm output impedance on the Ti HD sounds really really high, is that on the line out or headphone out? And here I thought my STX's 10 ohm output impedance was a bit of a nuisance.... If that's accurate, I would think the Ti HD would make almost every single popular headphone out there very loose on the low end.
Click to expand...

It is high but there are plenty of devices that are up there. The Echo Audiofire 2, a pro audio interface with a supposedly nice headphone out is 22 ohms. It is just pretty common since most people don't know to ask about it.
 
guitarslingerchris said:
I think the DT 770s are probably along the lines of a best case scenario for electrical damping considering they emphasize bass so heavily AND you came from a source with an inordinately high output impedance.

That said, good to hear.
Click to expand...

that makes sense.

Sycraft said:
Output impedance is one of those dirty little amp secrets. For speaker amps, it usually isn't a problem. Speakers are normally 8 ohms, which means you need a low impedance amp with good negative feed back. That stat has become a marketing term "damping factor" and most amps are plenty low.

Not the case in the headphone market. For various reasons, designing an amp with higher output impedance is easy to do and fixes several potential issues. So most do. They figure, rightly so, it is something few know about and thus won't care.

However low impedance is all the rage with headphones these days, due to portables and so on, so as such it DOES matter in most cases.

I got one since I have Denon D2000 headphones which are quite low impedance, and have good bass, and it does help for sure.

I really wish headphone outputs were better designed since it really doesn't take a ton of money/effort to get a pretty good output (TI makes a little chip solution that is good). However it is generally just phoned in, and output impedance is one thing that is often a problem.
Click to expand...

source impedance is an interesting subject (and new to me). i have a pair of HD280's laying around. i think i'll see if i can hear any difference with them plugged into the O2 versus straight out of the Titanium HD.

Impulse said:
32 [35.6] ohm output impedance on the Ti HD sounds really really high, is that on the line out or headphone out? And here I thought my STX's 10 ohm output impedance was a bit of a nuisance.... If that's accurate, I would think the Ti HD would make almost every single popular headphone out there very loose on the low end.
Click to expand...

it's not explicitly stated in the goldenears article but i assume it's the headphone out since the article is centered around headphones. can't find much on the RCA line out impedance from google searching.
 
P1010087.jpg

I love my O2 + Q701 combo! Excellent little amp. Input via RCA outs on Titanium HD, the result is audio bliss!
 
Is that the Belkin USB dial thing? I was gonna get one at some point (since my STX is currently my HP amp) but someone around here said they had a lot of driver issues with it... Ended up getting a K90 keyboard with a volume roller anyway.

Was the ODA gonna have some rear side connector (power at least) or were they doing the same thing as with the O2?
 
Griffin Powermate. I use it for volume control as my Deck kb lacks the option. I've had zero problems with it in close to two years along with the Deck.
 
NukeDukem said:
http://i960.photobucket.com/albums/ae82/supralex1/P1010087.jpg
I love my O2 + Q701 combo! Excellent little amp. Input via RCA outs on Titanium HD, the result is audio bliss!
Click to expand...

nice setup NukeDukem

Impulse said:
Was the ODA gonna have some rear side connector (power at least) or were they doing the same thing as with the O2?
Click to expand...

he said on his blog that the power and input connections will be on the rear panel. so that leaves the headphone jack (6.5mm), volume knob, power switch and gain switch on the front panel. that's the way it should be, much more convenient.
 
You must log in or register to reply here.
Back
Top