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ODAC Output Impedance Question

post #1 of 13
Thread Starter 

I have read of some people plugging their headphones directly in the Line Out jack of the ODAC.

The line out is designed to input 2V into a 5K ohms input which is perfect for an amplifier.

However, the designer of the ODAC recommends NOT to use the Line Out with headphones.

Most likely, the ODAC output impedance is too high for most headphones which leads to distortions in the frequency response.

 

I have searched the ODAC designer's website, Head-Fi and a few other forums to find out what the ODAC output impedance is.

The funny thing is that this specific spec doesn't seem to be published anywhere.

It is even more surprising when you know that the ODAC designer's trademark is based on extensive objective measurements.

 

Does anyone have the output impedance figure for the ODAC or is able to perform the measure?

post #2 of 13

I see 220 Ω resistors on a picture of the ODAC PCB near the line out connector, so that is the minimum output impedance. I do not know what the output impedance of the ES9023 itself is, so it may be more than 220 Ω overall for the ODAC.

 

A detailed article with extensive measurements and even schematics of the ODAC was promised months ago, but the blog does not seem to be updated recently.

 

Edit: I found in the comments section of the "ODAC Released" article that "The actual output impedance is around 400 ohms.".


Edited by stv014 - 9/23/12 at 11:46am
post #3 of 13

I don't know, I am poor in tecnical argument, I have an Odac an o2amp and sennheiser hd 800.

If I bypass the o2amp the pleasure of listening my music is vastly superior.

With odac I evaluate the listenig pleasure 8/10, with the hd 800 cable (reduction) directly on ephifany edac it is 10/10.

I can't imagine a superior setup.

Tried with neutron app and poweramp app and foobar(pc).

I use S3 as source, but tried with my pc and the result is the same.(I prefer s3 as source)

If anyone have an hd 800 and an odac, please try and share impression.

Pheraps my jds o2amp is faulty? I don't think, I sold my ttvj slim amp because I prefer the o2amp,

Ciao

post #4 of 13
Thread Starter 

Thanks stv014.

Among the 318 comments of "ODAC released" and 382 comments of "ODAC May Update", the one with the actual value of the output impedance is the one I missed, duh!

Of all the DAC design I am familiar with, an output impedance of "around 400 ohms" seems on the high side. I usually see values between 50 ohms and 100 ohms. I wonder, why the ODAC designer settled for such a high output impedance. Now I understand better why he recommends to connect the ODAC to an amp with at least 5K ohms input impedance so you get a damping factor above 10.

 

Gattari,

I tried similar setups with headphones directly connected into a DAC line out. I assume you adjust volume through your media player interface. I experienced similar results where the sound seems cleaner and more pleasing straight out of a DAC instead of running through an additional amp. The issue is that depending on the impedance of your headphones and its linearity along the frequency range, you will experience distortions. The most obvious being increased bass volume but at the expense of its definition (smeared or one-tone bass for lack of a better definition). This bass-boost is rather pleasing and especially with an HD 800 which tends to be "lean" on the bass. There are other issues associated with a low damping factor. If you want to learn more, there is an excellent article published by the guys at Benchmark Media (just Google "Headphone-Amplifier-Performance-Part-2.pdf"). Additionally, since you are handling volume attenuation in the digital domain through your media player, you are truncating bits out of your sound signal which can potentially lead to other audible distortions. That being said, an audio setup is always about compromises and if the sound you get straight out of the DAC is more to your liking, don't let these technical considerations get in your way.

post #5 of 13

R: ODAC Output Impedance Question

Thanks type35 for exaustively post.
I adjust volume yes!
If I use neutron player I set volume at about 65%.
If I use poweramp I adjust the volume at atout 85 - 90%, I don t know the cause of this difference between the two player, all the settings of the two player are flat.
I investigating on this.
I am not a fan of bass boost, the sound is better in all frequency range to my ears.
Perhaps this happen only with hd 800 and ephifany odac and....... my ears, but I like what happening.
Ciao

Inviato dal mio GT-I9300 con Tapatalk 2
post #6 of 13

Wow, if you're using your headphone directly with the ODAC I'd say its pretty much not recommended. You're essentially voltage dividing the circuit, also the damping would be pretty bad.

post #7 of 13
Quote:
Originally Posted by proton007 View Post

Wow, if you're using your headphone directly with the ODAC I'd say its pretty much not recommended. You're essentially voltage dividing the circuit, also the damping would be pretty bad.

You're saying there is any risk to damage my hd 800 also reducing the volume player?

If not, I will continue to use the edac jack for listening, to my ears the result is simply spectacular.

Ciao

post #8 of 13
Quote:
Originally Posted by Type35 View Post

Thanks stv014.
Among the 318 comments of "ODAC released" and 382 comments of "ODAC May Update", the one with the actual value of the output impedance is the one I missed, duh!
Of all the DAC design I am familiar with, an output impedance of "around 400 ohms" seems on the high side. I usually see values between 50 ohms and 100 ohms. I wonder, why the ODAC designer settled for such a high output impedance. Now I understand better why he recommends to connect the ODAC to an amp with at least 5K ohms input impedance so you get a damping factor above 10.

Actually 400ohm isn't high enough. My measurement show roughly 500ohm of output impedance, plus or minus 20~30 ohm or so. This makes 5K input impedance somewhat of a minimum recommendation since 1/10 is the general rule.
post #9 of 13

@gattari:

 

Not much, but you're essentially getting a variable response for different frequencies, and higher distortion. Everything that your headphone maker wanted to prevent, you're doing it deliberately. Not recommended.

post #10 of 13
 thanks proton007
Based on what you are sayng I like to listening with high distortion on variable frequency range, I will try another amp in the next future for my hd 800, perhaps the o2 don't match well with hd 800 I don't know what other sayng, to my ears the sound seem so natural, rounded, warm and with wide soundstage.
Ciao
post #11 of 13
Quote:
Originally Posted by gattari View Post

 thanks proton007
Based on what you are sayng I like to listening with high distortion on variable frequency range, I will try another amp in the next future for my hd 800, perhaps the o2 don't match well with hd 800 I don't know what other sayng, to my ears the sound seem so natural, rounded, warm and with wide soundstage.
Ciao

 

The O2 is not warm by any account. Its a lot more neutral, especially with the ODAC,  and harsh recordings *will* sound harsh, especially when coupled with the HD800, which some say is too neutral. (I use it with the HD650, and its pretty nice.)

Thats why you probably find the distortion as pleasant.

So as you say, you might want to go for a warm amp. Maybe a tube amp with warm sound.

post #12 of 13
Thread Starter 

Thanks ClieOS. 500 ohms out of the ODAC makes perfect sense with a recommended 5K ohms input impedance for an amp like say a Fiio E11.

 

Gattari,

As proton007 mentioned before, the voltage you will get in your headphones is equal to the output voltage of the DAC times the input impedance of your headphones divided by the sum of the DAC output impedance and the headphones input impedance. Since you are using the HD800 which shows an impedance of 630 ohms at 100Hz and 340 ohms at 3KHz when measured with an output impedance of 600 ohms (courtesy of Tyll Hertsens at InnerFidelity), your headphones will get up to 1.115 V at 100Hz and 0.810 V at 3KHz. This change in voltage between bass and treble is equivalent to 2.75dB which means that the perceived loudness of the bass will be roughly boosted by 20% compared to the treble (unless I screwed up my math somewhere along the way). If you like a darker, warmer sound, you might want to try the Audeze LCD2. They are relatively easy to drive and will give you a great bass response and very nice mids at the expense of the great imaging and instrument separation you get with the HD800.

post #13 of 13

The HD800 can give great bass response. But you do need to drive it with a headamp that can deliver the extra current required to motivate those 55mm diameter drivers.
 

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