[krohm]

so i have hd650 with custom cables.  and i had tried my friends hd558's and they sounded heaps louder ?  what am i missing here,... what am i not understanding
 
anyways i found myself an amp and want to run optical out from soundcard into the amp and plug headphones in and that is doing digital to analog ? 
 
such a newb,.. any help thoughts appreciated,... cheers

 

[Head Injury]

  so i have hd650 with custom cables.  and i had tried my friends hd558's and they sounded heaps louder ?  what am i missing here,... what am i not understanding
 
anyways i found myself an amp and want to run optical out from soundcard into the amp and plug headphones in and that is doing digital to analog ? 
 
such a newb,.. any help thoughts appreciated,... cheers

There are two things that determine the loudness of a headphone, impedance and sensitivity.
 
Impedance determines how much power a headphone will receive from some amount of voltage. Amps usually put out a certain maximum voltage, so the higher the impedance the less power.
 
Sensitivity, usually measured in dB/mW for headphones but sometimes dB/V, determines how loud the headphone will get with a certain about of power. The higher the dB/mW the louder it will be with the same power. Likewise for dB/V but with the same voltage. What's nice about dB/V is it basically combines impedance and dB/mW sensitivity, since the impedance determines power. 
 
Sennheiser uses dB/V so it's easy to tell the HD558 takes less voltage overall (112 dB/V vs. 103 dB/V). The HD558 is about twice as loud at the same voltage.
 
As for your amp question, you can't run optical to an amp unless the amp has a built-in DAC (digital-to-analog converter). Optical is a digital signal, and a regular amp only takes analog. You need something to convert the signal. You can always connect the amp to the soundcard's headphone out. This will be double amping and is not ideal, but is all you can do unless the card has an analog line-out (usually RCA connectors) or your amp has a DAC. It'll help if we knew what soundcard and what amp.

 

[krohm]

amp is a marantz sr6200 that i found on the street : )   someone was throwing it out.  i have to get a harmony 350 universal remote or something for it
soundcard is a soundblaster creative xi-fi extreme audio

 

[Head Injury]

  amp is a marantz sr6200 that i found on the street : )   someone was throwing it out.  i have to get a harmony 350 universal remote or something for it
soundcard is a soundblaster creative xi-fi extreme audio

That's more of a receiver than an amp. Nice find 

 
It's got a built-in DAC so optical is fine. I'm concerned about output impedance, though. Receivers aren't usually designed for headphones, and many have high output impedance that can cause coloration and lack of control in the bass. It affects low impedances the most so the HD650 is pretty safe with its 300 ohm impedance. Still, if the output impedance is high enough you'll get a midbass boost and a loss of subbass.
 
You might want to compare with the headphone out on your soundcard to see if you hear any of this. Try to match volume levels, doesn't have to be too exact since the receiver was free anyway. Otherwise, enjoy.

 

[pp312]

  amp is a marantz sr6200 that i found on the street : )  

 
Could you PM me what street you live on?  

 

 

[krohm]

i saw it and i was like what the hell, 1x optical out 2x optical in,.. sorry i should have been specific when posting about dac regarding the amp/receiver. 
 
so my headphones are beast enough to handle this?  the impedence.  so how would i be able to tell whether the mid base is increasing or subbase loss i dont know what that is.
 
so i can run optical in from xbox and pc running to either headphones or some studio monitors 2.0 i want to buy.  so the soundcard is just acting as a transport of the music digitally via the optic cable and then dac converts the sound for my headphones to hear an analog lossless transmission of the track (if using flac/apple lossless or 24bit 192khz).  ?
 
it transports it losslessly at all points to the headphones or speakers at a later point.... i could eventually upgrade amp and receiver etc but for the time being, this could do this.... ?  so there is no point in getting a soundcard that is a dac like the ASUS Xonar Essence STU.  what is happening at the pc end through the soundcard before it gets to the dac? 
 
can i run a dedicated headphone amp and use the amp/receiver as like a preamp?  i just dont understand the transportation method from pc end to headphone and where the bottle necks are , i want to be able to get the most out of these headphones from this setup.. any thoughts/feedback appreciated,.. cheers