[glenda]

For Grados I would try around 5 to 20,  for older studio type designs I would try the 100- to 120 ohm,  some were even used commonly on a 680 ohm ouput on mixing boards.  I would try those three groups.

 

[liamstrain]

Quote:

Note that the frequency response and waterfall plots of  headphones can vary with output impedance.   This is one of those black art issues rarely talked about.  Older headphones were voiced for a 120 ohm output impedance.   Another example is Grado's bass  changes with resistors added in series.   In general  newer headphones have dropped the old 120ohm standard and are voiced for modern <1 ohm output.  Its an interesting subject to say the least and worthy of experiementation.
 


 

 
The reason older headphones were voiced at higher ohms was, however, NOT just due to resistors added to the system - the voice coils and magnets (and driver membranes) were built for that resistance (and THAT is responsible for the change ins FR response, etc.). Adding a resistor to a headphone built/voiced at 32 ohm, does not magically turn it into a 120 ohm voiced headphone. Which is my point. 
 
 

 

[fubar3]

Quote:

Dumb question but help me out here, building a 75 ohm impedance adapter would require running a resister in line on both the left and right channels? Or does the resister connect the left and right channels?

Try testing your headphones with a decent headphone amp (not Cmoy) that has a low-Z buffered output. I think you will like it more than some impedance adapter. There are good DIY designs or you can buy something.  It will cause more than that resistor adapter thingy but will be more satisfactory.
 
 

 

[Hal Rockwell]

In fact I'm waiting for my first DAC/Headphone amp to arrive in the next week or so. It will be A Fiio E10. It's not much but from what I heard it's a good entry level DAC/AMP.

 

[dsavitsk]

To my ear, Grados seem to do well with amps that have some output impedance as they can otherwise be over damped. It is one of the reason they sound so good with transformer coupled amps -- not only do these amps generally have some impedance due to the tubes, but the copper impedance of the transformer is effectively in series with the phones, giving some Z. I also find that they can sound too hard with a lot of solid state amps. Anywhere from 8-12 ohms seems to work well, and a little higher or lower is fine. Too high and things will start to sound a little flat, unless you do a transconductance amp in which case lots of Z is good.

 

[luisdent]

I believe adding resistors in parallel will lower the output impedance, correct?  Can someone tell me exactly what resistors I would need to buy to make my 32ohm output something lower than 5ohm?

 

[DingoSmuggler]

Quote:

I believe adding resistors in parallel will lower the output impedance, correct?  Can someone tell me exactly what resistors I would need to buy to make my 32ohm output something lower than 5ohm?

Are you sure you're output impedance is 32 ohm? that is a very unusual value to have. I think the more likely scenario is the output is rated for use with 32 ohm headphones, not the amp actually having  a 32 ohm output impedance.
 
If you do actually have a 32 ohm output impedance and want to reduce this to less than 5 ohms, a 4.7ohm resistor from output to ground will achieve this, but it will attenuate the output about 18dB   in the process, which would likely make it an impractical approach. The amp might not like such a low resistance hooked up to it either, could degrade performance or maybe even damage it.

 

[luisdent]

Quote:

Are you sure you're output impedance is 32 ohm? that is a very unusual value to have. I think the more likely scenario is the output is rated for use with 32 ohm headphones, not the amp actually having  a 32 ohm output impedance.
 
If you do actually have a 32 ohm output impedance and want to reduce this to less than 5 ohms, a 4.7ohm resistor from output to ground will achieve this, but it will attenuate the output about 18dB   in the process, which would likely make it an impractical approach. The amp might not like such a low resistance hooked up to it either, could degrade performance or maybe even damage it.

http://www.apogeedigital.com/knowledgebase/duet-firewire/what-is-the-impedance-of-duet-firewire-headphone-output/  sorry, 30 ohm  it is from the company, so i would think it's accurate.  why is that odd?
 
my last interface was 75ohm headphone output:  http://www.qualitypcok.com/qpro/ProductFolder/firewire_410.htm
 
that would have been even worse on some of these headphones if it is in fact the issue. :-o oh my.

 

[UNOE]

I'm trying to build balanced connector for IEM's. So you only need to connect one resister to each positive lead (L and R) and the negatives will be wired as usual?