[sobebu2z]

Hi, just out of curiosity. Has anyone built an LOD and ohm out their cables? I know that it shouldn't matter, especially if it's on an inch or two.  I have access to a few BNC cables that are rated to be 50 ohms (mainly used for RF lines on aircraft), and I plan on using that to build a few iPod LODs and input to input connectors. Any input would be greatly appreciated.

 

[tzjin]

Quote:

Has anyone built an LOD and ohm out their cables?

 
Welcome to Head-fi!
 
Etymotics sells a 75-ohm extension cable for mini to mini but I have yet to see one made for a LOD. Why do you want to increase the impedance between the DAC and the amp?

 

[hoshiyomi]

You can build out with say 50R series resistance and terminating with another 50R at the receiving end but I won't really bother. Maybe consider inserting 100R or so at the source to isolate cable capacitance.

It may be a worthwhile practice if you are running long transmission lines, but a 50 ohm coax is not going to be 50 ohm impedance at audio frequencies anyway.

Note that the line out output stage may not look to good driving the resistance of a terminated cable. 100 ohm or so is quite heavy of a load, if you insist on using this the headphone out jack may fare better as line out in this case.

 

[DingoSmuggler]

Not a great idea, terminating a cable like this you lose half your signal (-6dB), as the source impedance and load impedance form a voltage divider. And at audio frequencies there are no benefits to be gained.

 

[tzjin]

Actually I was thinking about this. Would a high-resistance cable before the amplifier reduce noise that would be amplified otherwise?

 

 

[ClieOS]

Input impedance of an amp generally run really high, I don't see how adding a few ohm of resistance to the cable makes any difference.

 

[tzjin]

Quote:

Input impedance of an amp generally run really high, I don't see how adding a few ohm of resistance to the cable makes any difference.

New info. Thanks!

 

[samsquanch]

Quote:

Hi, just out of curiosity. Has anyone built an LOD and ohm out their cables? I know that it shouldn't matter, especially if it's on an inch or two.  I have access to a few BNC cables that are rated to be 50 ohms (mainly used for RF lines on aircraft), and I plan on using that to build a few iPod LODs and input to input connectors. Any input would be greatly appreciated.

 
Coax cables have an ohm rating for their intended operational frequency range, for RF signals this is important to reduce reflections in the signal which can cause distortion and signal loss.  There is no resistor attached to the line to provide this impedance, it's simply a property of the cable itself.  For audio signals (on coax or just individual wires) the impedance is not as important.
 
Quote:

Input impedance of an amp generally run really high, I don't see how adding a few ohm of resistance to the cable makes any difference.

 
Yup, typical output impedance is 100 to 600 ohms, and input is 10k or higher, this is done to maintain at least a 10:1 ratio of inpututput.  Let's say the source has an output impedance of 500 ohms, and the amp has an input impedance of 10k, you have a ratio of 20:1, if you place a 50 ohm resistor on the input this will change your ratio to 20.1:1, not much of a difference.