[Win0ver]

I searched the forum and all I could find was a link to this page :
http://www.fixup.net/tips/ety/ety.htm

The page suggests using two 0.1% 75 ohm resistors. The ER4P have an impedance of 27 ohm and the ER4S 100 ohm. Why bother using 0.1% resistors if they aren't the exact needed value (i.e. 73)? Or am I missing something?

 

[diredesire]

Quote:

Originally Posted by Win0ver I searched the forum and all I could find was a link to this page : http://www.fixup.net/tips/ety/ety.htm The page suggests using two 0.1% 75 ohm resistors. The ER4P have an impedance of 27 ohm and the ER4S 100 ohm. Why bother using 0.1% resistors if they aren't the exact needed value (i.e. 73)? Or am I missing something?

the percentage means how much the resistors will "drift" values when they are in use and/or heated (with current running through them)

The lower the value, the more true to it's value it will stay.

 

[Win0ver]

Quote:

Originally Posted by diredesire the percentage means how much the resistors will "drift" values when they are in use and/or heated (with current running through them) The lower the value, the more true to it's value it will stay.

I am aware of that, this is actually what I dont understand. At 0.1%, it will basically always stay at 75 ohm, but this is not the exact needed value! What's the point?

 

[robzy]

The fact that even if they arent exactly 100ohm, they are 101ohm for example - that they stay 101ohm always.

Rob.

 

[DaKi][er]

Measuring one of the 'official' adapters from Etymotic, i get -
69.5 Right
70.3 Left

I dont really see the need for 0.1% at all here

 

[Francis_Vaughan]

The usual argument for ultra tight specification resistors is that they should have intrisicly less dynamic resistance change due to changes in current. Or in simple terms more resistant to dynamic compression effects. Just why anyone would be worried about this in series with a voice coil in a headphone is hard to fathom.

Also, the resistance to such changes is not guaranteed by the 0.1% tolerance spec anyway.

 

[Garbz]

Quote:

Originally Posted by diredesire the percentage means how much the resistors will "drift" values when they are in use and/or heated (with current running through them) The lower the value, the more true to it's value it will stay.

No actually the 0.1% only guarantees the optimal value will stay within 0.1% of the rating. Often you can get 1% resistors and and match them to 0.1% and get the same performance.

The actuall deviation is the Temperature Coefficient of Resistance (TCR). This is found on the datasheet and measured in ppm/C. So a part with 1Mohm resistance with +/-15ppm/C for every degree change in temperature the worst case change is 15ohm

Also these are on the headphone output. Will you be putting anywhere near 1/2watt through ultra efficient headphones like this? I doubt the resistor will change temperature at normal (non deafining) operation at all.

 

[nikongod]

i prefered a 100 ohm resistor in my p-s cable, fwiw.

 

[Super-Gonzo]

I would think the real point to resister precision here, is matching the resistance values between the left and right channels. It makes little difference if its 99 or 101 ohms indvidually, but with a wider swing between parts (like say, cheap-o 5% resistors) You have a possibility of being off by 10 ohms between channels... which I imagine would not do good things to stereo imaging.

Of course, if you're willing to go to the effort of matching the pair, the point is irrelevent.