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Wrongly wired extension/volume control cable., Who said cables don't make a difference. ;)
post Jul 5 2012, 07:51
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I just bought an inline volume control (1m mini-stereo extension cable with in-line pot) and the pot seems to be wired up in the reverse of what I expected.

It appears that the input to the pot (output from the player) is connected to the slider, while the output side (to the phones) is connected to the other side of the pot. (btw First side of the pot still common/ground of course.)

Is this what I'm thinking, someone just wired up a bunch of these backwards and hence why they're flogging them for $1 on ebay, or is there an actual reason that someone would do it this way.

This post has been edited by uart: Jul 5 2012, 08:04
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post Jul 5 2012, 14:41
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I don't believe uart said that at minimum volume there is a dead short across the amplifier, just that the load is smaller and smaller.

This is actually a common way of providing non-linear volume vs. pot position with a linear pot. There is a small series resistor from the amplifier to the slider. At low volume settings this acts as a divider from the amplifier, with a large series resistance to the headphones to further attenuate the signal. At high volume settings the resistor divider aspect gives very little variation due to the series resistor being much smaller than the pot's resistance. Instead you have smaller and smaller series resistance to the headphones.

This is not a particularly good way of implementing volume control, both because it presents variable load to the amplifier, and variable source resistance to the headphones. The only way for it to work at all is to have a large disparity between the source impedance of the amplifier and the load impedance of the headphones.
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