Bob Marts Posted December 6, 2008 Report Share Posted December 6, 2008 I want to build a simple passive line level variable attenuator in a small box (can be unbalanced). Can anyone suggest what the best resistance for the potentiometer I should use for this "volume control"? It would be used to knock down the the output of a mixer to an amp/speaker setup. Quote Link to comment Share on other sites More sharing options...
John Blankenship Posted December 6, 2008 Report Share Posted December 6, 2008 What will the distance be from the attenuator to the equipment that it feeds? Your only real issue is that if this line is too long, its output impedance could be an issue. If it's a really short distance (say, three to six feet or less -- the less, the better) then there's no issue. A 10k (audio taper) pot would work well. It'll give you a sufficiently high bridging input impedance, and using an audio taper pot will make the volume change more even across the adjustment range. Connect the input to one side of the pot and output to the arm/tap/slider (whatever you want to call it) which is normally the middle connection. The ground in, the other side of the pot, and the ground out are all hooked together. If, at the highest output, the signal is way too high, you could put a resistor in line with the input going to the pot. With a 10k pot, a 10k series resistor would give you about 6dB attenuation (when the pot is wide open) -- a 30k resistor would give you about 12dB attenuation -- a 91k resistor would give you about 20dB attenuation -- and a 1meg resistor, about 40dB. These attenuation figures are for a 10k pot and are at the maximum position, then the pot would attenuate further from that. Having the higher impedance at the input would not affect the operation at all since this is a bridging input (the output of your mixer, which is a fairly low impedance is feeding a higher impedance). JB Quote Link to comment Share on other sites More sharing options...
Bob Marts Posted December 6, 2008 Author Report Share Posted December 6, 2008 Hey thanks, John! I'll heat up the iron tomorrow and use a 10k pot. Bob Quote Link to comment Share on other sites More sharing options...
Philip Perkins Posted December 7, 2008 Report Share Posted December 7, 2008 I've made a lot of "bone head" special purpose boxes like this over the years, and 10K has worked the best for me in most situations. See if you can find some "audio taper" type pots, the normal kind have a rather sudden up swing in apparent level as you reach the end of the pot (wide open). Philip Perkins Quote Link to comment Share on other sites More sharing options...
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