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4 bit volume attenuator
4 bit volume attenuator
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Old 9th October 2004, 08:08 AM   #1
luvo is offline luvo  Australia
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Join Date: Oct 2004
Default 4 bit volume attenuator

Hi peoples,
I'm after a little guidance on a small problem I have. My radio (Philips FM91) has a 4-bit volume attenuator that has gone wheels-up. It's unrepairable, and I only have a block diagram for it.

| | | |
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D0 D1 D2 D3

Truth table: 60dB = 1111 (Volume off)
56dB = 0111
52dB = 1011
48dB = 0011

0dB = 0000 (Full volume)

I've read on other forums, people reckon a few resistors chucked into a similar array will suffice? I can't see how. As far as I can tell,
at least four active devices are required to switch in/out each attenuator!!? Anyways, thats easy enough to do, what I'd like to know is - Is there an easier way? Does a logic chip exist that will do what I ask?
This radio is not a high-end audio monster, so quality is not too much of a concern here...
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Old 9th October 2004, 02:00 PM   #2
FLZapped is offline FLZapped  United States
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Location: Florida
Actually, a 4 bit attenuator gives you 16 steps, that's 17 resistors needed for an L-pad divider.

Can't you find a suitable replacement at someplace like Digikey?

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Old 9th October 2004, 09:08 PM   #3
luvo is offline luvo  Australia
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Join Date: Oct 2004
Yes, it is only a 16 step attenuator, using four address bits D0-D3.
Depending on which bits are set low, detemines which attenuators (resistors) are switched into the audio path. ie Set D0 and D1 low = 48dB attenuation.
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