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Old 26th July 2005, 03:53 PM   #1
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Unhappy 12 step 10k attenuator problem

Hi All,

I bought a non-shorting, 12 step, 2 deck Grey Hill switch recommeneded by someone here on some forum. I tried to build a 10k shunt type and this failed miserably. This attenuator is for a BOZ's output.

First off, the diagram I followed said to put the highest value at step-1. Step-11 has the lowest value and step-12 is to ground thru a jumper to a circlar ground wire that wraps around the whole switch. Stop pin set at the 12th position

What resulted was- at the left most position, the attenuator seemed to be set to mute. Then, I went one step up, the volume came on FULL. I turned the switch full clock-wise and the volume began to lower. However, at the lowest "setting" it was very, very loud (though it did sound good! ).

I know this much:

-The resistors are in the wrong order and possibly the wrong value.
-It might be the wrong switch because there was a "pop" when switching. Should the switch be a make-before-break? Or, is this happening because it is a shunt type attenuation?
-I had to use a 21k instead of a 20k resistor at 1 step along the way.
-The shunt resistor is 21k. Is this too high a value?

Is any thing from this attenuator switch salvageable into a working attenuator? I attached a text file showing the values I used.


Attached Files
File Type: txt 10katten.txt (592 Bytes, 74 views)
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Old 26th July 2005, 07:02 PM   #2
moamps is offline moamps  Croatia
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The "make-before-break" switcher type should be used in volume control applications. It's possible to use a "break-before-make" switcher in a type of ladder attenuator, but this one is rarely used. But, resistor values would need to be recalculated in that case.
If the attenuator is used in the preamp output, resistor values must be small (in order to create low output impedance for all attenuator positions). Also, as amplifier input impedance influences the chosen attenautor impedance and its accuracy, it may be necessary to take it into account when calculating resistor values.

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Old 26th July 2005, 07:10 PM   #3
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More mistakes I don't think I could have made.

Thanks for the advise.

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