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How to wire a Shunted, Fake Law Pot?
How to wire a Shunted, Fake Law Pot?
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Old 7th May 2002, 10:07 PM   #1
Sanaka is offline Sanaka
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Question How to wire a Shunted, Fake Law Pot?

OK, so I built a shunted voume control (as per HH's "passive preamp" thread) using my 10K linear pot and a 15K resistor. This worked pretty well and there was no "9 o'clock jump" in the volume response. More like fairly smooth vol. increase plateauing at about 180 deg. rotation - the last 90 deg. did not increase volume furthur.

This was a better outcome than I expected so since things were going well I decided to do the Law Fake. I put a 1.5K (10K/6.67) resistor from signal out to ground. Now the plateau happens at about 90 deg rotation! - the last 180 deg does not increase volume, and max level is very attenuated.

I realize looking at it now that this was pretty stupid. The Elliot law fake design [ http://sound.westhost.com/project01.htm ] is for a tradtional series wired pot.

Can anyone help me do a shunted, fake law arrangement? Again I'm using a 10K linear pot.
Help much appreciated

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Old 7th May 2002, 10:34 PM   #2
HarryHaller is offline HarryHaller  United States
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Location: Dallas,Texas
Wink Law faking

There is no reason not to use a resistor that gives the sensitivity that you want. The ratio is not set in stone and I have used different ratios before. The taper varies from logrithmic but so do many "audio taper" pots. What is the output inpedance of your source? You may be better off with a 100K pot and a larger shunt resistor. You really would like this shunt resistor to be larger than the output impedance of your source.
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Old 8th May 2002, 01:21 AM   #3
Sanaka is offline Sanaka
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Default Thanks for responding, Mr. H.

My main source (until funds allow, a cheap Sony CD player) specs: "Max output level 2v at 50Kohms" and "Load Impedance Over 10Kohms" It has variable line out which I don't intend to use (just leave wide open).

What I was attempting was a shunt volume control as per your passive-preamp-in-a-hockey-puck-box - i.e. in & out connected directly with a resistor, and out also to ground thru a pot. This as I said worked fairly well. Since this was a linear pot, however, I tried law faking it in addition, which didn't work so well. Is there a way to use both these concepts together?

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