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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets.

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Old 1st Oct 2004, 2:24 pm   #1
Radio_Dave
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Default Log or Lin Potentiometers?

Hi

I have a Bush PB53 and I need to buy a 500K pot for the volume and a 25K for the tone control. Can somebody please tell me which one needs to be log and which one is lin
Thanks

David

Last edited by Paul Stenning; 26th Dec 2004 at 8:28 pm. Reason: Fix link or code for vBulletin
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Old 1st Oct 2004, 2:35 pm   #2
radiogammon
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Default Re: Log or Lin Potentiometers?

David,

You need a log pot for the volume and a lin one for the tone.

Best wishes, John B.
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Old 1st Oct 2004, 6:50 pm   #3
ChristianFletcher
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Default Re: Log or Lin Potentiometers?

Yes log pots for volume. I have fitted the wrong type in the past and Have not found the difference to be such a problem.
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Old 1st Oct 2004, 7:10 pm   #4
AC/HL
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Default Re: Log or Lin Potentiometers?

I think it's to do with the ear having a logarithmic response to sound levels. If you use a linear pot for volume most of the useful range of volume is squashed into the first few degrees of rotation. Using a log pot spreads it out a bit.
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Old 1st Oct 2004, 7:13 pm   #5
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Default Re: Log or Lin Potentiometers?

I have a tin full of used pots and none seem to say whether they are log or lin. How can I check what they are with a multimeter?

David
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Old 1st Oct 2004, 7:24 pm   #6
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Default Re: Log or Lin Potentiometers?

Log pots normally have LOG printed after the value (Lin pots are sometimes marked, but not always).
Measuring with an analogue meter may be misleading, as they have a non-linear scale.
I would think that setting the wiper to the mechanical half way point & measuring to either end would give the game away.

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Old 1st Oct 2004, 7:29 pm   #7
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Default Re: Log or Lin Potentiometers?

Carefully set the potentiometer to its midposition. Now measure the resistance from each end of the track to the slider. If the readings are APPROXIMATELY the same the pot is linear. If they differ widely the pot is log.

A more sophisticated method is to fix a temporary pointer and a scale calibrated in degrees to the pot. Connect the meter between the slider and one end of the track. Plot a graph of degrees of rotation against resistance.

If the graph is a single straight line the pot is linear. If the plot is two lines of differing slopes the pot is log. The two linear portions are a good approximation to a true log track.

Graham.

Last edited by Paul Stenning; 26th Dec 2004 at 8:30 pm. Reason: Fix link or code for vBulletin
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