Potentiometer tap percentage question

[polaris26]

Hello all -

Sort of odd question here:

When a pot is advertised as having a tap at say 40% or 50%, are they talking about percentage of the rotation of travel, or percentage of resistance (in the case of a log pot)?

I.E. Does a 100K volume pot with a 40% loudness tap have the tap at about the 40K ohm point up from ground, or is it 40% of the rotation from the ( I am assuming) ground or counter-clockwise end of the pot's rotational travel as seen from the front?

thanks,
Dave

[GGBB]

Although I've never seen it written as "loudness tap," any time I've seen a percentage figure for a log/audio pot it has referred to the percentage of total resistance at the mid-rotation point.  So a 40% 100K pot would be split 40K-60K clockwise at the mid rotation point.  A 50% log pot would actually be a linear pot.

[polaris26]

Ah sorry if I was unclear -

I was saying the *tap* itself is specified as being at a percentage - not the taper of the pot.  In the old days, a lot of audio equipment came with so-called 'loudness' networks to compensate for perceived lack of bass & treble at lower volume settings.  This tone compensation network was tied to a tap on the volume pot.  I have seen some vintage volume pots described as having a "40% Loudness Tap".  I am just asking percentage of what?   I.E. is it tapped at 40% of physical rotation, or 40% of the (total) resistance rating of the pot.  If we were talking about a linear pot then the two things would be the same since the 40% rotation point would also (ideally) be the 40% resistance point.  However, the taper in this case would be the typical log taper used for audio volume pots and there would be a tap at some point around the resistance track.  I am just trying to find out what the 40% actually indicates.

thanks,
Dave

Although I've never seen it written as "loudness tap," any time I've seen a percentage figure for a log/audio pot it has referred to the percentage of total resistance at the mid-rotation point.  So a 40% 100K pot would be split 40K-60K clockwise at the mid rotation point.  A 50% log pot would actually be a linear pot.

[PRR]

Loudness tap is percent rotation.

Look at such a pot. The extra terminal is about 40% of the way around the body.

[Seljer]

I have an old Pioneer hifi with one of those loudness networks. Switching the 'loudness' switch doesn't do anything once you're past 50% rotation.

[polaris26]

Thanks Paul R - great stuff!

regards,
Dave

[dmillar01]

I would like to reaffirm the replies already posted. I also could not find an answer to the original question on the internet (except for the replies in this blog). So I ordered a 100K, 2-gang, 40% loudness tap, audio pot from RadioShack. Their customer service referred me to this blog. The pot they sent me had a center-tap at 50% rotation, not at 40%. To get the tap position I adjusted the potentiometer position to minimize the resistance from arm to center-tap (about 500 ohms). The rotation position was 50% of the total total rotation from stop-to-stop. The resistance from the CCW end to the center-tap was about 15% of 100K. My conclusion is that the previous reply is correct: a 40% loudness tap refers to the fraction of the rotation from the CCW end to the CW end, not the resistance fraction. Note that for a linear taper the answer is "rotation and resistance fractions are the same".

[thermionix]

Interesting, I would have assumed it was % resistance.  Learn something new every day on this board!