Pot with added feature. What & why ???

sam9 · 31st March 2004, 05:16 AM

I've got a 100k dual pot which is otherwise an ordinary cheap pot. It has something I've not seen before - a fourth solder terminal. While the resistance between the wiper and either of the standard terminals varies 0-ohms to 100k-ohms, the resistance between the wiper and this extra terminal varies from 10k-100k. This must have some purported benefit but it beats me.

Anyone know why this is here and what it is good for?

Steve Eddy · 31st March 2004, 06:15 AM

Quote:

Originally posted by sam9
I've got a 100k dual pot which is otherwise an ordinary cheap pot. It has something I've not seen before - a fourth solder terminal. While the resistance between the wiper and either of the standard terminals varies 0-ohms to 100k-ohms, the resistance between the wiper and this extra terminal varies from 10k-100k. This must have some purported benefit but it beats me.

Anyone know why this is here and what it is good for?

It's a loudness tap which allows for a reduction in volume without having to change the position of the pot.

se

sreten · 31st March 2004, 07:16 AM

I'd suggest it has something to do with loudness buttons.

They are not for changing volume, they boost bass at low
volume settings and have less effect as volume is increased.

sreten.

sam9 · 31st March 2004, 02:23 PM

Sounds plausible. I think it is a feature I can do without although I'm a little uncertain how it would work - some kind og filter parralllel to the wiper-end stop i suppose.

phase_accurate · 31st March 2004, 03:00 PM

Those are indeed used for the loudness function. These were quite fashionable in earlier days. It is wired in a way (using caps and resistors) that low and high frequencies are boosted with low loudness settings -- in order to "compensate" for Fletcher-Munson.

Regards

Charles

markp · 31st March 2004, 03:11 PM

Usually it is a 40% tap. Like others said for loudness compensation.

owel · 31st March 2004, 03:34 PM

>These were quite fashionable in earlier days

I feel old. Yes, it's a tap for the loudness circuitry. I like them... the bass boost circuitry is only effective at low volumes.

sam9 · 31st March 2004, 05:55 PM

Can anyone post a schematic as an example?

Steve Eddy · 31st March 2004, 06:01 PM

Hmmm. I guess it is for a loudness circuit of a sort, one which only gives an apparent bass boost at lower volumes. Since we lose sensitivity at lower volumes in both the lowest the highest frequency ranges, I couldn't see how such a tap could be used to implement both a bass and treble boost.

I did some poking around and the loudness circuit is implemented as a simple RC network to ground off the tap.

Learn sumfin' new every day.

se

Steve Eddy · 31st March 2004, 06:03 PM

Quote:

Originally posted by sam9
Can anyone post a schematic as an example?

From http://members.home.nl/kvdijke/Philips/B5X72A.html

se

31st March 2004, 05:16 AM	#1
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	Pot with added feature. What & why ??? I've got a 100k dual pot which is otherwise an ordinary cheap pot. It has something I've not seen before - a fourth solder terminal. While the resistance between the wiper and either of the standard terminals varies 0-ohms to 100k-ohms, the resistance between the wiper and this extra terminal varies from 10k-100k. This must have some purported benefit but it beats me. Anyone know why this is here and what it is good for?

31st March 2004, 03:11 PM	#6
markp diyAudio Member Join Date: Oct 2003 Location: L.A., CA	Usually it is a 40% tap. Like others said for loudness compensation. __________________ If it sounds good... it is good!

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31st March 2004, 07:16 AM	#3
sreten diyAudio Member Join Date: Nov 2003 Location: Brighton UK	I'd suggest it has something to do with loudness buttons. They are not for changing volume, they boost bass at low volume settings and have less effect as volume is increased. sreten.

31st March 2004, 02:23 PM	#4
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	Sounds plausible. I think it is a feature I can do without although I'm a little uncertain how it would work - some kind og filter parralllel to the wiper-end stop i suppose.

31st March 2004, 03:00 PM	#5
phase_accurate diyAudio Member Join Date: May 2002 Location: Switzerland	Those are indeed used for the loudness function. These were quite fashionable in earlier days. It is wired in a way (using caps and resistors) that low and high frequencies are boosted with low loudness settings -- in order to "compensate" for Fletcher-Munson. Regards Charles

31st March 2004, 03:34 PM	#7
owel diyAudio Member Join Date: Mar 2004 Location: Nashville, TN	>These were quite fashionable in earlier days I feel old. Yes, it's a tap for the loudness circuitry. I like them... the bass boost circuitry is only effective at low volumes.

31st March 2004, 05:55 PM	#8
sam9 diyAudio Member Join Date: Jun 2002 Location: Left Coast	Can anyone post a schematic as an example?

31st March 2004, 06:01 PM	#9
Steve Eddy diyAudio Member Join Date: Sep 2002 Location: Sacramento, CA	Hmmm. I guess it is for a loudness circuit of a sort, one which only gives an apparent bass boost at lower volumes. Since we lose sensitivity at lower volumes in both the lowest the highest frequency ranges, I couldn't see how such a tap could be used to implement both a bass and treble boost. I did some poking around and the loudness circuit is implemented as a simple RC network to ground off the tap. Learn sumfin' new every day. se

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