ALPS Potentiometer with 4 Terminals - diyAudio
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Old 28th March 2012, 10:18 AM   #1
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Default ALPS Potentiometer with 4 Terminals

Hello to all the Members,

Here is a Potentiometer which i Intend to use as a Volume control for my Pre-Amp based on LM1036 Chip. It is a 50K ALPS Motorized pot, since it has four terminals, it is unusually strange for me because i got my hands on such type of POT for the first time

I have attached the pictures of the Motorized POT with this post.

Now to the Trouble, When i use a Usual 50K Pot (The one beside the ALPS pot in the picture), the volume control seems to work fine, the sound level gradually rises as i rotate the Pot control. However now when i replace the usual pot to ALPS pot, the volume control acts differently in such a manner that until 50% rotation of the ALPS POT there is No Sound at all, the sound level rises gradually only after 50% rotation of the pot. I dont Understand why this would happen even though both of the Pots are of the same value (50K).

The connections i do on the ALPS pot is same as i do on the usual pot, about the fourth Pin, i keep it Disconnected.

I will deeply appreciate any Kind of Help.

Thank you & Best Regards,
SLAK
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Old 28th March 2012, 10:37 AM   #2
jaycee is offline jaycee  United Kingdom
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it has a loudness tap - the 4th pin is connected to the halfway point on the track.
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Old 28th March 2012, 10:39 AM   #3
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Originally Posted by jaycee View Post
it has a loudness tap - the 4th pin is connected to the halfway point on the track.
So, is there a way to disable this Loudness TAP?
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Old 28th March 2012, 10:55 AM   #4
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Originally Posted by SLAK View Post
So, is there a way to disable this Loudness TAP?
Identify the loudness tap pin (of the four) and don't connect it. Use the remaining three pins as normal. A multimeter set to resistance range will help identify this pin.
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Old 28th March 2012, 11:30 AM   #5
SY is offline SY  United States
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It may be a loudness pin. It may be a different pinout than the pot it replaced. Or it may be that you've got an Alps balance pot instead of a volume control.
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Old 28th March 2012, 11:44 AM   #6
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About one of the Pins Being a Loudness pin, That seems to be it. Either the Second one from the Left or the the first one from the right, One of these pins is the Loudness Tap.

I tried this method, rotated the Pot Shaft to Half Way (50%) tried checking the resistance between any two pin to check for 22K-25K (50% of 50K), but unfortunately none of the two pins is giving such resistance. Really strange...
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Old 28th March 2012, 12:11 PM   #7
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Originally Posted by SLAK View Post
About one of the Pins Being a Loudness pin, That seems to be it. Either the Second one from the Left or the the first one from the right, One of these pins is the Loudness Tap.

I tried this method, rotated the Pot Shaft to Half Way (50%) tried checking the resistance between any two pin to check for 22K-25K (50% of 50K), but unfortunately none of the two pins is giving such resistance. Really strange...
If your pot is an audio taper type, or logarithmic, you wouldn't expect the tap to show 50% resistance at the 50% rotational position. A better method is to turn the pot fully anti-clockwise (counter-clockwise) to represent minimum volume and see which two terminals give nearly zero resistance. One of these two terminals is the wiper. Now turn the pot fully in the other direction and check again. The pin in common with the two zero readings is the wiper.
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Old 28th March 2012, 01:19 PM   #8
tvi is offline tvi  Australia
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If it was a Bal-pot it would almost certainly have a centre detent, the mechanism of which seems to be missing from you photo.

So it should be as per the attached pic and just ignore the tap

Are their any part numbers on the unit?

rgds
james
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Old 28th March 2012, 01:49 PM   #9
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If it was a Bal-pot it would almost certainly have a centre detent, the mechanism of which seems to be missing from you photo.

So it should be as per the attached pic and just ignore the tap

Are their any part numbers on the unit?

rgds
james
Hello, I have already tried this type of connection method as you have shown, but doesn't seem to work. The problem persists.

The part number is 50KAMX2, just cant find the datasheet anywhere
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Old 28th March 2012, 03:58 PM   #10
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The problem persists.

The part number is 50KAMX2, just cant find the datasheet anywhere
Have you performed the test identified in post 7?
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