Strange volume pot behaviour
Nov 5, 2008 at 8:16 AM Thread Starter Post #1 of 9

kingbuzzo

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I recently hooked up a cheap stereo A 100k pot for an amp I was building, and noticed some strange behaviour.

The output is rather quiet and shows very little increase in volume until I hit the last couple turns, at which point I am blasted out of my chair with an extreme high output. I've tried two of the same pots with no difference. Is this just the behaviour of cheap pots (like this one)? Or is this some sort of behaviour from the amp itself?

thanks in advance.
 
Nov 5, 2008 at 8:28 AM Post #2 of 9

tangent

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That's the sort of behavior you get from using linear pots in an audio circuit. You need to use a log taper pot for it to sound right to your human, log-responding ears.
 
Nov 5, 2008 at 10:03 AM Post #3 of 9

-=Germania=-

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Is the Pot wired correctly?
The center should be the output, right is input, and left is ground.

If you wire the input to the center and the output on the leg, you will get that same experience.
 
Nov 5, 2008 at 3:40 PM Post #4 of 9

nikongod

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It dosn’t sound like a linear pot, a linear pot goes from low to high volume in about 1/6 of a turn and dosn’t change much after that. It could be a linear pot wired incorrectly though.

To the OP:
Measure the impedance across one of the inputs as you turn the pot. It should not change if its wired correctly. This is just quick elimination (or confirmation) of that possibility.
 
Nov 5, 2008 at 7:06 PM Post #5 of 9

kingbuzzo

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I'm certain that it's wired correctly. I guess it's just not the right pot to use.

I'm not too sure how to go about measuring the impedance with my mm.

It's really the last notch in the pot where everything gets crazy loud.

I have a ALPS A100k pot as well, should I try it?
 
Nov 5, 2008 at 7:58 PM Post #6 of 9

tangent

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Turn the knob to about the 50% position. Then measure from the center lug to either outer lug. If you get roughly half the rated resistance, it's a linear. If it's closer to 10% or 90%, it's log or something like it.
 
Nov 5, 2008 at 9:13 PM Post #7 of 9

kingbuzzo

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ok, I tested out the pot, and it is indeed linear.

This might be some sort of strange pcb behaviour. I'll try and find the schematic and take a look.

thanks for the help guys. much appreesh
 
Jun 21, 2009 at 6:25 PM Post #8 of 9

kingbuzzo

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I tried using an A50k stereo pot this time. After turning it up all the way the pot sparked and them smoked
redface.gif
. Yet I still get output through the speaker and can control the volume.

the pot is right in line between the amp and the output (speakers) as there are not pins for volume control on this board.

Am I missing something here?
 
Jun 21, 2009 at 7:55 PM Post #9 of 9

sanderx

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Quote:

Originally Posted by kingbuzzo /img/forum/go_quote.gif
the pot is right in line between the amp and the output (speakers) as there are not pins for volume control on this board.

Am I missing something here?



The part of the specs on the pot that talk about its maximum power ratings? Oh, and of course, putting it in line with input, not output, might be the other missing thing.
 

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