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Old 22nd April 2013, 03:16 AM   #1
DQ828 is offline DQ828  Australia
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Default Potentiometer Selection

I want to install a pot on the incoming signal to my amps as a way of speaker protection and limiting the maximum output volume (think kids, they wont know it's there)

The issue is, if I say install a 10K pot, the incoming impedance is 196ohms which is ok, but I assume the output impedance of the pot could be up to 10K & given that it would be feeding a amp that has an input impedance of 33K this is probably not a good thing.

I would appreciate any advice on whether it is possible to install a pot and still keep the impedance's at acceptable levels.
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Old 22nd April 2013, 10:31 AM   #2
DF96 is offline DF96  England
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The peak output impedance of a pot wired as a volume control (i.e. potential divider) is (source impedance + pot impedance)/4. This occurs near -6dB volume, when the pot is electrically (but not necessarily mechanically) halfway between the ends.

In your case a 10k pot fed from a low impedance will give you a fraction over 2.5k. This ought to drive a 33k input OK, unless the power amp has a particularly non-linear input impedance.

Why do you want to do this - don't you already have a volume control in your system?
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Old 22nd April 2013, 10:51 AM   #3
DQ828 is offline DQ828  Australia
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Quote:
Originally Posted by DF96 View Post
The peak output impedance of a pot wired as a volume control (i.e. potential divider) is (source impedance + pot impedance)/4. This occurs near -6dB volume, when the pot is electrically (but not necessarily mechanically) halfway between the ends.

In your case a 10k pot fed from a low impedance will give you a fraction over 2.5k. This ought to drive a 33k input OK, unless the power amp has a particularly non-linear input impedance.

Why do you want to do this - don't you already have a volume control in your system?
Thank you for the lesson in pot impedance, I appreciate it.

I am probably unnecessarily paranoid when it comes to protecting the speakers I spent a lot of time and money (mostly time) building. With my audio Receiver I have the ability to set the maximum volume via a software setting which stops the kids turning it too high. This is a manual version of that, they wont have access to the volume control.
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