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Reduce sensitivity of 100K ohm volume potentiometer?

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laga...@gmail.com

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Nov 13, 2012, 6:12:15 PM11/13/12
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I have an audio DSP filter for my amateur radio equipment. It uses an LM380 op-amp in the final AF amp stage, using a 100K ohm pot as the volume control. When using a speaker the volume control is fine, but when using headphones, the sensitivity from quiet to really loud is only a small tweak of the volume know.

Anything I can do to reduce this sensitivity for my headphone output?

Larry

Jamie

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Nov 13, 2012, 6:35:01 PM11/13/12
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Have you thought about using a resistor?

Just a thought really.

You could also use a rheostat voltage divider so you
can make adjustments to the range of the divided output for
head phones to match the speaker, but I would go for the
R..


Jamie

Michael Black

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Nov 13, 2012, 7:28:03 PM11/13/12
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It's always been pretty common to put a resistor between an audio
amplifier and any headphones. First, it puts a limit on how much can feed
into the headphones (which may not be able to handle as much as a speaker)
but it also acts as an attenuator with the impedance of the headphones.
IN the tube days, this meant that you wouldn't need to keep the volume
control low, where hum generated by the filament in the output amplifier
could dwarf the signal. If the signal is attenuated after the
amplification, you need to turn up the volume which then makes the wanted
signal larger in reference to the hum. This attenuator on the output
would also cause you to raise your volume control, making it work more
like it would with a speaker.


Michael

amdx

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Nov 13, 2012, 7:53:44 PM11/13/12
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I'm with the Jamie and Michael, Put a series resistor in the
headphone path.
Another option put a 10k potentiometer in series with the 100k
and use the 10k as a fine tune adjustment of volume.
Mikek

David Eather

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Nov 13, 2012, 7:58:49 PM11/13/12
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Check that the pot is in fact a log pot.

Les Cargill

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Nov 13, 2012, 8:29:29 PM11/13/12
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http://www.electronics-tutorials.ws/attenuators/attenuator.html

--
Les Cargill

Phil Allison

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Nov 13, 2012, 10:57:09 PM11/13/12
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<laga...@gmail.com>
** There needs to be a resistor of about 150 ohms in series with the
headphone jack, this allows for phones of 8 ohms rating through to 600 ohms
to be used without much change in volume.

The volume pot needs to be a " log" or " audio" taper - usually marked
with the letters "C" or "A" after the value in ohms.

Pots marked with a "B" are linear types.


... Phil


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