Reply by Phil Allison November 13, 20122012-11-13
<lagagnon@gmail.com>
>
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? ** 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
Reply by Les Cargill November 13, 20122012-11-13
lagagnon@gmail.com wrote:
> 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 >
http://www.electronics-tutorials.ws/attenuators/attenuator.html -- Les Cargill
Reply by David Eather November 13, 20122012-11-13
On Wed, 14 Nov 2012 09:12:15 +1000, <lagagnon@gmail.com> wrote:

> 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
Check that the pot is in fact a log pot.
Reply by amdx November 13, 20122012-11-13
On 11/13/2012 6:28 PM, Michael Black wrote:
> On Tue, 13 Nov 2012, lagagnon@gmail.com wrote: > >> 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? >> > 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 >
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
Reply by November 13, 20122012-11-13
On Tue, 13 Nov 2012, lagagnon@gmail.com wrote:

> 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? >
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
Reply by Jamie November 13, 20122012-11-13
lagagnon@gmail.com wrote:

> 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
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
Reply by November 13, 20122012-11-13
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 contr=
ol. When using a speaker the volume control is fine, but when using headpho=
nes, 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