Thanks, Jim.
Sent from my iPad
> On Aug 24, 2016, at 1:32 PM, Jim Brown <k9yc@audiosystemsgroup.com> wrote:
>
>> On Wed,8/24/2016 10:08 AM, Robert P. Santella wrote:
>> Impedance needs to be 30 ohms.
>
> NO! Headphone impedance is NOT critical. Audio power amplifiers are VERY
> different from RF power amplifiers. Virtually all audio amplifiers are low
> impedance sources, and are designed to drive any impedance greater than a
> design minimum. For example, the source impedance of a loudspeaker output
> stage is a small fraction of an ohm, and is designed to drive any loudspeaker
> load greater than 4 ohms. The relationship between these two impedances is
> called the "damping factor," and 100 is a typical value. A well-designed
> headphone amp will include a low-value resistor in series to protect the
> amplifier from being shorted when headphones are being plugged and unplugged.
>
> Most modern headphones are in the range of 20 - 300 ohms, and a well-designed
> headphone amp should drive all of them just fine. What matters a lot more is
> voltage sensitivity, and headphone mfrs generally get that right too. Many
> years ago, I carried around a set of crystal headphones in my toolkit when I
> worked on troubleshooting audio systems in buildings. They were sensitive
> enough that I could hear (weakly) the signal of an unamplified microphone,
> yet the impedance was high enough that they didn't load most circuits!
>
> 73, Jim K9YC
>
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