[TenTec] Ear Phone Audio

[Paul Christensen]

"Many years ago, I carried around a set of crystal headphones in my toolkit when I worked on troubleshooting audio systems in buildings. "

Jim, for this reason I still use a Harris telco "butt" set in bridging mode when identifying audio routing in the shack.  One of the best audio tools ever invented!

Paul, W9AC

Sent from my iPhone6

> On Aug 25, 2016, at 7:48 AM, Robert P. Santella <bobw2pnj at optimum.net> wrote:
> 
> Thanks, Jim.
> 
> Sent from my iPad
> 
>>> On Aug 24, 2016, at 1:32 PM, Jim Brown <k9yc at 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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