On 8/11/2010 7:02 PM, Jim Brown K9YC wrote:
On Wed, 11 Aug 2010 18:42:08 -0500, Stuart Rohre wrote:
You may
need to transform the audio to a higher voltage to improve your reception
Almost everything in this email is wrong.
See my tutorial on headphones in http://audiosystemsgroup.com/RFI-Ham.pdf
It's in an Appendix.
Most modern radios are designed to drive almost anything from 8 ohms up,
and are optimized for about 8 ohms to about 200 ohms. No matching required,
no matter how hight or how low the Z. With modern phones, the higher the
impedance, the less loudness you're likely to get from a modern output
stage.
And so the voltage swing is limited to keep from overdriving the low
impedance heaphones. Sometimes a voltage step up or impedance match will
get more signal to higher impedance headphones and that is most
conveniently accomplished with a transformer, such as an 8 ohm to 600
ohm transformer. Such transformers ARE available from Mouser and
probably digi-key among others.
73, Jerry, K0CQ
On the other hand, the very old crystal headphones are very high impedance,
and also very sensitive -- 40 years ago I used them to do field service
troubleshooting on audio systems, and I could even hear (barely) mic level
with them! Fidelity was not great, comfort was even worse.
73, Jim Brown K9YC
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