Jerry,
Thanks for your input. I think I'll fire up my audio signal generator and do
the old parallel variable resistor and a.c. voltmeter test to get an
approximate
reading of the impedance of these headphones. It could well be that they are
considerably higher than 8 Ohms. In that case, a transformer certainly would
help.
I always had more than enough sound level when I used these same cheap
headphones with my TS-440S and TS-930.
By the way, I'm a fellow SteppIR user, but mine is just a little fellow - the
two element version. I obtained it when Martti and Pertti did a small
DXpediton
in Sao Tome.
73,
Charles - KY4P
(ex VOA overseas TX engineer and later station manager)
________________________________
From: Dr. Gerald N. Johnson <geraldj@weather.net>
To: tentec@contesting.com
Sent: Wed, August 11, 2010 8:35:42 PM
Subject: Re: [TenTec] Headphones for ORION I?
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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