[TenTec] Low headphone audio level

[Jim Brown]

On 3/13/2013 8:27 AM, Paul K. wrote:
> Jim,
> Thank you.  You are the first one to post an explanation about the low 
> level audioon my Orion I.  I haven't seen many excellent postings like 
> yours since Dr. Jerry Johnson left the reflector.

Thanks.

> Now I am confused. Are you saying the series resistor on each leg of 
> the 2 channel audio should not be there?  There have been several 
> suggestions to cut the valuein half.  Are those recommendations 
> reasonable?

Since I haven't followed this thread from the beginning, I don't know 
the original question, and I'm not sure what resistor you're talking 
about, nor do I know its value in ohms. Which is part of why I went into 
such detail with my response. :)

What I'm saying is that the output impedance of a power amplifier, even 
a small one, is quite low, usually much less than one ohm, but that 
circuit designers add some resistance in series with the output to 
protect the output chip from being shorted when someone plugs something 
into the jack. That resistor simply makes sure that the chip doesn't try 
to drive a short circuit.

In general, it's a bad idea to try to second-guess a good circuit 
designer unless you KNOW that what's there is wrong (the Pin One Problem 
is an example), and that what you want to change won't cause problems 
you either haven't considered or don't know enough about the circuit to 
be able to predict.

Bottom line -- if you can't crank the audio gain up enough that your 
headphones aren't loud enough, or it's simply a matter of matching 
loudness between speaker and headphones, I'd try different headphones 
before I would modify the rig.Most good headphones (Sony MDR7506, Yamaha 
CM500, and equivalent Sennheiser or AKG) are in the range of 200 ohms 
and have enough voltage sensitivity that they get plenty loud when 
plugged into any decent ham rig. The only reason we should need more 
than that is if we have severe hearing loss.

73, Jim K9YC