[Elecraft] AF1 Audio Filter Question

[Don Wilhelm]

Paul,

If you look at the schematic, you should see that the output jack is a 
stereo type with both channels connected together.
That means your stereo headphones should receive the same signal in both 
channels.
Try turning the phones backwards and see if the louder channel reverses 
- if it does, then the headphones are not balanced (maybe one is 
faulty).  OTOH, if the weaker channel stays with the same ear, your 
hearing in that ear is diminished.

Your observation with the mono speaker plug is what is to be expected - 
when you push the plug in all the way, you are shorting the output due 
to the sleeve of the plug contacting the jack's normal ring connection.

73,
Don W3FPR

On 12/28/2013 5:01 AM, Paul Clay wrote:
> Just completed building an (external) AF1 audio filter mini module (Rev A board that required the cutting of a solder trace on the AF input and the addition of a jumper on the AF output).  Works great except, I've noticed two things I'm curious about:
>
> 1.  With stereo headphones plugged in, one the audio in one channel is noticeably louder than the audio in the other channel.
>
> 2.  If I plug a speaker in with a monoral 1/8" plug all the way, I get audio out but the volume is low and there's some significant distortion in the audio output; BUT, if I insert the plug in just part way, I get lots of volume and no distortion.
>
> Wonder what might be causing this?  Wouldn't think much of item two (figure I should just be using a stereo plug to connect my speaker), but the presence of the distortion and the lack of balance when using my stereo headphones makes me wonder if maybe the LM386 chip might be damaged.
>