[Elecraft] AF1 Audio Filter Question

[Paul Clay]

Hi, Don.

I thought to swap the headphones around to see if it might be my hearing in one ear; the reduced output swapped to the other ear.  Will check using other sound sources to see if it might be the phones themselves.

What's confusing me a bit is the distortion that's introduced by plugging in a monaural plug feeding speaker all the way.  It's a scratchy sound that I can make go away by reducing the volume control on the radio providing the audio in to the AF1 - I'm driving the AF via my Icom R-75s external speaker port, the receiver's headphone jack or rec line out - but then the AF1s audio output is too low to be enjoyable.

Suppose I could just do a mod to replace the AF1's stereo out jack with a monaural one, and then using an adapter plug between the output and my stereo phones, but would like to leave the AF1 unmodified if possible.

R,
Paul N6LQ

 
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On Sat, 12/28/13, Don Wilhelm <w3fpr at embarqmail.com> wrote:

 Subject: Re: [Elecraft] AF1 Audio Filter Question
 To: "Paul Clay" <mr_pookie_jr at yahoo.com>, elecraft at mailman.qth.net
 Date: Saturday, December 28, 2013, 5:46 AM
 
 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.
 >