AF1 Audio Filter Question

[Paul Clay-2]

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.

- Paul N6LQ
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[Don Wilhelm-4]

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.
>

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[Paul Clay-2]

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

 
--------------------------------------------
On Sat, 12/28/13, Don Wilhelm <[hidden email]> wrote:

 Subject: Re: [Elecraft] AF1 Audio Filter Question
 To: "Paul Clay" <[hidden email]>, [hidden email]
 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.
 >
 
 
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[GARY-2]

I use an AF1 for better volume and tone control of a VHF/UHF transceiver's
audio but I first removed the ring contact from each phone jack (their side
covers pop off easily) then when I installed the jacks to the PCB I also
soldered a short wire jumper from each tip pad to its mating ring pad on the
bottom of the PCB. This results in no modification to the PCB yet I can plug
in a monaural phone plug from the radio and a monaural speaker and it all
works fine.
Gary
N6LRV

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of Paul Clay
Sent: Saturday, December 28, 2013 12:32 PM
To: [hidden email]; [hidden email]
Subject: Re: [Elecraft] AF1 Audio Filter Question

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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