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Audio distortion/overload

 

Hi,
I have built two bitx40's and both appear to suffer audio distortion/overload, the audio sounds as though the speaker is "shot" I have tried three or four different speakers (all 8 ohm 3W) and on all of them I am unable to turn the volume up two much without getting distortion, it sound as though the output is too bassy for the speakers. I have done the rf gain control mod and this helps a little but the output is quite low. any ideas.
 

Try this simple solution!

Issue is, the collector of Q16 is at too high a voltage to handle a strong signal.

Either or 2 ways -

Change R114 to 220K or 180K the signal handling of Q16 will be larger, audio will be a little more mellow.

or

Change R112 to 10 or 12K it will do the same thing.

Ideally the collector voltage should be at half of Emitter to Supply voltage for maximum output ie volume.

The amp and speaker are innocent :-))

Raj

At 16/08/2017, you wrote:

Hi,
I have built two bitx40's and both appear to suffer audio distortion/overload, the audio sounds as though the speaker is "shot" I have tried three or four different speakers (all 8 ohm 3W) and on all of them I am unable to turn the volume up two much without getting distortion, it sound as though the output is too bassy for the speakers. I have done the rf gain control mod and this helps a little but the output is quite low. any ideas.

chris gress
 

Easy audio mod if you get audio overload add a 1.2k ohm between the 0.1yf and pin 1 on the audio amp ic so.?
Pin 8 ---0.1yf----1.2k----pin 1.?
Chris

On 16 Aug 2017 14:10, "Raj vu2zap" <rajendrakumargg@...> wrote:
Try this simple solution!

Issue is, the collector of Q16 is at too high a voltage to handle a strong signal.

Either or 2 ways -

Change R114 to 220K or 180K the signal handling of Q16 will be larger, audio will be a little more mellow.

or

Change R112 to 10 or 12K it will do the same thing.

Ideally the collector voltage should be at half of Emitter to Supply voltage for maximum output ie volume.

The amp and speaker are innocent :-))

Raj

At 16/08/2017, you wrote:
Hi,
I have built two bitx40's and both appear to suffer audio distortion/overload, the audio sounds as though the speaker is "shot" I have tried three or four different speakers (all 8 ohm 3W) and on all of them I am unable to turn the volume up two much without getting distortion, it sound as though the output is too bassy for the speakers. I have done the rf gain control mod and this helps a little but the output is quite low. any ideas.

 

I had issues with the audio to loud and had to adjust the value on pin 1 to 8 on the lm386 as well.

I 1st removed it but after adding agc had to add the feedback loop back to increase audio. I am still working with it to find the right level.

If your tx audio is hot take a look at a few of the mods here on the group. Also check R136 should be about middle stock from the factory.



This may also be helpful. I did this mod as well but did not use the same value for c102 I ended up around 40pf which was only 7 down from stock. The rx audio with 22/27pf was way to tinny for me.

?Hope it helps

73
?David
 

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Side note C102 is part of the BFO you will/should check to make sure alignment is good.

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