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SOLVED Re: [BITX20] Bitx40 low volume oscillation squeal

Graham <planophore@...>
 

Had some time to mess around with this problem before the supper bell and figured out at least what was causing the problem.

I started by getting several other new pots out of my stock of such items, a couple of other speakers and three clip leads.

After disconnecting the pot with the wired on connector proceeded to try several other pots starting with a 10K pot, three clip leads from volume connector on the bitx40 board to the pot and gave it a try.

Bingo! Works just fine, no "squeal" at a low volume setting.

Tried another, works just fine.

And another, works just fine.

Tried the original three pots which gave me the problem and all worked OK.

All this with 15" long clip leads strewn willy nilly on the workbench.

The problem turns out to be the be the three pin connector with six inches of wire. This was one of connectors and wire included with the kit. Replacing the wire and connector fixed the problem.

I don't know what the problem with the connector and wires is, looks OK to the eye but I guessing maybe some form of oxidation on one or more of the wires and/or connectors and/or ????? I have already put the problematic piece in the trash and moved on. I may just go dig it out of the trash and do a forensic dissection and see if I can figure out the actual failure mechanism.

Once you eliminate the impossible, whatever remains, no matter how improbable, must be the truth.

Thank you one and all for your suggestions.

cheers, Graham ve3gtc

On 2017-03-27 17:21, Graham wrote:
thank you for the suggestion.

However, doesn't help. Bitx40 is still not mounted in case, The wires
for speaker and volume control are the only ones near each other and
both are twisted i.e. volume control wires are all twisted together, the
two wires for the speaker are also twisted together, makes everything
tidier and is my normal course.

I am not using a raduino but rather feeding the bitx with an external
analog vfo connected through RG174 to the DDS connector on board the
bitx40.

I haven't had time to poke around at this problem so far today. Perhaps
I will find a wee bit of time later this evening.

cheers, Graham ve3gtc

 

Graham,

I figured out the squeal issue on my board. I was working on getting rid of the PTT noise that is annoying me.

If you interchange the VOLUME control wires RED and BROWN then when the control is low or zero then

the audio stages become unstable.

Cheers

Raj, vu2zap



Graham <planophore@...>
 

Hi Raj,

I found that my problem was with the connector I had used for the volume control. There was some form of oxidation one the spring "pins" in the connector that was causing the audio stage to oscillate when the volume control as at or near zero ohms.

A different connector and wires and all was better.

I have seen some strange things before but this was a first.

cheers, Graham ve3gtc


On 2017-04-01 10:50, Raj vu2zap wrote:

Graham,

I figured out the squeal issue on my board. I was working on getting rid of the PTT noise that is annoying me.

If you interchange the VOLUME control wires RED and BROWN then when the control is low or zero then

the audio stages become unstable.

Cheers

Raj, vu2zap




Lawrence Galea
 

Nothing strange in electronics

On Sun, Apr 2, 2017 at 1:51 AM, Graham <planophore@...> wrote:
Hi Raj,

I found that my problem was with the connector I had used for the volume control. There was some form of oxidation one the spring "pins" in the connector that was causing the audio stage to oscillate when the volume control as at or near zero ohms.

A different connector and wires and all was better.

I have seen some strange things before but this was a first.

cheers, Graham ve3gtc


On 2017-04-01 10:50, Raj vu2zap wrote:

Graham,

I figured out the squeal issue on my board. I was working on getting rid of the PTT noise that is annoying me.

If you interchange the VOLUME control wires RED and BROWN then when the control is low or zero then

the audio stages become unstable.

Cheers

Raj, vu2zap