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Bitx40 very loud, high-pitched, low frequency noise

SP9DEV
 

Hi! I've just finished assembling my Bitx40, and when I turn on the radio, I hear a terribly loud noise (link to listen below). The radio works fine, because I can hear some operators behind that noise, but I cannot tune the radio loud enough to hear them properly, as the noise is extremely loud even on the smallest volume. I don't really know what's happening gere. Any help?

The noise: https://www.youtube.com/watch?v=1j0ywo45N7I

SP9DEV
 

Fun fact, when I start to touch and move around the brown wire from volume control knob, I can hear local FM radio station.

SP9DEV
 

Please help

Ian Reeve
 

I don't recall the colors of the wires that go to the volume control but what I would do is unsolder the lead to the centre connection(audio to amplifier) If the noise continues it signifies a problem within the audio circuit.Try touching the lead you unsoldered to bare metal to see if the noise stops. I do wonder if the volume control is faulty.  It sounds like instability and you need to see whether it is the audio amp  or whether the sound is coming from the rest of the circuitry before the audio amp.  Hope this helps. Ian M0IDR


From: BITX20@groups.io <BITX20@groups.io> on behalf of SP9DEV <piotrekslawecki2@...>
Sent: Wednesday, August 21, 2019 10:33:37 AM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
 
Please help

SP9DEV
 

I tried unplugging the volume control completely, the problem persists

Ian Reeve
 

OK short the lead that went to the centre contact to the case and advise if the noise stops.


From: BITX20@groups.io <BITX20@groups.io> on behalf of SP9DEV <piotrekslawecki2@...>
Sent: Wednesday, August 21, 2019 12:50:25 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
 
I tried unplugging the volume control completely, the problem persists

 

If the problem is at low volume level then add any resistor value between 1-10K in series with center volume control wire
and see if that helps.

Raj, vu2zap

At 21-08-19, you wrote:
Please help

SP9DEV
 

@Ian Reeve the problem remains.

 

SP9DEV
 

@Raj vu2zap

The problem is at any volume

Ian Reeve
 

OK, I think we need to know a little more about the connections from the analogue connector.Firstly are you using a direct connection between this analogue connector and the sockets(earphone etc) or are you using the little pcb that houses the three Jack sockets. In mine I wire direct and the connections are. Green wire to volume low end orange to volume middle and yellow to volume high.There is no brown wire unless you use the pcb and that is a colour of the three wires from the Jack board. to volume.The speaker or headphones are connected to the brown and black wires on the right of the analogue connector.  Perhaps a few pictures of your unit


From: BITX20@groups.io <BITX20@groups.io> on behalf of SP9DEV <piotrekslawecki2@...>
Sent: Wednesday, August 21, 2019 2:33:20 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
 

@Raj vu2zap

The problem is at any volume

Ian Reeve
 

Perhaps a few pictures of your unit and connections might help a diagnosis as clearly the wiring colours do not match those on mine.


From: Ian Reeve
Sent: Wednesday, 21 August, 16:50
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
To: BITX20@groups.io


OK, I think we need to know a little more about the connections from the analogue connector.Firstly are you using a direct connection between this analogue connector and the sockets(earphone etc) or are you using the little pcb that houses the three Jack sockets. In mine I wire direct and the connections are. Green wire to volume low end orange to volume middle and yellow to volume high.There is no brown wire unless you use the pcb and that is a colour of the three wires from the Jack board. to volume.The speaker or headphones are connected to the brown and black wires on the right of the analogue connector.  Perhaps a few pictures of your unit

Gary Anderson
 

Ian, it's a Bitx40.  (good advice, just different radio)
wire-up
http://www.hfsignals.com/index.php/2017/11/23/wiring-up-the-bitx40/

Sounds like the LM386 could be oscillating around 4-5 kHz and making a faint barking dog-like noise.

SP9DEV what voltage are you supplying to the Bitx40?  Are you running or have run the LM386 at too high of a voltage?
The LM386 is set-up for a lot of gain in this configuration.  Amplifiers like to oscillate when the gain is pushed.

Rgds,
Gary

Ian Reeve
 

Ah my mistake,apologies.As Gary says,it sounds as if the audio chip is oscillating and as Gary says it is high gain and would seem to be some sort of instability.You could try a 10 ohm  resistor and a 0.1 if capacitor in series across the output pin to earth.Is your speaker 8 ohms or less?


From: BITX20@groups.io <BITX20@groups.io> on behalf of Gary Anderson <gary.ag5tx@...>
Sent: Wednesday, August 21, 2019 5:54:24 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
 
Ian, it's a Bitx40.  (good advice, just different radio)
wire-up
http://www.hfsignals.com/index.php/2017/11/23/wiring-up-the-bitx40/

Sounds like the LM386 could be oscillating around 4-5 kHz and making a faint barking dog-like noise.

SP9DEV what voltage are you supplying to the Bitx40?  Are you running or have run the LM386 at too high of a voltage?
The LM386 is set-up for a lot of gain in this configuration.  Amplifiers like to oscillate when the gain is pushed.

Rgds,
Gary

SP9DEV
 

I'm running the whole kit at 12V 3A from a wall-plug type of supply. The headphones are 23ohm apple headphones. Where would I exactly solder the 10ohm and 0.1uf?

Ian Reeve
 

The audio chip U1 looks to already have such a network across the output so scrub that idea. I see the instruction refers to the need for a linear power supply,perhaps if your power supply is switch mode,the noise you hear could be from the switch mods supply.To be honest I am running out of ideas but clearly  it points to a audio problem.It might be worth trying a non apple headphones and if you have access to equipment with a line in,disconnect the audio in to the volume control and pass it to a device with line in to see if the problem persists.


From: BITX20@groups.io <BITX20@groups.io> on behalf of SP9DEV <piotrekslawecki2@...>
Sent: Wednesday, August 21, 2019 6:18:43 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
 
I'm running the whole kit at 12V 3A from a wall-plug type of supply. The headphones are 23ohm apple headphones. Where would I exactly solder the 10ohm and 0.1uf?

Evan Hand
 

You might want to verify the 3.5 mm audio jack will connect correctly to the Apple earbuds.  Apple supplies a Tip, 2 rings and a sleeve to accommodate the microphone.  The supplied jack is audio out only with a Tip, 1 ring and a sleeve. 

FWIW
73
Evan
AC9TU

Ian Reeve
 

Not being familiar with Apple Jack plug connectivity,what Evan says and I suggested is likely to cause problems.A standard set of stereo headphones would prove the point.


From: BITX20@groups.io <BITX20@groups.io> on behalf of Evan Hand <elhandjr@...>
Sent: Wednesday, August 21, 2019 7:16:39 PM
To: BITX20@groups.io <BITX20@groups.io>
Subject: Re: [BITX20] Bitx40 very loud, high-pitched, low frequency noise
 
You might want to verify the 3.5 mm audio jack will connect correctly to the Apple earbuds.  Apple supplies a Tip, 2 rings and a sleeve to accommodate the microphone.  The supplied jack is audio out only with a Tip, 1 ring and a sleeve. 

FWIW
73
Evan
AC9TU

SP9DEV
 

Found 3 other pairs of headphones (nokia, motorola and some no-name headphones), the problem persists. However, I also found another wall-plug power supply, this one with a ferrite choke and rated 12V 2A. With this supply, the noise is a constant, high-pitched sound (different from the first one). Looks like this depends on the type of power supply. Both are probably switched mode, so I guess that's the issue. I'll try to get my hands on a standard computer ATX supply unit, solder a cable to 12V line and check what happens.

Woody
 

The PC supply is also a switcher.  It may also require a "power good" signal to operate and a minimum load to work properly.
I recommend trying a linear regulated supply or battery for trouble shooting.  Your wall-wart switcher may work if the problem is gone with good pure DC if a big filter capacitor (like >1000 uf) and enough ferrite choke beads/sleeves are added to the feed line - and it is not dropping out of regulation.
Woody 

--

kh6sky
 

I have a BitX40 that has the same issue.  When I run from a battery, the problem disappears.  . I tried lots of different bypassing caps with no luck.   As I prefer running it from a battery, it has not been a pressing issue