Very strange problem with *sound interface

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litebulb
Posts: 2
Joined: Sun Nov 17, 2019 5:12 pm

Very strange problem with *sound interface

Post by litebulb » Sun Nov 24, 2019 3:45 pm

Morning yall,

Let me open by saying while I am not a licensed HAM operator I currently perform all of my testing at the lowest power setting, with the antenna removed and on an unlicensed analog FRS channel.

Myself and my buddy are struggling with this very strange problem on our GD77's. The issue is not OpenGD77 specific, but I figured I would ask in the off chance that someone here has ran into this phenomenon before.

We have two UV5R's, two GD77's and two interface cables that I made. The interface cables are CM108 USB sound devices which I soldered directly to the Radiodity speaker/mic combo unit. My understanding is that the GD77's and UV5R's have the exact same speaker/mic pinouts and are both compatible with the connector on the speaker/mic combo unit. We tested the interface by transmitting sound from youtube from one UV5R to another, and from the UV5R to a GD77. The strange thing is that when you try to transmit from the GD77 the sound doesn't come through. Even stranger yet is that the keypad tones *do* go through indicating that there is a functioning radio link but just no audio from the K-Plug is getting out.

Any idea what the heck we might be doing wrong?

VK3KYY
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Location: Melbourne, Australia
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Re: Very strange problem with *sound interface

Post by VK3KYY » Wed Jan 29, 2020 11:25 pm

I know this is an old thread...

But recently I asked Jason VK7ZJA why the external speaker on my GD-77 makes a click sound every time the amplifer is turned on in the radio, but the internal speaker does not click.

Jason told me that this is because the internal speaker is connected as push-pull, but the external speaker is connected as single ended i.e single connection and return via ground.

The problem you are experiencing may be something to do with this and how the GD-77 speaker connection is different from the UV-82

VK3KYY
Posts: 1612
Joined: Sat Nov 16, 2019 3:25 am
Location: Melbourne, Australia
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Re: Very strange problem with *sound interface

Post by VK3KYY » Wed Jan 29, 2020 11:25 pm

I know this is an old thread...

But recently I asked Jason VK7ZJA why the external speaker on my GD-77 makes a click sound every time the amplifer is turned on in the radio, but the internal speaker does not click.

Jason told me that this is because the internal speaker is connected as push-pull, but the external speaker is connected as single ended i.e single connection and return via ground.

The problem you are experiencing may be something to do with this and how the GD-77 speaker connection is different from the UV5R

kt4lh
Posts: 67
Joined: Sun Jan 12, 2020 4:27 am

Re: Very strange problem with *sound interface

Post by kt4lh » Thu Jan 30, 2020 12:18 am

A lot of these cheaper radios have a VERY annoying click when the audio amp turns on/off, especially on a handmic it seems really bad. I've seen a few pages fixing this on various radios, here's one I saw a while back that I'd pondered making into an intermediate interface for a radio that's particularly bad, almost unusable, on a hand mic. https://softsolder.com/2018/08/09/baofe ... ppression/

Basically just two diodes across the speaker, opposing directions. I've not tried it but would be pretty easy to prototype.

VK3KYY
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Re: Very strange problem with *sound interface

Post by VK3KYY » Thu Jan 30, 2020 12:25 am

kt4lh wrote:
Thu Jan 30, 2020 12:18 am
A lot of these cheaper radios have a VERY annoying click when the audio amp turns on/off, especially on a handmic it seems really bad. I've seen a few pages fixing this on various radios, here's one I saw a while back that I'd pondered making into an intermediate interface for a radio that's particularly bad, almost unusable, on a hand mic. https://softsolder.com/2018/08/09/baofe ... ppression/

Basically just two diodes across the speaker, opposing directions. I've not tried it but would be pretty easy to prototype.
Thats interesting.

I did try putting a capacitor across the speaker, but it didn't help.

Putting back to back diodes will limit the max audio volume to around 0.5V, which seems a bit low.
I'm not sure what the impedance of the external speakers are. Probably 4 Ohms or 8 Ohms.

Do by ohms law

P = V*V/R

the max power would only be 0.25 / 4W i.e i.e 1/16W.

Perhaps an inductor/choke in series would be better at quenching these large high frequency transients

SP2ONG
Posts: 17
Joined: Sat Nov 16, 2019 9:47 am

Re: Very strange problem with *sound interface

Post by SP2ONG » Thu Jan 30, 2020 7:11 am

Hi,

I use an external speaker and microphone with my GD-77 and observe annoying clicks when the audio amp turns on. Maybe we need use some delay to turn on the speaker just like in audio amplifiers like on the below picture?
Attachments
SpeakerProtection.PNG
SpeakerProtection.PNG (30.5 KiB) Viewed 87 times

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