Problem on Speaker Output

[kruser]

This problem about the speaker has been discussed by upman and the answer is using a ground loop isolator.

Yep, it has.

It's all in the link I provided in one of my posts in this thread.

 

[BorisG]

I am currently using a front input (headset) has a bit of noise but no problem was before.

 

[kruser]

I am currently using a front input (headset) has a bit of noise but no problem was before.

Sounds like you are on the right track Boris.

Once you get the ground loop isolator, you should be able to use the rear port again.

The front port is a standard grounded port so it does not short anything out when you plug it into a computer like the rear port does.
A ground loop isolator may also get rid of the noise you are hearing while using the front port.
I can understand wanting to use the rear port though. I myself hate cables sticking out from the front of the radio where your fingers may hit it and snap it off.

Glad you have something working until you can get the ground isolator!

 

[cmdrwill]

I know see why there is so much problems with the scanner's external speaker out put.
It IS in fact a bridge audio amp, so neither speaker lead is grounded.

So the audio transformer AND an attenuator would be the way to begin matching the scanner output to a computer audio input.

 

[kruser]

I know see why there is so much problems with the scanner's external speaker out put.
It IS in fact a bridge audio amp, so neither speaker lead is grounded.

So the audio transformer AND an attenuator would be the way to begin matching the scanner output to a computer audio input.

You got it!

You can do it without the transformer by tying your output cable's shield to the chassis via chassis screw instead of tying it to the sleeve connector in the plug and then only use the tip wire from the 1/8th inch plug. Nothing would connect to the sleeve on the plug at all.
In effect, you are only using half of the BTL amps output when done this way but it does work and prevents damage to the audio amp output.

In the thread link in one of my posts here is a post from Mike_G_D that includes a zip file showing 4 schematics of how to do it with or without an isolation transformer. He also supplies drawings of variable or fixed attenuation methods.
Either way will work but I prefer the proper method which uses the isolation transformer instead of leaving one side of the BTL output floating high.

My design is also a fixed output level as I knew I'd never need to change the output level from the radio once I had the load impedance and audio level set correctly.

For those that may plug their outputs into different devices may find Mike's drawing with variable attenuation to be the better choice.
Here's the link directly to Mike's last revision to his designs: http://forums.radioreference.com/un...n-considerations-precautions.html#post2147479

A few posts older, he also has a link to his first design but I never really studied them to see what he changed. I'd already built my interface before he posted any of his drawings.
It's actually an easy circuit to put together with just a basic knowledge of electronics and soldering etc.

I did always agree with everyone here that Uniden should have included a fixed line level output jack like many of their older models had. Why they omitted that is a mystery unless they did such to try and not promote streaming. It would have been very easy and cheap to include that jack when the radio was still being developed on paper.

I think someone tried to find a point on the board where unamplified audio could be tapped but I think it was found that the audio at that stage was actually in a digital format or it came from several sources and was combined back together and turned back into an analog signal inside a custom chip making it impossible to extract.
I could be mistaken on that and I may be thinking of a post where someone tried to find a discriminator tap point in the 4/536HP models.

I wish they still supplied schematics for these things!

 

[BorisG]

Sounds like you are on the right track Boris.

Once you get the ground loop isolator, you should be able to use the rear port again.

The front port is a standard grounded port so it does not short anything out when you plug it into a computer like the rear port does.
A ground loop isolator may also get rid of the noise you are hearing while using the front port.
I can understand wanting to use the rear port though. I myself hate cables sticking out from the front of the radio where your fingers may hit it and snap it off.

Glad you have something working until you can get the ground isolator!

Thank you
Your help it is not obvious!!!!