BCD396XT Audio Popping Solved

[rvictor]

I've posted previously about the popping noise that I hear when I record or amplify my 396XT's audio. In one of the other forums Bob (Proscan) suggested that it might be a DC component on the audio and suggested that I try either a 10mf capacitor or a 1:1 audio transformer. I bought the parts yesterday and breadboarded them today so I could switch things in and out. The cap didn't help, but the transformer solved the problem. I then built a cord with the filter on one end in a small plastic case which seems to be working well. If you want to hear the audio clips which are about 3 minutes each, they are at YouSendIt.

https://www.yousendit.com/download/UmNLRGwrdzh6NFBIRGc9PQ

The two files of interest are unfiltered.mp3 and transformer.mp3 although there are also clips with the capacitor only and with the transformer and the capacitor together. It's particularly interesting to watch the waveform of the audio while listening with a program such as Goldwave.

73,
Dick

 

[mike_s104]

I've posted previously about the popping noise that I hear when I record or amplify my 396XT's audio. In one of the other forums Bob (Proscan) suggested that it might be a DC component on the audio and suggested that I try either a 10mf capacitor or a 1:1 audio transformer. I bought the parts yesterday and breadboarded them today so I could switch things in and out. The cap didn't help, but the transformer solved the problem. I then built a cord with the filter on one end in a small plastic case which seems to be working well. If you want to hear the audio clips which are about 3 minutes each, they are at YouSendIt.

https://www.yousendit.com/download/UmNLRGwrdzh6NFBIRGc9PQ

The two files of interest are unfiltered.mp3 and transformer.mp3 although there are also clips with the capacitor only and with the transformer and the capacitor together. It's particularly interesting to watch the waveform of the audio while listening with a program such as Goldwave.

73,
Dick

Bob pointed me to your post for the same issue. Do you have a schematic for this so I could build one as well?

 

[rvictor]

There's not much to it. It's a Radio Shack Audio Isolation Transformer 273-1374. (See attached pdf.) The hardest part is finding a store that has them and then finding them at the store. As you can see in the attached photo, the transformer has four very thin leads. A wire stripper that goes down to 26 guage is handy but not required. (You can probably strip them with your teeth, but I'm sure your dentist would not recommend it. Not responsible, etc., ....)

I connected the yellow and red leads of the transformer to the cable that plugs into the scanner with the yellow to the center conductor of that cable and the red to the braided shield. The black and white leads go to the 1/8" miniature jack (Radio Shack 274-251) with the white lead to the tip and the black lead to the ground or ring. Insulate the connections to the cable so that it doesn't short out. I used shrink tubing. You could also use the brush-on rubber insulation coating stuff.

I used a small plastic container (a 35 mm plastic film can would work) to mount it and drilled a hole on each end for the cable and the jack. If you tie the cable in a knot and pull that inside the container, it provides a strain relief so that you don't pull the delicate wiring apart. Carefully stuff everything inside and you're set to go.

Let me know if you have any questions.

73
Dick

 

[mike_s104]

There's not much to it. It's a Radio Shack Audio Isolation Transformer 273-1374. (See attached pdf.) The hardest part is finding a store that has them and then finding them at the store. As you can see in the attached photo, the transformer has four very thin leads. A wire stripper that goes down to 26 guage is handy but not required. (You can probably strip them with your teeth, but I'm sure your dentist would not recommend it. Not responsible, etc., ....)

I connected the yellow and red leads of the transformer to the cable that plugs into the scanner with the yellow to the center conductor of that cable and the red to the braided shield. The black and white leads go to the 1/8" miniature jack (Radio Shack 274-251) with the white lead to the tip and the black lead to the ground or ring. Insulate the connections to the cable so that it doesn't short out. I used shrink tubing. You could also use the brush-on rubber insulation coating stuff.

I used a small plastic container (a 35 mm plastic film can would work) to mount it and drilled a hole on each end for the cable and the jack. If you tie the cable in a knot and pull that inside the container, it provides a strain relief so that you don't pull the delicate wiring apart. Carefully stuff everything inside and you're set to go.

Let me know if you have any questions.

73
Dick

Thanks. I'll attempt to located the transformer locally and let you know how it goes.

 

[mike_s104]

I checked online and a local RS had the transformer in stock. I had the other parts already. Worked like a charm! No more popping.

 

[rvictor]

Glad that it solved your problem.

73
Dick

 

[rvictor]

I've found that the Radio Shack Ground Loop Isolator (270-054) will also work for this function. It's a stereo device so you can actually take care of two mono scanner outputs with the one device. Since it comes with male RCA connectors at each end, you either need some adapters or to remove those connectors and replace them with whatever suits your setup. I put 1/8" mono plugs on the side going to the scanners and 1/8" stereo jacks (with the two channels wired together) on the other since that side will connect to stereo cords going to the computer sound cards. By using the stereo jacks, I eliminated the need for a stereo to mono adapter in each line.

Dick

 

[kc2rgw]

Wanted to toss in another comment as a new owner that noticed this issue right away.

I run my audio into a Roland 10ch compact mixer that then feeds powered Bose computer speakers. I feed multiple HF radios, VHF, scanners and a PC into this mixer.

The only thing that was thumping in and out on sound was the BC396XT.

I pulled the remote control cable and it goes away. If the scanner is standing on battery power, it's just fine.

I assumed it is a ground loop issue of some sort and the reason the 1:1 transformer would work logically is just that. It's decoupling the audio electrically.

The audio circuit in the 396XT headphone output is likely not isolated properly.

 

[TAS]

Is this a problem with all XT's or just those that do not have the headphone output isolated properly? I never had any popping or noise with T but the XT sounds horrible. Maybe a request should be made of Uniden to prevent this problem on all future releases. Thanks.

http://forums.radioreference.com/sc...c-xt-pro-bcd396xt-recording-issues-again.html

TAS

 

[kc2rgw]

I would guess it is all of them. I tried running my feed with the 396XT and the thumping was very annoying so I removed it. I also noticed it was really horrendously susceptible to RFI from my ham operations...which are on the same desk to be fair, but the old Pro-2006 is a lot better.

I think the RFI issue is due to not isolating the audio circuit if I had to guess.

 

[TAS]

I tried the Radio Shack Ground Loop Isolator (Cat. No. 270-054) as posted by rvictor. It did take care of the popping and distortion but I find that the audio with it is very low and would fluctuate up and down on its own, sometimes down to the point that I could barely hear the radio with the speakers all the way up. Any ideas on what’s happening here? Thanks.

TAS

 

[911scanner]

I like the fix. One question....

Do any of you feel a bit torqued off for purchasing a $500 technologically savvy scanner that has this sort of a "low quality feeling" issue? I do.


MM

 

[kc2rgw]

I used to, now the marketplace has worn me out... just par for the course.

There are recent amateur transceivers $1500-$3k with flaws in them that are simply because the manufacturer saved $.05 in production cost and eliminated a component or saved a $1 and didn't QC the equipment well before it was boxed and shipped. Luckily I haven't bought any of those.

Household appliances now are lucky to last a year or two....want a laugh, look up reviews on generic budget microwaves...fine one that isn't piled up with bad reviews. They are all cheaply made now.

Just par for the course....someone wanted to save $0.25 a unit and skipped the isolation on the output.

 

[TAS]

Does the 996XT have the same problem with the audio popping?

TAS

 

[rvictor]

Is this a problem with all XT's or just those that do not have the headphone output isolated properly? I never had any popping or noise with T but the XT sounds horrible. Maybe a request should be made of Uniden to prevent this problem on all future releases. Thanks.

http://forums.radioreference.com/sc...c-xt-pro-bcd396xt-recording-issues-again.html

TAS

I can't generalize beyond my own experience, but my 396XT and 346XT both have the problem and there are obviously others with the same problem as noted in this thread.

Fortunately, the solution was pretty simple and relatively inexpensive. Still would have been nice if Uniden had built the scanners so that it wasn't necessary. Certainly running the audio through a computer for amplified listening or recording is not an unexpected usage.

Dick

 

[wolter]

This is a great tip! Sounds similar to the problem with Uniden's 780. Does it also happen when using headphones?

 

[W6KRU]

This is a great tip! Sounds similar to the problem with Uniden's 780. Does it also happen when using headphones?

Yes. Headphones/external speaker/internal speaker.

 

[ruiz02]

I just bought a 396XT and so far it has been great. I do have it connected to my computer and also get the popping noise as described above.
As far as the homemade fix, I noticed in the picture that you have a mono connection. The 396XT has a stereo connection and the computer does to.

How does that work for you and anyone else who has tried this fix? Do you get mono or stereo audio with this fix?

I saw the Radio Shack (270-054 ) comment about the low audio so I am wondering which would be the best route to go.

Is there another fix we do not know about?

73

W4DOJ

 

[frankcastle]

I've found that the Radio Shack Ground Loop Isolator (270-054) will also work for this function. It's a stereo device so you can actually take care of two mono scanner outputs with the one device. Since it comes with male RCA connectors at each end, you either need some adapters or to remove those connectors and replace them with whatever suits your setup. I put 1/8" mono plugs on the side going to the scanners and 1/8" stereo jacks (with the two channels wired together) on the other since that side will connect to stereo cords going to the computer sound cards. By using the stereo jacks, I eliminated the need for a stereo to mono adapter in each line.

Dick

Finally bought one of these this weekend. Works like a charm. I know this is a more expensive option, but my local radio shack had it in stock where as they didn't have the transformer.

 

[ruiz02]

Ok,
I decided to go for the Radio Shack Ground Loop Isolator (270-054) and it works great. No more popping noise. I can now relax and enjoy my new 396xt.

73

W4DOJ