536 output to feed, should i have a ground loop isolator?

[madrabbitt]

I'm temporarily running a BCD536 on half of a stereo feed.

Currently, the line in on the sound card has a split mono cable, with the left channel going to a BCT15x LINE OUT jack, and the right channel going to the EXT SP jack on the 536.

I'm seeing conflicting information on needing a group loop isolator required on a mono line out.

Also, i'm not using the FRONT jack, because its a mono cable.

 

[belvdr]

If you don’t hear a hum, then it’s not needed.

 

[RFI-EMI-GUY]

I'm temporarily running a BCD536 on half of a stereo feed.

Currently, the line in on the sound card has a split mono cable, with the left channel going to a BCT15x LINE OUT jack, and the right channel going to the EXT SP jack on the 536.

I'm seeing conflicting information on needing a group loop isolator required on a mono line out.

Also, i'm not using the FRONT jack, because its a mono cable.

You need an isolator, not only for hum, but because the speaker output is Bridge Tied Load amplifier. The speaker floats between the + and - buses of the radio. You run a risk of damaging the amplifier by grounding the + side. You need a transformer coupled output isolator to feed the unbalanced line inputs of the sound card. Radio shack used to sell a nice beefy one that was stereo and good for two radios. The Chinese ones on Amazon are sketchy with either a tiny transformer that can saturate with speaker audio, or they are simply capacitors blocking the audio. Try and find something and auto audio store might sell retail.

 

[madrabbitt]

You need an isolator, not only for hum,... Try and find something and auto audio store might sell retail.

Somewhere... i'll have to look... but somewhere in my garage i had one i used on a XM radio in the old truck (to the aux port)

It came from a stereo shop and was decent quality.

HOWEVER, its a stereo plug and jack... which i assume in this case wouldnt be an issue since both the jack and the line are both mono, and the sleeve would be shorted to the ring on both ends?

 

[RFI-EMI-GUY]

Somewhere... i'll have to look... but somewhere in my garage i had one i used on a XM radio in the old truck (to the aux port)

It came from a stereo shop and was decent quality.

HOWEVER, its a stereo plug and jack... which i assume in this case wouldnt be an issue since both the jack and the line are both mono, and the sleeve would be shorted to the ring on both ends?

You need to "ohm it out" to make sure you have an isolated transformer winding on each of the input and output pairs. I don't know why the Broadcastify wiki doesn't make a point of informing folks that the feeds need transformer isolation. They mention it regarding hum, but from the sounds of many of the feeds, the distortion is significant. A few people have mentioned damaged sound cards.

 

[RFI-EMI-GUY]

Pricey but true isolation. What is a ground loop? | Jensen Transformers




This one below, claims to have an isolation transformer , yet a lot of puffery. For the price I would buy one, ohm it out to make sure it has a transformer inside. If not send it back.

https://www.amazon.com/200W-15A-RCA-Noise-Suppressor/dp/B000BCDQ44/ref=sr_1_15?content-id=amzn1.sym.61284899-b26b-4d51-9b64-97dd2495a44f%3Aamzn1.sym.61284899-b26b-4d51-9b64-97dd2495a44f&keywords=audio%2Bisolation%2Btransformer&pd_rd_r=23cf2af4-34c6-496a-a488-6749f69eb673&pd_rd_w=qKmDD&pd_rd_wg=5pluD&pf_rd_p=61284899-b26b-4d51-9b64-97dd2495a44f&pf_rd_r=F83C4R6RRQ50SBFGAZKZ&qid=1702518566&sr=8-15&th=1

 

[prcguy]

The BCD536 AC power supply is isolated from any ground so the only potential grounding of the unit would be through the antenna. The OP also mentioned he is using the scanners line out and not the speaker out, so there would be no problem grounding the bridged speaker output. If there is no hum then no transformer or isolation needed at this time.

However, computers can change, ground connections can change and its not a bad idea to isolate for the future. You can buy a fine little line level 600:600 ohm isolation transformer for under $1 then I would get a mono 1/8" male to male cable, cut in half then solder each half to the transformer for an easy plug and play solution.

 

[madrabbitt]

The BCD536 ...The OP also mentioned he is using the scanners line out and not the speaker out, ...

Not on the 536. No line out jack. Hence the question

 

[prcguy]

Not on the 536. No line out jack. Hence the question

You can still use a cheap 600:600 isolation transformer. I would make a simple attenuator by placing an 8 ohm 2W resistor across the speaker output, then place a 10K ohm potentiometer across that 8 ohm resistor with the two outer ends to the 8 ohm resistor then the center wiper to one side of the transformer primary and the speaker ground to the other side of the transformer primary. Then connect the transformer secondary directly to the computer sound card input. Then do the 1/8" cable thing mentioned above.

This will place a constant 8 ohm resistive load on the scanner speaker output, isolate it from the computer card and give you infinite level adjustment.

 

[RFI-EMI-GUY]

The BCD536 AC power supply is isolated from any ground so the only potential grounding of the unit would be through the antenna. The OP also mentioned he is using the scanners line out and not the speaker out, so there would be no problem grounding the bridged speaker output. If there is no hum then no transformer or isolation needed at this time.

However, computers can change, ground connections can change and its not a bad idea to isolate for the future. You can buy a fine little line level 600:600 ohm isolation transformer for under $1 then I would get a mono 1/8" male to male cable, cut in half then solder each half to the transformer for an easy plug and play solution.

The moment he plugs in the mini USB to update or program the radio, a ground will be created back to the computer. The manufacturers really need to provide an isolated or unbalanced line out for such gear.

 

[madrabbitt]

The moment he plugs in the mini USB to update or program the radio, a ground will be created back to the computer. The manufacturers really need to provide an isolated or unbalanced line out for such gear.

I dont program with the computer the feed is on. Also, i usually just pull the SD card, format it, and write new programming to it. But thats good to know also.

 

[RFI-EMI-GUY]

I dont program with the computer the feed is on. Also, i usually just pull the SD card, format it, and write new programming to it. But thats good to know also.

It would not matter, if both computers are getting ground either via the AC plug, or some other cabling.