Radio Shack Ground Loop Isolator solved HUM!

[RiverRunner]

Hi Folks,

I recently had to replace the amp in my subwoofer and the new setup produced a loud HUM, where it did not before. The HUM went away when I pulled the RCA lead from the receiver (Onkyo tx-nr8009) so I figured the subwoofer was good. The sub is produced by a local speaker repair shop.

I put a Radio Shack Ground Loop Isolator, $17.50, into the line between receiver and subwoofer and it seems to solve the problem HUMMMMMMMM.

Question: Does anyone know what that Ground Loop Isolator did to the frequency response of my subwoofer? Do you think it passes the signal through pretty clean, or is it chopped up? Kind of hard to A/B when you need to switch cords.

Thanks very much for any ideas.

 

[jinjuku]

Hi Folks,

I recently had to replace the amp in my subwoofer and the new setup produced a loud HUM, where it did not before. The HUM went away when I pulled the RCA lead from the receiver (Onkyo tx-nr8009) so I figured the subwoofer was good. The sub is produced by a local speaker repair shop.

I put a Radio Shack Ground Loop Isolator, $17.50, into the line between receiver and subwoofer and it seems to solve the problem HUMMMMMMMM.

Question: Does anyone know what that Ground Loop Isolator did to the frequency response of my subwoofer? Do you think it passes the signal through pretty clean, or is it chopped up? Kind of hard to A/B when you need to switch cords.

Thanks very much for any ideas.

Your SQ isn't going to be impacted using the isolation transformer. You can relax. You are hearing everything you need to hear.

 

[highfigh]

Your SQ isn't going to be impacted using the isolation transformer. You can relax. You are hearing everything you need to hear.

Yes, the SQ can be affected by an isolation transformer. They're not all the same and the Radio Shack isolator is pretty cheap, so there's no guarantee the input winding will be equal to the output, but they do work. Usually, if an isolator isn't a good one (not 'good' in price or name brand, I mean from an absolute standpoint), it usually messes up the bass. When it's feeding a subwoofer, the level often drops below what was present before the isolator was used. I heard it when I did car audio and I have heard it in home theater/distributed audio systems. I have seen wireless subwoofer RF transmitter/receiver setups and they're made specifically so a ground loop won't occur when the sub can't be placed near the rest of the system or when the power for the sub comes with resistance on the neutral and/or ground.

 

[highfigh]

Hi Folks,

I recently had to replace the amp in my subwoofer and the new setup produced a loud HUM, where it did not before. The HUM went away when I pulled the RCA lead from the receiver (Onkyo tx-nr8009) so I figured the subwoofer was good. The sub is produced by a local speaker repair shop.

I put a Radio Shack Ground Loop Isolator, $17.50, into the line between receiver and subwoofer and it seems to solve the problem HUMMMMMMMM.

Question: Does anyone know what that Ground Loop Isolator did to the frequency response of my subwoofer? Do you think it passes the signal through pretty clean, or is it chopped up? Kind of hard to A/B when you need to switch cords.

Thanks very much for any ideas.

Let me guess- the original sub amp's power cord didn't have a grounding pin and the new one does, right?

To answer your question, an isolation transformer isolates the source end of the cable from the amplifier end. A ground loop is caused by resistance on the power line's neutral and/or ground, when referenced to the electrical panel when two or more devices are connected together. The difference in resistance means that, if you measure the voltage at each device, you'll see a difference. Electricity is like water- it likes to find its own level and in order to create equality, the voltage difference will be equalized in any way available- this is usually through an audio or video cable. When the power ground coincides with the audio/video ground, you'll have hum (audio) or noise bars (video).

 

[jinjuku]

Yes, the SQ can be affected by an isolation transformer. They're not all the same and the Radio Shack isolator is pretty cheap, so there's no guarantee the input winding will be equal to the output, but they do work. Usually, if an isolator isn't a good one (not 'good' in price or name brand, I mean from an absolute standpoint), it usually messes up the bass. When it's feeding a subwoofer, the level often drops below what was present before the isolator was used. I heard it when I did car audio and I have heard it in home theater/distributed audio systems. I have seen wireless subwoofer RF transmitter/receiver setups and they're made specifically so a ground loop won't occur when the sub can't be placed near the rest of the system or when the power for the sub comes with resistance on the neutral and/or ground.

I've put a few of the Radioshack isolation xformers in. Personal experience leads me to believe that the sub woofer SQ and output is going to be indistinguishable.

 

[TLS Guy]

I've put a few of the Radioshack isolation xformers in. Personal experience leads me to believe that the sub woofer SQ and output is going to be indistinguishable.

Very few audio transformer can bass a 20 Hz signal without a lot of gain reduction, and small cheap ones just about never.

The high and low ends of the spectrum are a problem for transformers.

 

[jinjuku]

Very few audio transformer can bass a 20 Hz signal without a lot of gain reduction, and small cheap ones just about never.

The high and low ends of the spectrum are a problem for transformers.

Been infinity and polk subs so they probably didn't do much below 30... Just my experience guys...

 

[RiverRunner]

Let me guess- the original sub amp's power cord didn't have a grounding pin and the new one does, right?

To answer your question, an isolation transformer isolates the source end of the cable from the amplifier end. A ground loop is caused by resistance on the power line's neutral and/or ground, when referenced to the electrical panel when two or more devices are connected together. The difference in resistance means that, if you measure the voltage at each device, you'll see a difference. Electricity is like water- it likes to find its own level and in order to create equality, the voltage difference will be equalized in any way available- this is usually through an audio or video cable. When the power ground coincides with the audio/video ground, you'll have hum (audio) or noise bars (video).

You are right on the power cord issue and grounding pin.

 

[bikdav]

Another Successful Fix

Good show. I'm glad to hear that it solved the problem. I have a ground loop isolator between my old MAC and the av receiver, because of a very bad hum with out it. The hum is practically inaudible and no it did not have any adverse effects on the frequency response top or bottom that I can hear. I very strongly recommend trying one.