Hello,
I've a sub which all of a sudden started humming - using an audio app, I see peaks around 60Hz and 120Hz.
I'm trying to troubleshoot and when I put one of the probes of multimeter on the ground anywhere on the board, it detects 60Hz frequency?
Is this normal or do I have a problem?
BTW, when I put probes on both sides of the power supply, which in this case are 2 different ones - +63/0/-63 and +34/0/-34, it doesn't detect any frequency at all.
Thank you.
I've a sub which all of a sudden started humming - using an audio app, I see peaks around 60Hz and 120Hz.
I'm trying to troubleshoot and when I put one of the probes of multimeter on the ground anywhere on the board, it detects 60Hz frequency?
Is this normal or do I have a problem?
BTW, when I put probes on both sides of the power supply, which in this case are 2 different ones - +63/0/-63 and +34/0/-34, it doesn't detect any frequency at all.
Thank you.
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And where do you put the other?
Voltages are not unipotential, they are always the difference between 2 points.
Hello,
Thanks for the quick response. When measuring the voltage, I had my probes on both sides of the capacitors.
However, I'm troubleshooting hum. I had my multimeter on 'Hz' and with only black probe on the ground, the multimeter started showing 60Hz.
Thanks for the quick response. When measuring the voltage, I had my probes on both sides of the capacitors.
However, I'm troubleshooting hum. I had my multimeter on 'Hz' and with only black probe on the ground, the multimeter started showing 60Hz.
Your meter is acting like an antenna and it sounds like you have a high resistance earth somewhere as leakage to earth should have provided a low resistance/impedance path to earth and its not.
Duncan2,
This JBL sub doesn't have a earth at all. The power plug and only 2 prongs 🙂 - so yes, its possible - thank you.
I'm not sure why they designed it that way. But since it was working fine all along, I'll not investigate this anymore.
This JBL sub doesn't have a earth at all. The power plug and only 2 prongs 🙂 - so yes, its possible - thank you.
I'm not sure why they designed it that way. But since it was working fine all along, I'll not investigate this anymore.
It is normal for hi-fi equipment to be built as IEC Class II appliances - this keepsground loops at bay.
Are you sure +/-34 V are the lowest voltages in there? I almost can't imagine the thing wouldn't have regulated +/-12..18 V for its low-level stages. If you see any opamps in there, it's basically guaranteed.
Are you sure +/-34 V are the lowest voltages in there? I almost can't imagine the thing wouldn't have regulated +/-12..18 V for its low-level stages. If you see any opamps in there, it's basically guaranteed.
I've a somewhat similar problem with my $200/"100 watt" Pioneer 10" sub. There's about 40VAC, at only a few microamps, riding on the grounded side of the RCA interconnects. My AC voltage detector will trigger within 4" of anything connected in the system.
No hum is present, however, in my case. Before I open the cheap sub, are there well known suspects on the PCB I should start testing? Thanks.
No hum is present, however, in my case. Before I open the cheap sub, are there well known suspects on the PCB I should start testing? Thanks.
That proves my point--radiated transmission , I also have a "spy detector " which will pick up LF as well I have used it to narrow down the area of HF oscillations in an amplifier , it saves a lot of tracing .
I am afraid I am not a "lover " of non earthed electrical products , okay with battery operation but mains fed or via a mains fed unit should be earthed.
All this "double insulated " and and "electrically isolated " leaves me cold.
If you read the actual "standards" used you will realise that they don't come up to scratch but are a means of providing cheaply made products.
As is "CE" which is printed in China for a start on products that are stamped "made in Germany" ( I had access to a German production engineers website at the time ) ,one of whom was in China supervising a production line , a colleague told him to "shut up " if he valued his job .
I am afraid I am not a "lover " of non earthed electrical products , okay with battery operation but mains fed or via a mains fed unit should be earthed.
All this "double insulated " and and "electrically isolated " leaves me cold.
If you read the actual "standards" used you will realise that they don't come up to scratch but are a means of providing cheaply made products.
As is "CE" which is printed in China for a start on products that are stamped "made in Germany" ( I had access to a German production engineers website at the time ) ,one of whom was in China supervising a production line , a colleague told him to "shut up " if he valued his job .
Possible related: Be aware that especially switch-mode power supplies use line filters that have a Y-cap that puts half the line voltage on "ground" unless the safety ground is connected to earth ground. IE, you can not lift the safety ground. It is a noise current sink as well as a safety ground.