ground loop

[ghinckley68]

Is there away to hook up my siginal gnereator which is tied to ground on the pnc to an amp that has no tie to ground with out hum.

[LaurentR]

Is there away to hook up my siginal gnereator which is tied to ground on the pnc to an amp that has no tie to ground with out hum.

If it's strictly for audio, you could use an audio ground loop isolator (basically a transformer specced for audio frequencies), which are <$10, like this guy:
http://smile.amazon.com/PAC-SNI-1-3-5-3-5-mm-Isolator/dp/B001EAQTRI

[danadak]

Use your scope in differential mode -





Regards, Dana.

[ghinckley68]

that was great think you for the video, but i need to go into an audio amp out of my BK 4040A and the audio amp hates that the bnc is tied to earth ground. No 60hz on the output if i hook it up direct to a speaker or a battery powered amp but yeaser when its hooked up to mains powered amp.

[uncle_bob]

that was great think you for the video, but i need to go into an audio amp out of my BK 4040A and the audio amp hates that the bnc is tied to earth ground. No 60hz on the output if i hook it up direct to a speaker or a battery powered amp but yeaser when its hooked up to mains powered amp.

Hi

I'd bet that the real problem is the power supply on the amp rather than the signal generator ....

Bob

[ghinckley68]

so when i use the ebay signal gen hooked to my bench supply no hum. when i use the bk hum. please excuse the amp miising the lm1875t it had a boo boo.  the power supply module is a lm317 lm337 job and just a torid core.
the amp has 10ohms between the inupt ground and(power supply ground and speaker ground)

[uncle_bob]

Hi

If everything is hooked to the same power supply, *and* the power supply has a TON of common mode noise .... you will never ever notice it. As soon as you hook any properly grounded gizmo into the mix ... lots of hum.

For example: Some supplies will have 60V AC on the chassis. The same 60V is also on the negative when it is hooked to the chassis. It also shows up (in phase) on the output in this case. Hook a voltmeter between positive and negative .... no AC to be seen. Hook a voltmeter to a good ground, check either one .... 60V AC ...

Bob