Speaker hum

[Cool Dude Ted]

Morning all

Powered speakers fed by a DAC using RCA inputs. Speaker volume set v. low.

Without realising speakers were still powered, RCA cables were swapped to establish if better quality RCAs improved SQ. 

Part way through the switch, the RCA plugs must have accidentally  touched together and produced a hum from the speakers. Noticed immediately and quickly removed the cable.

Powered down the speakers, Reconnected the secomd set of RCAs from DAC. Powered up the speakers again and all good. 

Tried it a second time with original RCAs and all good. Music plays fine; no distortion, etc.

Being a bit paranoid about this. Can I assume no damage has been done to the speakers?

Is this what’s technically known as a “ground loop”?

 

[MF 1000]

It’s technically a short circuit.  When you allowed the inputs of both +ve and -ve of the signal feed into the amp (inside your speaker in your case) to make a circuit joining two separate parts of the amp ….hence the hum.

Normally if this is brief and not involving lots of current (your on the input side of the amp ……on the output ie speaker side it can be deadly to an amp) it does virtually no harm, which is what I suspect has happened in your case.  
We have all probably accidentally done this at one point, just remember to power down the amp/ speaker next time or at least turn the volume control to 0.
 

Ground loops are a different issue altogether.

 

[bigrod]

It’s technically a short circuit.  When you allowed the inputs of both +ve and -ve of the signal feed into the amp (inside your speaker in your case) to make a circuit joining two separate parts of the amp ….hence the hum.

Normally if this is brief and not involving lots of current (your on the input side of the amp ……on the output ie speaker side it can be deadly to an amp) it does virtually no harm, which is what I suspect has happened in your case.  
We have all probably accidentally done this at one point, just remember to power down the amp/ speaker next time or at least turn the volume control to 0.
 

Ground loops are a different issue altogether.

Rule of thumb

“ never swap cables with the amplification powered up”

 

[Cool Dude Ted]

It’s technically a short circuit.  When you allowed the inputs of both +ve and -ve of the signal feed into the amp (inside your speaker in your case) to make a circuit joining two separate parts of the amp ….hence the hum.

Normally if this is brief and not involving lots of current (your on the input side of the amp ……on the output ie speaker side it can be deadly to an amp) it does virtually no harm, which is what I suspect has happened in your case.  
We have all probably accidentally done this at one point, just remember to power down the amp/ speaker next time or at least turn the volume control to 0.
 

Ground loops are a different issue altogether.

Thank you. This is what I was hoping to hear.

The hum only lasted for a max of 1 to 2 seconds.

The irony was that I had connected everything up and it was working well and the decision to try the second set of cables was a complete waste of time anyway, as I couldn’t hear any difference in SQ. It was just something I thought I had to try.

I thought I’d switched the speakers off!!!

 

[Cool Dude Ted]

Rule of thumb

“ never swap cables with the amplification powered up”

Thanks.

It’s something I’ve always known and normally I’d double check. Just slipped up this time.

In simple terms, if things sound all right then presumably I can assume no harm done?

 

[MF 1000]

Yup probably all ok 

 

[Cool Dude Ted]

Yup probably all ok 

Final question - hope you don’t mind.

For the layman/not technically trained, Is there any way of actually testing whether any harm done/problems caused or is it a case of using it and if nothing untoward is obvious and SQ is as expected, then having to assume all is OK and learning not to do it again.

Thank you for the help. It never ceases to amaze me to what extent a simple slip up (not just hifi related) can lead to so much worry - at least for me, anyway. I really should learn to worry about the really important things in life and not stuff like this!!

 

[simon g]

Without knowledge, training, experience and test kit, your choice of listening is the best course of action. If you think you detect a problem then call in a tech.

Try to avoid audiophile nervosa; easier said than done!

 

[MF 1000]

If you can’t hear anything different on a track you know well ….then all is well

 

[bigrod]

Thanks.

It’s something I’ve always known and normally I’d double check. Just slipped up this time.

In simple terms, if things sound all right then presumably I can assume no harm done?

Only your ears will know ‘ if you’ve had the set up for a while  ,,see my previous topic

You need to be sure in your own head 110% otherwise believe me you will never listen to the music , you’ll be listening for something that isn’t there..

 

[luxury_scruff]

Maybe run a track with a sweep into the speakers?

 

[rabski]

You cannot do any damage by what is descibed here. If you damage anything through shorting things out, it would only be speaker cables/connections, and believe me you'll know if you've done any damage that way, because it'll either be unlistenable or silent.

The only possible damage you can do with shorting/connecting/disconnecting inputs is if there is a 'pop' or noise loud enough to be amplified and damage speakers. You can't do any other harm. To do any damage to an input or gain stage, you'd need to overload it to the extent of actually burning out components or similar. An audible hum is about a tenth or less of the actual music signal that would normally go through equipment, so totally harmless.

Too much worrying here. If it sounds OK, it is OK.

 

[Cool Dude Ted]

If you can’t hear anything different on a track you know well ….then all is well

Thank you once again. Much appreciated.

 

[Cool Dude Ted]

Only your ears will know ‘ if you’ve had the set up for a while  ,,see my previous topic

You need to be sure in your own head 110% otherwise believe me you will never listen to the music , you’ll be listening for something that isn’t there..

Thank you. I appreciate your help.

 

[Cool Dude Ted]

You cannot do any damage by what is descibed here. If you damage anything through shorting things out, it would only be speaker cables/connections, and believe me you'll know if you've done any damage that way, because it'll either be unlistenable or silent.

The only possible damage you can do with shorting/connecting/disconnecting inputs is if there is a 'pop' or noise loud enough to be amplified and damage speakers. You can't do any other harm. To do any damage to an input or gain stage, you'd need to overload it to the extent of actually burning out components or similar. An audible hum is about a tenth or less of the actual music signal that would normally go through equipment, so totally harmless.

Too much worrying here. If it sounds OK, it is OK.

Thank you for this really helpful response.

I’ve now reached the point (with all the comments/help received on this thread) that I’m going to stop fretting and just enjoy the music.