Should the power be off every time changing cables?

It really is a good idea. Better safe than sorry. I always do. Just not worth the risk. With speaker cables its easy to short out the contacts.

Don’t ever do that with RCA cables. It may be ok with XLR cables, but personally I wouldn’t risk it with those either.

RCA cables make the signal connection before the ground connection upon insertion, and break the ground connection before the signal connection upon removal. So when inserting or removing those connectors there will be a brief instant when the signal connection is present without a ground reference, other than the ground reference that may be provided via the AC safety ground wiring and whatever impedance in the components connects circuit ground to AC safety ground. Depending on the specific designs, the resulting sound can be highly unpleasant for both you and the equipment :-)

XLR connectors make the ground connection before the signal connections upon insertion, and break the signal connections before the ground connections upon removal. So it may be ok to do what you are proposing in that case.

Regards,
-- Al

Definitely turn them off.

The amplifier is definitely a component you want to keep off during any cable changes. It and the speakers are the most likely to have ballistic failures (as in, things fly) if you do something bad.
All other gear will be OK, with low voltages and low currents.

@almarg  and others...   To clarify, component off or system off?  If the component (for example Pre to Amp), then the Pre or the Amp or Both? Thanks.

Power should always be off otherwise you can blow out a woofer or worse.

Where is Charles Darwin when you need him ?

To clarify, component off or system off? If the component (for example Pre to Amp), then the Pre or the Amp or Both?

@david_ten 

Hi David,

In the case of RCA line-level interconnections, at least, and particularly if the components involved are solid state, I would strongly advise turning both of the interconnected components off before doing anything with the cables. And that applies to connections between source components and preamps, as well as between preamps and power amps.

As I alluded to earlier, when an RCA connector is inserted or removed there is a brief instant during which the signal connection between the two components will be present, while the circuit ground connection between them will not be present. During that instant the signal voltage that will be seen by the component can be just about anything, depending on how circuit grounds and AC safety grounds are interconnected within the two components, and depending on how much AC leakage to chassis occurs within the power transformers of each component. (Such leakage normally occurs to a very small degree, and apart from being a possible contributor to ground loop issues would usually would only become consequential under this kind of circumstance). And many transistors, that might be used in the output stages of line-level components, have very low "absolute maximum ratings" on how much voltage their internal junctions can withstand in a particular direction (e.g. only 5 or 6 volts or so in many cases, if it occurs in the direction of "reverse biasing" their "base-to-emitter junctions").

Also, even if the cables in question are between a source component and a preamp, as I'm sure you are aware best practice is to turn a power amp on last and off first. So if the preamp is to be turned off for purposes of changing its connections to a source component, the power amp should be turned off (first) anyway.  

Best regards, and happy New Year!

-- Al
 

Good Lord! Does anybody ever read the questions any more?

I wonder I still need to turn off the power amp when I change IC cables between preamp and components.

No. Of course not. As anyone above can tell you the instant they come to their senses. You just need to change the source selector on the pre-amp.

I am actually ashamed right now to even be on a site where this is even in question. That's it. Done for the night.

You can make a lot of mistakes with an amp OFF, and it won't blow anything up. You make ONE mistake with an amp on, and it could be GOODBYE!  :) 

Miller’s suggestion about changing the preamp’s input selector switch while disconnecting RCA cables between the preamp and a source component will usually work ok, assuming that one remembers to do that.

But if the source component is solid state I would still not feel entirely comfortable about the possibility that depending on the specific designs a large transient could be briefly injected into the output of the source component during the instant the connection is broken, as I described earlier.

Also, if the preamp has a built-in phono stage it would be best to not set the input selector switch to phono mode when disconnecting RCA cables from a line-level source. If that were done it is possible that crosstalk of the brief transient I referred to could occur into the input of that phono stage, where it would then be greatly amplified by the phono stage, ultimately resulting in a significant thump in the speakers given that the preamp and power amp would still be powered up.

Regards,
-- Al

If muting is available does this mitigate risk?

I’m not arguing with the safer practice being to power down gear first but agree with the OP, it’s inconvenient, especially if tubes are involved.  

I’m guilty of doing IC and speaker cable changes while gear is powered up (though not speaker cables on a powered up tube amp).

My practice has been to switch preamp selector to an unused input (if changing an IC), turn volume to zero, and activate muting on both preamp and amp. Less risky?

My practice has been to switch preamp selector to an unused input (if changing an IC), turn volume to zero, and activate muting on both preamp and amp. Less risky?

Certainly! The only remaining risk that occurs to me is the one I described in the second paragraph of my preceding post, which IMO might in some circumstances create at least a slight risk of degrading the long-term reliability of the output stage of the source component.

Best regards,
-- Al

Thanks, Al.  

Wish I had read this thread a few months back. A couple of weeks ago, I was having a problem with my left mono block tube amp...no sound. So, I switched in my ss tube stereo amp ( which I run off my second output from my preamp). I had switched off my tube amps and had made the speaker cable change and the ic cable change while all amps were off. Nonetheless, I figured why not take a look at the ic's to the tube mono block amps ( which were off)...this while the ss amp was playing. NOT a good idea at all! 
The crackle through the speakers was pretty scary! Luckily, no damage done, but a lesson learned. Best to have ALL gear off when changing cables.

Playing with electrical components -always best to play it safe. Power off.

Real world-I've never been to a demo/show, where gear was turned off, with the exception of power cables.
This has been with the presence of the amp/gear designer standing next to their creation.

https://m.youtube.com/watch?v=byVrloNIcKQ

Volume down, source not playing, obvious precautions.
Also experienced hot swaps with side by side speaker comparison- music playing, quick swap of speaker cables to hear differences. 

Living on the edge!

Thanks for all advice.
Normally I turn off all gears before changing any cables, but I am about to play around with different speaker cables and IC cables with different power amps and preamps, and found out that it is hard to compare the sonic differences before and after changing cables if I power off, wait for a few minutes, and then power on.
I will follow the safe route most of times, but if I need to, I will change cables with preamp set to mute and input selector set to an unused input.

by switching the input you protect speakers not amps.
by turning the power off you protect everything .
the choice is yours 

Another voice from the "turn the system off" camp.