Should the power be off every time changing cables?

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

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

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
 

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