Endless confusion on input selector switches

[garak]

I've been lurking on and off here for a while and one piece of common wisdom I've picked up is that input selector switches should "make before break" to avoid a popping noise when switching between inputs.

But then I was just searching for random stuff about input switches on google, and came across this slightly quirky but intelligent and thorough-seeming article which basically says 1) you should break before make, and 2) you should also switch grounds.

The page I linked to is long-winded, so here are some quotes for the impatient:

"Why 4 pole?" demand plebs, stage left, "Surely we only have to break the live or positive connection, as no current can flow in a broken circuit and earth or ground is common in most audio gear!"
"Because it is inevitable that the disconnection is not of infinite resistance so some residual current may flow, and this will be proportionately more similar to the desired connection if that too has any resistance, which of course IT MUST HAVE", asserts the old scribe.

Whatever types you consider as selector switches it must be break before make type, otherwise you will have two sources simultaneously connected while changing selection which would probably damage at least one of the sources as its output impedance will be much lower than the pre-amp input impedance. Maplin sell a series of 12 pole switches, the one suitable for stereo is configured as 4-pole 3-way. This limits builders to 3 sources, so you might be tempted to use the 2-pole 6-way version and simply common the negative connections as is common practice (groan).

4 poles are needed to do the job for 2 channels simultaneously as it is wise to make and break signal & earth (+ & -) simultaneously.

I've posted about this before, but it was a tangent in another thread and I don't want to resurrect it yet again.

I'm still planning my first ever DIY amp, so I'm trying to figure out the "right" way to do things -- but I keep getting conflicting information!

What's the deal?

[pacificblue]

Originally posted by garak
one piece of common wisdom I've picked up is that input selector switches should "make before break" to avoid a popping noise when switching between inputs.

If switching would lead to a popping noise, it would do so, whether another source is still connected or not.

Originally posted by garak
1) you should break before make,

The article you quote, does not explain, how two sources connected at the same time would lead to the destruction of either, when both are designed for similar voltage and current levels.

Originally posted by garak
and 2) you should also switch grounds.

If the signal ground is the only common ground connection between the components, you should definitely not. If you interrupt all ground connections, different potentials can build up, e. g. through static charging. If that happens, a discharge will take place, just when the connection is made, and that could damage the equipment. That is one reason, why manufacturers usually recommend not to connect and disconnect cables, while the equipment is on.
If the signal ground is not the only common ground connection between the components, switching it or not will make little difference.

Use switches or relays designed for signal level switching. They are optimised for their task. That means look for switches or relays that do not have high voltage and current ratings, but low ones.