Amp Switching?

[tbryanh]

How much time might the relay contacts need to stop bouncing?

[tbryanh]

"Mercury wetted switch contacts do not suffer from bounce, as once the connection is made the mercury maintains a conductive path despite the mechanical bounce. However, mercury wetted switches, along with mercury-wetted relays and mercury switches are prohibited by RoHS because of mercury's toxicity." (http://en.wikipedia.org/wiki/Switch)

It appears wet contacts is the way to go, but mercury ones are prohibited by RoHS.

Are mercury wetted contacts still available?

Are there any other types of wet contact besides mercury?

[Steve Conner]

Yes, you also get soda and beer wetted contacts, as I'm sure Enzo will tell you. Rarest of all are soup wetted, you only get those if a gig in a restaurant goes horribly wrong.

I haven't seen a mercury wetted switch for years. RoHS is only for Europe though, they may still be perfectly legal in the US.

Contact bounce is usually over in 1-10 milliseconds. Bigger relays bounce for longer. You can measure it with a scope, but don't expect it to stay constant over the life of the switch.

Another kind of bounceless switch is a pair of back-to-back power FETs driven by a photovoltaic isolator (PVI). This is available as a module - a "MOSFET solid-state relay" - for lower currents, or you can buy PVIs and make your own. Two FETs are needed to make it bidirectional, since a single FET will conduct in the reverse direction through its body-drain diode, even when it's off.

Finally here's something to think of. Different speakers all add different flavours to your tone, and complement different amps. Maybe you don't want to put everything through one speaker.

[tbryanh]

Contact bounce is 10 ms max, and open and close times are about 50 ms (http://www.mercuryrelays.com/shoppin...&product=35amp).

Since it takes about 5 times longer for the switch to open or close than it does for the switch to stop bouncing, it does not appear switch bounce is much of an issue as far a switching time goes and that wetted contacts are not that helpful for switching time.

It seems as long as the input to the amp is grounded during the switching time and the contact bounce time, then no harm to the amp should occur.

[Enzo]

Bryan, bounce is not your issue here.

[tbryanh]

It seems if this tonebone cabinet switcher can be used backwards, that is all i might need.

Tonebone Cabbone speaker cabinet switcher - introduction

[zzzapfizzz]

Mute input

I'm been thinking about this for some time and one thing I always come back to is:

Do I really need a load capable of taking full load from the amp?
How many watt does the tube amp put out when the input is muted?

[tbryanh]

How many watt does the tube amp put out when the input is muted?

Zero watts. Muting means bringing the signal into the amp to zero volts. Zero in means zero out.

Do I really need a load capable of taking full load from the amp?

When the amp is muted, no load is needed on the amp speaker jack.

An exception to this might be if there is a power surge or drop at the ac mains supply that causes the power supply voltage to the PA in the amp to fluctuate.

[zzzapfizzz]

Exactly, my questions where rhetoric.

So amp switching can simply be made as a simple a input selector.
Although I would use a load resistor on the output "just in case".
Maybe with a couple of milliseconds delayed after input is muted.

[tbryanh]

The sequence is probably: Mute the amp in use > Delay > Switch the amp out and switch the new amp in > Delay > Unmute the new amp.

[Enzo]

The reason you want to protect the non-selected amp output is that while you may mute the input, that doesn;t prevent the amp circuitry from making a loud noise. Ever have something in your house cause a momentary spurious sound? Like when the sump pump motor kicks in, or the furnace, or just some anomaly on the mains. ANd since your input muting will be done at the selector pedal and not in the amp, all it takes is a faulty cord to send a large noise down the system. And we are assuming there is nothing in the effects loops with the potential to make noises.

Zero signal in only means zero out OF THAT SIGNAL.

[zzzapfizzz]

And we are assuming there is nothing in the effects loops with the potential to make noises.

Zero signal in only means zero out OF THAT SIGNAL.

Thanks Enzo. Although I had potential cable hum in my equation I had not enounced for the effect loop.

[tbryanh]

IT looks like HO'S HEAD SWITCHER might work.

Company

[tbryanh]

Also, Weber has the Two Head Amp Switcher.

https://taweber.powweb.com/store/2head.htm