Listening to Alternate Amplifiers through same Speakers

[crosstalk]

You do not have to turn off the amplifiers. Just ensure that you aren't playing music when you switch over.

That's true for passive switch-overs too.

 

[Fantastic]

It doesn't matter if it's actively or passively switched. The issue is with the design of the contacts. If they move a fair amount and can stop the formation of a spark then it is safe even with loud music playing. With inductance in the speaker system , suddenly stopping the current flow can generate larger voltages than normal and hence the possibility of a spark which is basically a momentary conducting path through the air.
I would guess with those power switches like Salzer they must resist the formation of sparks as they handle high voltages ( 390 V peak with 230 V 3 phase mains ) and routinely switch inductive equipment like motors. Maybe costs around 250/- for a 2 pole 3 way type ? Most electrical shops would have these.

 

[Santy]

While I agree that the contact area of the switch has to be maximum and the contact materials should be of good quality, do the speaker level signals work on that kind of voltage to cause a spark? Did you mean electric spark or the blips heard on the speaker while switching?

 

[Fantastic]

Yes ,electric spark. Voltage induced when you shut of a 'current' suddenly is L di/dt . With reasonable inductance (L) and fast di/dt which is rate of change of current , here it will be a few amps to zero in a very short time ( milli seconds), it can generate enough voltage to jump the gap. In normal air you need about 20 kV to jump 1cm . Here the gap will be about 0.05 mm or less as the contacts open. You need only about 100 V or less to jump the gap. This is easy to form. After a spark forms you need to separate the contacts quite a bit to kill it. That's why it does die out after the switch reaches a few mm away.

You can see this in a normal amp with an output relay which has a transparent cover. Play the amp loud and watch the relay ( preferably in a dark room) . You will see the spark if you shut off the speaker with the speaker turn off switch. Can do this only with amps that have a switch to shut off the relay. It might surprise you to see how big the spark can be at times. Remember that it depends on several things. How much inductance you have in the speaker load and the exact moment the relay is shut off. It's an ac signal and so varies a lot in amplitude and also goes through zero numerous times a second. Sorry for the techie explanation , I thought you might want to know what was going on.

 

[jayants]

Yes ,electric spark. Voltage induced when you shut of a 'current' suddenly is L di/dt . With reasonable inductance (L) and fast di/dt which is rate of change of current , here it will be a few amps to zero in a very short time ( milli seconds), it can generate enough voltage to jump the gap. In normal air you need about 20 kV to jump 1cm . Here the gap will be about 0.05 mm or less as the contacts open. You need only about 100 V or less to jump the gap. This is easy to form. After a spark forms you need to separate the contacts quite a bit to kill it. That's why it does die out after the switch reaches a few mm away.

You can see this in a normal amp with an output relay which has a transparent cover. Play the amp loud and watch the relay ( preferably in a dark room) . You will see the spark if you shut off the speaker with the speaker turn off switch. Can do this only with amps that have a switch to shut off the relay. It might surprise you to see how big the spark can be at times. Remember that it depends on several things. How much inductance you have in the speaker load and the exact moment the relay is shut off. It's an ac signal and so varies a lot in amplitude and also goes through zero numerous times a second. Sorry for the techie explanation , I thought you might want to know what was going on.

Hi Fantastic!!

Its nice reading yout posts which are so informative.

Can you please clarify me 2 things. Seeing my stuff (picture uploaded) in my 1st post :

1) Is there any signal / audio loss in the setup?
2) Is it safe using this or it can create harm to my speakers / Amps?

Please revert.

 

[Fantastic]

If I am permitted to 'nit pick' , there is no such thing as 'no' loss with a connection/switch . It should be referred to as 'negligible' loss !
Here you have three contacts in each speaker cable. Two connections for incoming and outgoing speaker cables and one for the relay contact. Hopefully the relay is a sealed unit and so should work well for many years. Do note that everything degrades with time. So contact resistance starts to rise as time goes by . It could be due to contact erosion and/or oxidation.

The contact is acceptable until it's resistance starts to affect the signal audibly. You just need to know that with good relays , the contacts will be good for several years.
Externally the connection of speaker cables to the terminal also undergoes oxidation as it's exposed. It's a good idea to remove the connection every 6 months or so, clean them well and reconnect them. ( Even RCA connections !) A lot of people do not think this is important. It's preventive maintenance.
Take a system that is a couple of years old and remove all connections. You will find them dull. That's oxidation and/or dirt build up.Clean them well till they shine again and reconnect them and listen to the difference.

Safety wise, there should be no problems with your switch. Just ensure that you switch with low level or no signal. Even with high level switching you may get by with no problems. But that unfortunate time when you switch with loud music during a loud transient might cause a spark ( at the relay contacts ) and blow the amp. Will it happen ? Often one gets by without a problem due to 'chance' that you haven't switched when the currents were high. It's like Russian Roulette ! You can't say when !
But like I said all this depends on the relay design and it's switching speed also. It's a possibility , so be safe.

While you don't have free speaker leads sticking out much, it's a good idea to twist the free ends together and solder the end so that a free stray wire does not hang out and cause an inadvertent short. I've seen this happen more than once because we often don't notice a couple of strands sticking out as they are so thin.
Better yet is to solder spade lugs to the speaker leads and use heat shrink tubes to insulate the junction between the cable and the spade lug. Otherwise if it comes loose and rotates, the soldered part could short out with the naked cable on the next terminal. While all this appears to be a long winded explanation , it's application is easy. Always be safe rather than sorry. Blown amps are a pain to get fixed, even if you can do it yourself !
Enjoy !

 

[jayants]

it's exposed. It's a good idea to remove the connection every 6 months or so, clean them well and reconnect them. ( Even RCA connections !) A lot of people do not think this is important. It's preventive maintenance.

Any particular method to clean the connections?

 

[crosstalk]

Gold is the only metal that forms no oxide film on it's surface in air at normal temperatures, meaning that it will never rust or tarnish.

One of the reasons, gold layered discs cost the most. That data layer does not get oxidised unlike the silver or other discs resulting into pinholes several year later.

So if the connectors are quality Gold Plated, they will NOT oxidise at normal room temperature.

Keep a gold and silver ring in two separate areas of a room. Watch how the silver ring will become tarnished in a few week. The gold ring will remain the same. You just need to ensure, that the connectors have been plated with the minimum micron required.

If quality connectors are used, you really do not have to worry about oxidation at least on Gold Plated stuffs.

The amp/deck RCA females need to be cleaned though once a year. Specially for older amps and decks.

 

[jayants]

Gold is the only metal that forms no oxide film on it's surface in air at normal temperatures, meaning that it will never rust or tarnish.

One of the reasons, gold layered discs cost the most. That data layer does not get oxidised unlike the silver or other discs resulting into pinholes several year later.

So if the connectors are quality Gold Plated, they will NOT oxidise at normal room temperature.

Keep a gold and silver ring in two separate areas of a room. Watch how the silver ring will become tarnished in a few week. The gold ring will remain the same. You just need to ensure, that the connectors have been plated with the minimum micron required.

If quality connectors are used, you really do not have to worry about oxidation at least on Gold Plated stuffs.

The amp/deck RCA females need to be cleaned though once a year. Specially for older amps and decks.

Thanks.Mine are all gold plated as uploaded in the picture.

 

[Fantastic]

Suggest you look at about 1 or 2 year old gold plated connectors on some exposed equipment that have never been used. Might surprise you !
You can get plastic caps to cover unused sockets. However they have silly prices for some. They will help keep unused connectors clean for a long time.
Maybe it's easy to fabricate them ourselves ? Always thought about it but never got down to it.

If you clean them regularly I guess plain Isopropyl alcohol and a clean cloth should do. If they are tarnished slightly , you can use something more abrasive. A rough cloth ? Rougher than that would be the green 3M abrasive pads sold in shops for kitchen use. You have different grades of roughness I think. They work well on old connectors. For worse conditions you need to use one of the proprietary solutions in cans like Deoxit etc. It would not be a good idea to use one that is too oily like WD40(!) . That can stay on for a while and collect dust. Wherever possible apply the liquid to the cleaning cloth and use it. A direct spray will deposit too much liquid.