# Relay Switching of Speaker/Amp Combos



## fractile

I want to be able to switch my main stereo speakers between the surround receiver and vac tube stereo amp.

Will a 120V/10A 60Hz relay work for audio with high quality? An alternative is a multi-pole ceramic and silver rotary switch.


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## WooferHound

Tube Amps do not like to operate with their outputs being disconnected, they will over heat. The switching that you use will need to provide a Dummy Load to your tube amp when it is not being used or you will burn it up.

Is there a reason that you don't want to use a standard switch instead of a relay ?


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## fractile

WooferHound said:


> Tube Amps do not like to operate with their outputs being disconnected, they will over heat. The switching that you use will need to provide a Dummy Load to your tube amp when it is not being used or you will burn it up.
> 
> Is there a reason that you don't want to use a standard switch instead of a relay ?


Yeah, I'd thought of a dummy load or :yikes: not turning it on without the speakers connected.

The idea with relays is to have an enclosed switch, avoiding oxidation of the contacts. Another reason is that the control switch can be placed anywhere without having longer power cables to the speakers. The thing I was wondering about 60Hz relays is if they'd work well at high frequencies; for example, some industrial power supplies operate at 480Hz or something, so I assume they'd need a relay with that spec.

Would I need to cascade switches or relays to put the dummy load in-circuit during the switch-over?


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## WooferHound

A relay is fine for switching speakers. I would use a DC relay powered with a Wall-Wart but a 120vac relay would be fine. Use a relay with the proper contact ratings to match your speaker wire to maintain full quality.
7 amps = 18 ga
10 amps = 16 ga
15 amps = 14 ga
20 amps = 12 ga
30 amps = 10 ga
If you use a 4 pole relay you would be able to do the speaker switching and add the Dummy Load all in 1 device & operation. If you need a drawing of the relay wiring I could make one up for you?


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## fractile

WooferHound said:


> A relay is fine for switching speakers. I would use a DC relay powered with a Wall-Wart but a 120vac relay would be fine. Use a relay with the proper contact ratings to match your speaker wire to maintain full quality.
> 7 amps = 18 ga
> 10 amps = 16 ga
> 15 amps = 14 ga
> 20 amps = 12 ga
> 30 amps = 10 ga
> If you use a 4 pole relay you would be able to do the speaker switching and add the Dummy Load all in 1 device & operation. If you need a drawing of the relay wiring I could make one up for you?


That's a good point about using a DC-controlled relay. The ones I was looking at had 12vac control voltage, and I can imagine that could induce some noise into the signal. The 120vac I mentioned was for contact rating.

If you could show me a drawing of the circuit it'd be appreciated. Well, now I can almost see it, using one 4-pole relay per channel. I had been looking at a single-throw relay (don't ask) :doh: If I'm right, connect 2 poles to a speaker and have the relay "throw" it between the two amps. Then jumper the tube amp terminals to a second pair of throws, with an 8Ω 100W resistor (for a 100W amp) across the other 2 terminals. A picture might be good for future readers, if you don't mind. Thanks for making me think!


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## WooferHound

OK I made 2 drawings
The first drawing uses two 4 pole double throw relays, one for the left channel and one for the right channel. The picture shows only the Left Channel using 1 relay, you would need a second relay wired the same way for the Right Channel. This method totally isolates your amps from each other and is completely safe









The second drawing shows both channels using a single 4 pole double throw relay. using this method ties all the Negative speaker connections together. This should work in most cases. To make sure you would need a multimeter to make sure that all the negative speaker connections are connected to the Chassis ground of your amplifiers. Each negative connection needs to read less than one ohm to the metal chassis of the amp or do not try this method.









Please ask questions if you don't understand . . .


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## fractile

WooferHound said:


> OK I made 2 drawings
> The first drawing uses two 4 pole double throw relays, one for the left channel and one for the right channel. The picture shows only the Left Channel using 1 relay, you would need a second relay wired the same way for the Right Channel. This method totally isolates your amps from each other and is completely safe
> View attachment 29828
> 
> 
> 
> The second drawing shows both channels using a single 4 pole double throw relay. using this method ties all the Negative speaker connections together. This should work in most cases. To make sure you would need a multimeter to make sure that all the negative speaker connections are connected to the Chassis ground of your amplifiers. Each negative connection needs to read less than one ohm to the metal chassis of the amp or do not try this method.
> View attachment 29829
> 
> 
> 
> Please ask questions if you don't understand . . .


Ok, thanks; your two-relay method is a cleaner way to to it than I thought up. The one-relay way will not work for me; my tube amp (Manley Snapper) has a fully balanced circuit and a speaker terminal cannot be grounded. Thanks for taking the time and your better circuit.


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## fractile

I should clean it up by saying that an 8Ω, *100W* resistor, at least (for a 100W amp), should be used; not 10Watt (as originally posted). I really should be careful about skimping on details like bypass resistors on expensive equipment. What if your cat walked across the knobs and sent 100W into a 10W resistor?


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## fractile

On a side note about power-handling (and why I upgraded my 100W ProAc Studio 100's to 200W Manley SGM-10's (Tannoy concentric) is because I was listening to some piano music with the level above 1/2 into "100W" (someone wrote that these 100W tube amps can put out, actually, 200W) Manley Snappers feeding the ProAc's. A piano can have a very sharp attack transient (think square wave); it is a hammer hitting a tense string, and a tweeter in one of the speakers went FZZZT! for a large fraction of a second (the speaker didn't break, it just hit something beyond linear it could not deal with ;-).

The ProAc's are beautiful speakers and can really sing when given a good signal; people recommend running them with a Macintosh 2105. That might suit them; My Manley Snappers are running a balanced signal from end to end, and powered by a Furman IT-20 balanced (+/-60vac) power supply.

The Manley ML-10 monitors... EveAnna told me I'd appreciate them more in time. I haven't A/B'd them against million dollar speakers, but for near-field monitors the timbre and coherence are perfect. I try to avoid fanaticism, but i really like dual-concentric speakers; I even found a new pair of vintage Fostex RP60 (RM765)'s for surrounds. I don't have the part numbers handy for the Thai-made "closest to Tannoy SGM-10 clones" I found. I'll get to those later.

And yeah... I have a set of Fostex T40RP (regulated phase) headphones.


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## Havor

Hi, I want to do something similar but with my Marantz SR6011+ Rotel RB-870BX and a low power class D amp (SMSL SA-98E)

The reason is twofold, first I work shifts and watch TV/films ad odd hours, and I don't wane wake up the whole house, and just use 2.0, instead of the whole surround including the two subs.
Next to that, the Marantz and Rotel uses about 500W idle, just turned on, that's a lot of heat that we don't need in this hot summer, SMSL uses about 4W idle

I have some questions I wane to ask you guys, do you need to switch the plus and minus, or just the plus (_or minus_)?









Switching one wire would have the benefit of not sending the signal twice true relays, downside, signal echo?

Would a switch module like this work?


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