Connecting two amps to one speaker

Is there a risk of damage when connecting two amplifiers to the same speakers?

[burtwatson]

I've wanted to ask you this question for a long time, and figured that a switch box was the only way to do it...thanks for your answer! I have been watching the show since you introduced us to big Nipper and that was early in the series!

[J.LuxeInstallations]

To the Reader. Try to find an integrated amp with a home theatre bypass option. Hegel, Naim and others have this feature. It's a great way to get the best of both worlds without moving speaker cables around.

[paulstubbs]

I've seen some amps where their speaker protector output relay actually puts a short across the speaker terminals when the relay is released - as in powered down, so if you connected that amp to another you'd have all sorts of problems as it would short out the other amp.
Also, apart from the above relay, often lifting the output of a transistor above it's supply rail effectively reverse biases that transistor, many cannot tolerate much of that, and guess what, a powered down amp had supply rails of zero, so any incoming signal over a volt or two is starting to stress them transistors - so Don't do it.
Go out and buy (or make) a speaker switcher. These can be used both to connect multiple sets of speaker to one amp, or as in this case, multiple amps to one set of speakers.

A while ago I wanted to do similar, however one of the amps had an output relay (speaker protector) so I rewired it so that in its off condition it switches the speakers over to the alternate amp. The main downside of this hack is the modified amp needs a extra set of speaker terminals fitted, as inputs to be connected to the other amp.

[Oystein]

I got a dual mono (dual power supply) stereo integrated amp with a dedicated power-amp input (also known as "home theatre", "processor" etc.) Mine also has 2x sub in and out so it can send the signal as pass-thru.
Then you can use it as an dedicated stereo amp for stereo and as a power amp when watching movies etc in surround. Brilliant solution and no switching cables anymore👌

[jamess]

If your AVR has pre-out for L and R can’t you then use your hifi amp to always drive your main speakers

[InsideOfMyOwnMind]

Best short answer is NO. The potential convenience is not worth the risk of damage in the case where damage is an issue and you don't know if it is an issue or not. A speaker switch in reverse will work IF the switch transfers and isolates BOTH positive and negative lines because a bridged amp could get quite angry if commons are tied together.

[donk]

I can strongly recommend Beresford's TC7720 Mk 2 speaker/amp switch boxes if they can still be bought. they have two amplifier inputs and two speaker outputs.
I have my HiFi gear in my man cave, the relevant components on the input side being 2 x Audiolab 8000M power amps, which are in the man cave, and a Denon AVR3805 AV amp which resides in the living room. The speakers involved are TDL Studio 1's and Tannoy DC3000's.
The Beresford boxes, I have to use two because of the mono blocks and bi-wiring, allows me full control of which amp drives which speakers. Most importantly they cause no audible degradation to sound quality and if I recall correctly they are good for about 200wpc.
I paid about £100 each for mine, worth every penny :).
Obviously only one source is powered up at any one time and I always turn the volume down before switching speakers, just as best practice, not because it causes major thumps.
PS, they will take bare wire or spades, but I'd strongly recommend 4mm banana plugs, they are not big units and banana plugs keep things manageable round the back making connections.

[Tsxtasy]

I have a friend with a switch box and we use it quite frequently to a/b test different speakers/amps/etc

[texeast]

Paul, I have a Mcintosh 2 channel with a home theater pass thru option so I can share my front mains with both my Yamaha Av receiver and my Mcintosh. I use the Mcintosh by itself for two channel play back via my turntable or cd player and I use both the Yamaha and the Mcintosh for all my multi-channel play back for satelite tv, movies, and surround sound audio. I have a Oppo 205 4K blur ray player that has a separate internal dac for audio only playback so I use the XLR outputs for that to my Mcintosh for two channel cd playback and I use the HDMI output on the Oppo player to the Yamaha for multi-channel playback. The Yamaha is connected via it's front pre-amp output to the Mcintosh, thus, in all cases I can share my front mains with both amps. It works out great! Another benefit is that even though my Yamaha is a 9 channel AV receiver I gain two more channels by using the front pre-amp to my Mcintosh and therefore I can have a full 11.4.2 atmos arrangement for movies and atmos blu-ray audio discs.

[karledwards]

Do not connect the 2 amps together, there is a very good chance of damage. The output stage is a diode to its power supply. When the powered amp drives the speaker, it will also try to power up the unpowered amp through the output stage diode action and then who knows what will happen. Depending on the specific design of the amps they might live but its a big risk.

[ロクアンドロールしかないでも好きだ]

Although I would use a switch box for the solution I had to mention that I have a Marantz two channel stereo receiver SR4123 I think, anyway putting a headphone cable in there is a relay disconnect with an audible click from the main output so that’s another solution.

[scottwallace]

The first comment was right. The Home Theater bypass feature is what you want. Honestly shocked Paul didn’t recommend this.

[musicman]

You need a Parasound p6 with home theater bypass, or maybe a used p5.

[SPLKINGS]

Thank you as always great content video audio commentary tutorial demo editing humbleness honesty lessons 🙏no one flexes knowledge better than you👍

[therealBozoDjTrump]

Or you could use a light switch has to be a double pole double throw for two speakers not a general single a switch used for your cooker would be ideal

[gotham]

Try to find an old Adcom GFS-4 (not the lower quality GFS-3 or GFS-6) and use it backwards. Be extremely careful to not have both amps selected at the same time.

[warrengday]

Something like this might be better for me—I have the LR line outs from my AV processor going as an input into my hifi pre-amp.

[ianyates]

I blue the output stage of an amplifier by doing exactly that thing, so I have never done it since if I have to do our use of switch box

[SimplyGetPaid]

@1:30 🤔🧐 HMM, NOW THAT’S A THOUGHT.. ..LIKE MY AMP HAS A SPEAKER TERMINAL SWITCH THAT ALLOWS THE CHOICE OF ‘A, B, A+B, OR OFF’..

[wfifa]

Why not buy a second set of speaker cables so that there is one set running from each amplifier? That way, you only swap round the cables at the back of the speakers, not at the amplifier end