Two amps into one pair of speakers

This is a newb question, but my friend has two integrated amps hooked up to his speakers, one McIntosh and a Prima Luna. One is connected with banana plugs and the other with spades. He said this will cause no problems as long as they are not both sending signal at the same time. Is this true. It just seems a little strange to me.



Does his speakers have separate binding posts to send signal to different parts of the speaker? For instance, many speakers have four binding posts in the back. A positive and negative for the woofers, and a positive and negative for the midrange and tweeters. If this is the case, then your friend is bi-amping his speakers. Typically one would want to ensure proper level matching through independent volume controls, or at least one should be able to gain match one amp to the other.

if your friend is using two amplifiers to hook up to the same set of binding posts, he shouldn’t as it could surge the amps, his speakers, and potentially his circuit/house. 

That is pretty dangerous if someone accidently turns one amp on while the other is also on. It will happen one day.

I have a preamp that outputs to 2 amps which are connected to 2 systems, a 2-channel and a headphone amp. I also make sure only one amp is on at anytime, however, I will not have a blowup if I accidently have both turned on. That has happened a few times.


i had a mcintosh speaker that you could connect 2 amps to it! 1 amp powered the woofer and the other powered the mid and highs!

I'm guessing from the OPs description that it's not an issue as long as they are not both sending a signal that it's two amplifiers connected in parallel and not a bi-amp setup.

I have a home theater receiver and Pathos integrated connected to my speakers in parallel, but I have an intermediate toggle switch in the speakers cables so that only one amplifier can send a signal to the speakers at any given time.  The custom switch even has a resistor to provide protection during the switch since it was first used with an all tube amplifier that needed a continuous load.

Not the best practice, the unused amp becomes part of the circuit the working amp is driving. Power is feed back into that amp. Some amps don't like that. 

Have your friend contact Mapletree audio an get an SCC1System Configuration Controller, I had them make me one last year it controls 2 amps and 2 sets of speakers along with 3 inputs, CD, phono preamp and streamer, you can switch from one amp to the other while both amps are on and warmed up you can even have them make the router for 3 amps.

My cost was $450.00 delivered and it only took 2 weeks to get. Just call them and talk to Al Freundorfer


Just because an amp is turned off, doesn’t mean it’s not still putting out some form of current, even if it’s only a few seconds or a few minutes.  I’m not saying it’s definitely an accident waiting to happen, but why take a chance??

It is a very dangerous thing to do unless he is bi-amping his speakers, meaning his speakers have more than one pair of connections suitable for bi-amping.  The outputs of the two amps will NEVER be equal and there may be high circulating currents between the amps, which may cause overheating and protection circuits to kick in.

I did this once in high school. Did not blow anything up but did end up sending smoke signals to the tribe across the river. 

I don’t understand why he’s doing this. Pick an amp and use only that one. They’re integrated amps so use the multiple inputs on one.

I also understand that bi amping a pair of speakers can be done with four amps, two per speaker, if the amps are balanced in some way with an umbilical chord. Honestly, I have no idea how this is done but I remember an old time audio dealer explaining this to me. If it were me, I would get a pair of jumper cables and pick an amplifier.

He should get a switch. The output of amp 1 is present on the secondary side of the output transformers at amp 2. Depending on the configuration, it could be stepping the signal down and getting into the circuitry of amp 2. There is probably a polarized capacitor in there that’s working pretty hard. Even if he can’t get a mapletree switch as another user recommended, a simple switch can be had cheap enough. There’s still a risk with a simple switch - tube amps need to see a load or in some cases a dead short to keep the smoke down. 
It also may be useful to measure the signal with and without amp 2 connected. Depending on the topology it could be affecting the load amp 1 is seeing. 

Accidentally having them both on at the same time is a great way to create memories. You can build a switch pretty cheaply, but need to use a different approach for tube versus solid state amps. Be sure the switch is rated for the current at or above the fuses in your amps

This switch can do 2 amps to one speaker or two speakers to one amp  



The output of amp 1 is present on the secondary side of the output transformers at amp 2. Depending on the configuration, it could be stepping the signal down and getting into the circuitry of amp 2.

I think you meant to say stepping the signal voltage up. Not down.

I also would think the secondary winding of the output transformers, (of the amp that is turned off), would add a parallel impedance load to the output transformers of the amp being used to drive the speakers. (Speaker coils + secondary windings of output transformers of the off amp.)


Either, or.

No need to build custom, use  a Solupeak P2.

There is no sonic benefit to running 2 amps at once and dangers galore.

Neither amp is designed for Armageddon.

Unless one of the amps is rated for above 100W @ 8 Ohms (not unlikely...McIntosh often are), the device suggested by fuzztone is perfect to resolve this dangerous situation.  But note, the PL should be powered off when not in use as the switch presents an open circuit when deselected, and tubes don't like that.  So this is not a good on-the-fly A/B comparator, just a disaster avoidance method.  If the Mac is a very manly model 200W, 300W, 450W...even 600W, then the "friend" should just get banana plugs for both cables and NEVER leave them both connected.

"Accidentally having them both on at the same time is a great way to create memories."


If you have no kids, no grandchildren, no drunken dates, impulsive guests, EVER, you might be ok for a while.


The peanut gallery chiming in here...  :)

If I were to use two amps on a speaker that had lugs for the bass module, and separate lugs for the mid + tweeter module, I'd find a cleaner way to bi-amp.  I'd use this - on the Pass Labs XP-30 and XP-32 preamps, there is a master volume control on one set of XLR/RCA outs, then there is something called a slave pair of XLR/RCA outs.  This "slave" output, its gain or volume control is controlled by a pair of small knobs on the front of the preamp; one can fine tune the "slave" output so that if one is using a less powerful amp for the mid/high speaker module, one can trim the "slave" gain/volume controls to obtain the right balance between the bass and mid/tweeter modules.  It's a very trick feature built into these preamps.  As the saying goes, I'm not sayin', I'm just sayin'...  :)

Just to clarify what one poster stated: you CAN run signal from one pre amp into two amps (via simple Y splitter), or?

Before I got my custom switch built by an EE friend (it's setup to protect a tube amplifier at all times), I used 10AWG Blue Jeans speaker cables with the welded banana plugs and just swapped cables back and forth with my home theater receiver.  I'm still using the switch and it's the barrier to upgrading speaker cables as there's more cables required and a clear sub optimization in the setup.

There are inexpensive speaker/amp switch boxes available on Amazon. I got Bryan from to build me a custom switch box which allows me to route two amps to single set of speakers and a sub. Added benefit, it has 4-pin balanced xlr taps for running hard to drive headphones. 

BAD idea!!   The output impedance of a power amp is a fraction of an ohm, so do you really want to connect both of your amps to nearly a dead short?  Depending on the amp design, when a modern amp is turned off, it likely has a protection relay that disconnects the speakers from the amp output.   BUT if you have an older amp, or maybe an inexpensive amp without a relay, then the output transistors are connected whether it is on or off.  It really depends on the design.  

And mistakes happen... what if you accidentally turn both amps on?  

Simply a bad, bad idea!!  

Smoking in bed.

Why is this thread even on Agon, the 2nd amp for a gaming system?

The tube amp won't be hurt if off. Tubes cannot be hurt because it has plates and need electrons to move via heat.  Not sure what would happen with the MAC because of the back EMF through the transformers. . In any case like others has said it is very risky and a bad idea.