Connecting 2 amplifiers to one set of speakers: making an amp/speakers selector switch

36 Replies

Gallery Recreation Renovations

Is it possible to use two amplifiers or receivers with just one set of speakers? This question gets asked a lot. There’s a numbers of reasons for trying to do that. You could have a home theater receiver for movies and a dedicated stereo amp for music (like I do) and not enough space to accommodate two separate sets of speakers for each amp (or a wife, who vetoes this solution). You could have one big, powerful “performance” amp for active or loud listening, and another, smaller amp that draws much less power for background music and nighttime listening, when the family’s asleep and loud music is a no-no (like I do in another room). Or you simply want to quickly compare 2 amps (like we do very often here at AR), A/B test them without having to make long pauses for switching the amps off, disconnecting speaker wires from one amp and connecting them to the other amp.

So, again, is it safe to connect two amps to one set of speakers? If you do that directly, simply run speaker cables from both amps to your speakers – definitely not. If you do that, and then turn on both amps, you will fry at least one of them, possibly both. Even if you think you’ll be extra careful and always remember to switch off one amp before switching on the other, and you actually are that careful, sooner or later someone else will try to listen to some music using your gear – and poof goes your nice amp. This exact thing happened to a friend of mine. He was careful, but his daughter wasn’t.

Is it possible to use a speakers selector switch in reverse for this? Well, not really. There are three problems with the majority of speaker switching boxes. One is that they usually have common ground. You do not want to have common ground between two amps, this could negatively affect their performance (and sound quality) and in some cases also case damage – there are amps that have fully balanced outputs and cannot have common ground between speaker connectors, for example some Class D amps. Another problem is that many speaker switches have protection and/or impedance matching circuits, and those could also affect sound quality, so you do not want that. But most importantly, most (actually almost all) of these switches allow to select more than one set of speakers at the same time – which becomes selecting more than one input amp when you use the switch in reverse. And if you do that, it’s exactly like directly connecting two amps to one set of speakers – if both amps are on, at least one of them will get fried.

But we’re on the right track now: what you need is indeed a switch – but it has to be a specific type of speaker level switch in order to accommodate 2 amps. Here’s what it needs to do:

1. It needs to be a “break before make” type (break connection to one amp before making a connection to the other amp) to prevent both amps from being connected to each other even for a split second – it should make it absolutely impossible to select both amps at the same time.

2. It needs to switch all 4 connections: L+, L-, R+, R- separately (no common ground).

3. Ideally it should not have anything else inside except binding posts, wires and the switch itself (no resistors, no protection circuits, impedance matching etc.).

With a switch that meets all the above conditions, you can safely connect two amplifiers (or two receivers, or an amp and a receiver) to one set of speakers. They can be on at the same time and you can switch between amps without having to turn them off.

There is one exception: for many tube amps it is very unhealthy to be on with no load (no speakers connected), so If you have a tube amp, better get another set of speakers.

The only commercially available switch I know that does all that is Beresford TC-7220. Unfortunately that switch is quite expensive – it costs $120, which is a lot for a box with a few binding posts, passive switches and some wire. Still, it is pretty much the only thing you can buy that will do the trick safely, so if you want a ready-made solution, that’s what we can recommend. But if you don’t want to spend $120 on a switch, you can built one yourself. Which is exactly what we did here at AR.

BUILDING AN AMP/SPEAKER SWITCH

The simplest and cheapest option is to built a switch box using a 4PDT switch. We’ve built two, the total cost is around $10-30, depending how cheap you can get the switch and what type of binding posts and enclosure you use. Here’s how we built one of them. It’s the more expensive one because of banana plug-ready connectors; if you use spring-type connectors, it becomes very cheap.

You will need the following parts:

1. One 4PDT switch or two DPDT switches (we recommend toggle switches)
2. 3 sets of stereo speaker binding posts
3. 1-1.5 m of speaker wire to connect binding posts to the switch (6 short sections)
4. An enclosure
5. Mounting screws and/or glue

Depending on the type of switch and binding posts, you might need solder wire and a soldering iron to connect internal wiring. Also, depending on the enclosure you use, you might need tools to make walls, drill holes etc.

We used an enclosure of a nice-looking but crappy speaker as a housing for our switch.

We removed the driver and the front wall, and the bass tunnel from the back. As a result, we had a nice box without one wall and with a round opening in the opposite wall.

We cut the missing wall from plywood and made holes for binding posts. We used speaker wire to connect the binding posts to the switch.

A 4PDT switch has 12 connectors, usually 4 connectors in 3 rows. In this application, the two outer rows are for amps. The row in the middle is for speakers. Like this:

A1 L+ A1 L- A1 R- A1 R+
SP L+ SP L- SP R- SP R+
A2 L+ A2 L- A2 R- A2 R+

A very important thing when connecting wires to the switch and binding posts: make sure that each wire is tightly secured with a screw or well soldered and there are no loose strands that could cause a short. If you solder the wires to connectors it’s best to isolate them with heatshrink after soldering. Test all connections after soldering for conductivity and possible short circuits between connectors. If you short connectors you will fry your amp, so be extra careful.

We installed the switch in the opening left after removing the bass tunnel.

Then we fitted the rear wall with binding posts.

Wires sometimes get loose during assembly, so at this point all connections of the switch should be carefully tested again for short circuits. Make sure you do that before connecting amps.

That’s it all done. This switching box works for either two amps connected to one set of speakers, or two speaker sets connected to one amp. You can select only one position at the same time. If you want a switch that will accommodate two amps and two sets of speakers (exactly like the $120 Beresford does), you will need one more 4PDT switch and one more set of stereo speakers binding posts. In that scenario, the connections from the amp binding posts to the outer rows of the first switch remain the same; the first switch’s connectors marked SP XX in the above table (the middle row) are connected to the corresponding connectors in the second switch, and the outer rows of the second switch are connected to speakers binding posts for two sets of speakers. The first switch switches between amps, the second switch switches between two speaker sets.

The whole process (including making the enclosure) took us about two hours. The result is a functional, safe, and aesthetic switch that allows to safely connect two amps to one set of speakers and switch between them even when the amps are on, just like the $120 Beresford switch, but ours costs only $22 in parts (again including the cost of speakers that we gutted to make the enclosure). The most expensive part was the speaker wire binding posts – the white ones cost $12. We used them only because they were already sitting in our drawer. There are much cheaper alternatives (both spring-type and banana plug ready) and if you use those, the total cost will be closer to $10.

EDIT (25.05.2019):

After 2 years of very heavy use, our switchbox broke. The 4PDT switch itself stopped working, contacts inside got loose or broke. It did not make short, just stopped making a connection.

Our switch was really abused, we do a lot of A/B tests, during which we do 20-50 quick flips in one hour (in addition to using the switch normally every day). We expect that with normal use (1-2 flips per day), such a switch should work properly for at least 5 years. But if you notice that it starts getting loose when you flip it, or doesn’t always make a good connection, it’s best to replace the 4PDT switch at once.

36 comments

  1. François

    Hello Rafal,

    I would like to create a selector-switch box for 3 amplifiers to my set of speakers.
    I’m using the speaker outputs A and B on every amplifier.
    The set of speakers includes : 2 columns (high-medium), 2 bookshelf speakers (med-low) and one subwoofer.

    Using the same principle that you’ve described for 2 amplifiers and 1 pair of speakers,
    – do you think this would be safe,
    – would you recommend it,
    – what would be the schema to make it.

    Very best regards.

    François

    1. rafal lisinski Post author

      Hello François,

      Adding switches in the signal path can always degrade the sound a bit. But with switches of this type any change in sound should be minor or even inaudible. My way of switching is safe for both amps and speakers, so it can be used also in your scenario.

      To accommodate 3 amps and 2 pairs of speakers you can daisy-chain 3 switches made according to the same principle as my switch. Or actually 2 switches like mine to switch between the amps and one cheap, ready-made speaker selector, because switching between speakers is a less sensitive issue and you can have both pairs of speakers playing at the same time and, unlike amps, they can have common ground. Unless one of your amps does not tolerate that, in that case it is better to use my (safer) switch.

      So we have:

      Amp A, Amp B and Amp C
      Speakers A and Speakers B
      Switch 1, switch 2, switch 3

      Remember that my switches can work both ways, this means that they can have either 2 inputs and 1 output or 1 input and 2 outputs.

      Connection would go like this:

      1. Switch 1: 2 inputs, 1 output. Amp A and Amp B are connected to the inputs of switch 1. It selects between Amp A and Amp B.
      2. Switch 2: 2 inputs, 1 output. Amp C and the output of switch 1 are connected to the inputs of switch 2. It selects between Amp C and whichever amp has been selected with switch 1 (Amp A or Amp B).
      3. Switch 3: 1 input, 2 outputs (this one can be ready made if all your amps can handle common ground and more than one set of speakers connected at the same time). The output of switch 2 is connected to the input of switch 3. The outputs of switch 3 are connected to Speakers A and Speakers B.

      With the above system, switches 1 and to select amp A, B or C (only one at the time). Switches 1 and 2 MUST be like the one I used in my project. Switch 3 selects speakers A and/or B. This one can allow to select both speakers and have common ground if ALL your amps can handle that. If any of your amps can’t handle that, use the safe switch (like mine).

      That covers amps and stereo speakers. To accommodate subwoofer I would have to know what kind of subwoofer you’re using and how it is connected to each of your amps. If it’s a passive or active “pass through” subwoofer that you connect to the speaker outputs of an amp, and then connect stereo speakers to the subwoofer – you can connect it the same way to one set of outputs of switch 3. If it has a different connection method, I’d have to know the details.

      Hope that helps,

      Rafal Lisinski

  2. Stephen

    Excellent solution!

    I have a slightly different question and want to be certain I have it right.

    2 receivers/amps, 2 pairs of speakers Utilizing Channels A & B.

    The first receiver is Surround-Using Channels A & B, + Klipsch Subwoofer.

    The second receiver, Marantz 2252, Using Channels A & B (same speakers), but no subwoofer.

    Thank you so much for the knowledge you’ve already imparted.

    Stephen

    1. rafal lisinski Post author

      Hi Stephen,

      Glad my article is helpful!

      Now to your specific situation. I understand that the subwoofer is not important because you only use it with the surround receiver and you only need to connect speakers A and B to two receivers. There are two possible scenarios:

      1. You use either speakers A or speakers B (but never both at the same time) with each receiver
      2. You use both speakers A and speakers B at the same time with each receiver

      I understand that your situation is the second scenario.

      Also, one of your amps is a stereo receiver (the same signal goes to speakers A and B) and the other amp is a surround receiver (different signal goes to speakers A, different to speakers B). That is also important. That means that even if you ALWAYS use both speakers A and B, they cannot be connected to the switch in parallel, because only the stereo receiver uses a parallel connection. The surround receivers actually works as two separate amps (front speakers amp and rear speakers amp). I understand that in the case of the surround receiver speakers are connected to front and rear outputs, and not to front A and front B outputs (that would be a very different connection and actually similar to using a regular stereo amp).

      In that case, the best solution is to use two switchers like the one I described. One switch switches speakers A, the other switches speakers B. Unfortunately there are no simple, sturdy and cheap mechanical toggle switches (that I can find) that would allow to switch a total of 8 separate signal lines (and that’s how many you get with 4 speakers), which is why you need a separate switch for each pair of speakers. It’s not a big problem, you just flip 2 switches instead of one. But it does mean two times the work, materials and time needed to build the switcher.

      The two switches and corresponding speaker binding posts can be fitted into one enclosure, obviously it would need to be larger.

      This solution (2 separate switches for speakers A and speakers B) will work perfectly fine in other scenarios, for example with 2 stereo amps that use speakers A and B, or with a stereo amp and a surround receiver where the speakers are connected to front A and front B outputs of the surround receiver (as opposed to its front and rear speaker outputs). But in some cases a simpler solution would suffice.

      Hope that helps. Let me know if you have any more questions and good luck!

      Rafal Lisinski

  3. Eric Martin

    Thanks for this post
    Managed to put a switchbox together this afternoon and It works a treat, no more ‘protect’ mode.
    Total cost here in Aus, including enclosure was around $17.
    Very happy with the result.

    1. rafal lisinski Post author

      Hi Eric,

      Glad my post could help. I’m curious to see your switchbox, send me a photo if you can. My email is in the ‘Contact Us’ tab.
      So do I understand correctly that you were using a different switchbox before and it was sending your amp into protect mode? What sort of switchbox was it?

      Rafal Lisinski

  4. Steven

    I am currently building one of these and had a question. Could this used to use one turntable with two amps subbing RCA jacks? I see no reason why not do you?

    1. rafal lisinski Post author

      Sure, but it’s overkill. You can also use a cheap ($2) AV switch for that purpose. Search for “AV RCA Switch Selector Box”. Common ground between channels is not a problem with turntables, and you can use the 3rd RCA socket to connect and switch the grounding wire.

        1. rafal lisinski Post author

          I disassembled 2 cheap passive AV switchboxes that I happened to have at home and I did not find any resistors or other components inside that would alter the signal, just sockets, a PCB with tracks and a switch. The quality of components if as poor as can be expected, but there are no wires, so it should primarily affect the switch durability, not signal quality. At least it shouldn’t do any more harm than an average quality cable would.

          I used one of these switches for a turntable in my decent (but not hi end) system without any problems or audible signal loss. I used the video socket to connect (and switch) turntable ground. But whether such a switch degrades the signal could vary depending on the quality of the audio system (there could be an audible difference with a hi end system – just like with better and worse quality cables).

          Active switchboxes are a different story, in my experience they do degrade sound and have their own background noise.

          Of course, toggle switches can also be used for this purpose. A 4PDT switch has the right number of connections (L+, R+, common ground, turntable ground). Common ground is not a problem with turntables in most cases. But i still think building a switchbox with a toggle switch is overkill for switching the source-amp line (including turntables), considering that a simple AV switchbox does the job and it’s very cheap. Unless it doesn’t work (or causes signal degradation) in your system.

          BTW, resistors should not degrade signal quality (unless they’re poor quality themselves), they should simply make the signal weaker, quieter. That, of course, is not preferable in the case of signal from a turntable, which is very weak to begin with.

    1. rafal lisinski Post author

      Hi Adam,

      Buying the speaker switchbox you mention might be an option but:

      – that speaker switchbox costs almost exactly the amount we paid for all parts (including the enclosure) of the switchbox in our article, since then we’ve built another switchbox that was 30% cheaper because we’ve found cheaper sockets; of course that depends on the cost of parts in your area but you would still have to buy some parts you will need to make the conversion: at least a 4PDT switch and probably some wires;

      – you would still have a lot of work to do, you would have to replace the two switches that are there now with the switch we recommend (a 4PDT switch), and fitting a 4PDT switch in an opening left after one of those flat cradle switches might be difficult and it might turn out that you can’t fit a 4PDT switch with screws for wires (it’s quite large and might not fit in this enclosure) and have to use a smaller switch that you have to solder wires to – soldering 12 wires is more tedious;

      – you will probably still have to rewire the speaker wire connectors: this switchbox probably has common ground (they usually do) which is OK if you switch between speakers, but should be avoided if you want to switch between amps;

      – you would still end up with a switchbox that has poor quality wire connectors (these spring-type connectors in the back – we do not recommend them, they are a problem if you use a wire that’s too thick or too thin for them and they break more easily than even the cheapest screw-type connectors).

      That’s the potential problems I can think of from the top of my head. In short: yes, converting that speaker switchbox should be doable, but it might not be easier or cheaper than building a switchbox from scratch. Buying parts could be cheaper depending on the prices in your area, conversion of that speaker switchbox might involve a bit less work or not, depending on its internal wiring and how easy or difficult fitting a 4PDT switch would be.

      Hope this helps. Good luck on your project. If you have more questions, drop me an email, and let me know when you’re done, I’ll be curious to see a photo of you switchbox (whether you build it or convert the one you’ve linked).

      Kind regards,

      Rafal Lisinski

  5. Petr

    If wired in reverse, will any of this product accomplish the same as your build?
    https://www.amazon.com/Stereo-Speaker-Selector-Switcher-Combiner/dp/B00CZNXKRA – I feel like this one might be the closest device to yours.
    https://www.firefold.com/stereo-2switch?gclid=Cj0KCQjw9NbdBRCwARIsAPLsnFZsZw8vn3YmlP2yhEH3RpnuOZEPaccx-JE-zKMrF6DJHOwPyEoXKu4aAipXEALw_wcB
    https://www.amazon.com/Stereo-Speaker-Selector-Switcher-Combiner/dp/B0184M4TVQ
    https://www.amazon.com/Switch-Stereo-Receiver-Speaker-Selector/dp/B00YNUICRQ/ref=sr_1_fkmr1_2?s=electronics&ie=UTF8&qid=1538688845&sr=1-2-fkmr1&keywords=ab+stereo+speaker+selector

    This one seems a bit different https://www.monoprice.com/product?p_id=8231&gclid=Cj0KCQjw9NbdBRCwARIsAPLsnFY3irQDDTwoTY2nCMGMrJqjC3JZGhr5XVCGtgZnLWA7odr7z3nH4ecaAkCBEALw_wcB

    If any of the above would work, could you please let me know advantages/disadvantages vs. yours and Beresford TC-7220? I really appreciate your insight. A tube amp just arrived and I’m looking forward to hooking it all up.

    1. rafal lisinski Post author

      I’m afraid the first 4 options would not work One reason is that it’s quite likely they all have common ground. It’s not certain, but it’s simply much easier and cheaper to build a selector with common ground and it is not a problem if it is is a speaker selector. But can be a problem if it is an amp selector. More importantly, they have the A+B selection possibility, which is what you select if you want to fry your amps (it would connect amps to each other and fry output transistors).

      The fifth option (Monoprice) is theoretically designed to work with 2 amps. But I would have to see its internal wiring to confirm that it does not have common ground. Also, putting an attenuator (volume control) in line is a good way to degrade the sound, so I would not do that. On top of that, it has impedance matching (also bad, unless your amp can’t handle a 4 ohm load and you have to use that.

      In short, I would not use any of these switchboxes to switch between amps.

      Also, many tube amps should not work (be turned on) without load (speakers connected). Make sure that yours can before you use it with a switchbox – it effectively disconnects speakers.

    1. rafal lisinski Post author

      Hi Remigiusz,
      The price is reasonable compared to the Beresford switchbox. Separate switching of L and R channels is less convenient (you need to flip 2 switches instead of one), but works just as well. The big question is whether it switches ground as well (like our switch) or has common ground (bad). Unfortunately I don’t see an answer to this in the description or in Q&A. I think there is a good chance that the ground is switched in this one, but I can’t be sure without testing it. Try asking the seller, maybe you’ll get a clear answer. But even if he confirms that ground is also switched, I would still test it before using.

  6. Jeremy Irwin

    Great article! I’m definitely going to try this build for A/B testing amps.

    Here’s another similar but much more complex problem. I’ve got a display wall of all of the early Mac tubes (49-70) which don’t have the issue of risking damage without load. My dream is to be able to select an amp (or set of mono blocks) to listen to on my main system from a central wall mounted switch box. The perfect scenario would be to control the power from that switch as well so that as I switched one, it would power it up and cut the power to the previous. (11 total- 8 stereo pairs, 3 stereo amps). Any thoughts?

    1. rafal lisinski Post author

      Now that is a challenge.
      Your scenario would require a rather complex and heavy duty system, you’re talking about switching power (2 poles), line level input signal (4 poles) and speaker level output signal (4 poles), a total of 10 poles at the same time, break-before-make, between 11 devices. And ideally it would allow to switch from any to any device (say from amp no. 5 to amp no. 8, not just 1 to 2, 2 to 3 and so on). I’d say a passive, mechanical system is out of the question unless you are a mechanical engineering professor with a group of eager students who would jump at the project. An active, relay-based system maybe? That would also require serious skills, but seems easier to design and implement. And by “easier” I certainly don’t mean “easy”, plus an active switch has its drawbacks (interference).
      I think I would try to do something very old-school instead, a manual solution. Imagine a 10-pin plug (for example a Chinch Jones connector, like P310CCT) and a board with eleven 10-contact sockets (like S310RP). You would have to manually pull the plug from one socket and put it into another, but it would allow to switch all ten connections in one move, break-before-make. One potential problem is that the power connectors would be right next to signal connectors, so there’s interference potential, but if you use shielded cables, that’s only at the connectors. And you’d have to use plugs that fit in sockets only in one position. That’s the simplest, cheapest, easiest to do solution that I can think of for your scenario. I know it’s very 19th century, but it might just do the trick.

  7. Pete

    Hello.
    I have many receivers, CD players, tape decks, turntables, speakers etc… Need to be able to switch between them.
    For example I want Auxiliary #2 on Receiver #3 through speakers #5. you get the idea.
    I could build something but do you know if there is any gear that does this already. I don’t want any modifications to sound or tone I just want to switch between the components. Switch between Receivers, speakers, Aux, and phono.

    1. rafal lisinski Post author

      I’m not aware of any single device that would do all that. I imagine you’d need a network of switches, and they should be passive if you care about sound quality. If you can accept some hum, you can use something like Pro.2 SP 200 between line level sources and amps/receivers: http://audio-room.net/pro-2-sp-200-source-amplifier-switch-gallery/
      For turntables, I strongly recommend a passive switch (active switches are likely to add hum/noise that would be amplified by the phono stage, resulting in a very high noise level). For speakers, you can daisy-chain a few switches like the one I’ve built to switch between amps (remember that break-before-make and no common ground are crucial here), and then connect their output to a commercial speakers switch to switch between several pairs of speakers (these switches can have common ground and allow multiple connections at the same time unless you’re using tube amps, class D amps or ones that can’t handle low impedance speakers). But bear in mind that the more switches you add to the signal patch, the more sound quality you will lose. One switch usually makes no difference, several switches could audibly degrade sound.

  8. Wilson Goodrich

    OK, my question is pretty simple but I want to make sure. I want to run my old Marantz and Phillips turn table thru the same speakers as The Denon powers the CD player, tape deck and dvd player. So the the same switch box as you describe function for this set-up?

    1. rafal lisinski Post author

      Assuming that your “old Marantz” and “The Denon” are amplifiers or receivers, the answer is yes.

  9. Mike Bartlett

    Do you think this principle would work on the pre amp stage. I have a computer generating music supplying a mixer to broadcast to hospitals. We broadcast 24/7 but being volunteers there are many hours when the mixer could be powered down and the music signal could go direct to webcast, but it is the switching that bothers me. Have you any suggestions?

    1. rafal lisinski Post author

      Yes, and you’d need a much simpler switch for that. Assuming you use RCA connectors, search for “AV switch”.

  10. CY

    Hello Rafal,

    When you’re doing A/B test to compare 2 sets of amp using the switch connected to the same set of speakers, are you using the same source (eg CD player) ?
    I am a little confused because if you are using the same source, you would have to manually switch interconnects between the source and amp every time you toggle the switch ( to select your desired amp), am I right?
    I guess what I am asking is if one were to do an A/B test on amplifiers with the same source and speakers, using your switch would still require the tester to manually switch interconnects (linking source to amp), right?
    Thanks a lot for taking the time to answer my query.

    CY

    1. rafal lisinski Post author

      We use one source connected to both amplifiers at the same time via Y splitters. It’s not ideal because splitters may slightly affect sound, but even if they do, they affect it the same way for both amps. We use identical cables (same brand, model, length) for connections to both amps and we switch these cables mid-test to exclude any differences between cables.

  11. CY

    Thanks for the reply.
    When you say Y -splitters, do you mean a switch? something like this: shorturl.at/mFLX5?

  12. Harry Dutt

    Hello,

    I just came across this project for two amps to one pair of speakers switch box which I’m interested in building.
    I have a question.

    Is the contact points inside the 4PDT switch equivalent to a 16AWG cable ? That is, is there sufficient
    contact area at each point to match the cross sectional area of say a 16AWG cable ?

    I admit I don’t have enough electronics knowledge to know whether my question is relevant.

    With one amp and one pair of speakers there would a pair of speaker cables going directly from the
    amplifier output jacks to the speaker jacks.

    With this switch box there would be suitably short cables (16AWG or other) from the jacks of the two
    amps going to the respective input jacks in the box. Wires from each set of input jacks will then connect
    respectively to each side of the 4PDT switch, then the four common (middle pins) of the switch will
    connect to the output jacks in the box from which the main speaker cables will be connected to the
    speaker jacks.

    So I’m wondering if with all these connection points there is sufficient contact area at each position
    within the switch suitable for the guage of cable being used.

    If I build this box to use, only one amplifier will be powered on at any time. It will be to select either
    a high powered or low powered tube amp.

    Thank you.

    1. rafal lisinski Post author

      Hi Harry,
      Yes, the contact points of the 4PDT toggle switch we used in our switch box can accomodate a 16AWG cable. As far as I recall, we used that or 15AWG. It wasn’t easy to catch it safely with these smallish screws, but doable.
      You got the connections and internal wiring right, that’s exactly how it should be connected.
      If you use this type of switch box with tube amps then yes, to be on the safe side only one amp should be powered on at any time and it should be selected (with the switch box) before you turn it on to ensure that the amp is not on without load.

      1. Harry Dutt

        Thank you for your response Rafal. I decided to go with a simpler but less convenient solution.

        You see, I only need to switch my amplifiers a few times per year. I use my high power tube amp
        mostly during the cold season and my low power amp during the hot summer months which lasts
        less than four months here in Toronto, Canada.

        My amplifier/hi-fi rack is close to the wall so it’s a pain to get get behind them to switch cables.
        I made a simple box to which I screwed a suitable piece of 2mm thick aluminum panel drilled
        with holes for the jacks.
        The cables from each amp are connected to the respective jacks for amp-A and amp-B via a bare
        wire connection in the holes for this in each jack. The speaker cables are then plugged in to each
        set of jacks depending on which amp is being used. All I have to do now is move the little box from
        under the rack to switch the speaker cables. Less convenient than with a switch but still a suitable
        solution in my case. I should also mention that this involves only one break in the cables from the
        amps to the speakers.

        Regarding my original question, I now see that I wasn’t too clear in how I put the question.
        By mentioning contacts I wasn’t referring to the screw terminals on the switch to witch the wires
        are fastened. I was thinking more of the contacts made inside the switch when the toggle lever is
        thrown to one side or the other to select either amp-A or amp-B.
        Are these contacts sufficiently robust enough to accomodate the electrical signal from the amp
        to the speaker. I’m not sure how this works as my electronics knowledge is very limlted.

        Thank you,
        Harry.

        1. rafal lisinski Post author

          Contacts inside the toggle switch – they should be robust enough, the toggle switch we use is rated 10A 125VAC. That’s much more than speaker protection fuses in most amps.

          So, your solution is basically a simple patch panel. Tried that too, but it’s inconvenient if you switch often (I do). If you only use it a few times a year – sure, it’s much easier to build.

  13. CY

    Hi Rafal,

    Now that I know what you meant by a Y-splitter, I just want to make sure that, if the source is a CD player, then I would need to have one Y-splitter for each of the RCA outputs (Left and Right). The left Y-Splitter should be connected to both the left inputs of Amp A and Amp B.
    The right Y-Splitter should be connected the both the right inputs of Amp A and Amp B, is that correct?

    Thanks in advanced.

    1. rafal lisinski Post author

      Exactly. Note that in some rare cases this connection (source connected in parallel to 2 amps) could cause sound degradation. So before doing an A/B test, make sure that the sound from source is not affected. The easiest way to do that by ear is to connect the source to both amps via Y splitters, play through one of the amps, and disconnect only cables going from the Y splitters to the other amp while listening. If the sound doesn’t change, it’s all good. Then do the same for the other amp.

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