Amp/speaker switch - DIY

[rlisin]

Every few weeks (or days) someone asks about a switch to connect 2 amps to one set of speakers, and whether a particular speaker selector switch will work. Most won't, the ones that will are usually more expensive. Some are unnecessarily complicated.

The problem is that it has to be a specific kind of a speaker level switch to accommodate 2 amps. It needs to switch all 4 connections: L+, L-, R+, R- separately (no common ground), it needs to be a "break before make" type (break connection to one amp before making a connection to the other) to prevent both amps being connected to each other even for a split second - obviously it should make it impossible to select both amps at the same time, and it ideally it should not have anything else inside except binding posts, wires and a switch (no resistors, no protection circuits, impedance matching etc.).

The simplest and cheapest option is to built a switch box using a 4PDT switch. I recently built two, the total cost is around $10-20, depending how cheap you can get the switch and what type of binding posts and enclosure you use. Here's one of them. That's the more expensive one because of banana plug-ready connectors, but if you use spring-type connectors, it becomes very cheap.

Parts:

That ^ plus some speaker wire and a few screws.

I used this for enclosure:

I gutted it:

I cut a wall from plywood for binding posts connected to the switch with speaker wire.

Assembled back:

And front:

That's all. This one works for either two amps to one set of speakers, or two speaker sets to one amp. The next one I will built will have two 4PDT switches, one for switching amps, the other for switching speakers.

 

[manu et deo]

Could you share a parts list?

 

[ferninando]

did you provide loading for unconnected amps?
I made the exact same thing about 15 yrs ago in a diff enclosure with a batch of slide switches
And no loading but was only switching SS receivers with no adverse affects.
Mite be a diff story with tubes.
U want break before make switching to prevent shorting outputs together.

Pics show all parts needed, no list required.

 

[manu et deo]

I was confused about the switches so somebody had any link so I'm looking at the right one

 

[rlisin]

All key parts are in the first pic: 1 4PDT switch (or 2 2PDT switches), 3 sets of speaker binding posts.
Apart from that you need about 1-1.5 m of speaker wire to connect binding posts to the switch (6 short sections), a box to put it all in, mounting screws and/or glue, probably solder and soldering iron.

I didn't add loading for unconnected amps because I don't use tube amps, solid state only.

Yes, the switch should be break before make, the one I used is also on-off-on.

In the first switching box I did a few years ago I used 2 2PDT switches (separate switching for L and R speakers) and no binding posts, just speaker wire running directly to amps and speakers. It was permanently installed in my friend's system who needed to switch between an AVR and a stereo amp.

 

[whoaru99]

Physical wiring of the amps, switches, and speakers as shown here using two DPDT switches. If you want just one switch use a 4PDT. It will have all 12 terminals on one housing but treat the wiring just the same as the two DPDT switches shown.

The pin numbers shown on the illustration are arbitrary. Don't expect them to be on the switches, just use the physical layout. Respect amp to speaker polarity through the switches.

As far as break-before-make, that is the inherent nature of the common toggle switch so it is nothing special to find/request.

The toggle switches commonly used are ON-ON or ON-OFF-ON styles. Both are break-before-make. Personally, I prefer the two-position ON-ON style because I always want one or the other connected, without the center OFF position.

 

[rlisin]

That's right, toggle switches are break-before-make. But most commercially available speaker selector switching boxes aren't, that's the main problem with them. The other is that they usually have common ground. It does not have to be a problem, but with some amps it can be.

I used ON-OFF-ON because i sometimes want to have speakers completely disconnected for various reasons.

If you want to build a box that also switches speakers, the wires from pins marked 2 and 5 in whoaru99's diagram above run to another 4PDT switch (or 2 DPDT switches) - same pins, and 2 sets of speakers are connected to the counterparts of the amp pins in the first switch(es).

 

[manu et deo]

So I found a 15a on-off-on 4pdt switch, that should satisfy the power requirements, correct?

 

[rlisin]

That's more than enough. Look at speaker fuses in amps, they're usually 1-4A.

 

[manu et deo]

I figured more was always better.

 

[rlisin]

It certainly won't hurt. Sturdy switch is better, and 15A switch will probably be quite sturdy. The one I used (pictured in my first post) was 15A/125VAC.

 

[ferninando]

So I found a 15a on-off-on 4pdt switch, that should satisfy the power requirements, correct?

15A on most switches is common

 

[twiiii]

I use to build switch boxes for an amp to be a back up for any where from 1 to 20 amps for big discos, Stadium, and convention hall systems. where they might not have a tech available and didn't trust the DJ to swap amps in an emergerncy. I used relays on the input and the outputs to be turned on and off by switch with a latching circuit. The original amp was connected with the relays in the normally closed position. When the back up or second amp was to be used the input from original amp was disconnected and the input of the amp was shorted to ground. The back-up amp was connected with the short being removed from the input then with a timing circuit about 2/10 of a second later. The speaker load was transferred from the first amp to the second immediately before the signal was applied to the back-up amp. . No clicks no noises and no need of load resistors on the first amp as there was no signal connected now to the amp. The speaker relays had 20 amp contacts and the operating switch just 3 amp contacts as it would only be handling 12 vdc to operate the input and out put relays. The input relays were 3 amp rated and hermetically sealed as the voltage levers were very low. If the back up amp was to be used with more than one amp their would be a selector switch to chose which amp was to be replaced. There were two DPDT relays for each output of the amp to prevent cross talk and two dpdt for the input connections two each amp. Rather than build power supply I used an Aiphone intercom 12 vDC power supply as they were very quiet. Some times I would add poles to the relays to power indicator lamps so folks would now which mode the system was in and which amp was selected. If some one tried to turn the sector switch while the back up was in use the relays would un latch and the entire system would shut down. Fortunately that only happened once. After system reset everything was ready to be reconnected. Of course with small systems with only 1 to 4 amps I left that feature off the system. By the time I retired all the systems from the 70's had either been replaced or were no longer inservice. The last one I installed in the late nineties is scheduled to be demolished as a new Sports complex is soon to be installed.

 

[rlisin]

15A on most switches is common

These are also quite common, they're 5A 125 VAC, which is sufficient for most amps. I used this type in the other switching box I recently built. A bit more soldering involved though, the bigger 15A toggle switches usually have convenient screw-type connectors.

 

[cmondetown]

Thank you both, for the very helpful instructions and diagrams

 

[srivenkat]

All key parts are in the first pic: 1 4PDT switch (or 2 2PDT switches), 3 sets of speaker binding posts.
Apart from that you need about 1-1.5 m of speaker wire to connect binding posts to the switch (6 short sections), a box to put it all in, mounting screws and/or glue, probably solder and soldering iron.

I didn't add loading for unconnected amps because I don't use tube amps, solid state only.

Yes, the switch should be break before make, the one I used is also on-off-on.

In the first switching box I did a few years ago I used 2 2PDT switches (separate switching for L and R speakers) and no binding posts, just speaker wire running directly to amps and speakers. It was permanently installed in my friend's system who needed to switch between an AVR and a stereo amp.

Hello,

Thanks for this post, I am trying to build this using 4PDT switching between SET (Tube Amplifier) and an AV Receiver (Solid State). You pointed out that this "I didn't add loading for unconnected amps because I don't use tube amps,.." . Is there anything I should do for switching between tube and solid state here? Appreciate your help.

 

[whoaru99]

Is there anything I should do for switching between tube and solid state here? Appreciate your help.

If the tube amp cannot be operated without load then usually adding 100-150 ohm resistor across each output affords some.measure of protection.

Right at the amp vs in the switch box means you don't have to be mindful of using a specific input of the switchbox.

 

[srivenkat]

If the tube amp cannot be operated without load then usually adding 100-150 ohm resistor across each output affords some.measure of protection.

Right at the amp vs in the switch box means you don't have to be mindful of using a specific input of the switchbox.

Thanks ...my amp is 45 SET (1.5 W output) I sometimes use 8Ohms 10W non-inductive resistor while checking left/right speakers. So, if I understand right, I can have a dummy-load to the switch box whenever the tube amp is not on? and remove the dummy load when I switch to the tube amp?

 

[rlisin]

If the tube amp cannot be operated without load then usually adding 100-150 ohm resistor across each output affords some.measure of protection.

Right at the amp vs in the switch box means you don't have to be mindful of using a specific input of the switchbox.

To clarify: Is the recommendation to put a 100-150 ohm resistor across each amp's output (for example + and - on the amp's speaker wire socket) permanently so that it acts as a dummy load and protects the amp (specifically its output transformers) when the amp is on but speakers are not connected to it? But when the speakers are connected, the effects of these resistors are negligible and they can be left in place, no need to disconnect them?

I understand that these resistors can be incorporated on the switch side, but the amp side is more convenient as this way they only work with the tube amp and not any amp connected to the switchbox (or the input of the switchbox to which they are added).

 

[triode17]

In the first switching box I did a few years ago I used 2 2PDT switches (separate switching for L and R speakers) and no binding posts, just speaker wire running directly to amps and speakers. It was permanently installed in my friend's system who needed to switch between an AVR and a stereo amp.

This is exactly what I did years ago for the same reason, to share my main spkrs. between the AV system and my tube stereo system. No special switches are needed except they must handle at least, say, 6 amps. I used radio Shack switches (remember them).