Hi all,
First of all, I apologize for potentially very long post, but I think this is an interesting topic and hopefully worth spending time reading it.
I am restoring vintage audio equipment, mostly receivers, and I already have small collection of different receivers and amplifiers that I keep for myself. The problem is that whenever I want to use one of the them I need to switch speakers cable which is very annoying.
I managed to find some kind of solution, the mechanical switch which supports using two different audio amplifier with single set of speakers, or other way around, using two set of speakers on single audio amplifier. Here is the image of that:
As this is mechanical connection only I was able to connect two different receivers to the same set of speakers and listen to differences in sound when tuned to the same radio station. Also, I use the same approach to test new set of speakers against the old one with the single receiver. It is really useful tool but it has few major limitations:
I decided to start building a better solution which will work for more than 2 devices with hopefully still acceptable price. The main goal that I would like to achieve is be able to connect multiple receivers into single set of speakers, but it also can be used for similar things.
Speaker Switcher
So I started to design my own solution. It is in very early phase, but I would like to share it anyway to get some feedback and maybe some ideas for improvements. I don't have any business on my mind, I will make it open source and hopefully other people can benefit from it.
Here are some requirements that I have on my mind
1. Modular approach. The idea is to be able to upgrade it as you grow in order to lower the initial costs.
2. Based on existing components. The parts should be available on most popular shops (DigiKey, Mouser, etc.)
3. Have mechanical connections for speakers. So nothing that can affect the sound.
The initial solution that I come with is consist of three parts.
On the image above is shown one switching "module". Left connector is where we connect output of the receiver, and the right connector goes to the third module that is connected with the speakers. The 3 pin connector above provides 12V for relay and signal for switch it on. The control signal is provided by control module.
Here is the schematic:
Schematic:
The idea is that there are separate "push" type switch for each input. Atmel (Arduino) will monitor which switch is pressed and will try to activate appropriate module. It does it through de-multiplexer 74HC238 which makes sure that only one of the modules can be active at the same time.
It also have 12V power supply (needed for relays) and 7805 for converting to 5V required by logic chips. I am also thinking to find some 5V relays to reduce components and need for two voltages.
As the initial post is already very big, I will not put all the details here, but in some other comments. For the end, here is the list of the things that could be helpful:
1. Recommendation for relays. Maybe you know some relays when can switch 4 circuits at the same time, work on 5V, etc...
2. In current design Atmel328p is used directly in the board. Maybe the whole Arduino mini or something can be used instead which will make programming easier.
3. Any suggestions about improving circuits, any obvious electronics mistakes., etc.?
4. Should it be a single board or multiple boards like it is now.
5. Any suggestion for case?
6. Really any feedback is welcome!!!
Looking forward to get some input from you!!!
First of all, I apologize for potentially very long post, but I think this is an interesting topic and hopefully worth spending time reading it.
I am restoring vintage audio equipment, mostly receivers, and I already have small collection of different receivers and amplifiers that I keep for myself. The problem is that whenever I want to use one of the them I need to switch speakers cable which is very annoying.
I managed to find some kind of solution, the mechanical switch which supports using two different audio amplifier with single set of speakers, or other way around, using two set of speakers on single audio amplifier. Here is the image of that:
As this is mechanical connection only I was able to connect two different receivers to the same set of speakers and listen to differences in sound when tuned to the same radio station. Also, I use the same approach to test new set of speakers against the old one with the single receiver. It is really useful tool but it has few major limitations:
- It is limited to two devices only
- It is not cheap (I paid mine ~80EUR)
- It still needs physical force to switch, etc.
I decided to start building a better solution which will work for more than 2 devices with hopefully still acceptable price. The main goal that I would like to achieve is be able to connect multiple receivers into single set of speakers, but it also can be used for similar things.
Speaker Switcher
So I started to design my own solution. It is in very early phase, but I would like to share it anyway to get some feedback and maybe some ideas for improvements. I don't have any business on my mind, I will make it open source and hopefully other people can benefit from it.
Here are some requirements that I have on my mind
1. Modular approach. The idea is to be able to upgrade it as you grow in order to lower the initial costs.
2. Based on existing components. The parts should be available on most popular shops (DigiKey, Mouser, etc.)
3. Have mechanical connections for speakers. So nothing that can affect the sound.
The initial solution that I come with is consist of three parts.
Speaker switcher
This part is responsible for real switching using relays. The circuit is pretty simple. There are two relays controller by transistors:On the image above is shown one switching "module". Left connector is where we connect output of the receiver, and the right connector goes to the third module that is connected with the speakers. The 3 pin connector above provides 12V for relay and signal for switch it on. The control signal is provided by control module.
Here is the schematic:
Control module
Control module is used for switching between inputs and also has the controlling logic. Controller is Atmel 328p, which is very popular controller used in most of the Arduino boards. Here is the initial design:Schematic:
The idea is that there are separate "push" type switch for each input. Atmel (Arduino) will monitor which switch is pressed and will try to activate appropriate module. It does it through de-multiplexer 74HC238 which makes sure that only one of the modules can be active at the same time.
It also have 12V power supply (needed for relays) and 7805 for converting to 5V required by logic chips. I am also thinking to find some 5V relays to reduce components and need for two voltages.
Speaker board
Speaker board is just physical connections between all outputs from all modules:As the initial post is already very big, I will not put all the details here, but in some other comments. For the end, here is the list of the things that could be helpful:
1. Recommendation for relays. Maybe you know some relays when can switch 4 circuits at the same time, work on 5V, etc...
2. In current design Atmel328p is used directly in the board. Maybe the whole Arduino mini or something can be used instead which will make programming easier.
3. Any suggestions about improving circuits, any obvious electronics mistakes., etc.?
4. Should it be a single board or multiple boards like it is now.
5. Any suggestion for case?
6. Really any feedback is welcome!!!
Looking forward to get some input from you!!!
Hi silence012,
I like your idea about electronic switching. My switcher box is way simpler but perhaps something from it helps in your process.
I had quite similar need like yours of connecting several amps (four in my case) to one pair of speakers plus a source selector (also four) to feed any of the four amps. What I constructed is a two-module unit consisting of a commercial line level switcher (called Heareal Z2 on Aliexpress/Ebay) and power amp output switcher (a couple of photos below). The commercial unit is re-wired to control both the line level inputs and power amp outputs in the other box which is filled with standard power relay boards (also available from Ali/Ebay for various voltages and number of relays per board). Mine have 12V relays which are driven through optocouplers by 5V trigger received from Heareal internal 5V regulator and selected by rotary "Output switch". The small signal relays inside Heareal are 5V types.
The whole thing is powered from a 12V DC wall supply into the Heareal which is connected to the other box through a round 8 wire connector (actually 6 would be enough, I just used what was available) supplying the 12 volts for the power relays and 5V trigger levels to the optos.
There seem to be quite a number power relays involved for just four amps and indeed there are four relays for each amp since they are all SPDT (single pole). The four relay contacts per amp are needed to connect both the hot and return wires to speakers since not all amps have speaker returns connected to common ground (class D, BTL). I see that you intend to use DPDT types which would be more space/cost efficient of course (perhaps you can even find 4PST?) but I just did not succeed to find any ready made relay boards with DPDT power relays and sticked with the quick solution. More space is necessary for SPDT but amount of wiring job would be the same for DPDT.
Please ask if anything from my unsophisticated configuration is relevant to your project. Anyways, have all the success with your electronic switching solution and thanks for sharing.
I like your idea about electronic switching. My switcher box is way simpler but perhaps something from it helps in your process.
I had quite similar need like yours of connecting several amps (four in my case) to one pair of speakers plus a source selector (also four) to feed any of the four amps. What I constructed is a two-module unit consisting of a commercial line level switcher (called Heareal Z2 on Aliexpress/Ebay) and power amp output switcher (a couple of photos below). The commercial unit is re-wired to control both the line level inputs and power amp outputs in the other box which is filled with standard power relay boards (also available from Ali/Ebay for various voltages and number of relays per board). Mine have 12V relays which are driven through optocouplers by 5V trigger received from Heareal internal 5V regulator and selected by rotary "Output switch". The small signal relays inside Heareal are 5V types.
The whole thing is powered from a 12V DC wall supply into the Heareal which is connected to the other box through a round 8 wire connector (actually 6 would be enough, I just used what was available) supplying the 12 volts for the power relays and 5V trigger levels to the optos.
There seem to be quite a number power relays involved for just four amps and indeed there are four relays for each amp since they are all SPDT (single pole). The four relay contacts per amp are needed to connect both the hot and return wires to speakers since not all amps have speaker returns connected to common ground (class D, BTL). I see that you intend to use DPDT types which would be more space/cost efficient of course (perhaps you can even find 4PST?) but I just did not succeed to find any ready made relay boards with DPDT power relays and sticked with the quick solution. More space is necessary for SPDT but amount of wiring job would be the same for DPDT.
Please ask if anything from my unsophisticated configuration is relevant to your project. Anyways, have all the success with your electronic switching solution and thanks for sharing.
Thanks a lot @nonills for sharing this. Looks really interesting.
What I am trying to build is basically something very similar to your switcher but with a little bit more user friendly interface. Actually now when I'm thinking about that maybe some kind of multi position rotary switch could be also a good solution for controlling.
The reason I chose to use Arduino (Atmel328p) is that controlling unit can be extended in future. For example, I can add remote control, voice command or any other things that is supported by Arduino. When I test multiple receivers against the same speakers, I need to go there, to switch, and get back to position where I was standing and you kind of loosing sound. If you can do the switching without leaving the place would be really cool.
Anyway, I am currently focusing on switching part. I changed a little bit initial design and switched to 5V 2PST relays. I am ordered few for trying and currently waiting for them to arrive. This is the relay: https://www.digikey.at/en/products/detail/panasonic-electric-works/DSP2A-DC5V/251824
Once they arrive, I will play around a little bit on breadboard and once I an happy I will order proper PCB.
It is a slow burning process currently but I will post my progress here.
Cheers!
What I am trying to build is basically something very similar to your switcher but with a little bit more user friendly interface. Actually now when I'm thinking about that maybe some kind of multi position rotary switch could be also a good solution for controlling.
The reason I chose to use Arduino (Atmel328p) is that controlling unit can be extended in future. For example, I can add remote control, voice command or any other things that is supported by Arduino. When I test multiple receivers against the same speakers, I need to go there, to switch, and get back to position where I was standing and you kind of loosing sound. If you can do the switching without leaving the place would be really cool.
Anyway, I am currently focusing on switching part. I changed a little bit initial design and switched to 5V 2PST relays. I am ordered few for trying and currently waiting for them to arrive. This is the relay: https://www.digikey.at/en/products/detail/panasonic-electric-works/DSP2A-DC5V/251824
Once they arrive, I will play around a little bit on breadboard and once I an happy I will order proper PCB.
It is a slow burning process currently but I will post my progress here.
Cheers!
Hi, sorry I wasn't looking into diya and missed your messages.
Unfortunately, no idea how Z2 would handle turntables, I just don't have one. If you mean connecting outputs from cartridges through Z2 before phonostage(s) then in my opinion Z2 is not the right device and unwanted noise could be picked up.
From your post before I see that you aspire to build quite an advanced and future proof piece of equipment. The relays you chose are definitely better quality than those I have in my box for their contact metal. First I thought that 5A contact rating might be a little on the low side (I have 10A rated ones) but if I understand your purposes correctly you are not going to run your receivers/amplifiers at high powers. I might be wrong and then it is something to reconsider. My use case for the switcher is home listening where amplifiers are seldom run even above some 10 to 15 watts.
Keep going and yes please post your progress!
Unfortunately, no idea how Z2 would handle turntables, I just don't have one. If you mean connecting outputs from cartridges through Z2 before phonostage(s) then in my opinion Z2 is not the right device and unwanted noise could be picked up.
From your post before I see that you aspire to build quite an advanced and future proof piece of equipment. The relays you chose are definitely better quality than those I have in my box for their contact metal. First I thought that 5A contact rating might be a little on the low side (I have 10A rated ones) but if I understand your purposes correctly you are not going to run your receivers/amplifiers at high powers. I might be wrong and then it is something to reconsider. My use case for the switcher is home listening where amplifiers are seldom run even above some 10 to 15 watts.
Keep going and yes please post your progress!
One more thing. The Z2 loads the connected source by internal 12 kΩ resistors (see pic below) which then appear in parallel with the input impedance of your connected amplifier. From loading point of view, this should not be a problem for any contemporary line level source unless the input impedance of the connected amplifier is already low (like in some HP amp designs). The resistors can be removed of course but their purpose apparently is to avoid the risk of loud hum by terminating unused inputs when you switch over one of them.
@nonills The initial design is for home listening so 5A should be enough. Although it would be easy to replace it with 10A in case you really need it.
I personally very rarely listen to more than 1W RMS, so I am far from the limits 🙂 Also, am pretty sure that these relays can handle a little bit higher load for a short amount of time without any problems.
At some point I will need something like Z2 but as I also have an turntable it should be able to support it without affecting sound too much. Honestly, testing these phone pre-amplifiers are really interesting topic. There are some lower rate receivers, like pioneer SX-550 which has very nice phono stage. I really like how it sounds.
Thanks for the motivation 🙂
I personally very rarely listen to more than 1W RMS, so I am far from the limits 🙂 Also, am pretty sure that these relays can handle a little bit higher load for a short amount of time without any problems.
At some point I will need something like Z2 but as I also have an turntable it should be able to support it without affecting sound too much. Honestly, testing these phone pre-amplifiers are really interesting topic. There are some lower rate receivers, like pioneer SX-550 which has very nice phono stage. I really like how it sounds.
Thanks for the motivation 🙂
