Power activated A/B switch

[pedro77]

Hi all,

 

I'm not sure if I'm using the right terminology and that's why I haven't found anything, but I'm looking for a stereo speaker A/B switch that's position changes depending on if it is powered or not. So I can have my front speakers wired to both a surround amp and a stereo amp but make sure it's never at the same time.

 

The reason I'm after this is that I recently upgraded my surround AVR which can be turned on over the network by selecting it as the remote speaker output. In most setups that would normally be fine but I have the front L&R speakers powered by a valve amp which is fed from the AVR preouts. The problem is the valve amp isn't on all the time and so if I wake the AVR with streaming I can get output to all the surrounds but not the fronts. My valve amp has a physical power switch only and to make things easier I've got it hooked up to an IR controlled power board.

 

So I'm wondering if such an A/B speaker switch thing exists that if I had it also plugged into the IR activated power board I could let it switch between the valve amp powering the speakers (via AVR preouts) when on, or from the AVR front speaker bindings directly when off. Obviously I don't ever want it to have an A+B option which if running the valve and AVR amps at the same time could do some damage. 

 

I hope I've explained it clearly. Any one heard of such a thing or got some ideas? Appreciate your help.

 

Cheers

Pete

Edited March 4, 2019 by pedro77
typo

[pedro77]

I thought this would be a more common issue to want to automatically switch between AVR and a stereo amp with the same fronts. Should I move this to DIY or Speakers/Subwoofer threads?

Cheers

Edited March 4, 2019 by pedro77
detail

[A9X]

Wire some relays to the 12V out on the AVR.

[Bunno77]

I thought this would be a more common issue to want to automatically switch between AVR and a stereo amp with the same fronts. Should I move this to DIY or Speakers/Subwoofer threads?
Cheers

Most use ht bypass I believe.
I used to swap speaker cables but now I use little Panasonic satellites for the avr l+r and it works good enough with a decent centre. I do this as I don't own anything with ht bypass.

[pedro77]

Thanks for the replies. I was thinking I would need some kind of relay switch. I think I have found a product that may be ideal but it's discontinued and a bit more expensive than I was hoping. It's a Niles SPK-1 which would allow the speakers to be fed by the AVR when the valve amp is off. When the valve amp is on (and the SPK-1 which would also be plugged into the same IR controlled power board) the speakers would be fed by the valve amp only (via AVR preouts but disconnecting the simultaneous speaker level output from the AVR).

 

As I often use the AVR and valve amp together for movies and TV I don't think the 12V trigger outs would work for that situation. My valve amp does have HT bypass but it would be good if it also had a 12V trigger out. I want to avoid having to buy additional speakers. 

 

The only DIY system I can see may work is to have relay switches (normally closed) that are plugged into the same IR activated power board as the valve amp and when it is on it opens the circuit on speaker level outs that go from the AVR to the speakers. I'm not sure exactly how to go about this but I'm thinking some kind of 12V wall wart and 4 relays (one for each speaker wire ie L+&- R+&-).

 

 

Edited March 19, 2019 by pedro77

[A9X]

41 minutes ago, pedro77 said:

As I often use the AVR and valve amp together for movies and TV I don't think the 12V trigger outs would work for that situation.

Then use a manual switch to control the selection and a 12V plugpack to supply coil voltage to the relays. It's not that complicated.

[Jventer]

Best site I know of is: http://www.dodocus.de/  He could possibly build something for you. Maybe a bit expensive?

I understand what you are trying to, but what I dont understand is how your AVR can output both main and pre out to the fronts? Do you have different "scenes" or menu options to be able to switch fronts between mains and pre outs?

[Jventer]

5 hours ago, A9X said:

Then use a manual switch to control the selection and a 12V plugpack to supply coil voltage to the relays. It's not that complicated.

I think I understand what you are saying, but it will be much appreciated if you could elaborate with more detail, schematics etc. What you are saying sounds great, I am not that tecnically educated/experienced and need all the help I can get.

Thanks

[A9X]

23 minutes ago, Jventer said:

but what I dont understand is how your AVR can output both main and pre out to the fronts?

Pre outs are in parallel with the (internal) power amp inputs. So when signal is going to say L, then there is signal at both the L pre out and the L speaker out.

 

I'll sketch up a schematic tomorrow if you'll be more specific what you want it to do, and also which AVR's trigger out you're using and it's rating (it'll be in the manual under specs, typically 100mA @ 12Vdc).

[Jventer]

1 hour ago, A9X said:

Pre outs are in parallel with the (internal) power amp inputs. So when signal is going to say L, then there is signal at both the L pre out and the L speaker out.

 

I'll sketch up a schematic tomorrow if you'll be more specific what you want it to do, and also which AVR's trigger out you're using and it's rating (it'll be in the manual under specs, typically 100mA @ 12Vdc).

Hi A9X

Will be much appreciated.

Thanks in advance

[pedro77]

Thanks again for the input. Reading my posts again I think I jumped a bit quickly into details without a broader context.

 

I want to make this as family and visitor friendly as possible so even though manual switching would be the simplest, it would be great if I could make the switching automatic. As the new AVR shows up as a streaming point in multiple formats even while on standby I want to be able to stream to the whole system without any user intervention apart from selecting the output on their phone.

 

That dodocus gear looks nice but it's going to be even more expensive than tracking down a second hand or new old stock of the SPK-1. The advantage too with a DIY path is I can leave my existing decent terminated speaker cables directly connected from the valve amp to the fronts (without having to add an extra set with the SPK-1). And also that way I can just have the less critical path of streaming from the speaker level outs involving the two sets of cables and routing via relays.

 

Jventer, A9X is correct is my experience of AVRs that there is no scene or control over output selection from speaker level outputs and their matching preouts. Admittedly, I've only owned a few AVRs but there has never been an option in any of mine to designate preouts vs speaker level outs.

 

A9X I think I know what I need but any practical advice would be really appreciated. I have googled this problem but haven't found anything. And I'm surprised there's not more people out there wanting it especially as according to a Darko survey that the majority don't have a dedicated listening space (https://darko.audio/2017/03/global-feedback-lounge-room-or-listening-room-or-both/).

 

So far I think I need a 12V DC power supply and 4 relays which are normally closed and passing current when unpowered and open when the relays are powered. I'm thinking 4 for each speaker level wire rather than 2 say just on the positives so no current leaks back from the valve amp to the AVR front speaker lines when the valve amp is on. I"m not sure if that's correct though? A9X do you know any models of relays which might be suitable? Thanks again.

 

Cheers

Pete

 

ps

I've made a schematic myself...it was harder than I thought haha. Hope it helps. 

 

Edited March 19, 2019 by pedro77
schematic!

[A9X]

10 hours ago, pedro77 said:

I want to make this as family and visitor friendly as possible so even though manual switching would be the simplest, it would be great if I could make the switching automatic. As the new AVR shows up as a streaming point in multiple formats even while on standby I want to be able to stream to the whole system without any user intervention apart from selecting the output on their phone.

Are they going to want the tube amp in circuit all the time, or will that only be you? My guess is it will be you only (based on the experience that almost all non audiophiles will not care either way). If that's the case, then the manual switch is the best option as it will leave the system easier for others to you, and you can modify it for your preferences, ie add the tube amp in when you want to use it.

[pedro77]

1 hour ago, A9X said:

Are they going to want the tube amp in circuit all the time, or will that only be you? My guess is it will be you only (based on the experience that almost all non audiophiles will not care either way). If that's the case, then the manual switch is the best option as it will leave the system easier for others to you, and you can modify it for your preferences, ie add the tube amp in when you want to use it.

For streaming, the valve amp will be off but we use the valve amp to power the fronts pretty regularly when watching TV and movies so an automated set up would be best. Plus I'm lazy...I'd probably spend an hour looking for a lost remote control rather than have to walk to the TV to change the channel 

[pedro77]

For anyone else interested, I got it setup and working.

 

I bought a 5V 4 channel relay board for about 3 bucks as I have a lot more 5V USB chargers lying around than 12V versions. This was the one I got:

https://www.ebay.com.au/itm/5V-2-4-8-16-Channel-Relay-Board-Module-for-Arduino-Raspberry-Pi-ARM-AVR-DSP-PIC/113672930560?hash=item1a776f4500:m:mW8AVUtErcN-MGJEhek8Shw

 

Each speaker wire goes through NC (normally closed) contacts which open when the 5V is powered. To activate the relay switches I have just taken the positive wire from the USB cable to VCC and then have the negative wire connected to ground together with all 4 of the the relay input switches twisted together. With this wiring I have left the JD-VCC and its VCC with the jumper on (see the yellow jumper in the pic). And that's about it. Hook one end of the speaker wires to the AVR speaker level outputs and the other to the speakers and have the 5V adapter plugged into the same IR controlled power board as the valve amp.

 

So if the valve amp and relay are off I can stream to the front speakers from the AVR speaker level outputs. If the valve amp and relay are on, the AVR speaker level circuit is opened ie off and the front speakers are then powered just by the valve amp (either via AVR preouts to the HT input on the valve amp or one of the other valve amp inputs).

 

Turned out to be easier than I thought. Hope it helps someone thinking of doing something similar.

 

Cheers

Pete

[pedro77]

Actually, having just explained this now, I am wondering if there is a risk that by leaving the valve amp speaker wires in place and the AVR speaker levels are active, could the current also be trying to "drive" the valves, even if the valve amp is off at the power board? Does anyone who knows anything about circuitry have any ideas?

 

If that is the case I would need to rewire the relays so the AVR outputs are connected each to a NC, the valve amp amps to the corresponding NO and then the speakers wires to the matching common. The only downside is I forgo my terminated speaker cables for basic wires or have to build a box for the relay and wire in some binding posts.

[A9X]

1 hour ago, pedro77 said:

Turned out to be easier than I thought.

Sorry for the slow reply, but I've been off with an injury and forgot all about it.

 

My intent was to use a similar relay board but configure it so that the relays were break-before -make, ie if using the AVR and wanting to include the valve amp, then the AVR relays would open before the VA relays would close. This means no potential short circuiting of the AVR outputs into the VA OPT. It's more important in reverse as if you had signal into the VA (eg playing music) and you suddenly open the OPTs to no load, then high voltages can develop and potentially damage the OPTs. The idea was to switch in a load resistor in parallel with the OPTs outputs (1/ch) and then open them and switch in the AVR. Trying to do it without a microcontroller was proving difficult and I didn't want to be responsible for supporting the idea if I added one. I also thought you didn't want a manual switch.

[pedro77]

Hi A9X

 

Thanks for the reply. No apology necessary. Hope you recovery quickly though.

 

You bring up a lot of interesting points. And a lot more than I considered but then again I don't know much ha. I can't find if the relays on this board are break before make or make before break. I had thought I would be fine when switching from AVR to VA as my valve amp has a fixed 30 sec warm up time before powering the outputs. I'm not sure though if when the VA is powered off at the wall but the manual switch on the device is on, whether there is any chance of the AVR feeding current back across the valves.

 

That is interesting about suddenly opening the circuit on the VA outputs while playing. I would normally always stop any music before that but there is always the chance of bumping or sitting on the remote. Wouldn't that also be a risk with a manual switch if someone flicked the switch and opened the circuit while the VA is playing?

 

It is amazing how quickly it becomes complicated when you want to have some delays and protection. I want to keep it as simple as possible but I'm seeing that may not be as easy I thought.

 

 

[soundbyte]

34 minutes ago, pedro77 said:

I can't find if the relays on this board are break before make or make before break.

See

https://upverter.com/parts/Songle%20Relay/JQC-3F-5VDC/

or

https://easyeda.com/component/bfa25414e2ad483dbf1c0bd5452e4fa9

for details of the relay.

Edited March 29, 2019 by soundbyte