Hard Wiring Audio channels

Thread Starter

Daan Lageschaar

Joined Jul 8, 2019
36
Hi there,

I want to hard wire 2 audio sources together and only have one of the grounds connected using a 2 way sliding switch (attachment) Will this work or will this do some weird things? The 2 ground wires aren't connected together in any way, one of them leads to a usb bluetooth reciever and the other one leads to a high level to low level audio signal converter.

Thanks in advance,
:)
-Daansliding switch.jpg
 

Audioguru again

Joined Oct 21, 2019
1,906
Your idea of switching only the grounds will probably case severe interference from the 50Hz or 60Hz electricity sprayed from electrical wires in the walls around you.
 

MisterBill2

Joined Jan 23, 2018
6,992
In every audio source the signal and ground conductors are connected to each other by the source impedance. Thus, by having the signal lines all joined and opening the shield connection pf one you would be tying the shield to the signal line through the source impedance. That would certainly add a whole lot of noise, mostly the AC mains hum pickup.
Why even consider switching shields and not the signal side of the connections? I am wondering what led to considering that option.
 

Thread Starter

Daan Lageschaar

Joined Jul 8, 2019
36
In every audio source the signal and ground conductors are connected to each other by the source impedance. Thus, by having the signal lines all joined and opening the shield connection pf one you would be tying the shield to the signal line through the source impedance. That would certainly add a whole lot of noise, mostly the AC mains hum pickup.
Why even consider switching shields and not the signal side of the connections? I am wondering what led to considering that option.
Well I'm building a little amp box using a pre assembled AliExpress amp, which I'm also going to put a Bluetooth module inside of, and since the sliding switch I had lying around has 6 poles (basically the one in the picture but just 2 of them together) I wanted to make the Bluetooth module turn off while I'm not using it, I thought I could use the other 'lane' (or whatever it's called) on that switch for cutting off the power to the Bluetooth module
 

MisterBill2

Joined Jan 23, 2018
6,992
It is OK to wire the audio signal commons together and only switch the signal lines, and that would give you the other side of the switch to control power with.
In addition, multi-pole multi position slide switches do not cost very much from some sources. So that is a cheap option also.
 

Thread Starter

Daan Lageschaar

Joined Jul 8, 2019
36
It is OK to wire the audio signal commons together and only switch the signal lines, and that would give you the other side of the switch to control power with.
In addition, multi-pole multi position slide switches do not cost very much from some sources. So that is a cheap option also.
You mean wiring the left and right channels together?
 

MisterBill2

Joined Jan 23, 2018
6,992
You mean wiring the left and right channels together?
I mean the SHIELD side of the audio signal pair. NOT the signal side of the pair. AND if you are talking about SPEAKER connections, that is different yet. Some amplifier circuits us an arrangement that does not allow speaker leads to be connected to anything besides speakers. That is often described as a bridging output, or a bridge output. It is a differential output in technical terms.
Tying stereo signal left and right to make a mono signal often requires adding some resistors to provide some isolation. Not a big deal but usually it should not be ignored. Possibly some audio wizard here can draw you a circuit showing how to do that.
 

Thread Starter

Daan Lageschaar

Joined Jul 8, 2019
36
I mean the SHIELD side of the audio signal pair. NOT the signal side of the pair. AND if you are talking about SPEAKER connections, that is different yet. Some amplifier circuits us an arrangement that does not allow speaker leads to be connected to anything besides speakers. That is often described as a bridging output, or a bridge output. It is a differential output in technical terms.
Tying stereo signal left and right to make a mono signal often requires adding some resistors to provide some isolation. Not a big deal but usually it should not be ignored. Possibly some audio wizard here can draw you a circuit showing how to do that.
Sorry for my late reply,

I'm definitely not talking about speaker connections, just low level audio signal stuff. But I guess I'll just leave the bluetooth module on all times then
 

MisterBill2

Joined Jan 23, 2018
6,992
Sorry for my late reply,

I'm definitely not talking about speaker connections, just low level audio signal stuff. But I guess I'll just leave the bluetooth module on all times then
OK, I was just presenting a caution in case it was speaker connections. Input signals are different, and now it appears that the amplifier is a stereo amp and the radio signal is a stereo signal, and so to switch them and also switch off the bluetooth module you would need a 3-pole switch with 9 terminals, or possibly two switches. I will need to think a bit and see if there is a way to do both with the switch that you have.
OK, here again is the description of the sources. "one of them leads to a usb bluetooth reciever and the other one leads to a high level to low level audio signal converter. " OK, now I have an idea, and a question: Does that high level to low level converter use any power? Does it include any active devices such as transistors or ICs? If so, does switching off it's power stop the output to the amplifier?
My reason for asking is that if both devices "go quiet" when switched off then the solution could be to connect them both at the same time using a simple passive fixed mixer circuit, and just switch the device power. So now the answer to the question could enable a simple solution.
 

Thread Starter

Daan Lageschaar

Joined Jul 8, 2019
36
OK, I was just presenting a caution in case it was speaker connections. Input signals are different, and now it appears that the amplifier is a stereo amp and the radio signal is a stereo signal, and so to switch them and also switch off the bluetooth module you would need a 3-pole switch with 9 terminals, or possibly two switches. I will need to think a bit and see if there is a way to do both with the switch that you have.
OK, here again is the description of the sources. "one of them leads to a usb bluetooth reciever and the other one leads to a high level to low level audio signal converter. " OK, now I have an idea, and a question: Does that high level to low level converter use any power? Does it include any active devices such as transistors or ICs? If so, does switching off it's power stop the output to the amplifier?
My reason for asking is that if both devices "go quiet" when switched off then the solution could be to connect them both at the same time using a simple passive fixed mixer circuit, and just switch the device power. So now the answer to the question could enable a simple solution.
nope, it's not powered unfortunately
 

MisterBill2

Joined Jan 23, 2018
6,992
nope, it's not powered unfortunately
OK, now an interesting possibility would be to add an analog buffer IC to that line and then switching would all be done at DC levels. A fair amount more complex, but it would work. OR you could use an analog switch IC such as the CD4066 to do the switching. More complex but another compact option.

Another simpler and cheaper idea popped into my head, which is to use diode switching. Simple, cheap, and easy, and it would allow switching the blue-tooth module on and off. Sorry I did not think of that earlier.
 
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