Switching 3.5mm TRRS headset signal

Thread Starter

clocKwize

Joined Oct 2, 2020
4
Hi there,

I have made a small device using a 4PDT switch, 2 3.5mm TRRS jacks for outputs and 1 3.5mm TRRS jack for input (from headset). Switching between my laptop and my pc.

It does the job great but I am unable to understand why doing this, the microphone isn't picked up by my mac?

When I connect the device, my mac goes from "internal speaker" to "headphones" indicating it has detected a device plugged in to the port, and indeed, audio works perfectly. The same isn't true for the input section, which when plugging the headset in directly, goes from "internal microphone" to "external microphone" - this doesn't happen.

Would anyone be able to shed some light on why this wouldn't be picked up, just because the signal is going via a switch? I've checked the continuity of the microphone signal and can't see any issues there!

Many thanks
 

djsfantasi

Joined Apr 11, 2010
6,962
Hi there,

I have made a small device using a 4PDT switch, 2 3.5mm TRRS jacks for outputs and 1 3.5mm TRRS jack for input (from headset). Switching between my laptop and my pc.

It does the job great but I am unable to understand why doing this, the microphone isn't picked up by my mac?

When I connect the device, my mac goes from "internal speaker" to "headphones" indicating it has detected a device plugged in to the port, and indeed, audio works perfectly. The same isn't true for the input section, which when plugging the headset in directly, goes from "internal microphone" to "external microphone" - this doesn't happen.

Would anyone be able to shed some light on why this wouldn't be picked up, just because the signal is going via a switch? I've checked the continuity of the microphone signal and can't see any issues there!

Many thanks
Please add a schematic to this thread, showing the wiring of the three TRRS jacks. And also add the specifications of the cables and plugs.
 

djsfantasi

Joined Apr 11, 2010
6,962
Does your Mac have a separate mic input? Does it recognize the mic on a TRRS cable without your device? You might need an adapter on the output connected to the Mac. A TRRS 4 pin to 3 pin adapter.
 

Thread Starter

clocKwize

Joined Oct 2, 2020
4
The mac does indeed recognise the headset microphone correctly without my device between them. There is no separate mic input, it's all via the TRRS jack.

Many thanks
 

djsfantasi

Joined Apr 11, 2010
6,962
Ok, so until a wiring error is counted out, that is the primary suspect. What’s the schematic, including cable, plug and jack specifications?
 

Thread Starter

clocKwize

Joined Oct 2, 2020
4
Apologies for my crude drawing!

the 4 signals for TRRS jack are as follows:
L = Left channel, R = Right channel, G = Ground, M = Microphone

The 4PDT switch I'm using is https://www.amazon.co.uk/gp/product/B07H6F2TJP

The jack ports I'm using are https://www.amazon.co.uk/gp/product/B007OH57G4

I'm going to recheck continuity through all wires, in case I confused which was the microphone signal, maybe the one I'm testing is in fact one I know is working already.

photo_2020-10-02_15-44-22.jpg
 

djsfantasi

Joined Apr 11, 2010
6,962
Apologies for my crude drawing!

the 4 signals for TRRS jack are as follows:
L = Left channel, R = Right channel, G = Ground, M = Microphone

The 4PDT switch I'm using is https://www.amazon.co.uk/gp/product/B07H6F2TJP

The jack ports I'm using are https://www.amazon.co.uk/gp/product/B007OH57G4

I'm going to recheck continuity through all wires, in case I confused which was the microphone signal, maybe the one I'm testing is in fact one I know is working already.

View attachment 218525
That looks like it should work. Do any of your jacks have a built in switch? Check continuity with a plug inserted and not inserted. A miswiring of a switched jack will actually disconnect the input/output.

If you can generate a test file, make one of you saying left and right just on its respective channel and verify it works.
 

MisterBill2

Joined Jan 23, 2018
7,309
If the headset works correctly when directly plugged into the mac, but not with the adapter in the loop, and if all of the adapter connections are correct, and the switch is working correctly, then it seems that it must be a connector problem, such as the positioning of the two rungs or the length of the ground sleeve on the adapter plug being different for the mac.
Mac products are notorious for intentionally being incompatible with the rest of the world. This is intentional.
 

Thread Starter

clocKwize

Joined Oct 2, 2020
4
As far as I can tell, the jacks don't have any switch built in, I guess I'd have to get a TRRS plug I can attach bare wires to to test against.

I've checked continuity of all 4 wires from both PC and MAC ports, to the HEADSET port (depending on switch position, and it all looks good to me.

I just went to test it works on the PC side (as I was more focussed on the MAC) and it worked there.. switched back and now it works on the MAC too.. Very confused.

I wonder if there is some kind of mechanism that detects the resistance or something that a microphone would normally provide and it wasn't quite right due to the switch or something :rolleyes:

I'll have a plan and see if I can work out in which scenario it does and doesn't work!

Many thanks
 

MisterBill2

Joined Jan 23, 2018
7,309
If it started working then it may have just been a particle of something preventing an adequate contact. So try it another 50 times and see if it malfunctions again. It might possibly be a cold soldered connection that will come back later. I have seen each of those cause problems and then stop causing problems for a while. Or the plug may not have been in quite all the way. Four-circuit plugs and jacks are very particular.
 

djsfantasi

Joined Apr 11, 2010
6,962
Solder joints are critical. If it’s a cold solder joint, it can periodically fail. If there is too much solder on a joint, it can short out against nearby metal. Besides continuity, test each point against ALL other connections in a jack or switch. There should also be NO continuity to the other points.
 
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