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I'm trying to amplify the headphones output of my laptop as the volume is too low during calls and such. The laptop has a combined TRRS female 3.5 jack output. I've used a splitter to split that into separate headphones and mic TRS, then using a reverse splitter I've connected the microphone directly and diverted the headphones to an amplifier (see picture).

The setup works correctly without the amplifier (ie if I connect the two inputs to the two outputs). Also, with the amplifier in the mix, the mic works fine. The issue is that when I connect the amplifier I can't hear anything from the headphones. Connecting normal headphones with a TRS jack to the amp output I can hear stereo sound and at the same time use the mic from the headset, it's just that the headset doesn't seem to receive sound when connected to the whole setup.

What am I doing wrong? Each component works well individually, so I've (perhaps prematurely) excluded a channels crossing problem...

connections setup

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The mic should only be a TS - it's mono. Simplest would probably be to take all the barrels off & actually check everything is managing to physically connect to the right connections. A continuity meter could be useful if you have one. If they don't match, grab a soldering iron & start swapping plugs. Make sure you get an accurate pin-out diagram of the compy & amp first. [though if the headset works fine when directly connected, you could use that as your pin-out 'map' for everything else.]

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  • Not sure why the mic out is a TRS, maybe compatibility? All images are exactly the component I'm using, so that's the way it comes from factory...
    – GCannizzaro
    May 14, 2021 at 11:38
  • I really don't know - it seems rather odd. First thing Id be doing is seeing exactly how they're wired & whether you're getting continuity. You might end up with either your soldering iron out, or one of those "works if I pull the plug out a bit" solutions.
    – Tetsujin
    May 14, 2021 at 11:44
  • The R on the mic connector could be DC voltage to power the microphone
    – Duston
    May 14, 2021 at 13:04
  • @Duston - not sure how the logic behind that works. TRRS - one is common, ground, two are stereo out, one is mono in - where does the 5th come from?
    – Tetsujin
    May 14, 2021 at 13:16
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You say "each component works well individually". Let's assume that your 3.5mm TRS-cable has been tested and that there is no problem with the adapters as such.

In that case there are still several opportunities for problems:

a) the conventions for ground and microphone input that your adapters use differ from the conventions your laptop uses. Ground can be on the second ring, or it can be on shield. You wouldn't notice from plugging adapters 1:1 (apart from the adapter cables being quite more susceptible to electromagnetic noise injection like from an active mobile phone). You wouldn't notice from running only headphones (then the possibly swapped connections are shorted anyway). If you'd plug the headphone adapters into one another for the headphones but keep the microphone connections unconnected and then plug the headset into this combination, what you should be seeing (and hearing) is that the microphone does not work but the headphones do work.

b) the computer tries figuring out things in a "smart" manner and does not see a load on the headphone connectors because the headphone amp has a reasonably high input impedance. It may then either use the normal loudspeakers, or may use the output as a "line out". Usually you should still see some output, but there may be separate volume and/or mute controls for line-out and/or the normal speakers, and those are substituted instead.

c) the computer even tries to figure out whether the TRRS connection has the ground on the second R and the mic on S or vice versa, and without the load from the headphones it fails and does something wrong.

You can probably narrow things down a bit by using a headphone splitter for connecting some arbitrary headphone in parallel with your headphone amplifier input.

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  • In saying "each component works well individually", I meant I've tested the whole setup connecting the amp out to a normal pair of headphones and keeping the headset microphone connected, and everything works: I get the mic signal from the headset in the computer and I get the sound output (stereo, checked) in the headPHONES.
    – GCannizzaro
    May 14, 2021 at 11:32
  • I've checked continuity with a multimeter and from the laptop male TRRS jack to the 6.35 mm adapter at the amp input the config is: T > T, R > R, R > S, S > nothing. So indeed a ring on the TRRS is going to the sleeve of the TRS at the amp input. Would that be the issue? That the second ring is being passed to the sleeve and no sleeve is passed through? But then, how is it working with the headPHONES connected?
    – GCannizzaro
    May 14, 2021 at 11:35
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wouldnt a Helm DB12 AAAMP solve this problem? inputs and outputs are trrs and the microphone functionality passes through this compact amp even when the unit is off.

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