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I'm still trying to figure out how this door intercom module works. It's a 18y old siedle TLM 611-0 module, I figured out the mic part, there the audio signal is modulated onto the current the mic amp draws. But the loudspeaker part baffles me. This is the circuit diagram of the speaker amp I reverse engineered from the PCB. I don't really know how it works. It's quite a strange design and I'm not really good with analog electronics. Help is very much appreciated.

circuit diagram

Apparently some people can't see the embedded image of the schematic, here is a link to it: https://i.imgur.com/rj3Cwcc.png

EDIT: Updated the schematic to a conventionally drawn one. Old hand drawn version of the schematic: https://i.imgur.com/Evuv3Wm.png

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  • \$\begingroup\$ Post a schematic or other technical documentation -- we can't help you without more information. \$\endgroup\$ – esilk Jul 24 '18 at 21:19
  • \$\begingroup\$ My question included the reverse engineered schematic, don't know why you couldn't see it, here is the link again: i.imgur.com/Evuv3Wm.png \$\endgroup\$ – masterbase Jul 24 '18 at 21:27
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    \$\begingroup\$ Offtopic: I've misread your name 3 times now. \$\endgroup\$ – Harry Svensson Jul 24 '18 at 21:45
  • \$\begingroup\$ @HarrySvensson Your brain is probably in a unbreakable loop after reading the profile. You need to kick yourself and engage your other brain. \$\endgroup\$ – jonk Jul 24 '18 at 21:48
  • \$\begingroup\$ Please redraw this conventionally, with the positive rail at the top and the input on the left and the output on the right. And double check it. \$\endgroup\$ – user207421 Jul 24 '18 at 22:40

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