Hytera SM09D1 hiss fix

Issue

The SM09D1 external speaker connected to the DM785 radio gives off a really loud hiss and plop when the radio is in use.
This due to the fact that the audio amplifier in the DM785 is always on full gain and the audio output via the rear DB26 connector is not filtered.

By installing an 4.7uF capacitor and a 100 Ohm resistor inside the speaker it completely removes the hiss, and reduces the plopping significantly.
It makes the audio more clear, but reduces the total volume output of the speaker. The audio level is still more then sufficiant for use on a desk.

Fix

• Disconnect the speaker from the radio
• Open the external speaker by remove the 4 screws from the rear
• Carefully open the speaker
• Solder the 4.7uF capacitor across the - and + of the speaker connector
• Desolder the + (red) speaker cable
• Solder the 100 Ohm resistor on the + pole of the speaker
• Solder the + (red) speaker cable onto the 100 Ohm resistor
• Re-assemble the speaker

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