Next to it there is a ferrite bead connecting to 7,4V. On the top side of the PCB back to the HM8872, close to the GPS connector, there is a yellow tantal cap 33uF which provides decoupling for the audio amp. voltage is 6V, recommended operating is 5V. This is far too much for a SSM2305, its abs. Most critical point will be the supply voltage: The HM8872 is directly fed with 7,4V nom. There seems to be an inverter stage with a single transistor close to pin 1 which can probably bypassed by removing the transistor and its collector resistor and placing a 0R resistor onto the free pads between collector and base. Pin 1 will be the most difficult one: Unfortunately shutdown polarity of SSM2305 is inverse to the original HM8872.Pin 3 mode pin is now In+, but already tied to gnd as required for single ended operation.remove the bypass cap connected to pin 2 as SSM2305 does not require an external bypass capacitor.It is available in 8-pin MSOP case and fits directly onto the available print of the HM8872.Īs the specs of the SSM2305 are slightly different, some additional modifications to the circuit are required: With a bit of fiddling it should be possible to use a SSM2305 amplifier IC by Analog Devices.
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