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Sure you need to assemble that cirquit and play with it. I got some problems with it before so I can give some advices:
TDA2822 has a very high gain 40 dB or it is equal of voltage gain x 100.
So in most cases you will need to set a divider to prevent your strong signal from metal detector to overload that amplifier.
In my cirquits usually I am shorting inputs with 100 or 200 Ohm resistors to ground and adding 10k pots as volume regulators before resistors to divide input voltage for x 100 times or less.
Also that 100 Ohm resistors providing low input impedance. With high input impedance I can hear local radio stations plays music in speakers because with high impedance that amplifier picking up and amplifying all EMI and noises.
Regarding separating power supply. If you using one power supply for metal detector and audio power amplifier you may see some problems.
Spikes of current in speakers will drop voltage in metal detector power supply destabilizing its work. So you can hear even "motorboating" or oscillation in speakers as well as current in metal detector power supply starts jumping.
That is why I am using separation of power when metal detector and power audio amplifier have individual tank capacitors and voltage regulators
(or 20 Ohm resistor filtering current spikes before tank capacitors in power amplifier instead of voltage regulator).
Original Surf PI has that influence of speaker current to metal detector power supply voltage so with loudspeaker you can see some instability like "motorboating" or oscillations.
Once I have added TDA2822 and make it powered separately using additional 78L05 I have noticed of very much more stable and quiet operation of my Surf PI.
Also before connect it to 14v please be sure that TDA2822 works with 12v max and TDA2822M works from 15v max.
TDA2822 has a very high gain 40 dB or it is equal of voltage gain x 100.
So in most cases you will need to set a divider to prevent your strong signal from metal detector to overload that amplifier.
In my cirquits usually I am shorting inputs with 100 or 200 Ohm resistors to ground and adding 10k pots as volume regulators before resistors to divide input voltage for x 100 times or less.
Also that 100 Ohm resistors providing low input impedance. With high input impedance I can hear local radio stations plays music in speakers because with high impedance that amplifier picking up and amplifying all EMI and noises.
Regarding separating power supply. If you using one power supply for metal detector and audio power amplifier you may see some problems.
Spikes of current in speakers will drop voltage in metal detector power supply destabilizing its work. So you can hear even "motorboating" or oscillation in speakers as well as current in metal detector power supply starts jumping.
That is why I am using separation of power when metal detector and power audio amplifier have individual tank capacitors and voltage regulators
(or 20 Ohm resistor filtering current spikes before tank capacitors in power amplifier instead of voltage regulator).
Original Surf PI has that influence of speaker current to metal detector power supply voltage so with loudspeaker you can see some instability like "motorboating" or oscillations.
Once I have added TDA2822 and make it powered separately using additional 78L05 I have noticed of very much more stable and quiet operation of my Surf PI.
Also before connect it to 14v please be sure that TDA2822 works with 12v max and TDA2822M works from 15v max.
. I'll definitely will try to build one sooner or later... I have one question though, are you aware of any longboard PCB designs of your pickini? I like the idea of putting everything in pvc pipe as done with Silverdogs surf pi.
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