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### Topic: Adafruit mono 2.5W Class D Audio Amplifier - PAM8302 not working (Read 1 time)previous topic - next topic

#### alex5678

#60
##### Nov 04, 2018, 06:26 pmLast Edit: Nov 04, 2018, 07:04 pm by alex5678
Hello,

Ok, your circuit on the book,

it has a gain of 57. I am thinking of building your circuit 2 times... Should I use any discrete element between the connection of the output of the first circuit with the input of the second circuit?

Thank you...

#### Grumpy_Mike

#61
##### Nov 04, 2018, 07:24 pm
Quote
it has a gain of 57. I am thinking of building your circuit 2 times.
So if you connect the output of one circuit with a capacitor to the input of the other you will theoretically get a gain of 3249. However at such high gains you might get stability problems unless it is constructed with due regard to this sort of gain.

Are you sure you want it so high? Or are you after something like a gain of 100, which is simply done by changing the resistor values.

#### alex5678

#62
##### Nov 04, 2018, 07:32 pm
So if you connect the output of one circuit with a capacitor to the input of the other you will theoretically get a gain of 3249. However at such high gains you might get stability problems unless it is constructed with due regard to this sort of gain.

Are you sure you want it so high? Or are you after something like a gain of 100, which is simply done by changing the resistor values.
I will do tests with POTs (on input and feedback resistors) to achieve a gain, that will not distort my output... but I do not know if I should put a discrete element between the first and the second circuit...

Thank you...

#### Grumpy_Mike

#63
##### Nov 04, 2018, 07:35 pm
I did say
Quote
connect the output of one circuit with a capacitor to the input of the other

#### alex5678

#64
##### Nov 04, 2018, 07:43 pm
I did say
A 10uF electrolytic, for example, is ok?

#### Grumpy_Mike

#65
##### Nov 04, 2018, 07:51 pm
Quote
A 10uF electrolytic, for example, is ok?
Yes, put the positive to the output and negitave to the input.

#### alex5678

#66
##### Nov 04, 2018, 07:58 pm
Yes, put the positive to the output and negitave to the input.
Doesn't go the other way? I mean I have an input signal, so I face firstly the positive side?

#### Grumpy_Mike

#67
##### Nov 04, 2018, 09:16 pm
Quote
Doesn't go the other way?
No. You are driving the positive end with the output of an amplifier.

#### alex5678

#68
##### Nov 06, 2018, 10:13 pmLast Edit: Nov 06, 2018, 10:13 pm by alex5678
Hello,

Two questions..

1) I have modified a bit this circuit:

book

and I get Gain = 50 from the fitst op-amp and Gain = 50 from the second, I have amplification on the input signal, but something extreme... If I use 12 Volt supply, can I get something bigger?

2) How do I read the input in a ADC of the Arduino, every 1 sec?

Thank you...

#### Grumpy_Mike

#69
##### Nov 07, 2018, 02:29 am
Quote
2) How do I read the input in a ADC of the Arduino, every 1 sec?
Use the analogRead function. See the blink without delay example in the IDE or read the sticky post in the programming section about doing several things at once.

Quote
If I use 12 Volt supply, can I get something bigger?
No the gain is determined by the resistors. Using a higher power supply will only allow a bigger output signal not more gain.

#### alex5678

#70
##### Nov 07, 2018, 09:59 amLast Edit: Nov 07, 2018, 09:59 am by alex5678
But the bigger output signal isn't a result of the gain?

Thank you...

#### Grumpy_Mike

#71
##### Nov 07, 2018, 05:14 pm
Quote
But the bigger output signal isn't a result of the gain?
No.
The gain is controlled entirely by the resistors.

To get more output when you just change the supply voltage you must put a bigger signal into it.

#### alex5678

#72
##### Nov 08, 2018, 09:36 pm
Hello...

Can I increase the Volts to 12, to the circuit on your book? Does it support 12 Volts?

Thank you...

#### Grumpy_Mike

#73
##### Nov 08, 2018, 09:44 pm
Quote
Does it support 12 Volts?
It is not the circuit it is the op-amp. You need to see the data sheet to see what the maximum voltage the chip can operate on.

In this case the maximum voltage is 7V but with a recommended maximum of 5.5V.

#74
On this circuit: