ISD1600B + PAM8403

[AssemblyLine]

Hello
ISD1600B is a record and playback IC that also has internal amplifier so you can connect a speaker directly to it . And also has an output to drive an external amplifier.
The output is single ended current ouptut .

I have an external amplifier with PAM8403 (that GF1002 pcb) .
On the ISD signal output I have put a resistor to ground and fed the resistor's voltage to PAM4803 inputs.
When I connect these 2 ICs together, the audio is very low, worse than with internal amplifier.
If I fed signal from my phone to PAM4803, the volume is good, loud.

Power supply is both 5V
What are the incompatibilites between these 2 ?

 

[KlausST]

Hi,

show your schematic. Hand drawn is O.K. (but it should be complete in the meaning of signal flow and power supply)

Klaus

 

[AssemblyLine]

Hi,

show your schematic. Hand drawn is O.K. (but it should be complete in the meaning of signal flow and power supply)

Klaus

This is ISD schematic,
The AUD pin has only a 3k3 to GND conected. And this voltage is fed to PAM4803 board on G and R pins

and this - which was not designed but bought,

 

[KlausST]

Hi,

If I understand right, then the upper is not exactly the schematic how you use it.
And the lower one is no schematic at all.

What you need to look for:
* What is the output signal of your ISDxxxx (how is it defined in range an offset)
* What is the operational input voltage of your amplifier (range, impedance)

To work propery both values need to match somehow.

Klaus

 

[AssemblyLine]

"What you need to look for:
* What is the output signal of your ISDxxxx (how is it defined in range an offset)
* What is the operational input voltage of your amplifier (range, impedance)"


ISD output signal is a current of max 3mA when Vdd=4.5V and R=390 Ohms

I have looked on it with a scope, the ac signal - on top of the dc voltage - is very small, 50-200 mV.
My phones outputs up to 2 V


This is internal view of PAM4803, I think it needs voltage on its inputs

" To work propery both values need to match somehow."

Thank you, but if I knew how to do that, I would not be asking here.....

 

[KlausST]

HI,

please provide links to datasheets.
(then most probably you get more feedback, because no one has effort to do search. And you should have them anyways)

I still don´t know the input requirement of your amplifier.
But try this:

R1 according with the 3mA should give a 1.5V offset.
C1 is a filter to suppress high frequency noise
C2 + R2: is a filter for DC and low frequencies (many audio amps are not happy with 1.5V DC Offset)

Component values may be adjusted on expected sound and device requirements.(it´s more guessing until now)

Klaus