Cap Voltage question

[jman 31]

Hi guys,

I have a question concerning cap voltage. In this schematic for a guitar/mp3 player amp, would a 16v electrolytic cap be enough for C10 and C15? And if not, what would a viable voltage be?

Thanks for any advice,
J

 

[AndrewT]

Hi,
for a 9V supply, 16V rated capacitors are OK.
C6 also needs the same rating.
You could also use a 12V car battery as supply with 16V capacitors.

What is the worst voltage across C12 & C17?

 

[jman 31]

Hi,
for a 9V supply, 16V rated capacitors are OK.
C6 also needs the same rating.
You could also use a 12V car battery as supply with 16V capacitors.

What is the worst voltage across C12 & C17?

OK. Thanks, that is what I thought but I wasn't positive since it is connected to a pin that has AC on it.

 

[AndrewT]

which pin is that?

 

[jman 31]

Doesn't pin 2 of the LM386 have an AC signal on it from the mp3 player?

 

[AndrewT]

No.
Pin2 (-IN) is connected to Gnd. The caps are connected +9V to Gnd.
The supply is connected to +9V to Gnd.

The inputs from the guitar and from the MP3 are on inp2&3 and the return signals are on inp1.

 

[jman 31]

OK. Thanks for clearing that up. For some reason I thought both pins 2 and 3 had to do with the input at the same time. I guess I don't fully understand how the opamp works. Pin two would only be live if it was used for inverted signal then?

 

[AndrewT]

if pin2 is not grounded, it can be used as the -IN input.
It usually picks up the Signal Return, the NFB loop and the input filters.
This more usual arrangement allows complete separation of Signal Ground from Power Ground.

But, the 386 is not an opamp in the usual sense.
It allows single polarity supply and yet gives an output referenced to Power Ground. That is unusual.

 

[jman 31]

Cool. Thanks for that tidbit of info! I appreciate your willingness to teach!

J