Instructables

Can i connect input to GND ?

Hello, i have a little amp based on this layout :
My question is : when i need to temporary disable the input, can i connect "IN" to GND ?
Thanks for advance!

Picture of Can i connect input to GND ?
verence2 years ago
An input should never be left open, floating around to catch whatever signal is around (like an antenna). In some ICs this is taken care of by implementing pull-up (or pull-down) resistors. So, yes you can and should connect the input with GND if unused. You might want to use a resistor, though (something like 1k should be good). As lemonie said, a switch might be a good idea,
I agree with all those that say use a switch to either cut it out or ground it. Whichever way you do it, you would want to place a 1M ohm resistor from signal to ground, on the side of the switch that is closest to the IC. The value chosen is high enough to not affect the signal when you want it to go through to the amp. That will help prevent "popping" when the switch is opened or closed. This scheme is used in many effect pedals in the bypass switch.

Qa
iceng2 years ago
Any sources you might use are impedance limited so not to worry.

But just add a switch like lemonie says. . . . . .. . A
gmoon2 years ago
With certain reservations, yes. You certainly cannot hurt the 386 by grounding the input pin.

In fact, it's not unusual to place a volume POT before the input in that circuit. Volume controls are wired as voltage dividers, so in the "off" position the input would indeed be grounded.

What reservations, you ask? That would depend on the output impedance of the device that's connected to the input. Very low output impedance devices (like a power amp) wouldn't like to be grounded. But using a power amp as the signal source for a 386 would be pretty silly...

Even that can't happen when using a POT voltage divider on the input. When the wiper to the 386 side is grounded, the input signal side of the POT would be connected to GND through the resistance of the POT itself, so the POT resistance value (say 10K for example) would always be between the input signal and the GND...
sshuggi2 years ago
Think back to the basics: Ohms Law
V=IR
I=V/R
When you connect IN to GND with no resistance, your current will go to "infinity." This will overheat whatever the source is and/or the wire connecting IN to GND. At any rate, things will get really hot and fail in a couple of seconds.
If all you want to do is disable the input, disconnect it. Or, put a switch in the circuit.
verence sshuggi2 years ago
The question was about an INput. Where does your your current come from? For an OUTput, your warning is right. Kind of. Even if you connect an output to GND, the current will NOT go to infinity as the resistance is twofold: Outside resistance (which will be zero) plus the source resistance (which depends on the kind of the output). That's the reason why a 9V battery block cant melt a paper clip when the former is shorted with the latter. Of course, that does not mean that it is safe to short outputs to GND - far from that. You might kill the output, the shorting wire or yourself. Not with a 9V block, but think of the mains power socket as an output...
lemonie2 years ago
When you need to temporary disable the input, use a switch.

L
Pro

Get More Out of Instructables

Already have an Account?

close

PDF Downloads
As a Pro member, you will gain access to download any Instructable in the PDF format. You also have the ability to customize your PDF download.

Upgrade to Pro today!