Battery Hum

[The Earl of Sandwich]

I'm still working on my NESp (albeit very slowly), and recently wired it so my battery and power supply can be connected at the same time. When they are both connected, I get a hum through the audio channel.
If it matters, the battery is a NI-MH
Any Ideas why it does this or how one might fix it?

[CronoTriggerfan]

A bit more info, please! Is the battery you have at the proper operating voltage, and do you have enough amperage to power the system?

CTFan

[timmeh87]

so you only get the hum when the power adapter is connected?

is it just an AC wall adapter? if so, its probably really noisy. try putting a big cap on it.

[The Earl of Sandwich]

@CTFan- Yes, it's at the right voltage, and it appears that I have enough amperage (the system works)

@timmeh- Where would I put the cap?

[timmeh87]

across the input. like:

Code: Select all

-------
|     |==
| AC  |
|ADAP.|
-------
||
||
| \
|  \
|   \
|    |
|+   |-
|    |
|-|(-| <- thats a capacitor
|    |
|    |
v    v
(to system)

try something like 100uF - 1000uF electrolytic or 10uF - 100uF tantalum to start. careful, they are direction-sensitive (backwards = explosion)

[The Earl of Sandwich]

I scrounged a 10uF cap from a NES quickshot controller, wired it up as follows:

and I still get the hum. Do I need a bigger cap?

[timmeh87]

hm well im not 100% sure that that is your problem.

still, 10uf electrolytic (as it probably is) might be a bit low to take care of the kind if ripple you might be dealing with.

keep the 10uf one there, and try to find a 100+uf one to put in parallel with it. reason is that the ESR on big caps might be a bit high to handle higher frequencies, but the capacitance of small caps might be too low to smooth it out. so you kinda get both working together.

sorry if i explaned that bad, i dont have a very firm grasp on the knowledge myself. someone like codeman could probably clear it up a bit.