Amplifier Interference Issue

[mtripoli]

I don't know what the output of PSP supply looks like. I have never seen what a "plug-pack" (what we derisively call a wall-wart) looks like for the PSP. I would be very surprised if it has any kind of filtering at all. Usually these things are a transformer, a bridge (if you're lucky) and MAYBE a single cap (it could be a universal input switching supply as well. If so the thing most likely has tons of high frequency component on the DC. Some ceramic caps strategically placed may be all you need. LM78xx devices don't respond at these higher frequencies and will let a lot of this through). The manufacturer places the caps and related circuitry in the device being powered (for lots of reasons). So first, whenever you are using a "plugpack" put some big caps on the input of the supply to the board. 470uF-1000uF is not unusual. Use some ceramics as well. Watch the voltage; don't use a 6.3V cap on a "5V" supply (higher voltage never hurts). Typically voltage rating is under load, so a "5V" supply may actually be much higher than that.

Mike Tripoli

[Byte_Butcher]

hmmm.... using a wall wart for power.....

Many "modern" wall warts now contain switching supplies instead of the traditional xformer/rectifier setup in order to meet minimum efficiency standards
that now apply in many areas.
That may well be the source of your noise. Like Mike said... an electrolytic cap of a few hundred uF, with 1 or more small (.01-.1uF) ceramic caps in parallel may help a lot.


steve

[Art]

Thanks Guys,
a 1000uF cap across the supply almost eliminates the noise
That's a bit big, but I'm sure I'll find a combination that works well.

[mtripoli]

That's a bit big, but I'm sure I'll find a combination that works well.

No it's not... 3x220uF is better, 2x470uF is ok... but 1000uF is not big...

[Art]

I just mean a bit big looking on the circuit,
and it might prevent PCB stacking with tight spacing (if I go that way).
I'd rather use a couple of smaller ones.

This one is to end up a talking clock radio.
At last, a project I actually use in day to day life

[Ioannis]

It is a big circuit and I can understand how difficult might be to change the connections.

But in most cases that involve audio amps or pre-amps, the problem arises from the ground loops. And I see a lot on your photo Art.

So, I would suggest to take cables from all the minus (ground points) of the circuit parts and connect them to a single point where your (-) of the power supply is.

This wll also help you reduce the spikes on your digital power rail.

I suppose that you are having different power line for the analog and digital parts, right?

Ioannis

[sayzer]

..
So, I would suggest to take cables from all the minus (ground points) of the circuit parts and connect them to a single point where your (-) of the power supply is....

Ioannis

And, from right there, have a bobbin serially connected to GND, thus, all of your circuit will go to GND via that bobbin.

The value of the bobbin is best found by experimenting.


-------------------------------------