PSU noise hum... Please help

[blindsjc]

Hi friends,
Again I need help... I used the search a lot, here at diystompboxes and google and dont find any solution.
I'm just finishing my amplifier with internal effects like blackfire. Made a lot of mods with things learned
at this forum and the amp is very quiet and good sound when using batteries.

Today I started final tests using a very simple power supply, and the noise comes. I dont know what to do
since the psu is so simple, and filter caps are 4700uF. The psu is connected directly to the amplifier, the power
comes from a transformer with 12-0-12 and the 0 volts is connected to the chassis like showed in ESP
project http://sound.westhost.com/psu-wiring.htm.

So take a lok at this pcb fragment:
obs: at headphones out theres a cap not shown at this image.



Link: http://blindsjc.v10.com.br/help.htm

Any suggestion is wellcome since I think this project is almost lost.
Thanks again.

[blindsjc]

Hi guys, please help...

[brett]

Hi
I don't know tooo much about these things, but...
It seems to me that you should use separate grounds for the pre-amp, the speaker and the PS.  Having them all hooked up on one line like this seems to produce lots of hum.
In the terms that RG uses, you've got "sewer earths" from the PS and speaker sharing a line with a very sensitive pre-amp earth.  The small resistance present in the sewer lines causes a little sewerage to back up into your pre-amp, where it gets greatly amplified.
cheers

[blindsjc]

Hi brett,
Thanks for reply...
So, how can I have different ground lines since at the end all of then will be
connected anyway. Imagine the preamp, the input have 2 connections, tip (signal)
and sleeve (ground), output have the same, these two lines will be connected to power amp
tip and sleeve, so the ground of these 2 circuits will be connected anyway.

Thanks

[Paul Perry (Frostwave)]

Yes, the grounds are connected.... but you only want them connected at ONE place, and that place is back at the power supply.

[blindsjc]

ok,
If I understand it, I need to bring all the subcircuits ground and the
input and output ground to a unique point and connect it to my ground
point at the psu (and leave the psu ground point connected to chassis ground).
Can we call it a star ground of all circuits ground points?


Thanks

[blindsjc]

Hi again friends,
Bring all grounds to the same point dont show
significant decrease of noise. Any other idea?

Thanks