Help, Aleph30 huming !!!

[arold19]

I need your help. I just finish an Aleph30 and it is huming.
I tried some modification, it help a litttle bit but a hum is still here.

How this is possible:
-When I connect only one input of the amp, there no hum at all.
-When I connect the 2 input of the amp, I have hum in the 2 channel ????

The only difference I have between the 2 channel is, the cable between the bridge and the PSU is 4 inch more long on one side, I don't think this can effect any thing....

I don'T know how to get out this noise of my amp.

Thank you

[wuffwaff]

HI,

this is a typical ground loop.
Where did you connect you input grounds? Did you use the ground lift resistor at the input?

Try to draw a schematic with ALL the ground connections, most of the time you´ll see the ground loop when drawing.

William

[Nelson Pass]

The usual solutions:

a) rotate the transformer to minimize the hum

b) attach a solid wire between the RCA grounds and use
it's center point as the star ground for the input and output
grounds of both channels , and send only 1 wire back to the
power supply ground.

also, it's very useful to ground the chassis well to the AC outlet
ground and then attach the circuit ground to the chassis through
a power thermistor like a CL60 or through diodes to give some
loop isolation while retaining a safety connection.

[arold19]

wuffwaff: I connect the input ground in the PC Board.
In my circuit board, there a "ground" connect to the power supply and the other "ground" is connect to the speaker output.

So, you think it is a good idea to remove the inout ground to the PC Board and to put a peace a wire between the RCA input directly to the chassi ground ??

Thank

[wuffwaff]

Hi,

I´m not shure. It would like to see a schematic of some sort.

Here´s what I usually do:

I always try to make some kind of star earthing with one central point per channel.
As central point I usually take the main power supply caps.
In my A5 I´ve got two earth points, one for each channel.
The two channels are not directly connected.
Both earth points connect to the chassis via a bridge rectifier.
The chassis is connected to mains earth.

If you connect both channels to the chassis the you get a ground loop via the preamp.

hope this helps,

William

[arold19]

Yeah,
Me, My 2 channel are connect to the chassis to a single point..... but if I disconnect from it, the hum stay...

But.... I have to ground only 1 channel???
I don't understand very well...


Thank you

[jh6you]

I believe that Nelson Pass adviced us in the most correct way.

Nevertheless, I always do this way successfully.
Due to increased number of wires, it might look stupid.
But, it works very well for me.

Hope this info will help.

Regards

[arold19]

Ok, If I make this schematic, I have to remove the cable between the RCA connector and the PC board or I leave them here and I add and other wire in parallele with the one here ??? I hope you understand what I'm saying ???

[Blues]

This is why I love making my chassis out of wood (cheaper, easier to cut). I just connect all grounds to a bus bar with enough screws. I still utilize "a diode bridge over troubled waters" though.

[Nelson Pass]

Like the diagram from Jh6you, it's important to run a wire
from the star point off to the heavy short wire between capacitor
grounds and a wire off to the heavy short wire between the RCA
input grounds. This keeps the ripple voltage on the capacitor
wires off the signal ground and the transformer magnetic field
from creating a noisy input ground (via a loop back to the
source component grounds) that gets amplified.

If there's a ground wire coming from the transformer, it should
sit on the heavy short wire between capacitor grounds, not at
the star ground.

Just my noise contribution...