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Old 10th April 2004, 07:53 AM   #1
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Default Aleph3 Noise

Hi Guis,
My Brother just finish assembly one Aleph3 and we have a noise
problems when we connect it another components for example: active preamplifier, passive preamplifier, CD.
We think that the problem is due at loops ground.
By itself doesn´t have noise.
Te system of the wiring is Mr. KLJUCARIC.
You can see that the ground of the signal only is connect in the PCB not at the RCA.

Somebody help us, thanks.

Jesús
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Old 10th April 2004, 11:28 AM   #2
MBK is offline MBK  Singapore
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Hi,

hard to tell... many thigs can be suboptimal in a layout. I once fixed a noise problem in my Mini-Aleph by moving a ground connection by 1 cm.

Inputs: If this is a stereo amp, you should tie both RCA input grounds together *before* they connect to signal ground.

Another possible problem is the layout of the power ground, that is, the return of the speaker. This ground should not connect to the PCB, but to a central point after the PSU caps. The PCB ground and the RCA input grounds should both also be connected at this single star ground point.

MBK
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Old 10th April 2004, 03:12 PM   #3
piewie is offline piewie  Belgium
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I sort of had the same solutions in mind.

Are both channels in one housing?
If so, did you make a single starground for both channels.
Are the RCA connectors isolated from chassis.
Do you have the noise when you connect the two RCA grounds together with a wire at the connector?
Is your preamp grounded?
Did you isolate the signal ground from the power gnd with a 100ohm resistor?
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Old 10th April 2004, 05:03 PM   #4
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Not knowing how well your actual wiring follows what you've drawn, you really should NOT connect directly to the junction of your electrolytic caps as the main star ground. The high charging current pulses flowing at this point will result in hum voltage along the current path.

That you have noise when ever you connect the input is becuase net hum voltage relative to the signal ground at your PCB is different due to the charging currents flowing and the resultant voltage drop. You can verify this by using an oscilliscope set to the more sensitive input settings (like 5 mV/div) and looking at the ground points with the probe.

A preferred method is to bring a heavy T connection out from the junction of the electrolytics, and make a star ground at that point.

In your case you might get better results without modifying the rest of the amp, simply by connecting the ground connection from the PCB to the RCA; but not knowing all the details of the PCB layout, that wouldn't be my initial choice.

Good luck getting this resolved; it really shouldn't be that hard; you're almost there, finishing your project.

Regards,

Jon
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Old 11th April 2004, 04:20 PM   #5
MBK is offline MBK  Singapore
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Jon,

Yes, that's what I meant with "star ground to a central point *after* the PSU caps", sorry if the wording was confusing. In my Alpeh case I used a point on the extended ground plane of the PSU filter bank though.

MBK
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Old 18th April 2004, 10:01 AM   #6
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Default Aleph3 Noise

Thanks very munch MBK, piewie and JonMarsh.

MBK.
Another possible problem is the layout of the power ground, that is, the return of the speaker. This ground should not connect to the PCB, but to a central point after the PSU caps. The PCB ground and the RCA input grounds should both also be connected at this single star ground point..

The return of the speakers are at the central point.

piewie.

Are both channels in one housing? Yes
If so, did you make a single starground for both channels.
Are the RCA connectors isolated from chassis. No
Do you have the noise when you connect the two RCA grounds together with a wire at the connector? Yes
Is your preamp grounded? Yes
Did you isolate the signal ground from the power gnd with a 100ohm resistor? in the futere I`ll put these resistors.

JohnMarsh.

That you have noise when ever you connect the input is becuase net hum voltage relative to the signal ground at your PCB is different due to the charging currents flowing and the resultant voltage drop. You can verify this by using an oscilliscope set to the more sensitive input settings (like 5 mV/div) and looking at the ground points with the probe.

A preferred method is to bring a heavy T connection out from the junction of the electrolytics, and make a star ground at that point..

You are righ.
The changes that we have been for delete the noise were connect the groung of the rca with the ground of the signal ground of the pcb in both points of the cable.
The ground of the pcb at the star point and from the star point by one cable at the central point.

Regars.
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Old 18th April 2004, 07:04 PM   #7
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Hi,

I would first try to isolate the rca connectors from the chassis. This is very likelyx the cause of your problem.

William
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Old 18th April 2004, 09:41 PM   #8
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Default Aleph3 Noise

Hi William.
Oh, sorry for the mistake.

piewie.
Are the RCA connectors isolated from chassis? Yes.

Now, I have not the problem,thanks

Jesús
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