LM3886 surround amp; problems with 50Hz noise

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infinia

infinia

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Joined 2005
I connected all the input ground wires with short wires on the PCBs, and all the hum is almost gone! I still got a little bit of hum in one of the speakers, but it's much better!
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I looked at the XY PCB layout seems you can put a small resistor in series on the input gnd leg to the panel conn. ( least this should check my theory ) EDIT , BTW this would of worked but its difficult now.
not sure about the sub amp , is that the worst one now?
 
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H

hansibull

Member
Joined 2013
infinia said:
I looked at the XY PCB layout seems you can put a small resistor in series on the input gnd leg to the panel conn. ( least this should check my theory ) EDIT , BTW this would of worked but its difficult now.
not sure about the sub amp , is that the worst one now?
Click to expand...

Can I just screw a 2 ohm resistor at the input terminal, and solder the input wire to it? that's a much simpler process than cutting all the traces underneath each PCB. Bu if I do this, what should I do with all the ground wires I've connected to each input terminals? Aren't these necessary anymore?


Mark Whitney said:
Hansibull, is it your intention to use the 5/1 diy amp in addition to the 7 amps already present in the receiver or are you building to upgrade the receiver?
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My idea was to use the pre out connectors that the Marantz have, and make my own, quality amplifier, instead of the the internal amplifier in the AV receiver. It will just be a 5.1 system, and no extension :)


When it cones to noise, the center speaker, left front speaker, the subwoofer and the surround right speaker is completely silent. I still got some hum in the front right speaker, and the surround right speaker.
 
infinia

infinia

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Joined 2005
Mark Whitney said:
I don't think any of the LM3886 kits sold on ebay will outperform the Marantz amps, not in quality or in power.
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hehe that's not helping him, it's sorta like kicking a guy when he's down.

Can I just screw a 2 ohm resistor at the input terminal, and solder the input wire to it? that's a much simpler process than cutting all the traces underneath each PCB. Bu if I do this, what should I do with all the ground wires I've connected to each input terminals? Aren't these necessary anymore?
Click to expand...

yes that would be in series with the input gnd, as a work around try 10 -100 ohms in series like you described, (yer still in trouble shooting mode).
Based on symptoms you reported, we are trying to reduce any stray PS or line AC currents from running thru the coax cables.
 
A

AndrewT

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Joined 2004
hansibull said:
Can I just screw a 2 ohm resistor at the input terminal, and solder the input wire to it? that's a much simpler process than cutting all the traces underneath each PCB..
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No. That puts the added resistance into the input pair and INCREASES the interference voltage fed to the amplifier.
Download D.Joffe's article. He shows where the ADDED resistance should be located to REDUCE the interference voltage fed to the amplifier.
 
A

AndrewT

R.I.P.
Joined 2004
infinia said:
I looked at the XY PCB layout seems you can put a small resistor in series on the input gnd leg to the panel conn. ( least this should check my theory ) EDIT , BTW this would of worked but its difficult now.
not sure about the sub amp , is that the worst one now?
Click to expand...
The ADDED 2r resistor is NOT in the signal pair feeding the sig hot and sig return.

Putting an added resistor into the sig return is NOT the place to locate the interference reducing resistor.
 
A

AndrewT

R.I.P.
Joined 2004
Mark Whitney said:
I don't think any of the LM3886 kits sold on ebay will outperform the Marantz amps, not in quality or in power.
Click to expand...

infinia said:
hehe that's not helping him, it's sorta like kicking a guy when he's down.
..................
Click to expand...
I don't agree with Mark.
I have only the experience of opening up one "all in one" surround capable amplifier.

If the Marantz is anywhere near as bad as the Yamaha, then a well built 3886 will easily beat it.
 
infinia

infinia

Member
Joined 2005
AndrewT said:
No. That puts the added resistance into the input pair and INCREASES the interference voltage fed to the amplifier.
Download D.Joffe's article. He shows where the ADDED resistance should be located to REDUCE the interference voltage fed to the amplifier.
Click to expand...


don't stop him, its just an experiment in trouble shooting. He reported the hum comes when the coax cables are connected to other gear. BTW maybe you missed the part where I gave him the link for a thread that describes a better fix for XY PCBs.
 
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