14+ multichannel 3886 hum

[kramer71]

How do I change ground wiring layout?

For Linkwitz orion, and dipole surround system 14+ channel.

http://www.linkwitzlab.com/images/graphics/3886amp.gif
With added local decoupling 100uf.
Hardwired.

Powersupply 100000uf Rifa 200peh, 2*22V Talema 1000w transformer.

Wiring:
Input ground connected together at indput and taken to power star ground
Indput ground wired to seperate channels with shielded cable
Output ground wired to seperate channels
Power star ground

Symptoms:
50Hz humming on all channel with or without connected input
Before i connected the input ground together at indput i could use one channel at a time without hum at all, but there was more hum when I connected more channels.

[Robert GS]

Hello Kramer.

I would do like this:

Star ground for all amp supply power ground is OK, but not for the input.

1.The RCA should be isolated from metal chassis.
2. Ground Lift done with 2 x 1N5404/1n4004 and 10ohm connected between starground and chassis near input RCA.
All three components in parrallel and the diodes opposite direction.
3.Twist +V / -V and Supply Ground for each Amp board.
4. Change Ro from 2R to 10R. - maybe it's okay with 2R.
5. Insert 10R between signal ground amp and RCA ground.
6. Take speaker ground from amp board where supply ground are connected.

You can get a little inspiration here: Ground Sound -Technical
- and download the Coolback Kit Assemble Guide.

There is absolutely no hum in the Coolback Amplifier.

Robert

[AndrewT]

Hi,
have a read of this post. It might give you some ideas
http://www.diyaudio.com/forums/showt...80#post1048580

[kramer71]

Robert:
I do not use Ro 2R. I do not understand why and how to use it?

I can not find a ground wiring scheme for one powersuply and multiple channels for chipamp. Anyone?

[Robert GS]

Hi Kramer,

I can not find a ground wiring scheme

There is non in the guide - but if you look closely at the pictures of the guide -you will be able to copy the scheme.

AMP Supply wires are the twisted black/red/blue taken from the PSU12SA. The white is also taken from the PSU12SA starground and goes through DCN23 which holds the ground lift and via the white wire to the chassis at the XLR connector.
You will also see that the speaker output ground is connected at the amplifier board.
The signal input to the amplifier boards can just as well be connected direct to a RCA.

You are welcome to contact me by phone if you want an explanation in Danish - number at the home page.

Robert

[AndrewT]

Hi,
can you get just two channels to connect up and work properly with completely hum and buzz free speaker output when two sources are connected?

This must be your first challenge.

Then extend the knowledge to extra channels.

[Nordic]

I have been haveing alot of success with this method, ground loops and hums are like a fond memory...



When something goes wrong/gets shorted to earth in your amp, you will likely fry the 10 ohm resistor (use 2W or bigger, flame-retardent ones would be ideal) before the fuse goes, at least it saves you a burnt chip. USE BIG 8A or bigger diodes, you don't want them burned out before the fuse goes.