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Old 13th February 2011, 11:28 AM   #1
OMaudio is offline OMaudio  Germany
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Join Date: Feb 2010
Default Question about star ground LM1875

Hello,

i have a question about star ground for LM1875 amp. I use a dual pcb, i buyed on ebay.

I build this amp with own parts an it sounds good.

Now i want to put in the amp into a chassis. The chassis is grounded, but how to ground the amp?

I hope, someone can help me.

King regards
Olaf
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Old 13th February 2011, 12:03 PM   #2
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Just run a earth wire from your amp ground to the case.. not much to it.
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Old 13th February 2011, 12:07 PM   #3
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Usually with a low ohm resistor and pair of diodes anti-parallel in parallel with resistor. This is done to prevent low ohmic current ground loops. Diodes work if large current fault occurs.
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Old 13th February 2011, 01:36 PM   #4
OMaudio is offline OMaudio  Germany
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OK, but wich point i use on the amp board for ground?

Here are some pictures of the amp.


Olaf
Attached Images
File Type: jpg Amp1.jpg (376.1 KB, 171 views)
File Type: jpg Amp1a.jpg (417.6 KB, 157 views)
File Type: jpg Amp2.jpg (340.3 KB, 153 views)
File Type: jpg Amp3.jpg (345.1 KB, 142 views)
File Type: jpg Amp4.jpg (396.6 KB, 139 views)
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Old 13th February 2011, 05:37 PM   #5
Minion is offline Minion  Canada
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I usualy use the ground that is between the Big PSU filter caps .......

From looking at your board it looks like you might need a bit more soldering practice ......
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Old 13th February 2011, 08:23 PM   #6
OMaudio is offline OMaudio  Germany
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OK, do you mean the points between the PSU Caps?

Can i use the cap who is near the transformer - C2.

I can use C1/C3 the - pol.

Or C2/C4 the + pol.

Is this ok?

Soldering is good, not so good on pictures.

Olaf
Attached Images
File Type: jpg Amp111.jpg (625.6 KB, 46 views)
File Type: jpg Amp22.jpg (229.8 KB, 37 views)

Last edited by OMaudio; 13th February 2011 at 08:33 PM.
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Old 13th February 2011, 08:29 PM   #7
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IMO is better to use the transformer connecting pin (left photo, middle screw - GND).
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Old 13th February 2011, 08:34 PM   #8
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Hey, leave him alone - if the amp works then he's done it's right - he can have another go on something else later.

One the subject of the amp - I connected all the signal grounds together ( with their own individual wires - NOT daisy chained ) and fed them directly to the chassis and mains inlet earth bolt.
It's fine like this.
Someone might have a better way but it works for me.

BTW - it's exactly the same board I used and is very sweet sounding.
It's driving my upper mid drive units and hf units of L and R speakers.

I'm still a newb and soldering is not that easy straight away but if your joints hold the component well, completes the circuit correctly and are not dripping all over an adjacent component then who the hell cares ?

Andrew
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Old 14th February 2011, 01:51 PM   #9
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Quote:
Originally Posted by OMaudio View Post
OK, do you mean the points between the PSU Caps?

I can use C1/C3 the - pol.

Or C2/C4 the + pol.

Is this ok?
Yes, any of those 9 pads in between the capacitors in the photo on the right will do.
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Tyler
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Old 14th February 2011, 02:10 PM   #10
OMaudio is offline OMaudio  Germany
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Join Date: Feb 2010
OK, thank you all for help.

King regards

Olaf
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