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Old 8th April 2014, 08:00 PM   #1
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Question Assembling my first LM3875 kit from Audiosector, some advice needed..

Hi Guys,
After luring around these forums, I finally got myself a LM3875 Kit from audiosector. However, I am a complete noob and never built an amp before. I have managed to get the Kits Assembled after referring to the guides.

However, I am completely stuck with this Toroidal Transformer thingy. I am in UK. Here is a pic of all the wires etc. How do I wire it? What goes to the mains and what goes to the Amp? (sorry, I have checked the guides but still being a bit thick)

Can someone help me with the wiring please?

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Last edited by dakku; 10th April 2014 at 09:21 PM.
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Old 8th April 2014, 08:14 PM   #2
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by dakku View Post
What goes to the mains and what goes to the Amp?
oh lord, I think we better go easy, step by step
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Old 8th April 2014, 08:14 PM   #3
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haha.. yes sadly..
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Old 8th April 2014, 08:18 PM   #4
tinitus is offline tinitus  Europe
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and you seem to have dual diode bridge

picture is too small for me to identify the solder pads
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Old 8th April 2014, 08:20 PM   #5
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thank you for the quick reply.. That pic helps immensely..
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Old 9th April 2014, 05:20 PM   #6
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Primary (mains)
Tie gray and violet together to set the transformer for 240v mains, and then blue and brown are the mains input.
Attach earth ground to metal amplifier enclosure.

Secondaries (to bridge rectifier):
Use black and red for AC1
Use orange and yellow for AC2

Using a voltmeter, test everything you can think of per safety. See also, Decibel Dungeon Building a Gainclone chip amp power supply. <--link
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Old 9th April 2014, 06:00 PM   #7
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by danielwritesbac View Post
Secondaries (to bridge rectifier):
Use black and red for AC1
Use orange and yellow for AC2
I was waiting for someone to post that

but I'm a bit confused about the way it's shown on the toroid, with red wire in the middle(CT)

is this normal color coding ?
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Old 9th April 2014, 06:55 PM   #8
AndrewT is offline AndrewT  Scotland
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the colour coding on the transformer is all quite clear.

The left side is mains or primary.
The red shorting link converts the dual primary to series connected.
That makes it suitable for the 230Vac available in Europe.
The Blu and Brn are the standard colours for mains wiring.

The 8 diodes on the rectifier PCB confirm that the poster has a dual bridge rectifier PSU.
He must keep the dual secondaries separate. There is NO CENTRE TAP.
As stated by Daniel and quoted by you
Quote:
Use black and red for AC1
Use orange and yellow for AC2
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Old 9th April 2014, 10:40 PM   #9
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Thanks again guys. I wired it up as per your help. I measured the voltages across v+ and PG+, I think I got 18v - will check again tomorrow. The most important thing is that nothing went BANG as yet..

I am waiting for the slow blow fuse and other bits to arrive, is 2.5A sufficient for this?

Also, I got some silver thermal paste thingy (used the same stuff on my motherboard CPU), would I need to scratch off some of that black paint before applying it?
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Old 9th April 2014, 11:09 PM   #10
tinitus is offline tinitus  Europe
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Originally Posted by dakku View Post
Also, I got some silver thermal paste thingy (used the same stuff on my motherboard CPU), would I need to scratch off some of that black paint before applying it?
isolating pad ?
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