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Old 13th March 2007, 10:34 PM   #1
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Location: Abbotsford, B.C. Canada
Default Help wiring power to 3 channel amp with one plug

Hi all,

I'm building a LM 3886 mono block amp, actually it's 3 LM 3886 amps in one enclosure. All are going to be monoblocks, but I would like to have 1 power cord to power all 3 amps. How do I go about doing this? I bought 3 transformers:

Avel-Lindberg Inc,

Input: 2 X 120Vac 50-60 Hz
3 3/4" Dia X 1 1/2" Tall
Output: 2 X 28.4V @ 2.67Amps over 150Va

from Apexjr ( thanks Steve) and he has posted a wiring connection guide and it states:
2 X 28.4V... For 115Vac Input - Tie the 2 blacks and Brown together along with
Tying the 2 Whites and Blue together
OUTPUT- Black is the center tap and each side Red and Yellow.

So my question is what is the center tap? How do I link all the transformers together so when power is on they are all working?

I have built one LM 3886 stereo amp and didn't have any issues with the wiring, but this is a little different for me. I want to do it right the first time.

Any advice on this would be great.

Cheers,
Chevy
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Old 14th March 2007, 01:28 AM   #2
Minion is offline Minion  Canada
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Location: Cowican Bay , vancouver island
Are you useing 3 Power supplies also??? (there is no easy way to connect 3 Xformers to One PSU)

This should give you a hint on how to connect them.....


Each PSU will have it"s own Transformer with the Primaries of each Transformer connecting to the AC Input from the Mains (With a Fuse in between the Mains and each Xformer)....

So the Hot wire from the Mains connects to the Hot wire on the Primary of each Transformer and the Cold wire from the Mains connects to the cold from each Transformer.....

You don"t connect the Center tap to the Mains Power as the Center Tap connects to the PSU (0v) connection......


Does this help??
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Old 14th March 2007, 02:32 AM   #3
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Quote:
Are you using 3 Power supplies also???
Yes, each tranny has it's PSU. Basically it's 3 monoblock amps in one chassis. I just want to have only one power cord coming out of the back of the chassis.


Quote:
Each PSU will have it"s own Transformer with the Primaries of each Transformer connecting to the AC Input from the Mains (With a Fuse in between the Mains and each Xformer)....
I was just going to use one fuse right at where the power inputs all trannys.


Quote:
You don"t connect the Center tap to the Mains Power as the Center Tap connects to the PSU (0v) connection......
I don't want to sound nuts at all, but what is 0v connection on the PSU? I'm using BrianGT's snubberized PSU.

I guess if I wanted to power all trannys I would have to connect all hot's from all trannys to the hot on the mains and all cold from the trannys to the cold on the mains, right?

Now the trannys I'm using have 9 wires that come out of them. I'm supposed to tie 2 black and a brown together and that is "HOT" and tie 2 whites and a blue together and that is "COLD". I now have 1 red, 1 yellow and one black. The black is the center tap and each side red and yellow. I assume it means AC1 and AC2 on the PSU. I just don't know the center tap (black) wire is supposed to go.

I think you have put me in the right direction. If someone can verify what Minion and myself have said that would be awesome.


Thanks so much,
Chevy
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Old 14th March 2007, 05:05 PM   #4
Minion is offline Minion  Canada
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Hi, I haven"t used any of those Kits (or any kits 4 that matter) so I can"t tell you Definitively that AC1 and AC2 are the 0V connections but I seem to recall reading somewere on this Forum that the AC1 and AC2 Pads on the PCB are for the Center Tap wires......

But you might want to wait till someone confirms this .......


Cheers
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Old 15th March 2007, 12:12 AM   #5
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Quote:
Hi, I haven"t used any of those Kits (or any kits 4 that matter) so I can"t tell you Definitively that AC1 and AC2 are the 0V connections but I seem to recall reading somewhere on this Forum that the AC1 and AC2 Pads on the PCB are for the Center Tap wires......

Can anyone confirm this? Did I get the wrong trannys?

Help,
Chevy
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Old 15th March 2007, 12:38 AM   #6
Minion is offline Minion  Canada
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Well it seems that if you look through the Building guide you will probably find your answer......


http://www.briangt.com/nigc_kit-users_guide.pdf


Greetings from the Island.....
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Old 15th March 2007, 01:28 AM   #7
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That guide is for an LM3875 and I'm building an LM3886. That PSU looks nothing like what mine is. That's where my confusion is. All I need to know is,

a. Can I use a tranny that has center tap?
b. If I can, how do you make the connection for that center tap?


Chevy
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Old 15th March 2007, 02:27 AM   #8
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There is a post about this issue:

http://www.diyaudio.com/forums/showt...ht=#post612794

While the power supplies are different, they both used dual rectifiers intended for dual secondaries.

On page 15 of the LM3785 manual he shows how to use 4 diodes and jumpers with a center tapped transformer.

The center tap becomes the GND (PG). You will have to work out how the jumpers should work on the LM3886 Power Supply PCB.
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Old 15th March 2007, 02:54 AM   #9
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Ok I think I understand.

On the Lm 3886 PSU only install 4 diodes, D1, D3, D6, D8. Then the other 4 diodes, according to the guide, get jumpered together. Put a wire from D2 to D5 and D4 to D7. The thing I'm not sure is where the HOT for AC1 connects to and where the COLD for AC1 connects to. If you look on the LM 3886 PSU, you will see AC1 and right below it you see AC1 again. Which on does HOT go to? I would assume the COLD goes to the other one right? So looks like PG+ is where the center tap goes, correct?


Chevy
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Old 15th March 2007, 03:45 AM   #10
Minion is offline Minion  Canada
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Do you have a Picture of the PSU Board or a diagram of the PCB Layout or even a schematic??

Wait I think the Hot wires go to AC1 and AC2 and the Center tap goes to PG....

If your Xformer is a True Center Tapped Transformer (3 wires on the Output) then you connect the Center Tap to one of the PG Pads on the PCB and then you put a Jumper between PG+ and PG- on the PCB......

A center Tapped Xformer has 2 Hot wires and One 0v(Ground/PG/Cold) wire....
A Dual secondaty has 2 hot wires and 2 0V(Ground/PG/Cold) wires......

If you are useing a Dual secondary (4 wires on the output) then you would connect each Cold wire to each PG+ and PG- Pad and each Hot wire to AC1 and AC2......


Without actually seeing a PCB diagram or Schematic I can"t tell you for sure......

I have never used a Comercially Made Kit or even a PCB before (I make my own) so I don"t have any experience with this particular PSU....


Cheers
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