Help wiring power to 3 channel amp with one plug

Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Jump to Latest
C

chevy2410

Member
Joined 2005
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
 
M

Minion

Member
Joined 2006
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??
 
C

chevy2410

Member
Joined 2005
Are you using 3 Power supplies also???
Click to expand...

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.


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)....
Click to expand...

I was just going to use one fuse right at where the power inputs all trannys.


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

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
 
M

Minion

Member
Joined 2006
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
 
Dane

Dane

Member
Joined 2002
Paid Member
There is a post about this issue:

http://www.diyaudio.com/forums/showthread.php?s=&postid=612794&highlight=#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.
 
C

chevy2410

Member
Joined 2005
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
 
M

Minion

Member
Joined 2006
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
 
Dane

Dane

Member
Joined 2002
Paid Member
Yes, PG+ is the Ground and would be the center tap.
PG+ and PG- will tie together as shown in the jumpers on page 15. Use a meter to double/triple check everything.

The secondaries of the transformer connect to the AC1 locations. One has a Bar mark over it. That would should be hot.

I don't have the PCB in front of me, but I can look at it when I get home tomorrow and re-check. But yes you are on the right track.

Definitely test the power supply with a meter to ensure that you see the expected voltages and polarities before connecting to the amplifier module.
 
C

chevy2410

Member
Joined 2005
Alright then. I pretty much understand now. I have one other question though. I want to have all Xformers powered by one power cord. Would I just take all the HOT wires from each Xformer and connect them together and then connect them to the HOT side of the plug and then do the same with the NEUTRAL? BTW I will be using a fuse in there as well. No worries.:D


Thanks so much,
Chevy
 
A

AndrewT

R.I.P.
Joined 2004
impsick said:
put a seperate fuse on all transformers hots, then connect to AC power cord. (well with a switch of course)
Click to expand...
Impsick is correct.
Fuse each primary separately.

You do not have three monoblocks.
You have a three channel amplifier.

The difference is the problem you are going to find when you connect up the power grounds and signal grounds and safety ground.
Three monoblocks will not hum when wired correctly.
A three channel amplifier based on PCBs that share power ground and signal ground will take some skill to avoid hum. Good luck and tell us how you did it.
 
C

chevy2410

Member
Joined 2005
Should I be using separate power cord for each amp?

On the LM3886 amp there is V+, PG+, CHG, PG- and V-. Now I know that V+ and V- connect to the respective places on the PSU. I know that CHG is a ground to the chassis, but where does PG+ and PG- connect to on the PSU?

If PG+ is where the center tap connects to and I'm supposed to put a jumper from the other PG+ to PG- that only leaves one PG- open and there are two connections to be made from the amp. Am I wrong?


Chevy
 
Status
This old topic is closed. If you want to reopen this topic, contact a moderator using the "Report Post" button.
Top Bottom