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littlerick 28th November 2009 08:46 PM

LM4870 Noob mess up
I have a situation that i'm trying to resolve.. I messed up the diodes on my rectifiers by only half reading the intructions.. Anyway they went in back to front.

Peter said that it is possible to reverse polarity and use it as normal... However I have already tried to remove the first 8 from one rectifier with little success. I ended up snapping the pins off a few MUR's.

My question is.. Would it be possible to use the one rectifier I have with diodes in wrong way, to power both amp modules.

This is my first project and I have only myself to blame for errors, but I would like to know if I can make it work.... More chance of the wife letting me do project 2 ;).

littlerick 30th November 2009 07:27 PM


Peter Daniel 30th November 2009 08:22 PM

Yes, you can use one rectifier board to power both amp modules; with a single transformer that's what I actually recommend.

Before you connect anything, check for proper voltages with a meter.

stratus46 30th November 2009 08:34 PM

Is the goal to remove and re-install the diodes in the correct orientation or are you just interested in not damaging the PCB? The clearance of the leads into the holes has a big effect on how successful you will be extracting the parts without damaging them or the board. Personally, I would cut the leads off the diodes and unsolder / extract the pins and then install new diodes. I know it's a pain getting more parts but getting new boards is usually much worse.

The (un)soldering tool has a big impact of how you might proceed. A cheapy not temperature controlled iron is most likely to damage the board and have insufficient heat to get the holes cleared. A decent temperature controlled iron (and not some piece of junk with a dial and a readout) improves your odds. A premo iron like a Metcal makes it almost easy - certainly for me. Still, if the hole / wire clearance is very small it _will_ be difficult and the best bet is to just clip them out and use new ones.


littlerick 30th November 2009 09:16 PM

Thank you

littlerick 4th December 2009 12:37 PM

I have both Amp sections completed. Gonna be after xmas before I get transformer so no more rushing!

Couple of questions I would like to ask...

Do I need to fill the zobel spaces with anything or does amp work without putting anything there?

Where do I connect my volume control?

I have got input and output sockets, would I be better testing before fitting these or wont it make a difference?

I know you guys can knock these kits together in no time, but its my first time with a soldering iron, let alone a kit like this.

Peter Daniel 4th December 2009 06:50 PM

Zobel is optional and I usually don't recommend it.

The volume control is connected to amp's input, see this for more details:

I guess it's actually easier to check the amp with input/output connectors attached.

littlerick 4th December 2009 07:56 PM

Should i solder a piece of wire thru to replace the zobels or just leave the spaces?

Peter Daniel 4th December 2009 09:27 PM

Not at all: putting wire there will short output to ground.

littlerick 17th December 2009 07:19 PM

Next bit... I understand that the LM4780 cannot be grounded to chassis. I guess this also means my heatsink cannot touch the ground too.

If I build a wood case do I just run a ground from my mains earth wire to a point and connect other grounds.

I was gonna go with aluminium case, but I think wood will be better for first go.

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