Zappulse PSU wiring problem

Hi, can anyone familiar with the LC Audio predator PSU tell me what I might have done wrong here.

I have wired my predator PSU up as shown in the photo below, since it's a dual mono supply I thought I was doing the right thing by shorting the inputs across as shown...

However, when I powered the thing on I promptly blew all the fuses, and on testing with a meter I can see that even with all these input power wires completely disconnected I have a short from any of the power input connectors to earth... There is also a short between any two power inputs

Does this suggest that I have fried something? Any ideas on what and why?


Ed W

I also have a predator power supply and I am very disappointed that LC have not produced any documentation to go with it.

For experts this is not a problem but for people like me it is, the module does not even have any markings showing where the DC is and the transformer connections have no markings either.

I am amazed that they have produced this board without any documentation.

I wanted to use mine with a centre tap transformer but I have not been able to work out if this is possible.

I have told LC audio all of the above :mad:
From what I have understood, this is incorrect. Wire both secondaries to one predator in the way shown in the picture and circuit

Then you will have to either get another transformer or just parralell wire the other predator of the other. That is, wire pin 1 to pin 1 etc.

Best option in my opinion is to buy another transformer, one for each predator. Mono blocks.
Hi Thanks for your thoughts. Can you expand on why you think my wiring is incorrect?

I am basically just paralleling one secondary into each powersupply. I could put two secondaries into one powersupply and then parallel across to the other I guess? Don't see that it would make much difference mind?

As for second transformers. These are 1Kva jobs, and I could never fit two of them into any practical case (or lift it), and I don't even know where I could get two reasonable sized 500Va ones from. So I think I am stuck with this one.

Basically, I'm not sure how I have blown up the board with this wiring...?
wytco0: We chose to publish our documentation online, not on paper.

In this case our online documentation can be found here:

This way people can browse our docs before purchasing anything, and even find it years after they may have thrown out the papers that came with the unit.

ewildgoose: You are trying to get one transformer winding to produce both negative and positive voltage simultanously. It can be done, but will never be a very good solution. And definitely can not be done by simply parallelling the two bridges for positive and negative supply directly like shown on your picture.
I think this is an example of how things can go wrong when the user hooks the module up in a completely other way than suggested in the instructions provided by us. (above). I suggest you get a transformer for each predator power supply, and then hook it up as shown in one of the two different examples on the above page.

Then you will have no difficulties at all getting it to work correctly.

Nice antique chair btw :)

All the best from

Hi Lars, thanks for responding (especially as I hear that you are out of town at the moment?!)

OK, I don't quite understand (yet), but I think I am starting to think that the second bridge rectifier is the issue...?

I definitely can't fit two transformers into this box (it's an 80mm high case of the max width/depth possible from the supplier. 500Va and above transformers aren't going to fit if I have two of them). Right now I have a 1000Va transformer in there.

So is there another way that I could wire this using only two secondaries, but with two predator PSU's? How about the suggestion above, to use both secondaries to one supply and then parallel each secondary to the other supply...?

Finally, I guess I have destroyed some components on the PS board? There is an open circuit to earth on both boards. I guess this means that I have at least blown the rectifiers? Am I likely to have also blown the ferrite beads and small caps? Nothing looks obviously damaged, ie there are no external clues like burned components.

Can you provide some advice on RS or Farnell codes for these items so that I can replace them (or would you be willing to repair the boards?)

Thanks Lars

Ed W

P.S. I see what you mean about the "antique" chair... Hadn't noticed it in the picture before! It's an old rocking chair which folds up - and it is rather nice actually!
I might be interested in your amp. Couple of questions:
1. How much is 1 Euro equal to US dollars?
2. How much would you estimate for a 2 ch amp with everything except the case, jack and speaker binding post?
3. For a 2 ch amp, what are the items that I need to order.
4. Does the amp has balanced input?
5. Is it really true that it can drive Apogee Scintilla speakers with ease?
Lars, Thanks for the link however I have seen that before, the problem is that it isnt documentation for beginners :)

In particular :-

It does not say what the connections are, there are 2 blocks marked trafo 1 and 2 (or similar) each has 4 connectors, what are they? what wire should go into each? What is each individual connection?

Ther is another block with 2 connectors, what is that for?

There are no markings on the board for DC connections, what are they?

I wanted to use a centre tap transformer, can that be done? if so how?

Sorry if this all seems basic stuff but I have not been able to work it out even looking at the pictures from your web site.

What would be excellent for me is a simple annotated picture showing which wire goes where for each of the different inputs and the same for each of the outputs. What I am suggestion would take at most one sheet of A4 and could be on the website as a download. It would make a huge difference to me.

So it should explain how to connect the AC with a single transformer, with two transformers and hopefully with a centre tap transformer and in addition how to connect the DC.
Lars Clausen said:
Ed: If you had a fuse in your primary, you will most probably not have destroyed anything.

Hopefully true. I had a fast blow fuse in the amp, and plenty of standard slow blow fuses (plus the distribution board rcd things).

However, I measure a circuit to earth on these two PS boards from any of the AC inputs. On a space predator board I don't measure this... This is why I suspected some damage?

If you are going to use 2 PSU's then parallel them after the bridges instead.

Bearing in mind that we are talking about your predator PS boards, does this effectively mean parallelling out the DC outputs?

You can see half my amp in the picture before. Basically, there is another setup the same on the flip side. There is only space for one transformer, and even fitting in two PS supplies is a little tight. To parallel the DC outputs I would have to have quite long wires across to the opposite modules (about 28cm).

If I go with a single predator PS then I will still have to have quite long DC wires to reach each side of the case (16cm or so).

So with the above info, what's my best alternative here? (Oh, and it's my big IB sub amp, so having a fairly stiff PS would be useful)

1..1 Euro is roughly 1$ 20 cents. You can also get the prices in USD on our
website, by selecting USD on the left bar, and hitting the Change button. (Or any other currency).

2..Around 660 USD with everything.

3..2 modules, 1 predator PSU, 1 transformer 500 VA that's it.


5..I believe so, you have to disable the protection circuit though (see how on our 'need to know' page about zappulse on

wytco: The 4 connections are for connecting the 2 secondary windings in the progress similar to the way you would draw it on a piece of paper.
A tooid always has 2 secondary windings, not a center tap, unless it is made artificially inside the transformer.
See also the schematic.

A center tapped transformer is not compatible with our power supply, sorry. Use a double secondary transfomer instead.

Best regards

Lars Clausen said:
Ed: yes your best option is to parallel the two outputs even if there s a long wire in between the power supplies. As long as there is a short wire from the capacitors to the modules, everything is fine.

You are giving me half the answer here...

I can't really see how it would make sense to do what you describe? The whole point of the predator board is to stick the caps on it... By the time I parallel the outputs of the rectifiers on these boards, then desolder the caps to place them closer... Actually, hang on, I'm not thinking straight, how am I going to wire up the two boards in the first place anyway?

Look, lets start again. My bag of bits is as follows:

2 Zappulse
1 case: 30cm wide with 1 zappulse on each side (want to leave it like this)
1 1000Kva transformer with 2 secondaries
2 Predator PSU supplies with 15,000 caps (possibly broken)

[also available, enough (4) rectifiers and 10,000 caps from Jan-Peter to build some PS supplies)

So to start again, can I get your recommendations to wire these things up please? I'm just a bit stumped since my original design is clearly flawed

wytco0: You are right that a straightforward wiring diagram might be nice. But to be honest, it you have those pictures and the circuit diagram, then the rest is not too hard to figure out.

You can see most of the traces by looking at the back or front of the board. The only tricky ones really are the gate drive connections.

In answer to your question though: AC input you can see by looking at the traces on the board and the photos. The DC outputs are two sets of +ve, ground and -ve. The -ve connection has a second hole above it which is the gate drive. So to be clear, that's two sets of three holes across the bottom of the board.

So are you clear now?

P.S. When you buy a bag of rectifiers and caps from RS you don't get a wiring diagram from them either. Please don't beat Lars up too much over this. Perhaps you would be interested in writing this info up if you find it useful..?
ewildgoose, I am sure your right but you are assuming I know more than I do, Some of us are happy to connect modules together but not to do more complex things like build circuits from discrete componants.

Over the years I have bought a few modules from different suppliers and they normally have a single sheet giving the inputs and outputs, thats all I want and need.

As I said earlier I have already made all these points to LC and they have chosen to leave things as they are, that's is their choice and its my choice not to buy their products in future.

If I have upset anyone, in particular Lars or anyone at LC then I apologize that was not my intension.