Armageddon Clone

Right, for those wondering, the Armageddon is an off board power supply for the Linn LP12 turntable made by Naim Audio.

It is possible to make your own very similar power supply with some simple components. Have a look over at Neil McBride's website for more background to this - there's a lot also on The Vinyl Asylum - do a search for "DIY armageddon".

I've now completed mine, and so I thought I'd shove some photos up - a lot of the info seems to be in plain ASCII drawings, which got me a bit confused at first.

One this to stress before we go any further is that this is all at your own risk, mains voltages are involved, your Linn/Naim dealer may never talk to you again, etc etc.

....Oh, and finally, I've tried to make this as understandable as possible, but IF YOU DON'T understand it, then I suggest you spend a bit more time reading up on the basics before attempting this - electricity can kill!

Preparation

Thought it might be useful to see some pics of what you're going to be dealing with, so here goes.

First things first - unplug your LP12 a good while before you get started, as the capacitors on the Valhalla board will take some time to dischage, and could give you a nasty shock.

Make sure you remove the platter and lid before you move the Linn - I was also able to take the arm off, as it's a Naim Aro, and easy to remove. If not, put the stylus guard on, and make sure the arem won't move around and get damaged.

First thing you'll need to do is get the baseboard off. This is held on with 6 screws - one in each corner which also hold the feet in place, plus two in the centre of front and back. Make sure the Linn is well supported while you remove these!!

Once the baseboard is removed, you can see what you're dealing with. The big circuit board in the pictures below is the Valhalla, which will be superceded by the Geddon - I guess you can leave it in place, or remove it and frame it, or something.

The Circuit

Here's the basic circuit, plus a twiddly one I'm trying out, based on suggestions from over on the Vinyl Asylum.

Component values seem to be the following:

R1 - 3.3K

C1/C2 - in fact, you can use 1 capacitor of 0.22uF (220nF), but a closer match is by summing two 0.1uF caps to make 0.2uF. I've used 250V polyester caps.

The Transformer

Right, so you've stripped the Linn, you understand the circuit, you need the components. The main component is going to be the transformer. It will be the majority of the cost, and is the thing that can kill you, so MAKE SURE YOU UNDERSTAND WHAT YOU'RE DOING!

It took me a while to get my head round these beasts, and I'm no expert, but for what it's worth, here's some info.

The transformer does what it says - it transforms mains voltage to a different one. That's it. We want a final voltage of around the 110v level, so we need a transformer that converts the supply voltage (240v) to 110v.

There are loads of different types, but the type we are using for this is a toroidal transformer - it looks like a doughnut.

If you look for a toriodal transformer, they will come in a variety of flavours - centre tapped, dual secondaries, etc. Have a look below for a photo of a couple, and notice the scary number of wires coming out of them - particularly the one on the left.

Look at the circuit diagram above - the bit labelled T1 is the transformer. If you look on the transformer itself, you'll see a similar picture, (see closeup), with the wire colours labelled.

Now as we're in the UK, we need the primaries (the left hand side of the diagram - where the supply comes in) to be set to 240V. Looking at the close up picture, you'll see that we have two sideways "U" with 0 at one side and 120v at the other. This is a dual primary setup. To make it work for 240 volts, we need to join the centre 120v (labelled grey below), and the centre 0v (labelled vio below). This then gives you the setup as shown in the circuit above.

The secondaries are more interesting, as there will be a variery of options. You may be lucky and just get a single set of leads out, like the one shown below - black and red. More likely there will be dual secondaries. In this case you may have two 55v secondaries, so join them in a similar way to the primaries - middle wires together. I found this page quite handy for seeing the different configurations a transformer can be used in - remember that the wire colours will vary by manufacturer.

Mounting the transformer

The transformer should come with a mounting kit - this will comprise a bolt, nut and washer, plus a large steel "washer" and rubber gasket (I know it's not really a gasket, but that's the best description I can give). Both are about two thirds the size of the transformer.

Decide where the transfomer will go in your case, then mark a centre point. Drill a hole large enough to pass the bolt through. Then sit the transformer on the rubber "gasket", and sit the large steel plate/washer on top, with the "bump" downwards. Pass the bolt up from underneath, through the gole in the top plate, and fit washer and nut. Tighten, but not TOO hard.

Make sure that the bolt cannot touch the top of the case, as this might allow current to pass through the centre of the toroid - a very bad thing.

Wiring it up

When joining the wire, make sure the connection is good - I soldered, then put insulation tape tound and finished off with a bit of shrinkwrap to keep things tidy. I have used crimp (spade) connectors on the ends that are going to the supply and board - the switch is bound to have these, and it makes things much easier to connect.

To use a spade connector, insert the wire into the top (narrow) end, and crimp it hard to hold the wire in place (best if you have the proper tool - you can buy sets with connectors and tool from most cheapy market tool stalls for about Ģ2). I've also discovered some nice ones that you can solder the wire to, and use some long nose pliers to crimp on to the insulating later. See parts list below for more details. So, finally, in my case I'll be connecting the incoming mains voltage to my blue and brown wires, and the circuit board will be connected to the red and black wires.

The Board

Here's my circuit, banged together. I didn't use stripboard, as I thought thicker connections would be better, so it's all hardwired using solid core wire (I just stripped a bit of twin and earth mains cable - the stuff you use to wire a house). If you don't have any of this (and you have to buy it on 50m rolls), then you can probably get away with bending the excess wire on the resistors and capacitors to fit. The letters refer to the circuit diagram above.

A is the connection for the transformer
My switch will go between B and C to drop the resistance (and therefore increase the voltage to the motor) for start up.
A variable resistor will go between C and D to allow me drop the voltage as much as possible (hopefully this will be a one off twiddle, but comments on the Vinyl Asylum suggest that it may drift and so need occasional adjustment).
X and Y will be the connections to the red and blue wires from the LP12 motor.

For any internal wiring, I'd just strip some mains cable into its individual cores - if you have bought some 4 way cable to run the power from the Geddon box to the LP12, then get a bit extra, and use some of that.

The Box

The case for the Geddon is made up of 1.6mm and 10mm aluminium sheet. It's a half width case, and I've been a cheapskate and also squeezed in a power supply (tranny and rectifiers) for my 4 channel power amp (not at all flat earth). Follow the previous link for more on the case.

It will generally be easier to buy a box "off the shelf". If you can, get an aluminium one - it's easier to cut and drill. By far the hardest part of handling the box is cutting the square/rectangular holes for the switch and IEC plug (yes, it's a panel mounted plug - the bit on the end of the mains lead is the socket!).
I tend to mark out the space required, and drill a hole in each corner. Then use a jigsaw with a metal cutting blade to join the corners, finishing off with a flat file. A Dremel is also great for hacking up aluminium, but hardly worth buying specially for this job - unless you want an excuse! I was lucky, and picked up a Black and Decker Wizard (their version of the Dremel) for Ģ20 a while ago.

The blue and white cables running from the board to the left (front of the box) are for the resistance dropping "extra grunt" switch. The blue and white cables running to the right (back of the box) are to the 3W variable resistor.

I bought a 3 way socket and plug for the connection to the LP12, then realised that I needed a 4 way one. For the moment, I have retained this 3 way item, but put the earth as a flying connector separately. Next time I'm ordering, I'll replace this with the 4 way version.

Connecting it up

OK, we have the Geddon itself built, now to connect it up. LP12 back up on the tables, and a good light source underneath. Out comes the Valhalla board - there are 6 lugs it is mounted on - long nosed pliers and a bit of patience. It goes without saying that you have unplugged the turntable first! I released the motor, mains cable and switch ribbon cable before removing the Valhalla.

I removed the mains lead clips, and realised it would be handy to leave the earth cable connected, as I could use that to connect to my new earth lead, and not disturb anything else. So I cut that off and stripped it back ready to go into the junction box.

The second mains lead retaining clip attaches to the crossmember (you can see it in the first picture below) - I re-used one of the self tappers to fix my junction block in place - even re-using one of the holes the screws used before.

I found it easiest to connect the motor wires before mounting the connector block - be careful they are held down well, as they're fairly thin, and could miss the screw if you're not careful.

Final Comments

There have been some reports by others that their fuses blow on a regular basis. I must admit I've not had this problem. This seems to be solved by powering the primaries at all times, and using the front panel switch to power up the secondaries only. If you decide to go this route, you may choose to go for a switched IEC chassis plug, so you can at least switch off the primaries if you wish.

Remember that different configurations will be needed for those in 110V supplied countries - the transformer primaries may well be laid out differently, and another fuse value will be required.

Tool List

Soldering Iron - 25W
Soldering Iron Stand with damp sponge
Long Nosed Pliers
Screwdriver (cross head)
Flat file
Wire cutters
Multimeter
Drill and drill bits
Good work area with decent light source
Hacksaw
Jigsaw with metal cutting blade (optional)
Dremel (optional)


Parts Used

Note - all parts numbers are from CPC. Where I've not given a part number, I'm assuming you can get the item locally, or already have it in your bits box.

Solder  
Heatshrink CB00742 CB00741
Misc wire  
Spade Connectors (push on terminals) CN04716 (4.8mm) CN04718 (6.3mm) CN04720 (6.3mm right angle)
Covers: CN04723 (4.8mm), CN04724 (6.3mm), CN04728 (right angle hinged)
500VA (approx) Toroidal Transformer Encapsulated: TF00812 Normal: TF00831
Flange Mount Fused IEC Plug CN06437 (switched version CN06432)
2.5A Slow blow/Anti-surge fuse FF00360
DPST Switch SW01122 (NB this is a non illuminated switch, as there is some thought that the Neon in an illuminated switch may add noise to the circuit)
2 x 3K3 3W resistors RE01852
2 x 0.1uF (i.e. 100nF) 250V polyester capacitors CA01264
Bulgin 4 Pole Minature 3A mains plug and socket CN04061, CN04062
4 way mains cable Better to buy locally by the metre - CPC will only do it on 50m reels!
Terminal block CN0707566
Case EN81249 - Please note I have not tried this case, and you should make sure it is big enough for the parts - particularly the height of the transformer
Feet CPC only do these in large packs