Noob LM3886 Kit Amp Questions [pics]

[MunkeeVegetable]

Hi all, I've just ordered Brian's LM3886 dual-mono kit from Chipamp.com and a 160VA 2x25V Toroid. I've been planning out how to build it. Please be patient with me as rather noob.

Here's a few pics of one of my ideas, I was hoping for some C&C regarding placement of things and potential problems/improvements. Keep in mind I currently only have a single toroid, so ignore the second toroid in the pictures.

Also any ideas into actually MAKING the damn box would be greatly appreciated too, as although I've done some metalwork for PC cases I don't have any special tools and I'm hardly skilled. I have a stack of 2.5mm aluminium panels and I have one 500x90x6mm piece for my frontpanel.

Another query... does anyone know where to get a good audio potentiometer in Aus.?? I have a few 10k stereo pots in my junk box, but I have no idea if they're any good.

And yet another, can I use my "Delta Electronics" EMI filtered IEC socket?? Will it actually be beneficial or am I better off using a standard socket (e.g. one from an old PC PSU)?




Here are my three basic plans, not sure which is best... all have pot near amps to minimise the length of the signal path.

1. Stereo setup, internal heatsinks for chips providing interference shielding from mains/toroid.

2. Dual-mono setup, external heatsinks for chips. PSU boards next to amp boards. Aluminium panels provide shielding from mains/toroid interference.

3. Dual-mono setup, internal heatsinks for chips provide shielding from mains/toroid interference. PSU boards 90° to amps on backpanel. (As per above pics).



Thanks all!!

--
Nathan

[anatech]

Hi Nathan,
A couple suggestions for you.

Try mounting a flat piece of metal behind each heat sink to create a tunnel effect. Open the metal case above and below to allow clear airflow through the fins only. Normal ventilation will be required for the other components. Now you have increased cooling efficiency and the transformers will not be warmed as much by the heat sinks.

One AC power entry is enough. You can route the AC to a front panel switch with a power indicator. You can use copper tubing if you want to shield the primary cables.

Other than that, your idea looks just fine.

Some potentiometers are over rated. Use what you have until you can pick up something you feel is better. Alps or Nobel controls are more than adequate. Don't obsess over the details or you will never finish it.

-Chris

[MunkeeVegetable]

Ok, I just went out and bought a bayonet "Battenholder" so that I could put in the 'safety' bulb tester thing for when I test my amp.... but I can't fathom how I can possibly wire the amp power cable in series... there are 4 terminals on the bottom, I've wired up live/neutral/earth and the lightbulb works fine. What is the 4th terminal for? Is that a terminal that connects to the circuit after the bulb for exactly what I'm trying to do? (In which case I'd also obviously be wiring neutral/earth in parallel.)

Thanks!!

I'm surprised that these sorts of things don't have basic instructions on the back (e.g. terminal identification at least) although I suppose that it's to stop people who aren't 100% killing themselves by even trying...

--
Nathan

[MunkeeVegetable]

Ok, now that I think about it.. if the "Neutral" wire is the 'return' wire.. then do I wire that to the live pin of the amp, then the neutral wire of the amp going to the neutral of the original wall plug?

I.e. Like below (please excuse the horrid description)

Wall-live --> Light-live || Light-neutral --> Amp-live || Amp-neutral --> Wall-neutral.

--
Nathan

[AndrewT]

NO!!!!
wire the safety Earth wire AND the neutral wire straight through from Plug top to socket outlet.
Wire the bulb socket in series (in line) with the Live wire coming from the plug top to the socket outlet.

All the current fed to the socket outlet MUST pass through the bulb filament.

If you plug in the test bulb with the socket outlet empty, the bulb MUST stay off, not even flash, however briefly.

[anatech]

Hi Andrew,
Did you come out of your chair there? Good catch!

Hi Nathan,
Listen to Andrew on this type of wiring. Is there any way you can power this up using a bipolar DC power supply? It's easier and you can come up slowly. Once you are sure it'll work, you can use the light bulb method.

-Chris

[AndrewT]

Hi Ana,
bum cheeks stuck fast to the chair, but quick arms/hands
But the mind games prepare me for the West Coast Swing class I was getting myself psyched up for.

Come home from that class and discovered I need more mind games for next week's preparation. My "dancing" was not nice to watch. Shame the girls had to take a hand in my attempts.
Now if you were to turn up for the Ceroc on Saturday, the girls will be purring.

[anatech]

Hi Andrew,

Now if you were to turn up for the Ceroc on Saturday, the girls will be purring.

Only if hunting has been poor for the cougars.

I don't dance. I refuse to. Therefore, I am worse at it than you are.

-Chris

[MunkeeVegetable]

I won't be wiring the socket in until I'm 100% sure. That's why I'm checking now, before I get any amp bits, so that I don't get excited and wire it up stupidly, at the moment I just have the lightbulb wired in, all wires are heatshrunk or inaccessible and the cables are zip-tied down, so no movement of anything dangerous. =)

Originally posted by AndrewT
NO!!!!
wire the safety Earth wire AND the neutral wire straight through from Plug top to socket outlet.

I just keep confusing myself. I realised that the wall-neutral had to be wired directly to the socket, and the safety earth has to be wired directly to both socket and lightbulb. So as to give the current a path to go through in normal use (lightbulb-socket-neutral) and in case of failure (straight to earth).

Wire the bulb socket in series (in line) with the Live wire coming from the plug top to the socket outlet.
All the current fed to the socket outlet MUST pass through the bulb filament.

This is the part I wasn't sure how to do. How do I make the bulb in series with the socket? Doesn't the current pass through live terminal on the lightbulb and out the neutral terminal?

So do I need to go.....like this? I'm thinking my previous description was unclear as to what I meant.

Wall-Earth ------------> Lightbulb-Earth
Wall-Earth ------------> Socket-Earth
Wall-Neutral ----------> Socket-Neutral
Wall-Live --------------> Lightbulb-Live
Lightbulb-Neutral ----> Socket-Live

Sorry for confusion! Thanks for your help!!

[AndrewT]

Hi,
yes, your reworded description confirms you understand the wiring.
I did not realise your bulb socket had an earth terminal.
It's OK to wire a Safety Earth to this terminal. But does it go anywhere? Or could it just be a termination point to joint the cable?