Hi Just trying to educate myself in the dark arts of electronics. Have a question on wiring up a Chinese amp board I bought. Has the following on the power inlet side 12v/0/12v Do I use just one + to one of the 12v hookups or do both have to have wires to them. Sorry complete newby at wiring so bear with me. Any help gratefully received. Tim
It is quite normal for amplifiers to use what they call a split rail power supply like you describe. It avoids the need for an output capacitor which can limit bass response. In theory the output of a split rail amplifier can go down to sub-sonic frequencies e.g 5Hz. The usual way to provide the positive and negative supplies is a centre tap transformer, with a capacitor for each rail, although some early transitor radios used two batteries. The size of the transformer will depend on how much voltage and current your amplifier needs hopefully the instructions will tell you. Toroidal transformers are best but more expensive To get the AC voltage required divide the DC voltage by 1.4. Don't forget mains voltages need to be treated with respect. Also make sure you have a corectly sized fuse in the circuit (3A unless you are going above 700W) Here is a complicated circuit which gives the idea https://www.petervis.com/electronics guides/split-rail-power-supply/split-rail-power-supply.html most amplifiers don't even bother with the regulators which will only give a small increase in performance. Looking at the picture you posted it looks as if you might already have the power supply components on your board. If so all you need is a centre tap transformer something like this https://www.ebay.co.uk/itm/220-240V...265259&hash=item5212861be8:g:aNEAAOSwteFb0x35 How many watts is the amplifier? You want the transformer big enough to cope with the amplifier wattage. How do I know all this ? In 1978 my college project was a 20W per channel stereo amplifier based on the one in this magazine. https://americanradiohistory.com/Archive-Practical/Wireless/70s/PW-1972-05.pdf Have a look at how the supply in it is done.
Hi thanks for this I think this is just on the limit of my under standing. I was going to use a straight up 12v 5amp transformer with 5.5mm barrel connection but clearly this will require a rethink. The thing was this was the only amp I could find that had the pots remote to the board so it was a bit of a punt on my part. And with the added issue of no instructions. I'll have to some more reading I'm sure. But thanks for your input, very much appreciated. Tim
+1 to what @Longman said. 12 volts are not marked as +12V/-12V and right behind it you see four diodes of a rectifier, so probably it is designed for a dual 12V ac transformer, like this one: https://www.ebay.com/itm/Dual-12V-24V-AC-5W-Power-Transformer-115V-230V-Input-/260791813163 and Welcome To The Club!!!
You probably want something a bit more than 5W unless it is a headphone amplifier. What are its specifications ? The transformer I posted was 72W so would probably be OK for most domestic systems. I was going to say you could use two separate 12V supplies but thinking about it that wouldn't be a good idea. If they started up at different times it would cause a massive pop in your loudspeakers. Using a single transformer ensures both rails will start simultaneously. It might be worth doing some more research on your amplifier. I get the impression that many of the Chinese products on the likes of Ebay are actually copies of magazine articles, semiconductor manufacturers example designs, or even famous Hi Fi manufacturers products from the past.
Hi And may I say a firm think you for both your inputs. The electronic fog seems to be clearing in my head now. So the board is not huge, as I may have said before I was looking for an amp that had the pots separate to the main board as I'm making a boom box 2.1 15w per channel and whatever the sub would handle. This seemed to the only board around. I've attached make pics as you say it's dual rail 12v @ 30w and 2amp . The board also has a breakout for 5v, which will drive the Bluetooth board and everything else is as indicated. So to recap as long as I find a transformer that will deliver 30w I'm good to go? I have and old DVD player that has a small one inside, I'm wondering if that will do? Once again the help is much appreciated. Tim
Did you get any amp board specs from the seller? If not, then check the rating of the parts used (DigiKey or Mouser are the easiest places to start) and maybe find an excuse to insert a fuse in the power supply. If gentle with volume knob, nothing dramatic happens if your amp board will be underpowered by a wimpy DVD transformer, at least not right away. But, as I suggested before, listen to @Longman The bigger the transformer, the better... and there is NO limit on how big it can be. Here is my 20W CD player, Naim CDX. As you see, its toroidal transformer is bigger than in some amplifiers: And once I upgraded to an external power supply (Naim XPS, with transformer taking half the space of the same box), the sound quality of my CD replay went to yet another level
Hi Yes sorry meant to post that pic as well here it is. I've got a 50VA toroidal transformer coming? So hopefully it will do the trick. Do you mean an online fuse in the UK we have a 13amp fuse in the wall plug.
50VA should be fine. The transformer in a DVD player is unlikely to be suitable. Hopefully your transformer will come with the mounting hardware. I saw lots of toroidal transformers on Ebay but the pictures didn't show any mountings. Looking at your pictures I can see three audio amplifier ICs which will be the left right and sub. Look at them to see if there is a part number. If so as Jorge suggests you can look up the data sheet. A 50w transformer will only take 0.2A so put a 3A fuse maximum fuse in the plug. You don't want too big a fuse as it won't give any protection against faults. In Europe a circuit with a 13A fuse can supply 3KW. Maybe what you need for a stadium but not a small home amplifier.
