 Hello everybody and welcome back to my V-LOG, to my channel. Now today is going to be a quick look at a basic unregulated power supply for our, in this case, for our AI math, I'll stick it on the screen, MX50. And now we looked at this last week and we could see that if we run at 25 volts on it, then we would be all right for the quiescent current. Else if we went up like 31 volts it started just climbing, climbing, climbing. It was going to basically turn class A impossibly and just end up breaking. It wouldn't be any good at all, but at 25 volts we seem to be okay. So we're going to build ourselves a power supply in theory, in using these components and I'll show you one that I've already built. But I think the main question is going to be for a lot of people is how would you know then what transformer you need for your power supply? So we said that this would be running at 25 volts positive, 0, and 25 volts negative. So we've got that sort of 50 volt swing. In the center there was some luscious, but we're not going to talk about any of those sort of things. We're just going to talk about the power supply for it. So what you need, you need a transformer and you need a rectifier. You may or may not want to use, but I'd suggest you do, an X2 filter capacitor just for that, you know, picking up noise and stuff, help suppress all that when handy. And you're going to need some capacitors because we want a positive and negative power supply. So here is a little diagram that I've put together. And in this we will have our primary side of our transformer. On there we're going to have a slow blow fuse, and we're going to have a switch. We're going to have the output from that transformer, the secondary, coming into the AC side of our bridge rectifier. It may not look like this. And then we're going to have the positive side coming out of our bridge rectifier, the negative side coming out of our bridge rectifier, and our centre tap from our transformer going through to the inside here part of the capacitors. Now I'm going to show you this on a natural thing. Where I say centre tap. So here this is a 18 volt transformer, 18 volt AC. These two put together like this will be our centre tap. So we will have positive, a virtual ground which will be our negative, our ground, we're going to say ground, our zero point, and then our negative. But how do we know which transformer to use? Well, we can work it out like this. I'm going to show you now, you might want to jot this down. So if we have our transformer, let's say here we've got 18 volts, and we can say right, so we want to know what do we get out of an 18 volt transformer. We have to keep it to our voltage, whatever voltage you like, but for this instance it's an 18 volt. So we're going to say 18 times 1.414. Now it doesn't matter about how you get these numbers or where they come from, and it's going to tell you straight away, look, down here, 25.452. That's the output you're going to get 25 volts. But let's say it's the other way around. Let's say we don't have that, and we want to say, right, we want 25 volts. We know we want 25 volts on this, 25 volts, zero, and a positive 25 volts, zero, and a negative 25 volts. So we're going to do it the other way around. We're going to say, right, we want 25 volts, we're going to say 25, and then we're going to times that by 0.707. And as you can see there already before even click the equals, we've got 17.675 volts. Now there isn't a 17.675 volt transformer, unless you spent a lot of money to get it all made, specifically, you just go straight for an 18 volt, and that's what we've done here, straight for this 18 volt. So that's the maths behind it. A little bit more maths when you think about, okay, so we want to have a bridge rectifier, right? Because we need to turn this AC into DC. So we use a bridge rectifier, I'm not going to go through how the bridge rectifier works, it's going to take too much time. But what we want to do is make sure that we have a bridge rectifier that's big enough, because we're going to have some in-rush current. We're going to have in-rush current because we're using a transformer, we're going to have in-rush current because we're going to be using capacitors. And so we want to say to ourselves, all right then, so ball rule of thumb, let's make sure that we've got a bridge rectifier that can handle, let's say, 12 times of what we want. So we're going to be pulling a couple of amps. We want a bridge rectifier that's going to be good for 25 amps. Let's just say 30 amp or 25 amp, that will do. And I'm going to show you how it's applied now because this is how this would be set up. This is the X2 going across the inputs. We should be this going across here, inputs to the bridge rectifier, and then everything coming off the bridge rectifier would have these capacitors here. And I'll show you on this what that can look like. So here we are, we've got our AC input. This is going to be, let's say, positive, negative, and we've got our capacitor in parallel with those. We've got the two AC inputs here. And this is for the zero, the center tap of the power supply. We'll just go in there like that. And they will go through here. And this is where our capacitors hook up. As you can see, there's a negative there going to the positive. The positive is then connected to the negative. And we've got the positive side there. So this will be the positive out. This will be the negative out. And this one here will be the center tap, which will give us our zero. And that's it. That's how I connected mine up. And this is what I will call my sort of semi-universal bridge rectifier on the capacitor bank for doing these types of audio thing because these are rated at 63 volts. And they're 330 microfarads. So five of these gives me about 15 millifarads. And you go any higher than that. And there's a law of diminished returns type thing kicks in. But that's great. If you've got a power supply and you're pulling off heavy base and it starts to try and pull your voltage down, at least you'll have some current in here to make up for that pretty quick. So you shouldn't lose anything. And that's good. If you have this sort of thing at 25 watts, you may not need all these. You may just have a couple of these. But it's up to you. You build up your circuit like that and you end up with something like that. So you can just plug in, like I say, your positive and your negative or go in here, positive and negative. These two go in here. And what you get out of here then is your DC. And we've done the math to show what DC you get out of here, which is just about 25 volts. Now you're going to lose one and a half volts because within your bridge rectifier you have four diodes and you're going to have two diodes working when you go high, positive, from zero to positive on the sinusoidal wave. You're going to go down to negative. And as you go down from zero to negative, you've got the other two diodes working. So you switch them between the two diodes. Different video for then how it becomes DC on the waveform. So you're going to take into account you've probably got a 0.7, 0.6, 0.7 loss of each diode. You've got one going out, one returning. So let's say one and a half volts. So you're going to have a little tiny bit of loss there, but on this, don't worry about it. It's going to be fine. So there you go. I mean, these building these unregulated power supplies are so simple. Now some may say, well, why don't you use regulated then? Why don't you put 30 volts in or something and you got your 25 volts out? Or 35 volts in 25 volts out. Because when you start using regulators, you've got to remember that your regulator is only going to be for a certain amount of current. Like this at the minute, it doesn't matter. You're going to be regulated by your transformer. So with this one at 18 volts, and we got what we got here, 3.3 amps per side, 0.18, 3.3 amps, 0.18, 3.3 amps. This is 120 VA. So this is good. This is more than what's needed for this. But it makes no difference. This is only going to pull a certain amount. You can't pull more. You put the voltage in and it's got that amount of swing. You can't pull any more really than that unless we're in some sort of failed situation, which is very enough. That's why you want to fuse and bits and pieces. But that's it. Simple as it is, my friends. You want to make an unregulated power supply for these types of amplifiers. This, because it's 63 volts on here, this means you can use up to 40 volts, let's say, giving yourself a 20% headroom. Just give yourself a 20% headroom on these things. It's a rule of thumb and you'll do okay. Hey, that's helped out at least one or two of you. And I shall talk to you in the next one. We've got another amplifier to build. And I'll catch you then. Bye-bye for now.