 Hello everybody and welcome back to my channel I'm going to show you quick now what we got on the bench today And this is a little kit you can buy off eBay. This is based around an LM 1875 chip Which is not a bad little chip really when you consider the size of it and they consider There are a few components that you need to make this work in a relatively well fashion So what we got today, then is we got it hooked up and we've got our input coming in this does take a negative and A positive supply meaning that we got a zero in the middle and we're swinging negative and swinging positive on the rails there And at the moment I've set mine up to 17 volts The reason why I've done it 17 volts is because if you have a 12 volt transformer, which gives you 12 zero 12 You can run this then on that or if you have another transformer that will quite happily give you a 25 volts Either side, which is what they sort of recommend You can go to 60 but setup doesn't really like it You can actually go to 30 volts aside in the specs. We're going to see it's 25 25 now Let me just show you the specs there Let me just bring this across here, and you'll see here what we got is up to 30 watts output power Low distortion naught point zero point zero one five one kilo it's 20 watts Wide power bandwidth 70 kilo and we can see the wide supply range here We are 16 volts to 40 volts high current capability four amps. So It's like it says it's a 20 watt audio Power amplifier on one channel now if we were to look at the Screen quick just very briefly you're gonna see where I've been playing around with this and you can see there's a bunch of numbers up There, but if we're gonna do it again now from the start and start running the screen I can just back that off one time. I'm gonna use my little music player here. This is a It's a high be high res thing. It's got pretty pretty low distortion rate on it I'll put the thing up very quick on the screen there All right, and yeah pause take a peek at that if you wish But it's a pretty pretty low distortion and I'm using actually here these one kilohertz With a naught point one reference on it and this is from John audio techs channel Which is very good of him to make these available for us And I'm now gonna put the power supply on and run this oscilloscope So let's put on we've got two channels going over there as you can see And I'm now gonna click go on the scope And you're gonna see that we've not really got a great deal going on there Because we don't have any real volume on here, and I'm actually gonna press play as well So if I press play there You see a little bit noise coming there. I'm gonna go and start going up on this Volume all the way up to where I see about clip We will see it as it gets clipping it gets quite nasty quite quickly and there we go Okay, I'm slightly round on the top. So I'm gonna just back that off I'm just gonna back that down like that and we can see here We look across here and we put our measurements on we can see we got a this is our four and a half This is the naught point one percent, and we're down at minus sixty four point nine Let's just say sixty five on that. This is a three kilohertz and We are at minus seventy one And this is a second secondary two kilohertz Even harmonic there, and we're at minus seventy three and this of course is our is our main One kilohertz side now that's coming in at minus four point two six Seven six four DB whole bunch of stuff there, but as you can see like this is all very very low minus 90s minus hundred All right, and that's at That voltage now you can see over here. It says eight point eight volts This is on the AC RMS. So if I just grab hold of the calculator I'm gonna bring that into view and we go eight point eight And I'm gonna square that and I'm gonna divide it by the atome with this time using as a load And that gives us nine point six eight watts And that's using that would be using a 12 volt AC Transformer and then once you rectified it, you know time that 12 volts by a point four one four And you get yourself pretty much just under the 17 volts Okay, so that's what we get with our 17 volts. So let's just Start up in the power and I'm just gonna turn this down like what I do that This is on a loop. So it's just looping round and round around I'm just gonna turn that voltage down while I turn this voltage up on here So, oh, let me get it to a reasonable rate of knots So we can go to 18 20 21 25. Okay, that's 27. So it reckons 25 All right, so we got that there and we can see up on the screen there that we're doing okay So we just start taking that up and you can see already Our fundamental We got our fundamental of course here and we've got that Provided by us by John I'm gonna keep going up there Till we get to where we're clipping and that we can see a bunch of distortion coming through All right, I've got that yet. Let me just adjust this Over here. I'm just gonna go down and slightly and adjust this to If I put it to five on you might want to stick that in the middle somewhere We start going up here So we've got a five on and I'm gonna keep going up we're in 90 now and now we're clipping so my little We're on 90 now On here And as we can see from here if we start using our cursor is when it's gone free Come back here cursor We can see here. We've got a minus 61 db on that We got a little bit either side with minus 83 minus 72 Minus 68 and this is the naught point one If I were just to click down off that just a couple of times Bring that down to more suitable back down to where we were before was 83. I think it was We'd see then we got minus 64 minus 74 Minus 73 there And we would be Minus four point two five again if I take that up Just trying to get as close as I can to the zero point Which is not really I don't know if that is because it's there already I Think I might already be on it Can't seem to Know the minus two sorry minus minus two minus one Minus naught seven There we go, so I've got that on minus point two and there we got minus sixty there for our naught point zero point zero one Pilot and Minus sixty nine there and a minus sixty seven there, so you're not even gonna hear these anyway So you can see you can see quite further down here when it comes to looking for Distortion you can see over to the side here. We've got thirteen Thirteen point three, okay, so we'll go with that And on the power supply there it looks like we can actually pull out Just trying to see if there's much difference between that and the third harmonic there isn't And this is still the difference here We could actually put this on this and take this from a 4.5 and drop this down onto here and we got a difference of 7.97 DB Between those two and that's our secondary harmonic we got a difference of 9.5 DB Between the peak of our thunder but for the peak of our pilot and our third harmonic there which Yep, you're on a 5.7 DB there just sat on the top 7.6 by sorry sat on the top Okay So 13.3 is what we're gonna use. I'm now just gonna Stop this for a moment Because that's one of the nice things I do like about this is you can stop that you can turn off the power to things and Still take your calculations Okay, so I'm just gonna put that down And we got 13.3. So let's bring back in our Calculator We sure look at this so we can see the first one there with 8.8 squared it divided by the eight times We've got 9.68 watts and now we've got 13 0.3 squared divided by our eight times and that gives us 22 point 111 25 Watts of power which is you know within spec That is within spec now very quickly. We're going to jump across to the other way of measuring this And that's using the audio analysing suite Okay, guys, we've got the audio analysing suite happening We're gonna look for a THD and we're gonna be going from the range of 10 hertz 30 kilo hertz And we are gonna be looking Let's say at our 10 watts to start off with just very quickly then we'll go up to the to the next number Okay, so let's just power this back on again So 25 watts there Oh made a slight boo-boo. Let's just slow this down a little bit Gotta do something else before we can do this Okay, so we got a slight little setup change and now we're using the the waveform generator from the analog discovery to We're still using the same scope lead, of course We're gonna turn on the power Okay, and now we are going to run We're going from 10 to 30 kilo hertz 10 hertz 30 kilo hertz Steps 50 average is one. We just leave on there. We're doing the THD We're just gonna run that at 10 watts Which is our level at 10 watts here as you can see and you can see the power going up on the power supply there So it shows it does the lower The lower frequency So now we're below the zero point one zero zero point zero six zero point zero five zero point zero four It's nice. We're sticking up that tracking around there zero point zero five And on the data sheet it actually says zero point zero one But that's at 20 watts, I believe Which is what we're gonna do next. I just wanted to look at it what it's gonna be like on the 10 watts So let's have a little look over this just see what was happening there. We're at 13 hertz So we go to zero point one and here's our 20 kilo hertz pretty much It's just not telling us that at the end, but that is a 20 kilo line. You can see that ring down here as well Just over So, you know, it sort of stays on track there Okay, now what I'm gonna do now is I'm just gonna bump that up to 20 That's now run 20 watts eight times THD again, and we're gonna run that straight away I'm gonna do a quick little hand check on the dummy load. That's fine That would be okay You can see what the current it draws as it's pulling those lower frequencies Now we're at 16 Hertz now we're at 20 Hertz And we're at 0.1 So I should say 0.0 45 Hertz 0.04 0.05, 0.04 As we go up that, it's going across 0.05 It's looking at 0.05, which is quite nice Nice bit of linearity That's how you say it, 0.04 0.05, 0.08 I went up to 0.2 there Now we jump across there and you can see that was a little bit a bit Ringy at the end, but we were up into a 10% distortion And we are at 21 Kilohertz, which is we want to be down Below that as the highest we can go to really on this is 20 That's what it sort of gives us our Data sheet for So let's have a little look at the Frequency response going across that And if I put this around about I don't know three line level 300 millivolts RMS Let's have a little look at what that is Just channel one again Coming from the low frequencies of course It's building up and now we're on 20 hertz Which is where we're calculating from And it seems to be Pretty bang on All the way through though So let's go to our 20 hertz That's where we finish off at 20 hertz here I've just done the 21 hertz And that's good enough That's nice That's pretty much a nice flat response Couldn't really ask for Better end up particularly Let's just do a Power So we're going to go from 1 watt To 100 watts And just see where we get to Now I This is only good up to 20 watts We'll see where we get to anyway on this We see before clipping we get to 22 watts When we measure it against the oscilloscope And using the FFT So it'll be interesting to see where we get to here So we're now Coming up to 5 watts We're on 5 watts now This is the 10 watt line in the middle here And we are at 0.05 Now we're coming up to 17 watts 19 watts 20 watts 21 watts 25 watts Alright Well we've managed to get then Let's just We're looking at it to the 0.1 percent 0.1 percent That's 26 watts That's more than What we said we're going to be having And if we look at where it gets to 20 watts Which is what it's really rated for We're at 0. 0.06 But still even here it still does pretty well Until we get to there I'm not even really looking at this We just put that thing in there It does pretty good Alright So let's get rid of that for the minute What does this thing sound like? I can only give you the sound out of A speaker Which starts I think it's like 72 hertz So it's response is not very good at all But I can tell you I mean it's going to sound clear It's going to sound Decent as you can see We'll just put that back for a second A bit premature there As we can see across the frequency response We can see that you know from the low level From those 20 hertz Even down here 14 hertz So we're running it from 10 hertz here There's not a great deal of change 25.560b to 27 So 1.5 dB difference between here and here It does use a bit more power there of course But if you were running this for me If you were going to set yourself up with a little bench Or desktop amplifier One of these would be ideal Little D class thing Ideal to make sure you give it good enough heat sink That's warm, it's not terribly hot And I think you can leave your hand on that That dummy load is going to be a lot hotter But yeah this would work alright Two of these Set up like this Personally I would get rid of the caps that are on here I'd get rid of the little ceramic things that are down here Don't like ceramic caps on these things I prefer to have films on there Get rid of these, put some decent on Because these are just Chong X Which you know you can buy like bags and bags of them for a dollar So they're as cheap as you like caps And these are tantalum things Yeah, no But I've got another one of these boards I'm going to build it up I'm going to put some film capacitors in Electrolytics and we'll see How it does with that They don't expect to see much difference But I expect for sound quality There might be someone there and we'll be able to do it It becomes Paris and sort of The best mic I've got for picking up stuff Is this road one that I'm wearing And that's what we can try and use And just see what that's like But this video's got too long So I hope you enjoyed that And I will catch you in the next one