 The great search brought to you by Aford and Digikey every single week lately have used their power of engineering to show you how to use digikey.com Search this week the great search is It's a Catalyst stereo headphone amp. That's very small, right? I want to want to optimize for board size on this design. So let's go to the computer and I'll show the schematic So for my design I've got I've got my board and it has audio out in this case. I only have audio on a zero, but I'm gonna change that in design There you go so audio output and I want it to drive stereo headphone output and I want to have like a nice little amplifier and The thing that was most important for me is I wanted a design that was capless and what that means is if you look here There is no DC blocking usually there's like 100 or 200 micro farad amp capacitors on the output of the amplifier into the headphone and that's because like you don't want to have any DC signal Going in normally a class a or class a B has a or you know even class D Whatever they have a DC offset, right? Usually you're you have your ground and then your audio signal is above it going up And down there's that DC offset But you don't want that DC offset going through speaker because it'll damage it and so usually have like big ass blocking caps That allow for the 16 or 8 or 32 ohm load And doesn't like diminish the spec of the frequency response You'll notice here. There aren't any and for the design. I'm doing it has to be so tiny You know if the whole thing is so small one capacitor would fit like here. It would be just way too big I wanted something that you know audio goes in. Maybe there's a couple resistors and capacitors just for like you know, but you know just getting the signal in and doing the Volume gain select but for the most part I don't want those like big chunky caps because even ceramic ones They're just way too big or tantalum. They're just too big. So this is a no-cap Headphone amp design and the way it works is if you notice here, you're like, oh, what's this? There's a switch cap Converter Can't remember the name of the not a boost converter. It's like a Inverter basically and allows it to generate a negative voltage by using a switch cap and That way the signal that comes out here is referenced To a negative voltage as well as the positive voltage, you know from the 4 volt to 3 volt power. It's generating a negative rail so that the output is right Center through ground which is like super cool. You're gonna pale it more But usually these amplifiers are quite nice in general so Let's go to dig a key and I'm going to search for our headphone amp Okay, and there's a whole bunch of stuff, but basically you want the you know the linear amplifiers and And so I'm gonna go with I only want the active designs because I want to manufacture this I want normally stocking now It might not be in stock right now because of the chip shortage But like something that I can probably get in the next few weeks I also noticed by the way a lot of chips are sort of coming into stock in the next few weeks So if you've been waiting on something And then I'm gonna exclude marketplace products Okay, and for the first pass Yeah, so like let's say like oh wow here's one for 60 cents. Let's take a look at it. So when you open this up You'll notice this design doesn't have That capitalist it was like oh, hey, you need you need some big ass On the output to do remove the DC offset So we don't want to use this so that's that's no good And there's no like thing you can signal a filter from that'll signal that it's capitalist Although sometimes they have it's called like direct drive or like No cap You know, there's sometimes names for for pretty much You just have to look at every data sheet real fast and just they'll let you know very quickly That said this size is very important for me, too And so I definitely want only surface mount This is the one that wasn't surface mount And I don't want a big ass package like eight SOIC or T-SOP is gonna be too big It needs to be TDFN or QFN or TQFN. Those are the only ones that are gonna fit So I'm gonna select only the packages that I think are gonna fit. So DFNs. I don't like BGA So I'm gonna skip those No T-SOPs Um More QFNs QFNs QFNs I think no more than 24 like that's at the max anyways Okay, next up. I'm just gonna check the voltage supply. You know, I'm running it off of three to six volts so Three to five volts. So I definitely can't run it off of the this 1.8 and 1.95 Volt version Not gonna happen Okay, so we only have like 19 options, that's that's much better So I went through these and there's a there's actually only a couple different families available, but when I sorted by price There were a few that weren't in stock the 488 was the one that needed the Amplifier sorry the other capacitors on the output and so the first one that was available that was in stock and Also, I had that no capacitors required was the max 9724 this looks like a really Nice amplifier. It's got depop. It's got shut down. It's adjustable gain, you know, and it's like basically 60 cents When you buy it in quantity so This was the part that I picked so I have some on order and maybe by next week if I get the The PCBs in we can hear how it sounds and hopefully it sounds pretty good But um, I like this. It's a nice little headphone amplifier I think this is I'll probably use a couple other designs as well. It's very simple But I really like that it has that negative voltage rail generator inside and this week is a special tree Yeah for the great search. We're gonna play a digikey 1991 promotional video. It's amazing So since we're doing all this retro stuff, I know let's check it out. All right put the floppy in the drive It started in 1972 an idea a new concept in distribution Today digikey corporation represents one of the fastest growing electronic component distributors in the United States At digikey service is the key The success of this effort depends on a team of talents employees Management and staff committed to making digikey the best In its first 10 years digikey's marketing efforts were focused on the electronic hobbyist Then in 1982 they began targeting catalog mailings to the commercial market