Parker and Stephen talk about an Audio Amp for Spooky Pinball based off the LM1875.
Podcast Transcript
Host 3
Hello, and welcome to the macro fab engineering podcast where your host,
Unknown Speaker
Stephen Craig and Parker Dohmen. Hey guys, what's going on?
Host 3
Hey, this is episode number 32. Yeah, getting up there. Yeah. So I finally took the plunge and I went all electric with my brew rig. Last weekend, right? Last weekend. Yeah. Which brew is the most important thing. I brewed a hazelnut brown ale, but minus the hazelnut because I just don't want to do that. So just a brown, so just the brown. Yeah, but the official title is hazelnut brown ale. It's actually so
Unknown Speaker
Host 3
A previous engineer at a previous job I was working at it was his favorite Brown. And he gave me the recipe for it. And I fell in love with it. So I've been brewing it ever since. And in fact, I actually owe him a keg of this because I have done or he's done some swirlies Yeah, sort of. Yeah, he's done a ton of work for me in the past like year, and every single time he's I tried to, like offer him cash or something. He's like, no, just brew a batch of hazelnut Brown and get it to me. So I told him the other day that I'm going to deliver a keg, but he has to have some lawn chairs out, ready for us to consume.
Unknown Speaker
Right when you show up. Yeah, that's awesome.
Host 3
So electric brew, I actually bought a full like electric conversion kit to turn my pot into an electric brew. But by the day I wanted to brew the heating element hadn't actually come in yet. So I went to Lowe's, and I just bought a hot water heater element for 18. And it totally worked fine.
Unknown Speaker
So what was what's the difference between the one that you're waiting on? versus the one you bought Lowe's,
Host 3
because they come in three types. There's high watt density, there's low watt density, and there's ultra low watt density. Okay, and that just basically means how many watts per inch? Or yeah, are distributed on the coil? And for beer brewing, since you're heating up? Liquid with a ton of sugar? Yeah, you want ultra low watt density so it doesn't scorch the sugar or carmelized normalized right on the center. Here. You don't want to make candy. Yeah, basically, sort of you kind of do a little liquid candy. Yeah, liquid candy. So I found one that was basically I think it fit in the middle category it was low watt density. It was 4500 watts on 220 volts. So this is where this is where things get kind of fun. I kind of had this brew day set in stone, and Mackey's over Mackey's. Yeah, he was he was on one of our Episodes Episode 20. Yeah, actually. He's one of the guys over at the iron yard here in Houston, say, school here in Houston. He's a friend of mine and hadn't ever brewed before. So I was like, Hey, let's set up a brew day. And I'm gonna make it all electric. And like, three days before I was like, Oh, crap, I gotta make it. So I got a PID controller that actually takes in a PT 100 RTD sensor. And I found these cool RTD sensors that are all welded. So they're hermetic and they have an NPT thread. So I can thread them directly into my kettle, and I don't have to worry about leakage or sanitary problems or any, any kind of issues with that. So I ran that into my PID controller that my PID controller has an output that controls a solid state relay, but a big monster 40 amp solid state relay. Okay. Yeah. Because the the coil, remember is the heating coil is 4500 watts at 220 volts, which is 20 amps over Yeah, if it's running full bore. Yeah. So this PID controller, basically PWM, the SSR, which turns on and off the heating coil. And there you go. You can set whatever temperature you want, boiling anywhere from whatever up to boiling. So worked out pretty well. But the biggest thing is that I didn't really have an enclosure to put all this stuff
Unknown Speaker
in. This is a great picture.
Host 3
The morning of the bruise session, I get up early, and I cut a hole in the side of a USPS box and I shove I shove Romex cabling, so some 10 Two, or 10 310, three Romex in there, along with the SSR and the PID controller and I even hooked up my RTD through like a connector on the side
Unknown Speaker
actually. hasn't bulkhead connect, I
Host 3
tried to make it look like it was actually intentional even though it was just, I've got I've got a USPS box like literally a cardboard box that's controlling almost five
Unknown Speaker
brand new box. This box has been like back and forth through like the apocalypse is what it looks like.
Host 3
Yeah. And so I had a water stain on the side, I've got 50 feet of Romex that's going from my laundry room all the way to my kitchen plugged into a USPS box. This is this is one step above bathtub. Gin, yo one step one. I tried to get all technical with it. And it turned out to be pretty good. But we'll post some pictures. Everything turned out well, it was actually one of the best brews have ever done. And things are permitting well. Cool. So. So that was cool. I did that this week.
Unknown Speaker
Yeah. And so I've been working on is for spooky pinball. Yeah, I'm kind of going into Stevens. Audio world a little bit. Whoo. Yeah. Cuz I'm working on this audio amp for their pinball machines. Yep. They've basically been having a lot of supply issues from China with their current amp. And the problem is, they have to get them from the legit source because they buy like from my, you know, on alternate source, they're getting basically fakes. And I sound like garbage. Okay. And so basically, we're just going to design one. So we had no, by this, it will work. Yeah. And don't give it to anyone have any supply issues at all right. So Steven showed me this thing called a game clone. Yep. And that's like 68 Watt, basically single channel amp.
Host 3
It's a it's a really popular little kind of kit amp that you can make in an afternoon. And it actually sounds really good.
Unknown Speaker
Yeah. And it basically uses a Texas Instruments, audio amplifier, big package thing. Yeah. And all in one package. Yeah, I can't remember the exact number. I'm not going to be using the exact game clone because I actually don't need 68 watts per channel and a pinball machine, because that would completely blow the doors off. The ball would bounce all over. Yeah, you would basically rattle the thing to death. Yeah. Right. So I want to use the smaller brother, which is the LM 1875, which is 20 watts per channel, which is still a lot, which is still a lot, we're actually probably gonna limit them to 10 watts. And that's still gonna be really loud. Yeah, yeah, their current app says 40 watts per channel with a 68 watt sub, which is impossible, because their power supply is 12 volt, three amp, which is 36 watts. Right? So it's just a view that amp was 100%. Efficient. You were not even get close to in one channel being full out on 40 watts.
Host 3
Well, and and even if it was 100%, efficient, you're still talking about RMS, not DC. Exactly. It's still not even going to output that much. Yeah. People People get people equate wattage and volume all the time. And it's there. You can't equate them. They're not the same. They mean very different things. And most of the time when someone has, you know, their car stereo cranked up, you know, you're not pumping out 1000 watts. Yeah, right. The license plates, right? No, it's not 1000 watts. You know, you're pushing five. Yeah. Your batteries not gonna continually pump out 1000 watts? No.
Unknown Speaker
Um, but we're gonna make it true. 20 Watt per channel. Yeah. So it's great. 2020 20. So left, right sub and then don't have tone control base. We just have to make a cut off. And a base the base adjustments? Yeah. And, and the high end adjustment. That's all we have to do on it. To do that, I found these really cool, low cost dual gang potentiometers on eBay. Yeah. Now, we usually don't like using parts you buy on eBay. Because there's always supplier problems and stuff, right? But first of all, the guy's got like, a bazillion of these things. So we're just gonna buy like, five years worth. Yeah. And a good thing we can do about that is they're also like 15 cents a pop.
Host 3
They're really, really cheap. Well, and the good thing is they're not they're not going to be used every day.
Unknown Speaker
No, they will be set in strictly pinball. They will set them you know, on the floor. And that's it.
Host 3
Well, maybe someone customer might move it sometime down the road. Yes. But it's not like it's not like an amplifier that you use every day where you're going to be turning it every single
Unknown Speaker
time. Exactly. So these parameters might get like 10 uses in its lifetime,
Host 3
right? So yeah, yeah, quality is not as much of an issue no.
Unknown Speaker
And the biggest thing I've been running into is because first of all the budget for the whole thing, and quantity 500 is gonna be like 30 bucks. Wow, total now also include the power supply
Host 3
for 321. Yeah, amplify, that's cheap.
Unknown Speaker
Yeah. So that's what I'm getting pretty close. The problem is the power supply. Yeah. Because we're like, oh, yeah, we're gonna make this badass sample. It's just us. You know, let's put a linear supply on the board. Yeah, make a clean making really clean. Transformers that can do 60 watts are expensive. Yep. Because we need to be able to basically we need to give it 18 volts. We needed an 18 volt, a 122 18 volt transformer that can handle three amps on the on the secondary. Right? And they're like, $17
Host 3
Yeah, I iron. You know, it's not cheap. Yeah. magnetics are one of the most expensive parts. Yeah.
Unknown Speaker
And so what we're gonna do is we're gonna do similar to what they currently do, they just have a switch mode power supply. And because you can get a 24 volt switch mode power supply for $7. Yeah, which is in budget, it was just going to go down. I don't really want to go that route. But it's just how we're gonna have to make it work.
Host 3
But but something Parker and I were discussing earlier this week, it's a pinball machine. It makes a ton of racket.
Unknown Speaker
It's just, it's not like the speakers are in like a designed enclosure to maximize the performance of
Host 3
them. You're not going to get an audio snob coming up. They're like, whoa, this pinball machine doesn't sound right now, actually, the
Unknown Speaker
thing is, people all they care about promotion. So they sound loud.
Host 3
Yeah, you got to know what what's going on? Yeah, yeah. Yeah. So.
Unknown Speaker
So you've you've you've met that require, and it's like, for $10 X, like, so the difference train, that's just the transformer $17. Then you need the, then you need a bridge rectifier, then you need caps and all that through the and all that stuff. I bet you per cost I bet you for like $10. So $7 in the switchmode plus $3 in the caps will be smoother than like $20 worth of the linear.
Host 3
Unknown Speaker
$17 of transformer plus, the last $3 is like rectifier caps. And I bet you the switch modes make cleaner.
Host 3
switch modes just aren't a big fan of inductive loads now, but because they because when they and when the load becomes inductive and starts to mess with the voltage, the switch mode goes, oh shit, what do I do, you know, like tries to adjust and we'll just but it shouldn't be an issue.
Unknown Speaker
Well, we can buy $3 A really big cat. Exactly. And that solves that problem, right?
Host 3
You decouple it from the inductive load? Yes. Yeah. You're not going to put a motor directly on the output of a switch mode. Unless you want issues.
Unknown Speaker
Yes, exactly. So we're just gonna do that. And it should work run. Yeah, so we get basically $23 for the amp, which is definitely doable. Oh, yeah. And the heatsink is going to be like four or $5. Yeah, and that's in there too. Well, it's gonna need a pretty hefty heatsink. Yeah, it's going to be well, or not going to be doing 20 watts per channel, because the speakers are only 10 watt speakers. Right. So we're going to limit it to 10 watts.
Host 3
So but but it's got to be able to handle 3130 Watt
Unknown Speaker
toll. Yeah. Which is actually not too hard. No. So I think I'm just going to actually get a I got a heat sink manufacturer over in China. Yeah. And it's going to send them like just use off shelf extrusion. And just tell them that Joe three holes gets it. Yeah, well, probably five holes. So I want to put a bracket on the bottom over the mounting the piece of mounting to the PCB. Yeah. And that should be it
Host 3
could also have some holes drilled in it such that it can mount to the side of the enclosure of the pinball machine. Yeah,
Unknown Speaker
we thought about that and it's gonna be a pain in the butt. I'd rather go through the PCB into the cabinet.
Host 3
Okay. Cool. Yeah. Are you gonna have any forced air on? Just ambient?
Unknown Speaker
Yeah. Cool. So it should be plenty loud.
Host 3
Oh, yeah. Well, it's what you got two five inch speakers and then 110 inch 112 inch sub 112 inch sub. Yeah, I mean, and both of the five inch speakers are in the, in the headcase right that are facing directly towards the player. Yeah, it'll be plenty loud enough.
Unknown Speaker
And it should sound better than what they currently use. Yeah, probably. But yeah, should be pretty cool. I'll probably have some more updates on that next week. I'm hoping I told I told him I have a prototype done by Friday. It's not looking like that yet. I was gonna work on a little bit tonight.
Host 3
You prototype as in like working prototype? Yeah. working
Unknown Speaker
prototype like a ship up? No, like the designs done and I ordered. Okay, okay. That might be not happen I think I've only thing I've designed is like the amplifier, like the actual schematic symbol and layout for it. I haven't actually laid anything else out yet. Maybe I'll do an all nighter mostly. And Xiao Well, how long are we in this yet so far? I don't know. us want to go right to RFO Yeah, why
Host 3
Unknown Speaker
So there was really cool article. There's a, okay. There's a really cool website for basically project project plat product engineers. Yeah, called EMC Fastpass. Okay. And this this this website, they basically put out a bunch of articles on like, how to design and pass FCC and CE testing. And most of their stuff is free. They got really good books, stuff like that. Ebooks, yeah, that you can download. But they had this really cool article about an actual use case for basically doing cost reduction. Yeah, for a product that has to be FCC certified. And so it's a story of a barbecue controller.
Host 3
And weight barbecue controller had to be FCC certified. Yeah.
Unknown Speaker
Has a clock over what? Eight? Eight kilohertz? Yeah. So yeah, you have to get FCC certified. So anyways, basically, for emission testing, make sure you're not messing up cell phones, right, right people stuff. So the original design was for layer, and they passed flying colors through FCC, ce testing, all that good stuff. And they were looking to reduce the cost of their products. And so they were like, well, a big cost of front is the PCB. So they could reduce the cost of the PCB by bikes, basically half the price. Yeah. And they would save a couple bucks on the back end. And so there was they went through all the challenges, basically, the first thing is he just like, they're two layer design, shifted out the door. And it failed FCC testing. It was really noisy on the spectrum. And basically, he went back, redesigned it did more testing, went back then more design test designing and then retested, they finally passed. Yeah. So it's really cool. Just going through the process of what it takes to become FCC certified. Yeah. And it's a really good article for people who have never done it before. Because like this, he actually lists out like, this is stuff you should bring when you get tested. This is stuff that you know, when you're doing your design, what's your best chance of success? What are areas to look for all that good stuff. So I definitely recommend anyone that's actually designing a product, especially Kickstarter, and that kind of stuff is the look at the stuff first.
Host 3
Yeah. Yeah, cuz because just getting your circuit working is like the first quarter of 30% of the work. Yeah, right. Yeah. And for guys, like us, you know, just the engineering type, that it can be really frustrating. Because we're sitting there the whole time saying, my circuit works. My circuit does what I need it to do, yet you, you can't do anything with it until you meet all of these specifications and certifications. And it gets annoying. But yeah, certainly the first time you go through it actually the first probably two or three times you go through it. It's really eye opening. Yep. And then you kind of just get numb to all the things that you need to do you know,
Unknown Speaker
yeah, when you look at a lot of my designs, people look at me like why are you designed that way? I'm like, if I have to pass FCC testing, yeah. This is I'm laying it out exactly. Like it should be.
Host 3
And it's funny because Yeah, you look at you look at a PCB by some people and you're like, Man, that's really dumb. Why would that guy do that? Stop and think he probably had some kind of reason to do that. You know, and a lot of times it is FCC. So
Unknown Speaker
the like, one of his examples is analog inputs. And most time for these kind of products is you just like, you know, run a wire right into analog and on your Arduino. And now, it would work unless you start bombarding it with with EMF radiation. Now, it's a little crazy. And so he's like, always low, pass your inputs with like a capacitor resistor, then you're good to go.
Host 3
We always used ferrite beads. Yeah. And we had, gosh, on some of our boards, we had upwards of like 7080 analog inputs, and so it was just pockmarked with. Oh, 805 ferrite beads everywhere. Right at the input as close to the input as you possibly could. Yeah, yeah.
Unknown Speaker
So yeah, put the link in the podcast description. Yeah, yeah go check it out
Host 3
guys. It's a really good read
Unknown Speaker
another cool article. I really liked this because we had the topic of this like, what two weeks ago? Something like that. Yeah. Top 10 reasons to not buy fake MacBook chargers number eight will shock you a clickbait article awesome electronic clickbait this is by Hackaday this is like one of my favorite articles that came out this week cuz I'm like ah
Host 3
see you they're talking about crappy MacBook chargers. Yeah, cuz I'm Chinese offshoots stuff.
Unknown Speaker
Yeah, so sure they will charge your device, but they will also kill you in the process,
Host 3
right? All of the protection measures gone
Unknown Speaker
are removed. So it's like basically like on the mag mag love or not mag mag, mag Connect.
Host 3
Unknown Speaker
let's whatever trademark Apple uses for it. Basically, on the cheap ones, the outer casing of them or is connected to live on the AC mains. And so if you dropped it on like a metal table, there probably weld itself to the table.
Host 3
That's almost as bad as running 5000 Watts through a USPS box. Almost almost. I wouldn't know anyone who's done that. I forgot to mention earlier. Maybe I shouldn't mention this, but I didn't have the neutral or the ground connected to anything.
Unknown Speaker
Yeah, you're lucky you didn't die.
Host 3
Unknown Speaker
Host 3
And I did it. I did a good job of the actual wiring to the heating element.
Unknown Speaker
Oh, yeah. Yeah. This wiring on it?
Host 3
No, no, no, no, no, no, I it was all crimped, it was all spade terminals. It was all okay. I did the to the terminal connection. I did a good job. Now to everything else. Parker has requested that I take a picture of the inside of the box. Do not judge because I created a tasty five gallon batch of beer off of this. Yeah, but But yeah, no Chinese Chinese chargers? Yeah.
Unknown Speaker
Basically. Yeah, they just basically, quote, cost reduce the charger? Yeah, that's
Host 3
Unknown Speaker
Host 3
I've seen a bunch of tear downs of these fake chargers and including the little USB five volt wall warts. There is, gosh, the market is just completely flooded with garbage, USB chargers. And some of those are dangerous as hell yeah.
Unknown Speaker
I would basically recommend not buying any thing that's like generic chargers.
Host 3
Yeah, even be like be pretty wary about you know, you see that rack of chargers at your gas? Yeah, be careful about that. Because you never know. I mean, they can catch on fire, they can explode. They can shock you they there's so many things that can go wrong with them. And if you know from the outside, they have that like, Ooh, they're white and they are they look really like clean and so if you open it up, it's like oh god, what's gone gone wrong and here
Unknown Speaker
and ever they have a CE mark and might not and BCE it might be there's also another CE mark that actually means Chinese export. And it looks just like the CE logo except the spacing slightly different.
Host 3
See, he has a very specific required image but even going further
Unknown Speaker
is even going further than that. It's like if someone put a CE mark on how do you know any difference? Well, I
Host 3
mean, half the time they come with you well marking and CSA and all the others to because you can just download that and slap it on a product. What are they gonna do fly over to China and auditing that factory and be like, Nope, you can't build this? No. Yeah.
Unknown Speaker
Yeah, it's, um, basically buy any, any low cost product at China. That's got markings. Be very wary of it. Yeah, right. And that's the thing is like even companies like meanwell that are supposedly really good power supply manufacturers. Sometimes they get a batch from China and it's
Host 3
bad. Yep, you got it. I mean, you got to watch out if you know where your stuff is coming from. If if possible. eBay Alibaba and Aliexpress are not necessarily the most trustworthy out there except for cheap,
Unknown Speaker
potentially amateurs. That's true.
Host 3
But but a cheap potentiometer is probably not going to kill you
Unknown Speaker
know, well. The pens and this application I'm using No, no high voltage
Host 3
no But I mean, the potential motor would would burn up if you put any anything on it, especially to see
Unknown Speaker
where if some manufacturing faults and let's say you're you had a high one your legs on a high voltage line. Yeah, like 50 volts, and it's bridged over to the knob. Oh, yeah. A knob to like internal isolation was not high. Yeah, well, they just filled it with like, basically, you know, conductive grease. Like really old. Really old potentiometers are just for that crappy grease. Yep. Yeah. The
Host 3
so a typical potential ometer. Like, just the old school ones that the 24 millimeters that you see all over the place. The the internal wiper is a phenolic base with a carbon track on it. Yes. If they don't use phenolic I mean, there's nothing saying they have to use phenolic which is like, a gazillion Giga ohms. Yeah. They Yeah, they could just use some kind of crappy paper that's impregnated with something that's conductive. Yep.
Unknown Speaker
Oil. Bubble gum wrappers?
Host 3
It wouldn't surprise me. I've seen some stuff man.
Unknown Speaker
That was not 1000 yards there.
Host 3
1000 yard Alibaba. That whatever that weird like italics face they have as their logo. Yeah. Alibaba, like, what kind of logo is that? It just looks. What's your face? I think yeah. But like, why?
Unknown Speaker
I don't know. Yeah, exactly.
Host 3
It'd be like, what if what if he Bay's logo was just like a smiley face? It just wouldn't make sense. But for some reason, Alibaba does it. Yeah, it works. Alright. Well, I think that's good. Yeah, I think we're good. So that was the Mac fab engineering Podcast, episode number 32. Number 32. We were your host, Stephen Craig and Parker. Dohmen. Take it easy, guys later.
