Create And Build An Electronic Circuit!

hi everyone and welcome to another episode of mr carlson's lab about 15 years ago i designed an otl amplifier for studio monitoring reasons so for example the design intention of this amplifier was to take a low impedance low level audio signal give it a bit of amplification and then furnish enough drive power to drive some studio monitor headphones studio monitor headphones have a very flat frequency response and therefore this amplifier had to be very flat as well and that's why i chose an otl design otl stands for output transformerless so there is no iron in the audio chain within this amplifier whatsoever consequently no audio input transformers or audio output transformers the only transformer in this design is the power transformer itself now you may be asking yourself why did he do that transformers are expensive they give you isolation they do all these things well they're also a bandwidth limiting device transformers will limit your bandwidth so will capacitive coupling to a degree as well but i wanted this to operate in an extended range and any of you that have been on my channel for a long time know how incredibly fussy i am i want that extended range to be within 1 db and that's why i designed this amplifier like this and it performs very well so coming up to now basically the last five six years however long i've been making videos i've been here for a while now i use this setup to master the audio for these videos so for example the audio output from my video editing computer is flat all right it's very flat and i want to keep the drive level from my computer's audio output very low that low level audio signal goes to the input of this otl amplifier the otl amplifier gives me just a little bit of audio gain and then the output of the otl amplifier goes to my studio monitor speakers which are powered as well so that allows me to keep all the gain levels very very low and by doing that i can keep everything very very flat and it allows me to master my audio here very very well now i can get into you know coloring audio and enhancing it and you know using processing and all that stuff but that's probably better held in another video this video here is going to be about the design of a protection circuit for this otl amplifier so basically what happens is if i don't turn everything on in the correct order i get a very big thud out of my studio monitor speakers because they are powered and when i click the power switch on on my otl amplifier if my studio monitors are on already what ends up happening is the capacitors in the otl amplifier charge immediately because i turned the power on remember there's no audio transformer so quite a jolt gets sent to the input section of my studio monitors and i get this really overpowering thud and when i say overpowering i'm not kidding it's a big thud so pretty much everything that those studio monitors can put out it happens within that moment so i have to be very very careful now this isn't my original set of studio monitors and i've gotten pretty comfortable to turning things on in the correct order this is my second set and this hasn't happened with this second set but every time i turn things on it's at the back of my head you know one of these days i'm going to accidentally you know turn the monitors on and then turn the otl on by accident or i'll have the the otl amplifier off and not realize that the monitors are on and you know click the switch by accident or something and i'm gonna it'll you know blow me out of my chair so at any rate it's pretty loud when it happens so this will prevent that from happening now i'm going to share the circuit with you i'll design the circuit and i'll share that with you here and we'll take a look at the design i'll go through the whole thing and i'll talk a little bit more about flat frequency response and amplifiers and things like that there's a lot of really good information in this video that will really benefit you and oddly enough the information that has to do with this otl amplifier will help you better understand switch mode and linear power supplies as well out of all things so lots of really good information in this video let's get started here's a closer look at the otl amplifier so as you can see there's no audio output transformers to power transformer so this power transformer was taken out of a hewlett packard vtvm this is 15 years ago remember so this taken out of a hp vtvm i had a whole slew of these old hp vtvms and they had these wonderful shielded power transformers in them and they were all in some form of disrepair like people had pulled tubes out of them and the cases were dented and wrecked so i i didn't feel too bad about removing the power transformer so so at any rate i got a bunch of power transformers and i built a few amplifiers of this design so three or four at any rate and they they all work very good this amplifier has never been serviced since it was put together same tube same everything everything just works nothing has ever failed in it so nice design power transformer gets i would say very warm i wouldn't say hot but i would say very warm and that that would be for example being left on for 10 to 12 hours something like that so it's well up to temperature by that point so yeah no problems with that whatsoever and of course it's you know just not powering a whole bunch of tubes i knew the current draw of these tubes is a little bit more than most so and just a volume control now the original design this is one of my very first ones i think this was actually the first one i experimented with uh i believe it was a base and a treble control one or the other or something a bunch of controls on either side in here just to experiment and then play with it and see how absolutely flat i could get things so if there was a signal source coming in that was supposed to be flat i could try and trim it up with the controls on the face so there's not a whole lot of room here and then i found that most of the signal sources that i was dealing with at the time were very flat so i didn't need them so i ended up removing them now this box here the actual little box itself was from a local electronic supplier they had a bunch of these things and maybe they can even still get them they're very nice little little project boxes to put amplifiers on and such so i've gone through a whole bunch of these and built you know all sorts of different projects on these boxes it's a very nice little little box six sn7s only one half of the triode is used the other half of the tryout is just all tied to ground if you keep things quiet and the six as7s both the triodes in them are attached in parallel and they're just in really just in class a so some really large resistors on the bottom of the chassis uh just a little power switch a little power light here so that's all in fact i'll turn on the supply over here and you can see that light up there it is so yeah just a little power switch with a lamp on it and a nice smooth volume control that worked out very well i graded a whole bunch of potentiometers before i put them in there to see if they you know make sure that they match in resistance it's a big problem when you have dual potentiometers one for each channel i'll just turn off some of the lights here and you can see some of the glow of the tubes here these tubes they glow very very nice in service let's see here lots of light around i don't think i can get the light off the tubes there but um at any rate yeah they're very nice looking tubes when they're when they're glowing and they're fantastic for audio service for class a otl you'll find a lot of manufacturers a lot of companies use these because they're a relatively low impedance triode this is a these are pass elements for for regulators right these makes excellent right pass elements for you know any type of control regulator and i built my fair share of them using these tubes and they work very very well so it's just two triodes in each one and very big triodes designed to control quite a bit of current in in a linear power supply of some sort for example like a 300 volt regulator or something like that these are commonly used in tektronix oscilloscopes like those two big oscilloscopes that you see in the intro shot there they have the industrial version of the 6as7 in them so yeah success and sevens uh as i say all original nothing has been changed and uh it'll be interesting to do a sweep on this thing to see how well it's still performing so and that's it and then on the back side spin this around it does have a little bit of weight to it because of that transformer nothing special on the back fuse line cord inputs and the jack for the headphones that was it nothing nothing too special the build inside really isn't very spectacular at all either it's very built to do a purpose and it works very well this thing sits silent and when i say silent i mean silent you can plug a pair of 600 ohm monitor phones in there put them on your ears and you will hear nothing it sits dead silent until of course you put a signal in it and turn the um the volume up on the front there the gain control on the front here's the underside of the amplifier and you'll see that i have a bunch of shiny screws here and the rest of them are black and the reason being is the paint is removed underneath each one of these screws so when i tighten these down it makes good contact to the rest of the frame a lot of manufacturers failed to do that and i actually showed a video early of an example of this and those of you that watch this channel may even be able to bring it up so it's a well-known amplifier manufacturer and they didn't even do that at any rate it's very important to have proper grounding of the bottom lid to the case where you get hum it's just the way it is so everything needs to be shielded in here you can kind of see some of the components already i see a 33k two percent resistor right there right through the grille here and i see some ceramic resistors and i remember that blue capacitor just all from looking through this bottom again it's been like 15 years right so i haven't had this apart at all so i figured well this needs that protection circuits time to do it now before i uh you know possibly damage my new studio monitors and i definitely don't want to do that or newer studio monitors at any rate so what i'll do is i'll start taking out all these screws and i'll be right back all the screws have been removed and let's take a look inside that's what's inside not a whole lot very simple design so these here are the resistors that run to the plates so these two 1.2 k resistors are attached in parallel on each vacuum tube these get pretty warm not incredibly warm but they get pretty warm and these are the capacitors that couple the signal to the output jack these here are filters down here there's two 10 000 microfarad capacitors down here that are doing the filtering for the filaments on the six sn7s and this is the b plus filter right here and there's a nice big choke here to make sure that dc is very clean and again you know as i say this thing is just silent so that's really doing its job in there and uh little blue coupling capacitors there and the resistors underneath are the cathode resistors these are the plate resistors really just a brute force class a trio design is what this thing is all right let's design a circuit let's take a look at some of my chicken scratches here with this uh so so part in the uh the paul chicken scratches here so what i think i'm gonna do is i'll use a 555 timer for this because it's just the easiest thing to use i have the seven five five five version which is the cmos version so i'll use one of those all right so i'll draw the 555 timer nice and big so that we can see this so we'll put the uh the two together so this is eight this is the positive and this is the reset line which is pin four all right so i'm going to tie six and two together as well so pin number six is the threshold and pin number two is the trigger all right very common configuration here pin one is a ground and then pin three is out and uh this is so many designs in a 555 timer this is drilled into my head so very easy ic to use very few external components and since i'm using the 7555 which is the seamless version i don't need to couple pin five to ground through a cap so that's one less component that's very nice to do so i don't want that extra component in there so this is going to be running off the heater line the rectified heater line so it's going to be 6.3 volts maybe a little higher because it started out as 6.3 and it's rectified and all that kind of stuff so between 6.3 and 6.4 volts all right is going to be the positive for this pin one is the ground now i've built a lot of circuits with 555 timers and i would have to say that in order to get about 30 seconds out of this i'm going to put the cap on the top side here to positive and i'm going to put the resistor on the bottom side here to ground and what this will do is this is going to have this remain off so when this voltage gets applied here so when i apply current i should say to pin four and eight here all right this is going to be low nothing's going to change this will stay low and that's very important then after about 30 seconds this should go high now in order for me to get about 30 seconds out of this i think i'm going to use 4.7 uf so and i'll use a 4.7 meg hey look at that isn't that nice so that should be 4.7 and 4.7 and that should give me around 30 seconds okay so 30 seconds and this will go high this will go up close to the rail now i want to drive a relay with this okay so i'll draw my my relay coil over here we'll say this is this side and we'll draw the coil and hey how does that look okay so what i'm going to do is i'll use a npn transistor to turn this on right because if this goes high after 30 seconds high means the voltage is going positive so if the voltage goes positive and npn transistor will turn on so what i'm going to do is use an npn transistor here so so we'll say uh 3904 or something like that i have uh lots of transistors like the 3904 3906 combination i have the bc bc817bc807 combination so i may use either or so let's just call it 3904 because that's a nice standard everyday you know component that you can pretty much find in your backyard in the soil so they're very common common is dirt okay so now since we have a relay here we want to protect everything so let's uh let's put a little diode across here why are we putting a diode across the relay coil like this and why do you find this across relay coils well what happens is that when the relay lets off so basically when this transistor turns off you get an inductive kick out of this thing so it creates a little high voltage spike and by putting this diode across there it saves damage from you know happening to our surrounding components and things like that so it's the same thing with an ignition coil in in a car so if you recall the old breaker point systems if you're old like me and you require you remember old breaker point systems what happens is when the breaker point closes nothing happens you don't get a spark it's when the breaker points open is when the spark happens so when the breaker points open what happens is is the field on the coil collapses and it creates that high voltage spark on the secondary winding so the breaker points close all right the coil itself you can look at it as it's charging so what happens is now there's current across that coil so there's a circuit there's 12 volts going through the coil into ground and then when the breaker points open it releases that out the to the spark plug on the secondary winding so when it's opening the field is collapsing you get a basically a high voltage spike and that's what this does is it stops it from damaging surrounding components that's why you find diodes across relays and things like that depending on the configuration and depending on the circuit sometimes it doesn't need diode but i just add them just as standard practice that's all i'm going to have a capacitor across this as well so i'll have a capacitor across this to ground so right across the supply lines we'll make this 10 micro farad at any rate right across here now this will be ceramic and this will be tantalum and you're probably saying why are you using tantalum well if you put a ceramic capacitor in a timing application you're gonna find out why because one moment it'll be 30 seconds the next moment will be 22 seconds depending on the weather it'll be 35 seconds ceramic capacitors of these values move around quite a bit so a nice stable value is to use a tantalum they're pretty temperature stable not incredibly temperature stable but enough for a timer like this when you get into faster times you know and you get below you know say a micro farad so you can start using npo style or mp0 style capacitors you want to start using those mp0 capacitors they're very very accurate so this is a pretty high value 4.7 microfarad is still pretty high so you know you'd be using a tunnel up there that should be fine then again between these two here actually get around 30 seconds in this configuration oh here's something that's really kind of interesting if you are into designing with one of these things so if you reverse these two okay so if i say i want to put the resistor this resistor up here and this capacitor down on the bottom this will be the opposite as soon as you apply power this will go high for about 30 seconds and then after 30 seconds it will go low in this configuration this remains low when you apply power and after 30 seconds it goes high and i definitely want it in this configuration because i don't want any movement in these relay contacts with in the first power up all right so i'll draw some relay contacts here i'll go one two three and this will be the bottom this will be the top and this will be the center contact okay so this is the normally closed position this is center and this is the normally open position right here so we'll say that either one of these it doesn't matter we'll run to ground okay and then this would run off to that speaker output terminal and keep it grounded now you can see if i turn power on i definitely don't want these to move i wouldn't want this to go click down here and then make contact for 30 seconds and then go click and let off again because as soon as you apply power with this configuration this is going to go click wait 30 seconds and then let off in this configuration nothing moves for 30 seconds and then it goes click pulls down and opens this connection you can see if you had this reversed for that for the milliseconds that it's going to take for this relay to close i would get that high voltage spike still at that terminal so you can see why it's so incredibly important that nothing moves right so that's why i want it in this configuration now this other configuration is useful for other projects right so just just one very easy way of reversing its function if you want and of course you can you know put a transistor a little differently on the output here if you want it to also function differently as well so that is basically the circuit right there there's not a whole lot more to it i have a lot of five volt relays well i have a lot of small ones i have those nec ones surface mount ones maybe i'll use that so i'll have to put a resistor in line with that to uh the 6.3 volts will say 6.3 volts in the coil consumption maybe 30 million i will say 33. we'll say 33 ohms should safely drop that down to a little over 5 volts maybe around 5 volts okay and because this is going to be 5 volt coil all right right here and to bring this into saturation it's nothing accurate really 10k should be fine and that'll reduce the load here right so we have 10k and that should bring that in pull this down and we'll have half happy relay application right here yeah that's looking like it so i think we should add some maybe some leds maybe an led a red led for off so when you first turn the power on nothing is happening so the led is red so it's in protection mode and then when the thing turns on it goes green so that shouldn't be too incredibly hard to add so what i would want to do for say a red led okay so take another 10k resistor here try and keep all the values the same just for simplicity so run this down here and we'll say run this to a pnp transistor how does that sound so the emitter is going to run to positive here and the collector of the pnp is going to run out turn that on angle run out through a resistor and we'll say through red led to ground so this will be a current limiting resistor right here this is going to run up to the 6.3 volt line okay so 6.3 volt that's running to the same point as this and now since this is a pnp transistor okay so this is npn right here so we'll go npn okay so when you're looking at a transistor all right if you look at it like this all right so this is npn okay so i'll draw another npn transistor like this this is n p n okay so we know the base is always the middle right the base is always the middle so we know that it takes positive to turn on this transistor so we need current transistors are current driven devices right so we need a bit of current there to turn this thing on and of course we have a current path here through the arrow that's why we need a current limiting resistor here because if we apply too much current we're going to damage the transistor or pull the output of the the 7555 rate down to ground or close to it right through this transistor right because we have 0.6 of a volt through here because it looks like two diodes inside here okay so the whole idea here is in order to turn this on we need positive one here so after 30 seconds this goes positive right so this goes up to the rail we have positive on here this turns on right so if it turns on it's technically connecting this to this okay if it connects that to that it's going to turn on the relay right because this is acting as a switch so now since this is pnp what happens is when this is low so when this is towards ground what's gonna happen here is it's going to turn this on okay so so when this is low this will be red okay so this is in protection mode so when i first turn on the power this is low so if it's low since this is a p n p transistor negative turns this on okay so now this is low towards ground so it's negative so we get our red led glowing this will be a current limiting resistor here 220 330 ohms something like that so we'll say for argument's sake 330 ohms okay so this will indicate the off portion okay so now i have a red led indicating the off portion now we want this to switch over right when the relay gets powered up and indicate on right so why don't we add an npn so we'll draw another resistor here so these will both be 10k just to keep things nice and easy i'll draw an npn transistor over here i'll draw the base on this side okay and then what i'm going to do is i'll draw this up to here and this down to here like so use this kind of like a pass element so this will go to 6.3 volts as well so i'll jump this over here and this will connect to here and then this will just go up to the 6.3 volt supply what i'll do is i'll have another resistor here with a green led and this should go down so this is an led right led and and to make sure that this is on correctly in everything i will add a resistor here to here so i'll put 22k here that looks like that should work so 22k here 10k there that should be fine and depending on the current draw of this it's going to be 220 330 ohms something like that say 220 okay and yeah pardon my scribbles as i said this is going to be very chicken scribbly so so what will happen here now is when this goes high what's going to do is it's going to turn this transistor on and this is going to allow current to flow through and we're going to have a green led light over here so red for when you first turn the switch on and then once this clicks over and you know basically lets off on the ground this will go green saying that it's out of protection mode and i think that should be okay now i don't think we're gonna get any type of noise or oscillation in this circuit this resistor in some cases would use there's only a 0.01 one here to stop any type of oscillation depending on the layout so i'll probably just add that anyways it may not need that so i'll probably just add that anyways so point zero zero one thousand pico for ed would be fine at that point i think that is about it yeah it's looking like everything's gonna flow properly in this positive side here of the tantalum this is going to be ceramic so it's a non-polar capacitor ceramic capacitors are absolutely fantastic for decoupling purposes and things like that i think that is going to work just fine so here we have it so this is a pnp so this would be like a 3906 or something like that again i have the bc 807 vc817 combination i may use those as well and again this would be a 3904 and uh same thing like that so npn npn pnp and um i just need to figure out a red and a green led hey you know what i have some really neat leds that look like an sot-23 transistor i bought these a while back and uh kind of forgot about them so an sot-23 transistor surface mount transistor looks like this all right the big version of it and i have a red and a green led inside one of these packages but the package is clear it looks like a clear transistor and i call it kind of funny but that's one of the reasons i just bought it because they look like transistors these uh little leds so maybe i now have a purpose to use some of them so what i'll do is i think i will use one of those and they were a common cathode so this would go to ground and one side was red and one side was green i'd have to look that up on the data sheet and and uh put that on the layout accordingly pardon me i'm just looking at this here making sure everything is correct it looks like everything is going to work so this is going to be the schematic so what i need to do now is put this onto a small circuit board and again i want to make this all surface mount just because it's going to keep the you know footprint of the design small use the largest surface mount stuff that i have really is like 1206 right and then of course maybe some larger resistors for areas that may pull a little bit more current like that so i'll try and keep it all 1206 and uh go from there normally i default to whenever i build anything like this i default to a 402 so for example an oh 402 resistor is about that big that's about how big an 402 resistor is whereas a 1206 resistor is maybe about like so all right so it's quite a bit larger so i'll i'll use this i'll zoom in with the camera and i'll show you everything when it's all done so i'll go lay this out in fact you know what i'll do i'll go find these leds and i'll show you the similarity between these and an sot-23 package transistor so these are clear whereas transistors are normally dark you know in color it's an epoxy body these are really neat so go find those and i'll be right back and i'll show you what those look like all right so after some more digging i found the leds i also have a little transistor here for size comparison so i'll just put that down here and i'll zoom in on this stuff here in just a moment i'll grab one of these leds and i'll show you the similarities here so i'll just uh open this up and drop one of those out okay here we go i'll zoom on in okay so here's a standard transistor like a bc807 or bc817 and i will grab down here i will grab the led so i don't know if you can see that hopefully you can focus in on that you can see the little transistor here it's the same package an sot-23 packaged led it's really kind of kind of a cute little device clear device right there so good for indicating on circuit boards and things like that so same footprint same layout except instead of a transistor an led so kind of a neat little component so i'll use one of these as the indicator gives me the perfect excuse to use one of these things here's an example of what i do when i create a file for something and the schematic for that otl amplifier would be in the same type of file put away so what i do is i design everything up and i put everything in a folder like this now when i'm designing circuit boards like this what i'll do is i'll create the layout like i've already done this is the actual sized layout i'll explain this in just a moment so i print two of them off just because the reason i have this on here so i can show you one and have one populated at the same time normally i wouldn't make two because i'm just making one for this right now but i'll make two of them just to do this okay so this is all ready to print they haven't been built yet so i'm gonna print this here in just a moment i use a toner transfer method and i'll get two circuit board made and i'll show you so this is what i do i just put it all in a file folder so this is what i just scribbled on the bench with you so that's the schematic okay and this is the layout which has been drawn so some time has been spent at the computer drawing this and then this here is the component layout map okay so this shows where everything goes and all the values are pretty much identical to what i drew the only reason i amended these two values is just because these are the closest resistors i have in 1206 so i don't have a 220 i have a 214 and i don't have a 330 but i have a 332 so you know buying up surplus resistors and things like that this is what you end up with but everything else is exactly the way it is 4.7 meg here the tantalums up at the top 22k resistor on the base of the bc 817 i did use the bc 817 and 807. reason being is i have some rolls of these things so i have rolls of about 4 000 of each of these transistors whereas my 2nd 3904 2 and 3906 supply is going down so it's even it i'll use these instead it'll be absolutely fine here's the 10k resistors there's that little led right here this is going to be a relay and nec relay that i'm going to use that'll fit right here a little diode across that so this will go to one speaker terminal this will go to the other speaker terminal or output terminal if you want to call that to the headphones it'll go from you know one here and one here and this will mount to that spot that i showed you in the chassis i'll show you that here in a moment again so i'll use a 632 screw for that i believe i'll drill all these holes to zero three three that should be absolutely fine that'll fit most wires that i have and this is just a spare ground so this is gonna be screwed to the chassis so there'll be a nice ground there but i never trust that so if that ever comes open or gets crowded or who knows right over time right i want an actual solid soldered ground so i'll run that to the ground at the speaker jack there so positive and negative in and uh yeah it's pretty much ready to go so i just have to take this now and this is an ink i've printed this off with my inkjet printer so i have a toner uh laser printer so i'll print this off and of course this will be mirrored so the way this will print off it'll look like you know if you could shine a light through the back of it it will look like that on the top side of the paper and then when i put the transfer onto the copper it will you know when i flip the copper over it'll look just like that so this needs to be mirrored this is just a fence around the outside here so the reason i put a fence around the outside this will etch in copper and this will also be toner right because this will you know the toner will be covering copper is what that does is it seals this in so basically it seals it when it's running through the laminator because i do the toner transfer method i explained that in one previous video to this so how i end up doing all this so that just shields it all in and make sure that everything just stays you know nice and solid in place and uh again it just makes a fence to protect everything it makes it a much more a solid transfer by doing that now if you have a very hot laminator like i have i have a very hot laminator it's a custom thing that i've built myself like most things i own i've built myself so um it uh you know the laminator is extremely hot so i usually don't need a fence but you know it's just good practice and a little bit extra toner who cares right so i'll print these off and get these onto some copper again if you're interested in seeing that process that's in the previous video and i'll get these built this is very much like many of the projects that i release on patreon it's just like this so all the files are up there on patreon you can these are direct print these are already sized so if your printer you know prints to scale which most printers do if they're set on their default settings uh this prints out just the way you would see it again this would be mirrored right this here is not mirrored because i'm showing this to you but the actual layout would be mirrored you just print it off everything's sized so you could take the little ic the 7555 drop it right on to it and it's sized all the resistors and parts everything you just make your own circuit boards that way so that's how things are are done on patreon when i do the um when i share all of these projects and there's a lot of these projects up there and i will most likely share this on patreon as well i'll ask some of the patrons now if you would like to actually have a copy of this up there i haven't put this up there yet because i'm just doing this right now right but anybody here that would like to see that i'll definitely add this up there if you guys you know think that you have a need for a delay circuit and you could you know just change the valves if it wanted to be faster or slower just down this value you know change that from 4.7 to 4.7 meg to maybe 2.2 meg and you know you'll change the timing and make it either faster or slower by depending on which way you go right so the relay is a common relay sold by digikey all these parts are common and current so everything is uh very easy to do so at any rate what i'll do is i'll get this printed off now and i'll get it all populated so i'll have one unpopulated and one populated to show you here in the next shot and just like magic it'll take no time at all and through the magic of the camera in seconds i have a bunch of circuit boards made so in all reality to make two of these boards took 15 minutes that's all and that's excluding drilling the drilling would take an extra couple of minutes so about 15 minutes for a single sided board and if i was to make five single-sided boards it would still be 15 minutes because they would all just be on the the same thing right so 15 minutes for both of those boards or 5 or 10 or whatever i want to make at any rate that's the little board right there pardon the dust and stuff on it so that is the unpopulated version right there and for size reference i'll put this here i should have done that for the last one here is the populated version right there now of course populating the board takes a little bit of time as well but no big deal so there's that little led that i was excited to use there so i figured it would go good between the uh you know the relay and the seven five five five there's a little tantalum up here four point seven micro farad tantalum one thing to keep in mind about tantalum capacitors and this applies to many tantalums well pretty much all of them is the line end on a tantalum is positive so it's kind of different than electrolytics and other capacitors right so of course they have to make things confusing right so something you always want to keep in mind always check to make sure the line end is usually positive on tantalum capacitors you don't want to hook tantalums up backwards because they get pretty grouchy if you do so there's the timing set up there there's the uh 4.7 meg and the 4.7 micro fred tunnel and the switching transistors and everything else so i'll get some wires attached to this thing and we'll time it and see how close i come in all right i have my crusty old lab timer here let's see how close this comes into 30 seconds so i have the power supply set to 6.4 volts so i'm sure that the supply in that amplifier is going to be very close to that and all i have to do is turn the output of the power supply on so what i want to do is hit the start of the timer and turn the output of the power supply on at the same time so what i'm going to do is put my finger on the button here my finger around here and i'll see if i can collect them both at the same time so here we go so let's see how close this comes in so keep my finger on this ready to stop this so you can see how horrible my reaction time is i'm sure my reaction time at the racetrack at the tree is a lot better than this i used to get very good 60 foot times here we go look at that 30 seconds spot on now that's just with a random value tantalum capacitor and just our you know uh and when i say random i mean un you know not graded so when you pull them off the reel they're all a little bit different than each other and the same thing with the resistors i didn't grade anything and what does this indicate this just indicates that i spend way too much time designing circuits with this you know with these seven five five fives this is all that indicates i guess at any rate that's um was that fluky or not i don't know at that point so some of you more experienced builders may ask you be asking this question now what if you quickly cycle this is it going to you know hold off for 30 seconds well probably not if it's very quickly cycled because there really is nothing there to drain that capacitor off but it is such a small value that it's going to be well into a safe zone so it's going to be well beyond 20 seconds at probably 25 seconds or something like that so in order for vacuum tubes to heat up and stabilize takes about 15 seconds or something like that and if this was to cycle on and off again say they you know i had a very quick power outage there would be way enough time for this little timer to basically you know stabilize let the circuit stabilize against the power goes off and comes right back on the tubes are already warm right at that point so basically we're just holding off for the power supply and that would you know that's we're talking seconds would be absolutely fine for the power supply maybe you know even milliseconds if it's just a cycle that fast so if one was to use a larger value capacitor than this tantalum here and you wanted to make sure that it drained off very quickly you know a couple extra components could ensure that no problems again for the circuit i really wasn't worried about that and believe me i thought of that already when i was putting this together so what i'll do is i'll reset the timer here and i'll quickly cycle this and we'll see how close this comes into 30 seconds after it's cycled so it'll be a little bit lower i'm sure so i have to shut the power supply off and then turn it on as well as hit this at the same time so here we go okay we'll call that a very quick cycle maybe a second something like that three quarters of a second so we'll see how close this comes in i would guess 25 seconds something like that 26 maybe we'll see so yeah we could comfortably say 25 seconds all right say and that was just a very quick cycle so you know a faster cycle might bring that down to you know 23 but you know it's still well within a safe zone and again you know everything is warmed up in the amplifier at that point it's basically just holding out for the power supply and that's pretty much immediate so i have to get that inside the amplifier chassis now and get it wired up so i'll get that all happening and i'll come back and show you how everything works the little board is now installed so what i did is i put a screw through the top side and put a nut and a star washer on the bottom tighten that down to the chassis put another star washer on the screw put the circuit board down and then put a washer lock washer and nut on this side so it spaces it away from the you know the chassis just a little bit so i can run the wires on the underside to keep it nice and clean and the star washer that's on the back side of this bites into the rear side of the circuit board and holds it nice and stable on that screw so everything worked out very well so what i'll do is i will turn this on and we'll make some checks here so turn this on like so so right now this should be shorted you can hear that it is and this too on the other side this one here i'm doing this by looking in the monitor if i was to look forward i would stick my head in the camera so wait till this turns green and then it should be open okay so i might get a bit of a beep here for a second oh that's pretty good it's open and no problems so i'll shut it off and again should be shorted and shorted so it's working well so let's take a look at the frequency response let's check out the frequency response of this otl amplifier using the stanford research sr780 so there's a signal coming out of the sr 780 going into the amplifier and then the sr780 is watching the output of the amplifier across a 600 ohm load and that's what's going to give us our response on the screen here we can check out the 1db 2 db and 3db down points so i'll just start this now this will take a few moments because it is quite a long sweep and it is only 300 points but it still takes a while because it is down at five hertz so the start is five hertz and the end is 50 kilohertz and then what i'll do is i'll move the marker around and we can check the one two and three db down points here in just a moment so right now it's sweeping the amplifier and what you're seeing on the screen is it's reading the output of the amplifier and this is what's giving us this result here and as you can see it's 1 db per division that's why you can see such a steep slope right here so as it gets further along it'll speed up just takes longer at the lower frequencies all right so now we can check it out so i'll move the marker around here so we can see that this is one db right here so flat along this area here and i'll just hit backspace to stop that so you can see that right here we're dealing with 1 db 1db down from its flat area and the start is 17 hertz okay so this is within 1 db from 17 hertz all the way to about 22.5 if you want to call it that so that's pretty good within 1db so within 2 db we can see the top end is 33.5 kilohertz and then of course 3db down which is quite common for amplifiers to be rated at is 44 kilohertz so if we go over to the other side so 2db down it's at 11.8 hertz that's only 2 db down and then you can see 3 db down we're dealing with 9.2 so because i'm picky i pay attention to this area right here the 1db down area and that's 17 hertz all the way to almost 22.5 so that performs extremely well and that's how i wanted this thing to perform i wanted a very extended frequency range when we're talking about the operating frequency of a power transformer nowadays it's very common to hear 50 or 60 hertz 50 or 60 cycles depending on where you live in the world and this is the standard core size for a smaller power transformer that runs at 50 or 60 cycles all right in fact if it was 50 it'd probably be just a little bit bigger standard 60 cycle transformer well way back in the day we used to have 25 cycle electricity now 25 cycle electricity requires a lot more core size in a transformer this is a 25 cycle transformer this is a 60 cycle transformer now the same thing is true for audio transformers if you want an audio transformer to perform down at 25 cycles you need a lot more core size than if it was designed to you know perform at 60 cycles so you can see the difference just from 60 to 25 now you're probably thinking to yourself well new switch mode power supplies have really small transformers in them and they make a lot of current why is that well switchboard power supplies operate at much much higher frequencies so for example this is 25 cycles this is 60 cycles if we were to look at a standard switch mode power supply many of them operate in the hundreds of kilohertz so hundreds of thousands of hertz so as the frequency gets higher the core size gets smaller and that's why we can get so much current out of such a small power supply nowadays now you're probably thinking well switch mode power supplies are the magic solution to everything right well no they're not everything has it's i guess you could say it's good and it's bad points switch mode power supplies make a lot of noise and it is hard to get rid of that noise so without a lot of extra filtering on the outside and some pretty good shielding a linear power supply is a much much easier thing to design and to work with they sit silent because they've got a nice clean sine wave or at least whatever's coming out of your wall going into the transformer and there's nothing that's really switching at a very high frequency and you don't have square waves basically you know oscillating a transformer at a very high frequency square waves are you know very harmonically rich and create lots of noise so there are ups and downs to everything yes they're small they provide a lot of current and they're efficient nowadays but they are noisy and you know of course there are other things as well that i won't really get into in this video but anyways that's a representation of you know core size and operating at lower frequencies so whenever you're looking for a very nice audio amplifier that's supposed to have a very good frequency response make sure that you pay attention to the audio output transformer core size because more is really important when you want to get way down or really low in the audio frequencies if you're enjoying my videos you can let me know by giving me a big thumbs up and hang around there'll be more videos like this coming in the near future we'll be taking a look at vacuum tube and solid state electronic devices alike so if you haven't subscribed now would be a good time to do that as well if you want to be notified as soon as i post a new video don't forget to tap that bell symbol if you're interested in taking your electronics knowledge to the next level and learning electronics in a very different and effective way and gaining access to many of my personal electronic inventions and designs and a whole bunch of just other random circuits you're definitely going to want to check out my ongoing electronics course on patreon i'll put the link just below the video's description under the show more tab and i'll also pin the link right at the top of the comments section so if you click on the link it'll take you right there alright until next time take care bye for now you

Channel: Mr Carlson's Lab

Views: 113,298

Keywords: build a circuit, make electronic, create a circuit, circuit design, designing circuits, electronic lab

Id: mIRGc8U-Q9w

Length: 54min 15sec (3255 seconds)

Published: Tue Oct 13 2020