Buying an Oscilloscope and Accessories For Audio Bench Work and Testing

[Music] hey welcome everyone mark here at blue glow electronics today we're starting a new series that's been in high demand from you guys entitled oscilloscopes for audio okay it's going to be a 101 type series very practical in nature hopefully get you kind of grounded in the day-to-day how to how to work with audio equipment using an oscilloscope and it's going to be a multi-part series this first one today is focused on acquiring a basic oscilloscope for audio usage and some other handy bench tools that you'll likely need to get going so this will be our five part syllabus for our oscilloscopes for audio 101 series as we mentioned part one here today buying an oscilloscope and some other things you need to go along with that because there's not a lot of audio work you can do with simply just an oscilloscope okay also going to mention here that this is not just for hi-fi nuts okay this this video series should be great for people that work with guitar amplifiers preamps stereo receivers anything of the audio nature part two we'll get into it was one of my most requested when i made a facebook post about potentially doing this series a lot of people said hey i'm just not comfortable um getting in there and working inside of something that has high voltages with an oscilloscope so there again hopefully a very practical guide on some oscilloscope safety basics and working with probes in and or around high voltages part three then we'll get into just some basic oscilloscope usage what are all these buttons on my oscilloscope what do they mean what do they do how do they work that type thing part four we're gonna get into real life use cases on the bench so i'm gonna put up set up some gear and we're gonna do some troubleshooting and uh see if we can figure out maybe what's wrong or at least walk through some uh some audio setups here um and then part five which is really what i started this whole series about but when i made a post about making part 5 a lot of people replied saying hey but i need this precursor stuff first so part 5 will be a very advanced video on analyzing audio signals using an oscilloscope looking for things like distortion frequency response power output etc so if you follows one through four you should be in a good enough place then to do part five so stay tuned we hope to put this together over the next few weeks and uh as i mentioned here each video should be 30 to 60 minutes long so a little longer than our normal videos but i believe the uh content is worth it all right let's dive on into this uh part one series here all right before we go buy an oscilloscope we need to understand a little bit about what are they designed to do so oscilloscopes kind of operate based on two functions that they display in one domain here they display time and in another domain they display voltage okay so so if you draw a little grid with axis and your x-axis being voltage and your y-axis here being time that is what oscilloscopes are good at displaying so if we're talking about in the time domain then we need to learn how to speak hertz here otherwise the measurement unit that is used to measure frequency and so let's take a look at this let's consider this a one hertz signal in other words this this signal oscillates or changes one time in one second so it goes full cycle from beginning to end here and back to beginning all in one second that's considered one hertz if that same thing happened twice in one second then it's two hertz okay and so when we start talking audio work we've got to realize the spectrum we're dealing with typically the audio range is from about 20 hertz so in other words your signal is varying and it's not always a perfect sine wave like this it could could be a square wave a triangle wave it could just be random movement up and down of the audio signal but either way if it completes a cycle 20 times in a second okay that would be the bottom end of the audio frequency spectrum all the way up to 20 000 times a second that would be the high end so kind of what's considered your base notes go all the way up here to about 300 times a second 300 hertz your mid range goes from about 300 hertz up to about five kilohertz and in this range here is where our voice falls okay so where you can actually hear a person's voices in this mid-range then the high end you're getting into where your tweeters come into play uh symbols high end that's from 5k to 20k so we need an oscilloscope that will cover the 20k range to 20 kilohertz range okay so what i just displayed for you was the audio spectrum which is a very small part of the overall frequency spectrum here and if you take a look here kind of the radio broadcast spectrum here gets up into the 88 to megahertz you know you get up here into like um wireless for your your house 2.4 gigahertz um and on up until you get into x-rays and so on and so forth so this is the whole spectrum that um that is out there from a frequency standpoint i drew a little pink line here we need a little an oscilloscope that handles just this little end now the reason i'm showing this picture a lot of oscilloscopes you go to buy they may cover from say here at the beginning all the way way down here into the middle and so we only need the most basic of oscilloscopes to handle this audio work all right so let's make our little list here of things we might need to get an audio setup going on your bench so that you could use an oscilloscope well if you're going to measure the output of an amplifier or a receiver or a preamp or something you're going to want to send something into the input of it that you know is a known quantity so that way when you send something in on the input you can then look at it on the output and you can compare the two make sure they're the same and see if there's been any change to do that you're going to want to use a simple signal generator that covers the audio range so basically zero hertz or as i mentioned earlier 20 20 hertz up to 20 kilohertz then you're going to want a basic oscilloscope the good news here is even the most basic of basic inexpensive oscilloscopes will cover from 0 hertz up to 5 megahertz and you only need 20 kilohertz so even the lowest in scope will cover the audio range but many oscilloscopes will be 100 megahertz 200 megahertz one gigahertz scope while they can cover that whole range we really only need them to cover the 20 kilohertz part of that you're gonna need ideally something with two scope probe inputs okay you're gonna want two oscilloscope probes remember a lot of times you're going to want to compare what you're feeding in to what's being what's coming out the other side you're going to need some bnc to rca alligator clips and i'll show you this here in a minute you're going to need some adapters here and i'll walk you through those otherwise other without these it's going to be hard to connect these things practically okay you're going to want some type of 8 ohm non-inductive resistor okay and that's going to be for your dummy load we'll talk more about that and you're going to want some kind of isolation transformer for your dut and if you don't know what that stands for it stands for device under test all right as i mentioned earlier feeding something into the device under test i.e the amplifier receiver whatever that you're trying to do some quantitative measures with using your oscilloscope you're going to want to feed a signal in that is a known signal feeding an audio signal in from say an ipod or something you know playing music is not really good for measuring and we'll show you that when we get to our practical bench setup video but you're going to want a simple audio generator and sometimes these are called function generators sometimes they're called signal generators sometimes they're called audio generators but the bottom line is you're going to want something that covers the audio range well 0 hertz up to 20 megahertz okay you're going to want something that covers the af range the audio frequency range not the rf range radio frequency range and the whatever you buy should be able to generate both a sine wave and a square wave you're going to want those two at a minimum now this little device on the left here here and i've got i'll have links down below this is something i found on amazon um it will do everything you need okay so same as this probably 50 year old rca unit right here and if you'll notice it's titled audio generator these are really common it's an it's an older heath kit audio generator and this can do your sine wave your square wave whatnot this is what i use here a b and k precision and while this will do a little ways into the rf range it does a really good job down here in the audio frequency range and you're going to want to be able to connect via b and c connectors so if you'll notice these units here have bnc connectors and these do as well but this one and these do not you're going to need these little adapters that plug in the little tab here on one side will be the negative it would plug in and it would give you bnc output for this so just some basic specs you're going to want to look for if you are going to go online and find one you're going to want it to put out an output voltage of at least a half a volt okay that would be considered line level preferably maybe it can go on up into maybe the 20 volt range or so you're going to want it to have an adjustable output level so if it doesn't have a knob on it somewhere that you can grab and turn to adjust the output level that generator is not for you and then some of these units have a nice little switch on them that will give you 20b of a attenuation so in other words you'll have a full sweep on one of the knobs and then you could maybe flip a switch or pull the knob in or out and it would attenuate that signal by 20 db and the one i use over here i can tell you it'll do that this little knob right here is kind of your volume knob and if you pull it out it gives you 20 db of attenuation i use that function all the time okay it needs to cover 10 hertz or down to zero hertz or whatnot all the way up to 20 kilohertz sometimes you'll find one of these that'll cover part of the af range and the rf range but it may start at 100 hertz or 200 hertz you don't want that you do want something that will go all the way down to around 10 hertz you're going to want something that has distortion specs of preferably around 0.1 or lower otherwise you're feeding a lot of distortion into your device under test and then on the output you might be trying to measure the distortion you don't want to add a lot of distortion from the signal you're feeding in one that has a frequency meter is a nice thing to have so like this one will display the frequency this one displays the frequency this one does but it it does it in terms of you know the analog dial and where you're at on the dial same same over here these will have little dials that did the counter but it's showing what you want to put out not exactly what is being put out [Music] and then last i mentioned here you might need some banana 2 bnc adapters okay so i came over to ebay and i just did a simple search for audio signal generator you can see here some new ones that cover 0.1 hertz all the way up to 10 megahertz and you know got these are new digital units 139 here's some older used ones 34. looks like this is a low frequency you know if you are buying a digital one check on the things i mentioned around make sure it can put out at least a half a volt make sure it does have the right distortion numbers um here's an old rca sine wave square wave generator there's just lots of options because these things were made for many many years so there's no shortage of what you may want to use here just kind of look for some of the things i mentioned earlier all right let's get to actually selecting our oscilloscope there's a lot of options out there literally just as many as there are audio or signal generators and you may say well wow i'm really confused i don't know what to go get well here's the short and narrow answer all of these will work for audio work okay this here is the analog discovery 2 which is a kind of computer-based digital oscilloscope this here is a just a an old tektronix simple two-channel scope matter of fact this was what i started out on uh back in college uh this is a touchy two-channel scope an old ico oscilloscope even this old ancient looking with the round tube here will do five megahertz so no worries of that this is a modern day rigel ds1054 i've got one of these on the bench as well and this is the tektronix 2246 that i like to use some of the differences between these starts to get into how practical they are for you okay so first off i find computer-based oscilloscopes not the most practical the reason being is you have to have this device on your bench and then you kind of connect your probes to this and you connect your probes into your into your device under test but then you've got to have a laptop or a computer screen there and it takes up a lot of bench space um so that side of it not that not that it's not a great scope and won't work great for you i just find it limiting and taking up bench space and being a little awkward to work with whereas something like this little two channel scope right here fits well on the bench or maybe on a shelf above your bench and would work out well for you if you'll notice here though if i'm trying to measure this signal right and these little lines here are called gradients and each gradient will then tie down to a meter a setting on a switch here you're going to have to count these one two three gradients maybe 3.1 gradients then you've got to multiply that by the the value set on your scope here and you might know because of that because it's set on 2 volts per division that 3.1 is really 6.2 volts and you're going to have to do that math yourself whereas some oscilloscopes have the ability to measure the signal that you're reading and display the value for you almost all modern digital oscilloscopes do a really good job of measuring and showing values on on the screen for you whereas if you get into some of these older scopes it won't do that for you doesn't mean these scopes aren't great scopes and that they won't work well like i said i used i used a scope like this for a good 15 years or more before i made an investment in something that at the time was much more expensive but now even these because of the new digital ones even these old analog scopes with the digital readout on them have gotten inexpensive okay so one question i see a lot and i've been asked a lot is should i get an analog oscilloscope or a digital oscilloscope or computer base i've already talked about what i thought was the downside of the computer based however if you've got a small laptop and room for it on your bench there's nothing wrong with going with a computer-based oscilloscope nothing at all the analog versus digital let's talk a little more about that all right let's simplify this a little bit and just call it analog versus digital and we'll lump computer based right into that bucket with digital oscilloscopes so on the left here what we have is a signal on a modern day digital oscilloscope and on the right here we have a signal on a vintage tube based with phosphor screen analog oscilloscope okay and you may look at this and say wow look at the signal here on this analog look how jittery it is look how rough it is on the edges and then look at the signal over here on this older analog oscilloscope well here's the reality the exact same signal is being fed into these two scopes okay what's going on here is the older tube based oscilloscope that has sprays an electron beam onto the back of a phosphorous screen well the reaction time to this screen is slower so it has a tendency to smooth out your signal and this is actually a more true representation of the signal being viewed than on the older analog oscilloscopes having said that i still like the older analog oscilloscope because i'm an older analog kind of guy okay it's just what i grew up on however there's nothing wrong with using a digital oscilloscope a little bit of this granularity here is the pixels on the screen and some of it is actual noise that it's able to pick up and display that this that that noise came and went so fast that the screen couldn't display it over here so um e vlog does an entire video on this topic i'll put a link down below and it goes into a great depths on the on this whole phenomenon and the difference between those two but that's just one difference between analog and digital oscilloscopes and for me i like the analog but you know i didn't grow up on modern day digital scope so if i had i'd probably say well i don't want that slow old unresponsive scope i like seeing everything real lifetime here and i might would like the newer scope better another difference between modern day digital oscilloscopes and older analog scopes is how you control the functions of the oscilloscope and i'm speaking in general generalities here but digital oscilloscopes tend to be menu driven and button driven let me give an example on an older analog scope if it had four channels you might have four independent knobs for your time domain and four independent knobs for your voltage domain here you have to push this button and then you use this one knob for channel one then you would push this button and use this knob for channel two if you wanted to measure the peak-to-peak voltage of this blue sine wave here you may have to push one of these buttons over here which may bring up a menu on the screen and then you may use this button up here to scroll up and down through that menu to say hey i want to measure peak to peak okay so it's very menu driven very button driven and sometimes that can be considered more complex and more time consuming than to have discrete buttons and individual switches and knobs for individual functions now i'm sure if i had grown up on a digital oscilloscope i would be so good at these things that i would say this is so much more efficient and effective than those older digital analog scopes and there's so much more i can do here because of the menu driven capability so it's kind of a what are you used to and um whatnot but i do find for audio work personally the older analog scopes to be a little more practical and a little more time efficient here you can see an example of this you know each channel has its own little switches here each button has its own purpose there are no menu driven functionality right every little um capability on this on the oscilloscope has a button or switch for it so if you learn every button and switch you've learned the oscilloscope where the more modern digital oscilloscopes have lots of menu options which can give you a lot more features and functionalities also comes with more complexity of which one do i use when do i use what and when so that's why i think learning on an older analog oscilloscope may be better and then after you've kind of got the basics you could move forward to a more modern digital oscilloscope me personally i've not quite made that jump yet and for all the things i do analog based these older scopes work great for me okay so if you buy a scope and you buy a new one it's certainly going to come with two oscilloscope probes but if you buy an older scope it may not you can get this little set of probes right here on amazon for dirt cheap and they will serve all the purposes you need for ammo for audio work similarly here you can see just different styles and kits these are some older probes tektronix probes but you basically need two probes to get you going all right there's a few other things you're going to want related to the probes that come in a kit here on amazon you can see the price on this entire kit is 21. and for for the audio work you're going to be doing this kit would work fine so it's going to give you your two probes that you're going to need and it's going to give you various colored rings to identify left channel or right channel or whatnot it's also going to give you some other connections here bnc type connectors that you could use with not necessarily the oscilloscope but maybe with your function generator and i'll show you here it's going to give you a bnc to bnc a bnc to test lead probe and i use this little connector right here all the time because i'll inject a signal somewhere midway in the amplifier using little probes like this okay you'll get a bnc to alligator clip and some bnc looks like to um some type of little probes here but great little kit for 21. i'll put a link down below so this is where things start to get very practical okay you probably won't find any video out there on how to use an oscilloscope that'll teach you this kind of stuff okay first off you're going to want to have a way to connect your signal generator into the amplifier that you're feeding okay and this is a picture of my actual bench so this is this is my bk precision what is it 43 oh 4003 a function generator that i use okay if you'll notice coming out of it i've got a b and c here to a little adapter to then another adapter which then feeds a cable which then allows me to plug into my stereo or my amplifier via rca jacks and i'll show you more on this all right so you're going to need a 3.5 phono to rca and i would say five or six feet long if you get much longer than that it just gets kind of clunky on your bench and if you get shorter than that you'll find yourself stretching it all the time so you may wonder why would you use the one on the left and not the one on the right they both look like 3.5 millimeter phonos to rcas well here's why if you'll notice the distance between this little um device here that keeps the cable where it splits out at you notice there's a good distance around here to this so in other words you could spread these rca jacks apart maybe 10 12 14 inches okay whereas these if you'll notice this thing is really short right here and you could only spread these apart about five or six inches well i run into frequently with two amplifiers where one rca jack is on the right hand side of the amplifier on the back and the other is on the left hand side and you need to be able to spread those out a good 10 or 12 inches so get something where you can spread out the distance here up next you're going to need a bnc male 2 rca female adapter okay and it's it's a simple little device one plugs onto your piece of equipment which gives you an rca jack on the other side this was a 10 pack for 6.99 or for 11.99 and i'm not endorsing any of these products i'm just showing you what i'm finding online this comes with a bunch of different types of adapters that you might use for different purposes so make your choice but you only need one of these so um even the 10 pack is overkill but i couldn't find anybody that sold just one and this is the tough little booger to find um but here you can find monoprice and there's the part number it's five bucks but what it does is it takes one end rca and then it puts it into a stereo jack but it feeds it to both sides of the stereo jack that way whatever you're coming out of your function generator signal generator with it's getting fed to both sides of the 3.5 millimeter stereo jack which then ends up feeding the same signal into the right and left channel at the same time so handy little gadget to have so when you stack all three of those together you're feeding into the bnc jack here you are then um going into the rca adapter here to 3.5 millimeter phono which then sends the signal out to both channels feeding down the line and goes into your left and right channel if you happen to notice remember earlier i can change the amplitude of this using this unit and if i pull it out it drops a 20 db attenuator in inline absolutely love that feature probably 90 percent of the bench testing with audio gear i do is with the cable setup i just showed you hey if you happen to be a guitar guy and want to feed into your guitar you can just change the adapters to be something that fits the larger phone jack for that or sometimes coming back around to this i might just clip on to my function generator here with this bnc connector and then i may feed down and insert somewhere in the middle of the amplifier so let's say maybe i'm trying to bypass the driver stage and feed directly into the output stage i may use this little connector so that's why having this little kit would be very handy okay and finally here for your little audio bench setup you're going to want an 8 ohm non-inductive dummy load and two of those okay and there's a couple options out there you know here there's one listed that says it's not inductive but i also noticed that it's a wire wound resistor which has inductance so maybe they found a way to overcome it but that one i'm not going to go with parts express has an 8 ohm 100 watt 22 dollars you could get two of those wire them up into a little box or something and use some banana jacks um speaker jacks like this to wire it up and you would have the perfect um output load for a bench setup or you know here's some even for five bucks you could get some 20 watt if you didn't want to go 400 watt this is about what i use um i actually use some dale resistors that are really hard to find these days so these parts express 800 watts would work perfectly for a nice bench setup okay another device you're going to need if you're going to want to do a lot of oscilloscope work with audio is an isolation transformer and you're probably going to want one of these for other purposes as well but as it relates to audio work and oscilloscopes your typically your oscilloscopes are grounded on the inside thus your scope probes the outer leads of them are grounded not only to chassis ground but back to earth ground and in some cases for audio work you're going to want to be able to isolate that so you're going to want to be able to plug your device under test a the amplifier or receiver or whatnot into one of these devices that electrically isolates it from the ac mains in your wall and separates it from the earth ground and so these all these little devices here i've got pictures of they plug into your wall outlet and then you plug your device under test into these devices and what it does is it does that electrical um isolation there and ground isolation so um some of these devices will have three prong plugs on them i mean it won't have three prong plugs yet the device under test you may be testing requires three prong plug so you might need an adapter to go from three prongs on your device under test into one of these this little rca device down here in the bottom right hand corner is exactly what i use underneath my bench i plug my devices under test into this i actually feed out of i feed out of one of these into one of these little three prong plugs then from that i go up into a power strip mounted on the side of my bench and then from that anything i plug into that power strip i know is isolated from earth ground at that point and electrically isolated from the ac mains so probably want to get one of these you can find these little units anywhere from forty to seventy five dollars on ebay somewhere in that range you can buy new ones for you know in the hundred dollar range type thing so um definitely something you will you will need so with all that you should have all the practical aspects you need to do start doing some audio bench testing if you've obtained those components if i were to make some recommendations on an oscilloscope and these are not endorsements here's some options i might point you towards um this rigel dz 1054 it's 350 dollars it'll it'll go up to 50 megahertz um and it has four channels in it i've got one of these on the bench i use from time to time um this one i've been actually looking at for myself a dxox1202g it's basically a 70 megahertz oscilloscope two channels but it has a built-in waveform generator and it can do frequency response plots so that's this little black keysight unit down here about a thousand bucks maybe you want to spend that much maybe you don't i don't know but i've actually been eyeing one for myself um this is what i started out on the tektronix t935 you can find these for like a hundred bucks a lot of times in good working condition there again you're gonna have to count the gradient gradients and do the math yourself it doesn't do any on display on screen display similarly the techtronics 455 or 465 these things are workhorses there are thousands of them out there they're on the used market all the time you can find a nice calibrated one in the 250 to 300 range there again doesn't have any on screen math or or display so you'll have to count the gradients but these things are great scopes and then i use the 2246a here which you can see it will measure and give you the voltage rating here um pretty simple and believe it or not these used to be big big time expensive scopes now you can get one of those fully calibrated for 300 or less so you know my recommendation getting into this either get one of these rifles or spend the 300 or less here all depend on depending on your budget also don't get wrapped so much around specific models like 2246 there might be a model 2256 that i'm not aware of that has the same functionality and maybe it's the same price range or maybe hitachi makes a scope that has the same functionality you know don't get wrapped so much around the specifics here as much as i am talking in generalities about capabilities and price ranges of scope so you don't need a thousand dollar oscilloscope to do audio bench work with all right so i've shown you the oscilloscope options are a few of what many are out there i've also shown you some of the little auxiliary pieces that will make your life easy if you're trying to to do some audio bench work but in reality the best scope for you is the one that you learn how to use and that you get comfortable with that 2246 you see me quote over and over it's not the best scope on the market it's probably not even a great scope it's just the one i've used for the last 20 years so i know it inside and out i'm very quick with it i know which knob to turn when i know which button to push when because i've learned it very well if i had started out 20 years ago on a certain model digital oscilloscope i'd probably be as fast and familiar with it and that would be my go-to scope so whatever you pick learn it well learn all the intricacies of it that will be your best friend the one that you know and that you're comfortable with all right i'm going to put these links down below and these are not necessarily endorsements by me of these products they're just ones i know that i have bought and that work one i'm gonna i've got a link here for the why oscillos digital oscilloscopes up here noisy that's a good video to watch that rca mono to 3.5 millimeter stereo adapter the 8 watt inductive non-inductive dummy loads 100 watt isolation transformer if you were going to buy a new one rca to bnc mail the syncwire rca cable and the universal oscilloscope kit i've got a link all those links i'll put down below for you all right i hope you've learned enough from this video to kind of get you going and uh we're going to move to part two next which will be the uh safety precautions and working with probes inside of uh inside of gear with high voltages so stay tuned we'll try to get that one wrapped up here in the next week or so and get it posted online i'm figuring about a week in between each of these videos so hopefully over the next month we'll get all these topics covered hopefully this is hitting on for you guys and uh stay tuned for more thanks everyone you

Channel: Blueglow Electronics

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Keywords: dynaco, heathkit, AR, audio research, cary, klipsch, marantz, luxman, knight, mcintosh, altec, sencore, tektronix, fluke, fisher, hh scott, western electric, akai, pioneer, sansui, harmon kardon, gibson, fender, mesa, 300b, single ended, tube amplifier, tube amp, solid state amplifier, bottlehead, output transformers, transformers, hammond, alinco, atlas, collins, drake, dentron, elecraft, flexradio, hallicrafters, galaxy, gonset, icom, yeasu, hy-gain, kenwood, national, swan, ten-tec, passlabs, Rigol, Agillent

Id: CoaI9lJsNgA

Length: 34min 8sec (2048 seconds)

Published: Mon Dec 28 2020