The Power Supply

 

Guitarist's Tech Workshop

 

Lesson Info

The Power Supply

Talking about the power supply then kind of going through each of these stages just talking about the way these two his work saying like you know for example uh like like these have a voltage appear on the way down well this voltage comes from someplace and that voltage comes from the power supply so it's important to talk about how that all works because it even though you can kind of treat it as a battery that just runs the whole thing it actually does have a good amount to do with the way an amplifier sounds and feels the way it responds so we talked before about power transformer and how it takes one hundred twenty volts from the wall and converts it into voltage is that the amplifier can use a d c battery so there's a couple things to think about their one hundred twenty volts coming in out of the wall say it is one hundred twenty bulls I'm standing in front of it sorry one hundred twenty bullets comes out the wall and it goes into the power transformer and it comes out as this hu...

ge version of and then you take that huge version of the signal that they are the voltage supply that came in from the wall and you put that through its called the rectifier and then the rectifier comes out and it makes that signal look like this directive fires job is to take these negative sides and flip him up. So you end up with something like this. Now he send out into they just too little p s you for power supply filter and the output of the power supply filter looks more like I'll do this. So I wanted tio. So this business here gets filtered so that it tries to approach a d c battery. Because though the whole and goal of this thing is to end up with something, it just looks like this is just say, like, a five hundred volt dc battery for this thing to work off of. And so the power supply job is to take the wall voltage, step it way up, flip the negative sides, ups you end up with this rectified version of what came out of the power transformer. Send that through a bunch of filter stages that try to approach this d c that battery mean what you realistically end up with is a lot more like see, most all these are the best way to do this. Something that goes like that. So it's, like, you know, this is this is what you're trying to get your your d c bolted say, this is five hundred volts and that's what you want, for whatever reason, that secure tubes one well, you have that little bit of ripple up there. So it's not quite exactly a dc battery that you need for these tubes to work off of. But it's it's a start. So just kind of working through this is a much better picture than the one I just tried to draw. Um, if you have the power coming in from the wall here and hitting the power transformer and then it goes through this rectifier, which here they use silicon die odes. Um then the output ends up of the rectifier, which is the locked the negative side flipped up that whole business. Now you can send that through this capacity to ground through this choke tio capta, ground resister, captain ground and each one of those captain grounds through a resistor is again just like this business here. So remember, every time you have a resistor of here and a cop down here it's gonna want to let high frequencies go to ground and just let the low frequencies through so that's, you know, you don't just use that phenomenon when you're dealing with the signal, but that's exactly how you filter out some of the ripple and all of the high frequency stuff that's going on with the power coming from the wall that's been stepped up through the transformer the way to get that to be a good d c battery is to use these filters and use a bunch of them and this is if the old school way to do that there's a lot more sophisticated ways to do filtering but kind of the old approach brute force rc filtering is just to go resister cap resister cap and every time you have one of these filters you sent mohr of the this little bit of ripple to ground further approaching a perfect d c battery and he go back here you can see this is a a filter here to ground be a capacitor so a bunch of trouble just shot to ground there and then even more trouble actually got stuck at this choke here this is that I have a stupid red line through it but it's ah that's the signal the symbol schematic symbol for a choke choke is an inductive saying exactly and as we said before in doctors are resistant to change in current so high frequencies see that induct er is a brick wall so all this stuff that came out here all this ripple the trouble is going to want to go to ground to this cab it's also going to be stopped at this in dr so it zoe all that troubling stuff is going to be stuck their finest way to ground there's still going to be a little bit left which then will further find its way to ground through this capacitor and then you have another resister to capacity air filter another resister to capacitor filter another resisted a capacitor filter and there's an important thing to keep in mind in that every one of these filters further makes that d c bolted you have closer to an actual d c battery which is what you want and another thing is that every time you drag current through one of these resisters you lose some voltage so this might be five hundred volts and then you might be down to four hundred bulls three hundred bowls to fifty volts so it's kind of a two a purpose deal you're cleaning up the quality of your supply as you're stepping its quantity down and if you can see this is the most sensitive part of the amplifier signal path your guitar comes in here and it gets amplified, amplified, amplified, amplified. So if there was a bunch of ripple right here in this supply you would end up with a bunch of ripple that would find its way into the signal here they would then be amplified, amplified and by the time it gets your speaker you would hear some of the ripple that noise that high frequency hum in you're saying oh so by filtering filtering, filtering, filtering the power supply you end up with the most filtered most pierre d c supply toby the battery for your very most sensitive, very first gain stage, and the crude supplied stuff ends up being here to supply these power tubes, which are doing a lot of amplifying. They're just there to make the speaker wiggle so it's not like a gain stage, as much as it is a a workhorse kind of thing and there's another thing about especially a push pull amplifier stage that is helpful when it comes to a creed power supply. And if you have some good amount of this ripple in the power supply that's feeding these power tubes, because it's only had a chance to be filtered once, twice, and then you're on to the power tubes. Well, it's ok, because what happens is that, uh, these pushing and pulling tubes are seeing the same amount of ripple. And the same amount of ripple is that that signal is going to be in both tubes, which are drawing current in opposing directions, so they actually cancel out completely. So even though there's ripple, supplying both of those tubes, they cancel each other out because there's some ripple here going into this, some ripple here going into that, they cancel each other out because a lot of face from each other, and then you it ends up being dissolved in the upper transformer so that's the place where you can get away with the most ripple is that that output tube stage and then you clean it up some more cleaning up more federal etcetera that's the basic job of the power supplies to just give you that battery um thing to think about is rectifier is for example um you can do lots of different things that affect the tone of the and so here we've got some silicon rector fires these little silicon sand rector fires the's die o ds they are actually very efficient doing the job of rectifying and they don't lose a lot of voltage they're very simple and efficient and most people use them for that purpose. But if you were to use a tube instead of a silicon dialled like we're talking about the very beginning of this whole thing to rectify irs tube die o ds they actually have some output resistance and remember we talked about anything with output resistance will drop some voltage on its way to get to where it's trying to go. And so that is oh thing that is inherent of old vintage two vamps that makes them sound the way they do, which is cool sound it's it's a segi kind of spongy sound, so if you're going for something a little bit more on the spongy sandy vintage vibe that's one way to get it but if you want something tighter and high head room and cleaner than actual silicon die owed rectifier would be the way to go and it's funny because people always talk about director fires and triple rectifier is and how direct fires you gotten there's an association I think about how brutal is going to sound or but it's just you can choose between a silicon rectifier and two rectifier so I thought it was kind of funny but you have a question real quick just to go back where you were talking about the choke oh yeah, I know some like peavy butcher instead of having a choke it has a very large resistor and you can actually buy from, you know, transformer companies will make a sub in part now if you're looking at doing something like that p d made it with the resistor from what I understood that was more of a cost saving decision if you do want to put in a choke in place of that a it won't hurt anything and then be, do you want to make sure that you're still providing a similar resistance with that show component to what you're replacing? Well, yeah, a couple things to consider, so if if the resister that was there is of some substantial value if it was like a thousand owns or something like that a choke which is just a coil of wire around a magnet it will have some resistance to it but usually it's only on the order of one hundred few hundred homes so if if the next thing in line if say this was a resistor of some large value and you needed that to be there so that you dropped enough voltage across that resister so that the supply for the next place in the signal path was correct by just dropping a choke in there which has very little resistance you might end up with, you know, save your five hundred volts here and you want to have four hundred goals here the resister here is what provides that drop and if you just take a choking there, you might end up with four hundred eighty volts here but you needed needed four hundred and four eighties too high and now you're doing something to hurt this stage so you have to I know what you're doing I imagine if they're making a kit for like a replacement with that mind, hopefully somebody did their homework. So maybe if you're thinking about doing this, measure the resistance and then provide an appropriate value resister behind it although on I don't know I mean the thing about it it's kind of strange is the only reason I could think of to use a choke instead of a resistor is that you know, if you have a resistor, you are going to have some segue thing happen and using a choke in its place could in theory kind of clear things up and give you more headroom and less sag you hit allowed note and it drags across that resistor and it kind of stagg's things a bit. But if you drop a choke in there, maybe it's clear and higher, but if you have to stick a resistor after it in order to get the correct voltage is down the line that it will still say have the sag yeah, so it's just a matter of what you are trying to get out of the choke the choke doesn't add something inherently it's more like an improvement in place of but if you have to stick a resistor and as well, then it's not the choke magic goes away that's very clear actually, thank you. Quickening negative feedback is cool you can send some of the output of your amplifier back to the input of the of the power amp and it will clean up the signal in real time and that's a really cool way to kind of keep things clean and correct any distortion in the power and a lot of people complain that too much negative feedback and be a real stale stiff sound, which is true to some extent but you can actually stick some rc components in that feedback loop. That's. What presidents control works and kind of tailor, what frequencies get linear ized and cleaned up. And which ones don't that's that's something that the trick? Um, yeah, always twist your a c wires, shield, sensitive wires, anything connecting to a grid at the input end of a high gain. Amp. You want to shield that, um, you don't need a super wide bandwidth, and if you have high bandwidth throughout the amp, you could get oscillation that way. So, you know, using those miller capacitance is, and using coupling caps, show the way anything you don't need, it will help the whole thing behave a lot more stable.

Class Description

Performing a proper setup for your guitar can seem like a dark art requiring a copper chalice filled with incense. Reading a schematic of a tube amplifier can seem like you’re staring at ancient Sanskrit. Guitar and tube amp masters Kurt Bloch and Ben Verellen are here to help.

In this two-part workshop, Kurt and Ben will show you exactly how to get the best sound out of your gear.

In part-one Kurt will teach the basics of setting up your guitar – you’ll learn about:

  • Truss rod adjustment
  • Bridge and nut adjustment
  • String gauge and playing style
  • Guitar maintenance and upkeep
  • Guitar electronics and pickups

Part-two is your primer on tube amplifiers. Kurt and Ben will explain how they work and show you how to keep them sounding great. You’ll learn:

  • Tube biasing
  • Block diagrams and understanding schematics
  • Basic amplifier maintenance
  • Capacitor, resistor, and transformer replacement
  • Speaker repair and power-matching

Kurt Bloch is not only Gibson Guitar’s in-house guitar guru, he’s a legend in the Seattle music scene. He plays in The Fastbacks and Young Fresh Fellows and has a producer credits for his work with The Presidents of the United States of America and Tokyo Dragons. Ben Verellen started Verellen Amplifiers in 2000 and now has a full-time staff churning out hand made custom tube amplifiers for some of the most respected artists in rock and metal. He also fronts Helms Alee, a rock band based in Seattle.

Don’t get caught with crappy tone and blown out speaker – let these two masters show how to take care of your gear and get the best possible sound.

Reviews

Andrew Synowiec
 

I bought this course for the amplifier section and skipped straight there. It's fantastic. Right at the perfect level for me, a newbie DIY-er with a few pedals, a kit amp and an Electronics 101 course under my belt. Well done! I'll update my review if I have time to watch the guitar section.