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Guitarist's Tech Workshop

Lesson 11 of 18

Power Matching Speakers and Amps

Kurt Bloch, Ben Verellen

Guitarist's Tech Workshop

Kurt Bloch, Ben Verellen

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Lesson Info

11. Power Matching Speakers and Amps

Lesson Info

Power Matching Speakers and Amps

Speakers loud speaker this is a common one people ask about so eight own speaker forum speaker what does what does that mean? Well it's really important to think about those numbers as really just a nominal description of the impedance of a speaker and what I mean by nominal is a speaker is not a resistor it's not a fixed resistance in fact a speaker if you were to look at it as a realistic I'm a realistic electrical model for what a speaker is. It looks more like this diagram here where if a speaker you want to think about it as a fixed eight on speaker it's not that instead of actually there's some resister in siri's within induct er and now those drive another resister with the induct er and a capacitance and parallel because the speaker is just a coil of wire and it has all this mechanical movement happening and there's it's a complicated device. And so really if you're looking at a speaker across the frequency spec shin now this chart here we're looking at from left to right low f...

requencies to high frequencies, so base signals and all the way up to really high trouble ebright signals each one of those signals is going to see the speaker as a different resistance so if it's an eight own speaker down here this is scale, you can see it eight homes is right about where we are d c maybe just a bit lower d c meaning zero frequency not moving at all just a fixed signal will see that speaker as an eight homes as a download but as you move up as he start to make us a signal wiggle back and forth you this huge huge spike here in resistance right here around one hundred hertz which is a really low note say on a bass guitar or something it would see right there that point as a very, very high impedance and then it dips back down and then it curves back up again. This eight owns figure is kind of a baseline average for some mid band frequencies, but I mean even hear it, you know, two thousand hertz, which is a very middle range frequency that super common two guitars mean at that frequency or all the way up past ten own somewhere around it looks like fifteen own something like that but the eight on speaker but it's just important to consider that it's a nominal figure it's not a fixed thing and all speakers have a different impedance curve and so um just worth keeping in mind that the basics of a speaker and what it does um and that's important, especially when you're talking about two of amplifiers because you need to use the correct output of an amplifier to translate the speaker impedance of what you have to the tubes in the power amp of your and so you know it's a common question as well what's what's going on if I plug into the wrong output if I I only have a four own speaker cabinet but my amp only has an eight home output can I use it what's going to happen? Is this going to blow my amp up isn't going to blow my speakers you know what's what's the down down sides of that how important is it? And the answer is not totally simple but you can kind of have an idea about what's going on. Um the way to think about it is that you have your power and docking tubes that are connected in such a way that they're designed to drive a specific load and that load khun b whatever it ends up being say ends up being twenty two hundred owns so now you need these tubes to see two twenty, two hundred homes well, you have a forum speaker a forum speaker isn't twenty two hundred owns so how do you make that happen? Well, that's, how the output transformer works it's there to translate your four own speaker to your tubes toe look like twenty two hundred owns that's what it's doing so if say you have an eight home uh uh I'm sorry if you have a output transformer this designed to translate a tones to the tubes for the correct impedance, but you only have a four own speaker cabinet. Well, now you're connecting that forum speaker, cabinet and it's reflecting back something completely different, you know, she reflects back about about half so you end up the tube, seeing something that's different, and what happens is if you go the wrong way and save the lower, so you go for owns. So now you're the tubes air saying something much less impedance than they would want to see? Well, if they see less impedance than they want to see, then the tubes will be drawing more current and swinging less voltage if you go the other direction. So you put a sixteen home load on that output transformer now the tubes they're going to see more than they're supposed to see. And what that ends up meaning is that you swing more voltage and he's suing less current and the way that the transformers design is going to dictate how drastic that is and the design of the out, the transformers going to dictate how much of a a difference that can take without things going wrong, but just some basic consequences that you can count on happening if you go larger if you go. I've got it it's supposed to be a tones, but I've got a sixteen owns you apply that sixteen owns, and now the amp is seeing more than it's supposed to? Well, because now you're swinging more voltage that you're supposed to. If if you're doing a really drastic mismatch in some threatening cases that large bolted you're swinging, it could become a large enough that you can experience an arc meaning, just like the voltage gets so high that it just shoots through the things it's not supposed to shoot through. You getting are concurrent, and that can blast through the output transformer and destroy it, or that can blast across the tube, sock it and destroy the tube destroy the socket blew your fuse bunch of work has to be done so that's a threat that's the best, the best, the biggest threat going in the large direction. If you go in a smaller direction without put speaker now you're swinging more current and less voltage. One thing that could happen is that you can work the tubes harder because they're drawing more current, they're heating up more, and that shortens the life of the tubes, and in both cases, in that situation, you're going to get less output power and that's that's the most inherent one no matter what's going to happen and I don't want to say it's a rule, but I would say that if you're mismatching by about one hundred percent on either side, you should be ok as faras things destroying themselves. But you are going to get less power. Uh, yeah, so that's it's worth keeping in mind? Um, and another thing to consider if you're going in the lower version. If you go for owns a speaker cab on a dome output it that's going toe in addition to draw more currents of the tubes, working them harder, it's also going to draw more current through the output transformer, which can have a saturated sound. At some point, things could get murky and weird that, as well as the fact you're not getting as much output power can make what's supposed to be a really powerful amp sound mushy and quieter and not is good. So some things to consider as far as that goes, any questions about that? Does that make sense? And I grabbed the mike away? Yeah, I feel like I'm blab through that little bit I was falling pretty good, but just to clarify. So what you're saying with one hundred percent power on either side say you had a four rome cabinet? Yes, you'd be ok at eight, but not at sixteen, you know, slightly more off you're getting the more you're rolling the dice, right? Yeah, it just depends on the amp some ants can can do a big mismatch there's some things you can do in the circuit to prevent disasters from happening but the further you go away from what you're supposed to be getting because the idea is to have a match you're supposed to be matching the speaker to the tubes that they see the right thing and the further you go away from that the more you're gonna have bad performance power wise and in extreme cases you can have some real bad things. So so without condoning it let's say you have one of those weird, weird, oddball six speaker cabs and it's a six own cab. Okay, might be okay at four or eight, I would absolutely do that. Definitely stay away from the sixteen out put up. Yeah, I mean, like he said without condoning, no responsibility taken, but personally, I mean, like I said, I showed you that chart of the speaker and you saw how much an eight on speaker is not it owns so many frequencies that you're using it at. So that should tell you how locked in that coupling is, you know how critical that is? I mean, a six sounds load on a forum output that's a I mean it's a difference, but huge I just I know I get asked about that I imagine you get probably eight million more questions than I'll ever get about that. So yeah so what what seems like there's actually like a communication in between the output transformer and the speaker themselves rather than just like a your guitar goes runs right through it runs right out the speakers is that kind of it's kind of translating your small resistant small impedance speaker to this amplifier that's designed to see a very large impedance yes, exactly writes it's transforming ah four own speaker into a twenty two hundred home or whatever it needs to be load for the the tubes to see yeah it's interesting you know that that relationship there was usually I guess for me and maybe most of us we've seen it more linear where no kind of one run track act like that that they are actually kind of that transformer is the thing that makes that makes it happen. So is my speaker blown it's kind of hard won my thoughts on this kind of thing or just if you hear something weird you can try and isolate it with your ears that's the clearest way to know that something is wrong if it's getting scratchy um if it's you know, not making any sound at all maybe you've got four speakers in a box and you can kind of pinpoint put your ears right on a really loud speaker cabinet and just don't do that but if you can you can pinpoint it that way that's I mean if it sounds bad and it likely is bad obviously sometimes you can just see when things around you can see uh you know the speaker it has a hole in it the speaker could just be like protruding sort of not the way it ought to be. Sometimes when things get warped inside you could get I think the voice coil warped and it can be shooting out weird which means it's probably rubbing on something and that could be a visual cue that it's time to replace the speaker um you can just use your own meter and you could go back and measure the impedance of what's supposed to be an eight own cab for example and realistically most times an eight on kabul measure up something with a d c volt meter around six and a half owns so if you have your major it own cabinet it's like this is six and a half this is wrong this is all that's not the case a sixteen own cabinet might measure up around forty no in the fifteen owns ah forum cab three point two homes something like that but if you are measuring your aid own speaker cabinet and it's an open circuit then something is definitely wrong and so that can give you some clues and if things were wrong, looking at the big picture than it could be time to go in and analyze each speaker individually, you know, disconnect a speaker and measure it's ray assistance doesn't measure what you expected. Tio, um, as faras repairing speakers, I mean, if you have a really old speaker that you love and it's something that you can't replace, it could be worth doing a re cone, but really, I just think, it's one of those things where it's almost you nine times out of ten it's more affordable and it's a sure fire way to fix the thing to just replace it. My thoughts on that, um, speaker wiring. So if you have okay, so this could this could be a solution to a problem like we were describing before, where maybe you have, uh, a four or a dome out put on an amplifier. It needs to see an aide on speaker, but you have tio we'll see that's not a good example. So I guess what I'm trying to get into here is that you can connect speakers in different ways to get a total impedance for the cabinet that's different, so if you have two, eight on speakers in a cabinet and it's connected and they're connected in parallel to each other meaning the positive side of the speakers are connected together and the negative sides of the speaker connected together that's going to give you a four own speaker cabinet but say you have ah ah amp it wants to see sixteen owns well, you can take that staying set up on instead of wearing them in parallel take those two eight on speakers and wire them in siri's and now you have sixteen on speaker cabinet um and you can go the other way around as well but it's worth considering a couple things so you need to make sure that the speaker's themselves can handles much powers the amplifier is putting out, so sometimes people like to do speaker swapping and like I've got this eight on speaker in the state on speaker I really like the way this one sounds and I really like the way this one sounds. This one can handle twenty watts this one can handle seventy one it's and say your amps putting out, you know, it's a hundred lots. You know, if you had two of the seventy watt speakers they in total can handle to some of their their power handling per speaker so seventy watt speaker and a seventy one speaker can handle, you know, one hundred forty watts total and each speaker will be seeing half of the power that the amp is putting out well if you have a twenty watt speaker in there and a seventy one let's say ah thirty one speaker and a seventy one speaker now the total sum of what they can handle is one hundred watts so in theory you might think this adds up it's going to say it's going to find but because they're both the equal impedance of eight homes each they're both going to see half the power so you're big beefy seventy watt speaker is going to see half the power is going to see fifty watts and it's going to be doing just fine but your little thirty one speaker there's only going to be able to handle thirty watts but you're putting fifty watts across this so it's going to be struggling along so you just have to kind of go through and major those things and make sure same goes with the parallel connection each speaker and a parallel connection will be seeing half of the impedance on behalf of the power that and is putting out and some people like to do things where they use different impedance is and connect them and that gets things really weird so if you have two fifty watt speakers they could both handle fifty watts but one is forums and one is a don's well the forum one is going to be doing a lot more work than a dumb one and so you have to kind of keep that in mind it could sound really weird one speaker can just be worked a lot harder than the other one um so I don't recommend that I think in general it's a good idea just stick tio equal impedance equal power handling just keep it safe keep it simple one trick you khun dio is about because I skipped over syria's parallel so a lot of four speaker cabinets connect in syria's parallel meaning you have so drawing the speakers as resistors which I know they're not so the speakers will have positive and negative sides so serious parallels if each of these is a tones for example so if you take two eight own speakers and connect them together in parallel like this positive to positive negative too negative that makes the equivalent impedance of those two speakers for owns that's what happens when you take two impedance isn't connected in parallel if they're equal think they solve into their half of that value there's a more complicated equation for in general for parallel connections but we'll just this is the typical situations and I figured to stick to that and so the same down here connect these two guys in parallel so now we've got a four own speaker here quote unquote for own speaker here and a quote unquote forum speaker here and if you connect those in siri's to each other well in siri's the impudence of the speakers will just added they'll just some together like like four plus four equals eight in this case so this four own and this four own equal eight total and so this would be the overall impedance of your cab so that's serious parallel deal and it's a way to take you know eight, eight or four eight home speakers and make it into one eight on speaker cabinets and you can kind of bias on this stuff to using multiple speaker cabinets if you have um you know, two cabinets you want to connect together to your amplifier it's it's worth keeping in mind that any cabinet that just has to out puts on the back that are usually unlabeled those with the connecting cabinets together in parallel in that case so you have a nato own speaker cabinet here and don't speak your cabinet here you go out the amp into this one and out the am I'm sorry out this cabinet into this other cabinet that is a parallel connection so you get this sort of behavior happening where eight and eight people before so if you have a dome cabinet here eight own cabinet here and they're connected in parallel to the amp now that's a four own load and so you need to make sure you have an output on amplifier that can support a forum load or roll the dice with a mismatch and see how it does um yeah, I guess another thing to talk about maybe as far as that stuff is when you're talking about an amplifier that has multiple outputs, it's really a mess, because every maker does this a little bit differently. A lot of amplifiers will have multiple outputs for speakers and a rotary selector that switches between a forum uh, a dome or sixteen ome expected upload, um, some places are some companies do it where they have multiple outputs, poor per impedance, which is the way I like to do it, because the switches can fail and things can blow up, and if you have everything hardwired, then you don't risk that sort of thing happening. So yeah, it's really just worth do a little bit of research and the figuring out how each if you have an amplifier and you're looking at and saying, I don't know what they mean by this let's, do a little research and find out because there are lots of different, confusing ways that people name this stuff, and the poor thing to consider is what impedance you have and how to get it to the power tubes. The other correct tap of the output transformer um, so there's no brilliant, simple answer for that it's really just a matter of wrestling through each manufacturer's deal, I just said a go on the internet a while back and he was trying to go off the multiple output to have so normally if it says they don't see plug in a dome so good and I just wanted to hear it from the master ok plug in to in a home tap within eight on cap and a sixteen own tap with the sixteen on cab or a forum all at the same time it's not a simple and there's lots of different ways people can do out the transformers if you have secondary multiple secondary taps on your output transformer so say you've got to see it if you've got a transformer that so here's your tubes and they are driving the primary of your output transformer and somebody could make another transformer that has two different secondaries and say this one is designed to translate for own load back to the tubes as you know, say, four thousand homes for example and you have an eight own secondary this designed to taken eight own speaker load and send it back. So yeah, I mean, if you if you had an eight own speaker and you connected it to there and you had a forum speaker and connected it to their, you'd be reflecting back to the tubes four thousand homes for this guy in parallel with four thousand owns from this guy well four thousand owns in parallel with four thousand owned it could be two thousand pounds so now the tubes that want to see four thousand owns are seeing two thousand owns so you're mismatching but you can't even get away with this kind of thing realistically even if you tricked it by saying I'm going to put a sixteen own cab here and a home cab here therefore reflecting back four thousand homes which follows all the rules and that's what the tubes want to see I wouldn't even try that because realistically the out the transformer probably doesn't even work like this it probably works more like this where it's one coil with taps and there's so many tricky ways that people manufacture those toe work the way they're supposed teo I wouldn't I wouldn't bank on anything the best case if you like your amp don't do that I just yes why roll the dice on that one? I mean that's that's one I wouldn't think around with, you know, just just to be safe. I mean somebody could absolutely making up a transformer that's designed to work that way, but if you don't know that specifically is probably best toe just stick to the way you think it supposed to work um, regardless of like the mismatching business, have you noticed or preferred any kind of specific uh like own load, so to speak like I know that it's like you got certain scenarios that are designed to work with each other. Like I've got an aunt that runs at eight homes. I use a needle cabinet, and I know some guys have a sixteen up in the cabinet. Matching or whatnot. Is there any kind of sonic difference or performance like, ah, benefit toe having certain loads? Um, like on the back my if you could put it up to two if you want a power couples, refrigerator sized cabinets or anything like that. But is there any benefit, uh, different on loads? If you're not trying to go for crazy power or or less power would not like. The answer is maybe maybe yeah, and the reason I say that is that electrically, ideally no, absolutely not. Okay. Forum secondary is designed to translate a forum speaker toe looked to those tubes exactly like what they're supposed to see. Obviously what? You know what? A songs they're working together the way that they should be. Yeah. Everything's connected. Yeah, totally. Everything should work the way it's supposed to. But in reality, it just depends on how the transformer maker is making these things. They might cut some corners and maybe even though it's supposed to have a forum secondary and eight on secondary sixteen on secondary, there might be a little subtle differences, depending on how cheap the thing was made to where the forum is. Better couple ing the correct impedance to the tubes than the eight home is ok sometimes, you know, there might be little differences to where you're getting. I've had ants before, where I've measure the output for own speaker load, too, the forum output and gotten one hundred watts, and I've gone to the adam had been like, I'm only getting eighty six watts, we're never and got to them, you know? And so it could just be a matter of like, oh, they kind of screwed up the secondary winding for that speaker impedance one of them might be more efficient. Yeah, yeah, just they just a bigot that ago they got the turns, right? You know, or whatever. Some, there might be some argument to be made for the sixteen own tap having more quoyles more turns to translate that correct impedance back that might have some better frequency response characteristics, because, I mean, the way those coils work big, you know, there there's lots of we're black magic going on an album transformer, and, of course, saturation and it's, it's, a lot of voodoo. And I just think that it's just case by case, you know, if you one thing you can depend on his power measurements and see how my, how you're getting, and we'll do some of that. But I think that some of that stuff is going to be using your ears. And, yeah, but I mean, I don't. I don't go down that carson. If he rode too much, you know, I just if I don't get the right power, cool. But I mean right.

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.


Patrick Marc

This is a fantastic course. I was forever looking up Youtube videos on how to set up all of my guitars for different things, and opinion varies wildly on-line, so it's really great to have these videos detailing the entire process in clear and easy terms. The information on the amplifiers is intensely interesting too. Fantastic!

Alan Williams

Excellent course. Slow start with the guitar set up but Kurt knows his stuff so worth watching it to the end before deciding you don't like it. I came across valves (tubes) at the age of 12 (I'm 66 now) and it was a great refrresher for me. Ben really knows his stuff but he can put it into layman terms that are easy to understand. I definitely recommend this course.

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.