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Guitarist's Tech Workshop

Lesson 18 of 18

Final Q&A

Kurt Bloch, Ben Verellen

Guitarist's Tech Workshop

Kurt Bloch, Ben Verellen

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Lesson Info

18. Final Q&A

Lesson Info

Final Q&A

First of all, one from there's a big decision in about power scaling in general, we had somebody said, what do you think about power? Skilling, building an old of alcove eyebrow over bin was wondering if it would help bring out more gain at low volumes. If not, how can I achieve higher game at lower volume? And then joe jones had said, I'm assuming you're referring to a variable voltage regulator. I tried one of my last design that scaled the whole amp. I wasn't very happy with it. If you want to try it, I highly suggest only scaling the power tubes lashed section scaling only the power section will probably much better scaling. The pre empt makes it sound mushy and unpleasant. Talk a little bit around that subjective power scaling general. Yeah, in fact, I didn't one of those lamps for somebody who wanted the exact same thing, and I was impressed. I agree that some of those kids that do well first of all about will power scaling is basically the idea is that you could set it up so tha...

t the voltage that your power tubes air running off of as well as the negative bias voltages and as well as the screen voltages, and in some cases, all of the power spy bill does in the am are scaled down via knobs you turn the knob and there's some active circuitry, and he thinks that show the way some of the power supply and it makes the tubes all run off of lower voltages, the idea being you can get the entire sound of ah full blown app cranked up and driving a speaker at full full volume, but at bedroom levels that's kind of the thing every is after, and I thought it was really especially bad with the pre empt stuff, and I ended up doing this exact experiment I made the pre empts continue to run off of their full voltage is that they would normally run off of so based on correct the cramp is untouched, incorrect, but the power amp side of it. You can scale down it's a tricky thing because you really have to make sure that things they're scaling proportionally in a way that they that they behave not just proportionally in voltage, because if you have, like, say you need a negative bias voltage of negative fifty volts, you need a power supply voltage of five hundred bulls, you can't just scale them the same exact linear they have toe you wanted to be biased, correct at whatever lowest voltage you're at, you don't want a bunch of crossover distortion because you're biased voltage with the plates at twenty, volts needs to be the there's just a lot of variables that it seems like you have to be on the scope to adjust it and have everything work correctly, and that was my experience. In fact, I'd put in one of these power scaling kids, and I did the whole thing, and and I was like, man, that sounds really gravelly and weird, and sure enough, when I I had the power scale, anything happening, it was like, wow, this is a really, really cold, biased app, and it sounds really kind of clunky and placing weird, so I I think without voodoo it's, I I'm sure it can be done, but it seems like you really have to have things dialed in not only just the high voltage is, but the the negative by supply bolted just as well, and I agree that making the pre ample enough of local, too, just like that isn't good. A lot of people do that sort of starved plate mode, um, thing for pre empt circuits that run off of a vacuum tube in a pedal that runs off of a nine volt battery. It's never going to sound like a vacuum tube running at three hundred volts it's never going to do what it's designed to dio quite the same, so I don't know, I think, and then do all that stuff and have it work right? But it's, still not going to be hitting a speaker, is hard, is a full crank and is going to sound so you still are missing that part of the equation. So I think it's, if the dream is to have a marshall stack sound out of something this big, but I I don't know it's a very fair answer. We have somebody who says I'd love to know what's happening with the traditional master volume and a post phase inverter master volume. Yeah, ah, a lot different. So common example of the post phase inverter masterful in control is, I think some of the box stuff did that's in the natural stuff, and what they're doing is you slam all the signal from the pre empt into the phase inverter so that you get the phase inverter to add its distortion and its characteristics. And then what you do is you have a resistance between those two out of face signals you created, and as you shrink that resister by turning the pot down, it actually lets those out of face singles touch one another more and more and more, and they as they get closer and closer to each other as that resistance strength they canceled, they face, cancel out, which is a really weird way to turn the volume down because that phase cancellation isn't a simple is attenuation it can change the the timber and the quality of the sound as you let those sides cancels one another doesn't happen linearly like a one that's just on the end of like a a master volume after a tone stack on its way into the power and so I'm not a fan myself I think they're kind of I've seen it done cool sometimes but in general I think that um might be better to do like one thing I have done some answers put a regular master volume type control on each leg of the two out of face signals so it's like a concentric pot that u turn down and it turns both signals to ground at the same time and that could be cool as long as the pot is really well dialed in and it it's turning them dual down exactly the same way because if they start sharing one down more than the other then you get a phase difference that can make some weirdness happen so that's the better of two evils I think though personally great and one final question before we end from progressions would it be possible to run the bias all the way hot to achieve class a since the cut off for the tubes are way past zero I don't even know if that makes sense is this he say one more time yeah would it be possible to run the bias all the way hot to achieve class a since the cut off for the tubes are way past zero? Well, you have to so we'll see so class a amplifier would typically be biased at one hundred percent of its maximum dissipation and the reason being is that how this is such a hard question? Answer without drawing pictures I really feel that but there's a basic just you have a maximum dissipation curves so this is no man's land you can't go here without hurting things and uh, you might bias right here and this is the load line of your amplifier I know even talk about low lines, but basically just imagine your signal here swinging back and forth along this line well, that will be basing it at class a and I guess I don't see why you couldn't use fix biased to a point of totally class amplifier I've never done that for nobody's ever asked for that, but but the last part the question was sense it ah let's see put backup site since the cut off for the tubes are way past zero since the cut off for the tubes are way past ciro, we'll cut off is all the way down here, so back to this diagram that means nothing is we haven't been through so these would be like the load the plate curves for a tube, a power tube. And each one has curves is like negative five. Negative ten. Negative fifteen negative twenty, twenty five votes. This is like your biases. You're adjusting your bias and all the way down here. It's a negative fifty. That would be the point of in theory approaching cut off. But you could be biased here and be swinging back and forth. And as long as the tube is is working, the entire signal swing I mean is once you breach this point here and here, you get cut off that's distortion. But up here, the zero vote marked f distortion as well. So, um, you know what that works like? He said, I think the person who asked it wasn't necessarily even sure what they're asking makes sense. I think that was a perfectly good response to it. That's telling the email me they all right, folks, I want to say thank you. Huge. Thank you, teo, ben. And to kurt as well, for earlier today. Thank you all for joining us.

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.