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Guitarist's Tech Workshop

Lesson 16 of 18

The Phase Inverter

Kurt Bloch, Ben Verellen

Guitarist's Tech Workshop

Kurt Bloch, Ben Verellen

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Lesson Info

16. The Phase Inverter


  Class Trailer
Now Playing
2 Problem Areas of Maintenance Duration:14:08
3 Proper Stringing Techniques Duration:04:31
4 Proper Standard Rock Setup Duration:34:10
6 Proper Drop Tuning Setup Duration:39:49
7 Electronic Maintenance Duration:22:11
8 Electricity Basics Duration:24:06
9 Reading a Schematic Duration:06:53
10 Using a Multimeter Duration:10:20
14 Preamplifier Circuit Design Duration:28:25
15 Power Amplifier Circuit Design Duration:10:36
16 The Phase Inverter Duration:03:58
17 The Power Supply Duration:15:03
18 Final Q&A Duration:08:44

Lesson Info

The Phase Inverter

This is an important piece of the picture is the phase inverter and a phase inverter. It does the job of creating the two signals that a class, a b or any push pull amplifier for that matter needs to drive the two different phases of the of the amplifiers signal swing so this signal turns on and then turns off so it needs to be fed a signal that is one hundred eighty degrees out of phase from the single that's driving the other power tube. So basically, this differential pair is one topology that makes the phase inverter thing happen. And basically, what happens is your signal goes into the sky and just like a common cathode amplifier like we were talking about for preamble tages it swings up, and now current comes down through the tube dragged across this cathode resister. Well, this capital resister now raises and voltage here with respect to ground for this tube as well as itself. And what happens when that happens is that it now draws less current. So you get a seesaw effect if thi...

s voltage goes up that one spits current this way this one spits current that way and you end up with two signals that come out of the thing one out of this tube and one out of this tube, they're out of phase from each other and you can send this signal off to one of the power tubes and send this signal off to the other of the two power tubes and that's. What makes the push pull power? Everything work. Um, that makes him throw. You see it that the final boxes of that, wouldn't they cancel each other out? Do you need to cut off half of each of those wave forms? No. And the reason you don't is because you have the power tubes biased such that they can on ly turn on for one side, the signal swing when this signal here tries to go negative, the power tube is off, so it gets cut off at the two at the power to exactly totally. And then when that one yeah, yeah, yeah. That's what's going on there? Yeah. So the output from this or the full way form to totally accurate way forms that are out of phase from each other. And the idea is this that that one is able to make a one of the power to banks work while the other one is off. And then when it turns off, the other one turns on, so the switching the reek, like the division is happening at the power tubes yeah, bias voltage is what kind of determines that. Where they automatic cut off, yeah, that makes me bring it down a little bit further. Absolutely. And in fact, you know, like the box, a c thirty and in some of these class a amplifiers are marketed. His classes are actually class a b amplifiers, but they run hot, they are approaching class a, so the cut off point, something all the way here they might be, you know, way down here, you know, and the other one might cut off, you know it's the same. So they're working so much more of the signal swing that it's it's a truer, more accurate, hot running hot, biased deal let him yeah, that happens because the cutoff isn't set to happen well into the up opposing tubes. Signal swing. Yeah, so this to number two is, has been working for a while before two number one turns off, and so that transition is very smooth and heat expensive and electricity expensive, but sounds cool from like a thing.

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.