ECE4448 L42: Inductor-Based Wah Pedals (Cry Baby) (Guitar Amplification and Effects, Georgia Tech)
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- Опубліковано 22 лип 2024
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Here is the class playlist: • Guitar Amplification &...
0:00 -- Introduction
2:28 -- RLC core
5:49 -- Black's feedback formula
6:25 -- Block diagram
7:48 -- Closed-loop transfer function
11:11 -- Natural frequency
11:44 -- Transfer function analysis
12:35 -- Implementation question
13:15 -- Citing sources
14:21 -- Vox V847 Wah
14:43 -- DC bias circuit
18:55 -- Small-signal circuit
22:33 -- Another complication
24:27 -- Input impedance
25:38 -- Dunlop Cry Baby
26:15 -- Analog electronics class
27:17 -- Wrapping up
"it's going through the world's most complicated voltage divider" simply amazing delivery
Time stamp please?
I used to watch these videos for the wealth of knowledge, now I watch them to hear you say "Squooooooosh" lol, thanks for all your effort!
Considering the things I search for and watch regularly, I am very surprised to have found this channel today.
Welcome! :)
As a guitarist and electronics nerd, I'm loving these videos. Cheers from Valdosta.
Cheers back from Atlanta! :)
Would love to see an analysis of the "seagull trick" where the input and output connections to the wah pedal are reversed. A good example is the mid-section of Echoes by Pink Floyd.
"wow wow effect" certainly sounds better to the marketing department!
@aaaaa Hah!
Finally someone with a legitimate background doing guitar effects circuit analysis. Can I ask you a question, I have a background in physics. I read about guys mentioning leakage inductance. I have never heard of this quantity. I assume they are referring to what I learned simply as inductance. But nobody ever sources an equation so I can tell what they are talking about.
I'd start with wikipedia: en.wikipedia.org/wiki/Leakage_inductance
Now if people are using th term "leakage inductance" specifically when talking about wah pedals -- well, then I'm not sure...
@@Lantertronics ok thanks for the reference!
I'm going to have to circle back to pick up the 80% of this that went straight over my head.
Pretty much all of that 80% goes over my head too. :)
This one is particularly complicated because it's implemented using raw transistors. An op amp style version of this circuit would be a lot easier to sort out, but I couldn't find any commercial implementations along those lines.
Hi Prof. Lanterman. Can you look into the "Seagull effect", where you're connecting the Wah in reverse (guitar -> output jack, input jack -> amp), why the circuit reacts and behaves the way it does (responds to the guitar's volume & tone knobs and even the pickup switch)?
Also wanted to say thank you for all these amazing videos. I got into EE because my passion for music, electric guitars, amps and effects, and I could only wish my college had classes like you're teaching
I recently built a wah using an SSI 2144 as my filter element.... I've maybe watched a TON of videos on this channel.
This is great. Subscribed. I want to run a circuit by you that I fumbled together, if I may. It's a Wah effect I originally designed with a pentode/triode pair. You'll need to picture this. The triode acts as an input impedance buffer to drive the second stage. The output of which goes through a decoupling capacitor (with a 1M to ground) and a 1M Ohm variable resistor through to the control grid of the pentode. The pentode has a 1k or so cathode resistor and a large inductor on the plate (1 Henry). The screen grid is connected to B+. There is a small 100pF capacitor feeding back from the plate to the control grid. Varying the 1M ohm adjusts the cutoff, and to a lesser extent the pass band. A bandpass output can be taken from the plate (carefully), and a low pass can be taken from the cathode resistor. My mathematics skill are ordinary but I figure it's a rearranged version of the standard Wah pedal. Just wondering what your thoughts are? Cheers!
That's cool, I've never imagined a tube-based wah pedal.
qq over
It sounds like ECE 3050 was a lot like the Analog Electronics course I took in 1978, but with better study aids. Aaron, is that website open to people outside the University?
Never mind, Professor, I just found out for myself. I didn't see the tiny URL at the top of the page, the first time around. Hey, it wasn't such a long lecture -- I was surprised that it ended so soon! Thank you again for a whirlwind of a lecture, but always fun. I'm glad this stuff isn't going to be on the test!
Transforming a transfer function into canonical form always felt tedious to me. Is there a list of identities that could make this process quicker?
Heh... if I was aware of any way to make it easier, I'd be using it. For simple ones you can sometimes guess the form and fill in some parameters by thinking about what happens to the circuit at DC or and at infinite frequency. If *you* find a quicker way let me know!
Control theory people probably have some tricks I'm not aware of.
Gyrators for the win when I am too lazy to buy inductors
I was thinking it would be interesting to add some diodes to gyrators to create some nonlinearities.
what does s stand for?
I'm not sure it stands for any particular word. It's the "Laplace domain" variable, a complex variable.
If you are interested in learning more, you can check out the playlist for my ECE3084 Signals and Systems course where I talk about Laplace domain analysis.
ua-cam.com/play/PLOunECWxELQRYwsuj4BL4Hu1nvj9dxRQ6.html
All I know is that Electrosmash's first name is Ray
Hat's off to Ray -- it's excellent work across the board.
MEMS!!!
MEMS???
@@Lantertronics 5:50 mark: www.memsproject.info/ - Those are my boys!
@@darksparklermusic Oh, right! I thought you meant "Micro-electromechanical systems" and got confused. ;)
@@darksparklermusic Yeah, they're doing great work.
When did the wah designers use negative feedback for bootstrapping the input impedance to make it very lower input impedance for tone sucking? The guitars pickups output a low impedance and the wah input impedance is a low impedance/bootstrapping
I don't think the lowering of the input impedance was on purpose. I think they came up with the feedback approach to moving the peak frequency around, and the lowering of the input impedance was an unfortunate side effect that they learned to live with (or just put a separate buffer in front like in the Dunlop version).
@@Lantertronics how does the negative feedback move the peak frequency around?
@@waynegram8907 That's a classic technique from feedback amplifier design and control theory. I cover some of it in my ECE3084: Signals and Systems lectures.
@@waynegram8907 My Signal and Systems lectures are also on UA-cam: ua-cam.com/video/VtSlmdshqrI/v-deo.html
@@waynegram8907 Look for my lectures on Black's feedback formula and control systems.
My playing. Lol