Tube Screamer Schematic Analysis
Вставка
- Опубліковано 22 чер 2023
- A look at the circuitry under the hood of the legendary Ibanez Tube Screamer Overdrive Pedal for guitar gear nerds. Schematic analysis. Aimed to give understanding in broad terms, as well as providing some of the relevant equations.
Great video, thanks for posting. At 6:44 I believe the equation should be Av = 1 + Rf/Rg for a non inverting op amp
You're right! I'm always forgetting about that +1. Luckily my error is fairly negligible compared to the influence the distortion pot has. Good catch!
Dude! I need this lol, I’m brand new to building pedals but I’m seriously fascinated with everything. PLEASE do more of these videos for the other popular circuits. You’re the only one I’ve found that actually explains what all the components are actually doing and it’s super helpful. Thanks!
Great, great explanation! funny and to the point. Exactly what I needed. Thaaaaannnnks!
C3 actually blocks DC gain. With the input sitting at 4.5 vdc, the gain of the op amp would drive the output constantly to the positive rail
True.
Hmm, I'm new to this, am I understanding correctly? I get the gist that if the op amp sees, say, 5v on the noninverting input, it's output must be ~5.7V to compensate for the D2's voltage drop (minus whatever gets through the level pot). Hopefully got that right. To soft clip a "negative" signal like 4v, we need a negative voltage crossing D1. C3 and R4 are a high pass circuit with a center frequency of 720hz. So lower frequencies, including DC, are blocked. That means C3 is usually charged to 4.5v, which means the opamp sees 4.5v on the - pin and 4v on the + pin....it tries to sink .5v of current but has to sink an extra .7v to overcome D1's voltage drop (minus whatever flows through the level pot), and it sources that current from C3?
So the saturation curve is linear with some slope (set by the feedback resistor), and when the output of the curve hits .7v, the curve is linear with a slope of 1?
Thanks in advance. And, if I'm wrong all over the place, I apologize and don't expect a super thorough correction, I just need to go back to basics if so I think.
Excellent
R4 4.7k and P3 100k are both connected to 4.5V V bias instead of Ground. You can open up an 808 or 9 and see. I've studied TS/ DS-1/ Klon schematics from ElectroSmash so far, lots of time spent, and I found that all of them had a little bit of differences. An object or a reliable replicant is needed when you really want to understand the whole thing through.
Interesting. Thanks for the insight!
Yeah, did a quick google search and I found an example that's biased like you describe. Luckily those differences don't really change what's going on in the circuit. R4 could be biased to either voltage or even +9V and not have any audible difference since audio sees all kinds of stuff as ground, and if I'm not mistaken the gain on the input amp would still be very close to 1 if you bias R3 to either 0V or 4.5V, so that's no biggie either.
I wonder if these differences are accurate depictions of different circuit board revisions, or if somebody made an error while copying the circuit.
I'd actually really enjoy an explanation of the JFET bypass circuit! Is it a common bypass utilized often in pedals?
I think the website electrosmash has a good walk through of that buffered bypass circuit. Check there.
Most pedals are “true bypass” in my experience. I
can this bypass be replaced by a dpdt switch ?
Dumb question about the JFET Bypass switch in the very beginning: The first schematic is an example of a pedal WITHOUT true bypass? And true bypass is a simpler way to do it than the JFET Bypass switch?
Yeah, true bypass is basically a switch that flips between your input passing through the pedal circuit and then to the output, or simply connecting your input jack straight to the output jack.
What's the resistor labeled RA?
Surely, the battery negative will be disconnected from all parts of the circuit as soon as the input has anything plugged in! Likewise, the Power Supply negative has no connection to any part of the circuit at any time. Is this intentional?
Not sure I fully understand your question, but the negative end of a power source here is what we call ground. If it's not connected to the circuit you'll have an "open circuit" and the circuit wont work. All those points with layers of lines are the negative terminal of a power supply. So, there are a whole bucket of connections from power supply negative to the circuit. Hope that answers the Q.
@@theandromedacorporation Thanks for taking the time to reply, that clarifies the point behind the query as there are plenty of connections to ground showing on the schematic, but nothing showing the connection between the battery negative and ground.
@@mikegardner5859 Right. It's pretty typical in this sort of schematic to see multiple nodes labeled as voltages and ground without actually including a symbol for the power source that supplies those voltages.
How would you boost the output volume in the output section of the schematic?
@@stephenmonike1906 I wouldn't. The circuit amplifies the signal up, and then the volume knob turns it all back down. If you're building a tube screamer and it's quieter than your input signal you've probably got the wrong resistance somewhere in the opamp stages, or something like that.
thought that was a filter cap on the power there.. (C17)
There's no bypass path for when the pedal is not engaged.
Actually that whole orange section labeled "JFET Bypass Switch" is the bypass path. It's not a typical "true bypass" though, so even when you switch the pedal off there is at least a buffer and some other stuff going on. So in that sense this circuit never fully turns off. If you want to mod it with a true bypass that would be super easy though.
Mouse noise is driving me crazy. How about a Bluetooth pen?
Buy me one and I'll use it.
Or just using Ctrl-Z?
@@spotlight-kyd 100% The drawing tool I was using doesn't support ctrl-z and it's absolutely maddening. Lol
What if you had dinner with him. Would you complain about his food chewing noise?
@@ramencurry6672 I'm a quiet chewer, but I exclusively eat fettuccine alfredo with my hands. It gets pretty messy.
Normalised =/= Normalled. Thanks for the walkthrough!
I love Norm Macdonald.
Yes. Normalled is the word for breakable default connections. Did I say "normalized" in the video?
@@theandromedacorporation it's all good, you aren't the first, you won't be the last.
Diodes are a bit too rounded!
Marshall had a better idea using LEDS
Dude! I need this lol, I’m brand new to building pedals but I’m seriously fascinated with everything. PLEASE do more of these videos for the other popular circuits. You’re the only one I’ve found that actually explains what all the components are actually doing and it’s super helpful. Thanks!