Simple VCF & Transistor Amp Design!

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This time we're going to do something a little more involved! We're taking an old PAIA discrete VCF design and we're going to try and design an amplifier for it's output. This is a tough one!
In this video we have a look at a common-emitter amplifier, as well as some emitter-base bootstrapping to try and improve this circuit!
Schematics: drive.google.com/file/d/1ydC5...

[@mardav1545]

I've watched a lot of videos on transistors and just couldn't follow along to figure those things out. When you explain them, I go AHA, now I see. Thanks greatly, I really appreciate you.

[@TheAudioPhool]

Too kind!

[@jacobmccollum1206]

I've been trying to wrap my head around analog design lately, and your videos are some of the best i've found. Your detailed breakdowns have helped me have several different "aha" moments. I hope you keep making these videos for a long time, man

[@jimreineri6166]

Best explation I have seen for transistor analog amplifier. I am a long time digital circuit guy that has never wrapped my head around analog transistor circuits. I am still not there, but you have gotten me much closer. Kudos.

[@jackevans2386]

I regard myself as very competent at digital hardware design and firmware design for Atmel AVR in ASM, but have to take my hat off to your analogue design skills. It's a plessure watching your videos. Subscribed, of course.

[@jimmy_jamesjams_a_lot4171]

I’m thinking that my Behringer Neutron needs this as an output stage. I wound up With an EXTREMELY QUIET Neutron. So quiet, that I ALWAYS send it’s signal through the two utility attenuators. My Neutron seems to NEED to get sent through those attenuators after the filter, the delay, or after it’s overdrive circuit. With your buffer/filter stage here, we’ll this is likely just the ticket, I’m thinking! There’s a really great file floating around online that’s a decent collection of buffer circuits, meant for DIY effect pedal builders, I think it’s on a site run by a Mark Hammer, or possibly he wrote the file. He has shared a whole slew of schematics over the years. THANK YOU ONCE AGAIN, Mr. PHOOL!! I find your series and videos to be just the proper pace to suit me, and not too far over my level of comprehension! Your enthusiasm and thirst for EE theory and understanding is proof by example that there is great value within the books we sometimes loathe. Otherwise, why would you be quite so genuinely excited to dedicate so much of your time to directly experience these lessons that seem to be rather mundane to the uninitiated?! Thanks again!!

[@cashewmilkfan]

"mathamaticians look away we've got an infinetly lowered imput impedance" I love that :)

[@m_riatik]

i did EEE in uni and when we learned about bjt amplifiers, we always used the hybrid-pi or hybrid-t models to analyse the small signal behaviour and often didnt conflate it with the large signal model. but, your way of thinking about bjts with how a change in voltage at the base is reflected in the emitter really changed my intuition of them! though it was hard to grasp at first it makes a lot of sense in the end. wonderful video!

[@TheAudioPhool]

That is how I learned it at uni too and it makes 0 intuitive sense. I much prefer my way because it expands intuitively to differential amplifiers which (again) are very difficult to grasp from the textbook way of learning them

[@m_riatik]

@@TheAudioPhool it's always great when you have that aha! moment with this kinda stuff and the way you explain bjts helped me achieve that!

[@TheAudioPhool]

That makes me very happy :') So glad you're finding it helpful!

[@jamesmawson3483]

I love how simple this VCF is.. even I can understand it! Haha. Is there a way to add a resonance path to something like this?

[@Jan-dB]

The Paia VCF design is very interesting. As to minimize the load of the following simple transistor amplifier, you changed it into a more complex bootstrapping-stage ... but would it not be simpler to add an emitter follower between the filter part and the amplifier part?

[@CoolDudeClem]

Interesting filter circuit, i might try that. As for amplification, I usually use a much simpler amplifier circuit than this, with just 1 transistor (I have a ton of BC547's lying around), 2 caps and 2 resistors. One resistor (usually 2.2k) between the supply and collector, a much larger resistor (like 680k) between the collector and base, emitter connected straight to ground. Then I just add an input cap at the base, an output cap at the collector, and that seems to work really well. I get a lot of amplification, and with those resistors, about half of the supply voltage at the collector.

[@KnowName33]

You dont get bad distortion?

[@CoolDudeClem]

@@KnowName33 If there is any distortion, it's so little that I can't hear it, also it looks very clean on the scope.

[@daviddawkins]

We divided the bias circuit resistors by 10 to maintain their ratio, and therefore kept the bias voltage at 1.6v. However, when we reconnected the bias circuit to the transistor base, I feel like that additional resistor introduces a voltage drop and we get considerably less than 1.6v at the base. I'm also certain that I'm wrong about that; what's the right way to analyse that resistor's effect on the bias voltage?

[@ChristianKrupa]

I’m learning, but really not keeping up…

[@twobob]

And Comment. You didn't say comment. Or introduce an open ended question to be answered in the chat... All good techniques to get more "YouTub" Traction.