I went to school with a guy who could explain a weeks worth of classroom lecture in math in 10 minutes over a beer. Clear, concise, and simple. You're like that guy. Great video!
I'd like to thank you W2EAW for demonstrating that those who truly know their stuff can be so comfortable with sharing their knowledge and professional insight with those who like to watch and learn. I am a retired technician who got his initial training in electronics in the US Navy and worked in the field of avionics for several years before getting civilian jobs in the field of test and electrical service and test/calibration for a muni. in electric substations. I am impressed because usually EE's wherever I've worked at are usually very tight lipped about sharing anything professional and you differ with your easy to understand tutorials. I'd like to give a huge thank you for that and keep them coming. Thank you for sharing with us. Oh btw, I have several pieces of t.e. including scopes (dig. and analog) sig. gens. , imp. meters and other various peices but your test bench makes me want to buy a whole lot more!
I've been 3 days trying to understand how the different values for the resistors are choosen and how can I calculate them to have a defined gain. You explained it very clearly in this video, and with the other videos that you pointed I think I finally fully understand it. So thank you very much
Just about every other tutorial gets lost in the math. I appreciate your approach from the angle of design philosophy : especially in how you clarify the decision tree of a typical design. Chef’s kiss.
I regularly recommend your videos as high quality electronics tutorials. Those videos you mentioned really helped me through my post-bac work in microelectronics. Thanks for all your hard work and attention to detail. Much appreciated.
Bravo sir, I have been driving myself crazy with math, Ive been attempting to learn the hybrid and R(pi) models. But all these videos leave out simpler insights like the bias string to base current ratio. You are doing a great service to humanity with these videos, and I hope you keep making them
A lot of times I read similar notes like this in a book and find myself having to go back and read again and again. Your tutorials and demonstration process makes this so much better to understand. Very well thought out video approach. Thanks for sharing. Your knowledge is amazing.
This one took me about two weeks of off-and-on thinking, postulating, scribbling, experimenting, planning, etc. in order to just come up with a plan for presenting in a logical, easy to understand way.
Folks often don't appreciate how much effort goes into what we used to call "platform time" that when I was an instructor at Ft Leavenworth (no, not on the prison side!) I found that you put in at least 3 hours of prep time for every hour teaching, sometimes even more; I imagine it can be even more than that when you're shooting a video...at least your questions here don't come in real time! Thanks for all the hard work Alan, it's really appreciated. 73 - Dino KL0S
@@w2aew A lasting legacy of invaluable knowledge shared to all, saved for posterity. A simple 'Thank you' just doesn't cut it, but... Thanks (very much) anyway!
There are good teachers and bad teachers. You are one of the very best. I've been watching several of your videos. The knowledge that you hold and then make relatively easy to understand (certainly easier than other tutors) is first rate. I actually find myself understanding what you are saying because you teach it in such a great way. Theory and practical to show your workings is especially great instead of pure theory which can be mind boggling. I'm a visual learner predominantly and with you showing the electrons wobbling around on a scope is brilliant. With excellent short cut methods that only a real engineer can pass onto a student is invaluable as a way of referencing quickly and easily to verify that the build or design is going in the right way without over complicating things too much. Its bite sized snippets of information like that, that make it more manageable to remember. As others have said and especially at my age (50) I find myself going back to reference books several time to read the theoretical text, which is very important, but very time consuming. Your time and huge efforts are very much appreciated. Your other videos pick up on much more theoretical detail which is also superb. Please keep up the excellent work and thank you.
I appreciate your kind words. I do put a lot of effort into these videos to convey good, concise, practical information. Even with all this effort, some people are still not satisfied (there are 12 thumbs down on this video), and I'm not sure why...
Hi Alan, I discovered your channel recently, 3 months or so. I watched each and every one of your old videos one by one, I am up to date now. I have never commented before (I do give a thumb up to every one of them, though, obviously), but I thought I would this time, for a change ! ;-) I mean, as you said it took you quite some time to come up with this video, but the result is excellent and I do, like many others it seems, appreciate it immensely. So I hope that the recognition you get and deserve, will keep you motivated and that you will keep doing great stuff like this whenever you find the time. Every second of your videos is pleasing to look at and listen to. I love every aspect of your videos. The technical content, the way you present it, your lovely hand drawn notes and schematics, your experiments, quick calculations to demonstrate the point... you act and talk like a proper engineer that you are, as well as a man of passion, a pleasing and efficient blend. I think that's why many electronics teachers here in France just aren't good... most of the time they actually don' t have ANY experience in professional electronics design (and not much passion in them either). They just study EE then go straight to teaching, zero "real world" professional experience ! :-/ I also studied EE in the UK as well, at Uni for 3 years (did a B.Eng there, 20 years ago), and the teachers also looked clueless and uninspiring, couldn't sense any trace of passion in them either. Was pretty depressing... Anyway, enough rambling. Just wanted to comment at least once, to express my true appreciation for your contribution to EE education. Keep up the excellent work ! :-) The number of subscribers, 75K to date, is a good metric I think. This alone should convince you that your are doing something good and valuable here. Sure, EEVBlog is much bigger, nearly 500K subscribers, but I think this is largely due to, as I remember him confessing once, the fact that he is more (overall I mean) of an entertainer and show man, than a teacher. Your videos however target more those interested in the educational value that an experienced design engineer can bring. This obviously is a narrower audience. In this respect, I think 75K is a really strong number which I hope you appreciate as well. Thanks again for the time and effort you put in all your videos :-) Vincent Trouilliez, from across the pond.
Wow, you've watched every video?? That's a lot of time invested, and I certainly appreciate that! I hope you've seen that the production quality of the videos has improved since the early days of my channel. Thank you for your very kind comments. I received my engineering degree in 1985, and I remember that many of the professors were as you described. I did have a few that had a real passion, but many did not. Most of my videos take a lot of thought and planning - typically 10x or (much) longer than the video duration. Others are a bit more impromptu (like my video on the Z-Match tuner that I did while on vacation). Even these often require many "takes" until I'm happy with the content and flow. I'm certainly not the "entertainer" that Dave Jones is, so I definitely understand the differences in the size of the following. Of course, he also has a blog and a very popular forum - I have none of those, just no time to do that type of thing. Thanks again for your very nice comments - knowing that the content I put together is truly appreciated and *used* by my viewers is very rewarding and inspirational. Thanks again for being such a loyal viewer! Alan
Yep, every one of them, watch I did ! LOL I don't have a TV anymore (gave up on this thing 20 years ago). These days I replace it with YT videos. So instead of watching silly and brain damaging stuff on TV, I instead spend it on watching selected/hand picked quality content on YT. I find it much more interesting and useful than TV... I also like TheSignalPath and watched all his videos, then once I had finished TSP (and subscribed of course) I looked at your channel because YT suggested it in the "Related Channels" list on TheSignalPath page. I am glad I clicked ! :-) Then I listened to your interview with Dave on TheAmpHours radio show to know more about the man. Yes the quality of the videos did improve ! I just re-watched your video #2 for a side by side comparison ("using the delayed time base on your Tek 485"), to refresh my memory, and the improvements are obvious... The camera is on a stand now, makes a world of a difference. Picture is neater/sharper too, and the lighting is much better/brighter. It's indeed very well sorted out in your newer videos :-) The technical quality of your videos is now great and I don't see/feel any particular area that would need improvement. Now we just concentrate 100% on what you say and what you do on the bench, which is great. We can focus on learning rather than bitching about such or such technical problem in the filming. Anyway, back to the lab, my old Tek 317 is waiting for my assistance.... yeah like you I have this "disease" of "collecting" various Tek scopes (mainly) as I go. They have this little something that keeps me coming back for more no matter how reasonable and rational I try to be... Regards, Vince
Hi Allan I just wanted to say thank you for all the thought that goes into these videos. They are by far the most simple and informative videos on this subject. Im 15 and I’m learning electronics purely for the fun of it but even at such a young age I am still able to clearly understand these videos because of your simple and straight forward way of teaching. Thanks again.
I'm getting back to basics for an ongoing project, destined for modularity and miniaturization, the potentially tiny bipolar transistor circuitry is really important for these applications. W2AEW is by far one of the most useful and enjoyable sources for this really important subject matter, thanks dude!! I'm a long time fan , and I am really thankful for your sense of detail and nice way of explaining things. Thanks to you I am a proud owner of 2 Tek 4 channel scopes, an old crt from ebay :) and a TBS1064. For what I'm doing they are more than sufficient, the latter being my basis for accurate measurements, and quick and easy to look at comparisons, thanks to the trace colors. Especially coupled with your expert advice and great quality video productions, I have lots of 'fill in the gaps' for my general knowledge in relevant areas. Cheers!!
Another great video! I've been researching information on BJT common-emitter amplifiers for over 2 weeks using several books. This is, by far, the most comprehensive series of videos on the subject. Thanks for taking the time to put this together
I must really thank you. You are one of the few who bothers with the math in a demonstration. I have re-watched almost every one of your videos, most more than 3 times. However, I want you to understand, the math portion of your tutorials is what makes them great for me.
I notice you did not treat the "swamped emitter" where the emitter resistance is partially bypassed to give better gain and low distortion. For example: implement the 1.2K resistor as a 400 ohm from the emitter to an 800 ohm to ground then bypass the 800 ohm. Then gain with Rc=20K will be 50, but the distortion will be very low.
VERY good video. A simple, detailed explanation that didn't skip over important points and just assume I knew what you were talking about. I have watched a bunch of these videos and you are the best instructor I have found. You got a sub.
You are such a good teacher Alan. I just love the videos like this, they make the subject so understandable and enjoyable. If I had the time I could immerse myself in transistors. Many thanks for all your hard work putting these video together.
I'm working through some textbooks as a hobbyist and while I understand all the equations and rules etc, I find myself not following it as well when I actually go build something. You really made it a lot easier to find a starting point for me and I'm going to go enjoy building some amps for a bit now. Thank you for the awesome videos!
Great to see you back doing the theory to practical. Always reminds me of college, and one teacher I had was Chinese. When he was doing transistor theory his accent was so bad we made him write it down. Image Vbe in a Chinese accent (no disrespect intended) and your acronyms just brought back old memories. Cheers and glad to see you back in the class.
It's important to emphasise how much extra distortion is introduced for larger signals if you bypass the emitter resistor. With a bypass capacitor in place, the gain is directly proportional to the collector current, so if the output swings close to the positive rail, the gain drops to almost nothing. If the output swings low and doubles the voltage across the collector resistor, then it doubles the instantaneous gain. That's a recipe for really nasty distortion. The formula for gain is actually Av = - Rc / (Re+re) where re is the incremental emitter resistance = 25mV/Ic at 17°C. To reduce the effect of transistor variations and to reduce the distortion caused by the non-linear re, it makes sense to set Re at least ten times re. But the voltage across Re is Ie.Re = 10.Ie.re = 10 x Ie x 25mV/Ic. Since Ic=Ie for all practical purposes, that shows that the voltage across the emitter resistor should be at least 250mV. Making it higher reduces the gain, so a practical upper limit on the gain is achieved by designing for 250mV across Re. Another tip is that because you want to bias the collector around half-way between Vcc and Vb, the voltage across the collector resistor will not be too far different from Vcc/2 (assuming Ve=0,25V and Vbe=0.6V). That means that the practical upper limit for the gain without bypassing the emitter is approximately -Rc/Re = - Ic.Rc / Ic.Re = - Vcc/2 / 250mV = Vcc / 500mV. So for a 12 volt supply, you won't get more than x24 gain unless you bypass the emitter resistor and then you have to keep signals below about 10mV to avoid the non-linear distortion. A final tip: with an emitter bypass capacitor, the gain becomes Av = - Rc / (Re||Xc + re) where Re||Xc is the impedance of the parallel combination of Re and the reactance of the bypass capacitor. If we want the gain to be flat with frequency down to low frequencies, then we need the reactance Xc to be smaller than re (note: *not* just smaller than Re). For the circuit shown, with a collector current of 0.42mA, the resistance re is 25mV/0.42mA = 60R. A 47μF capacitor has a reactance of 60R at 57Hz, so that is the -3dB frequency. If you want to have the roll-off occur below 20Hz, you need around 150μF for the bypass capacitor.
Bravo. Reminds me of my electronics class in engineering but much better explained. Thank you for being considerate enough to share your practical knowledge.
Thanks once again for a well presented video. I think your videos are the best electronics videos on YT when you calculate the ratio of useful content over length. If you did a one hour video it would be like a full semester at a University.
I really appreciate your videos. I have not fully watched all of them on bjt biasing but #113 answered a lot of questions I had previously. I been trying to understand these topics for a few years and biasing outside of a simple single resistor base bias is confusing. Hopefully this makes more sense to me. Thank you.
I am only afraid YT is not really the best way to show your amazing knowledge. I often see the subscription to your channel going down in the list, based on the fact that you don't release videos often enough. Quality content takes long to be produced! The education you give us must to be protected for future generations, and I am not joking here. Ideas anybody?
I wish I had the time to produce videos more often, but my *real job* and family life take first priority. I hope that the videos I produce will be preserved for generations - that would be a nice legacy to leave behind.
Great video... I always go back and re-watch those linked videos. This video answers some of the questions I've had. Thanks. Passive/active components always fun to learn about.
It's been along time since I did some calculations of this so I so when I did this a couple of weeks ago I had totally forgotten these shortcuts. Thanks for reminding me :)
Another great video as always from an exceptional teacher. Can you please do a video on common base amplifier and its main features and also a video on tuned RF amplifiers. There are not many tutorials out there on these curcuits.Thank you.
Fantastic video Alan! I would love for you to explain how you set up your scope. Is the attenuator really necessary for low voltage and low frequency work? Just curious!
I used the attenuator (as shown at 2:18) for two main reasons: 1) To provide a 50 ohm termination for the generator, so that the applied voltage wouldn't vary with the frequency dependent input impedance of the amplifier, and the main reason is: 2) To make a larger signal available at the scope for input signal monitoring. If we just probed the signal at the amplifier input, it would be quite small, and the signal-to-noise ratio would be poor, resulting in a noisy calculation of gain in the Math waveform. By measuring a larger signal, and then simply scaling it's value with the attenuation value, the scope sees a larger signal with better SNR.
Love your videos, thanks for the refresher courses! At 23:29 you show and state the led current being 700 uA. How is it possible to light an led with that little current?
I keep revisiting this lesson, have a curious amplifier mind now. Any other important lessons on amplifier design, matching components, testing... would be much appreciated. If possible would love to see a lesson on DC servo for an amplifier, theory and operation...
Sir, your videos are amazing! I learn more from you than I do from my own teachers in the university! Couldn't thank you enough. please keep us posted and thank you.
Most [Class A Common Emitter] amps have a transformer on the output for impedance matching and removing DC bias. A follow up on transformer design & build would be great. Building transformers is rarely documented, and is at risk of becoming a lost art.
Hi! It looks like there is an oscillation in the circuit. It is more pronounced with the 20k collector resistor at 12:32. Or a picked up noise? Is it there? What it colud be?
Thanks a bunch. Very helpful as always. Can you please do a follow-up demo on those direct coupled multi stages? They are really confusing. Thanks again 👍🏻
Alan, as always a magnificent effort. It goes in my library of w2aew videos on theory. (Now that I have retired, I build and test as you do and verify which makes me understand better.) My only question is who in hell gave you two dislikes? 71/72 Bill, k6whp dit dit
Another wonderful video - well done! You explain that by adding a bypass cap can cause distortion but provides higher gain. You described the higher gain, but you did not address the distortion issue. At what point (cap value or res value) might one expect distortion to become an issue?
The distortion is due to the fact that the transconductance (gm) is a function of the collector current. In the bypass case, the gain is -gm*RC, so if the transconductance changes from the highest to lowest level of the signal, the signal will be distorted. So, the more that re (1/gm) dominates the emitter resistance, the more distortion you can have.
I love this topic. Biasing is a hard thing to wrap the brain around. This year I finally pulled off putting several amps together some worked well and other needed tweaking. How would you set up a transistor as a digital switch for high current like a 3055 on pwm?
When doing switching, you generally want to switch the transistor between OFF and Saturation. For OFF condition, make sure that Vbe is near 0V. For the ON (saturated condition), make sure that Vbe is fully forward biased, with a base current ~10% of the expected collector load current.
Another fantastic video. Thank you. Can you tell me how to calculate the input and output impedance? If you covered it in another video please direct me. I know how to measure it, but how do you design a circuit with a specific impedance in mind?
Output impedance is simply the collector resistor, RC (or R3 as shown in this video). The input impedance is slightly more involved. It is the parallel combination of R1, R2 and the input impedance looking into the base. The input looking into the base in the "emitter bypassed" case is something called r_pi, which is simply r_e * Beta. From the video, r_e is 1/gm, or v_t/Ic. In the case with emitter degeneration (no bypass), the input impedance is r_pi + (Beta+1)*RE.
I would like to clarify that r_pi + (Beta+1)*Re is an input impedance (!) looking into the base, not an input impedance of the amplifier. The overall input impedance is R1 || R2 || [ r_pi + (Beta+1)*Re ] which can be approximated as R1 || R2 || Beta*(r_e + Re), since Beta is unknown and >> 1.
Thanks for sharing. If you have a moment, can you please comment on the criteria used for selection of the bypass capacitor size? Is the goal just to have a cutoff frequency well below the signal frequency? Thanks.
The goal is to have the capacitive reactance be much smaller than 1/gm at the signal frequency. 1/gm is also known as re, so the gain can alternatively be written as -RC/re. If there is any emitter resistance, then the gain is -RC/(re+RE). If the bypass cap is not much less than re, then it will reduce the gain the same way that an addition emitter resistor (degeneration) would.
In my pile of books the CE biasing examples start with a "given" collector current. Some choose quite small values...half a milliamp say. Here you talk about several hundred. I'm pretty hazy on how to select this current value and if I am connecting stages -say a CE to CC buffer that is not driving something like a speaker ) do I keep them about the same?
There are several factors that contribute to the choice of collector current. Things like power dissipation / current consumption requirements, output impedance requirements, transistor characteristics for best performance (noise, distortion, saturation, headroom, etc.), and more. There is no single universal answer regarding how to choose the desired collector current. The most common consideration would likely be the load impedance / output impedance needed in the application.
The big difference between the MDO3000 and MDO4000 is that the MDO3000 can *not* acquire RF vs time and show the RF signal characteristics along with the analog and digital signals. The MDO4000 can do this (spectrum vs. time, RF amplitude, frequency and phase variation vs. time vs. analog and digital signals).
Fantstic video as always, thanks. Idea for a future video: Calculating input and output impedance of 2, 1 transistor amplifiers, after each other, and calculation of the size of the dc blocking cap between the 2 stages, especially the last of the two, i have searched youtube and i have found none that have made a, for me, usable video on the subject, maby you could make that video. Greatings from Denmark Morten
Thank you. I did answer the question about calculating the input and output impedances of a common emitter amplifier in one of my comment replies below. I agree that a video on how to select the interstage capacitors would be useful. I can add that to my looooooong list of topics...
great explanation Alan, thank you. How did you calculate the values needed for the decoupling cap and bypass cap? Those are pretty large components... what would be the effect of using much smaller caps?
Nothing too critical. I just wanted to be sure that the impedance of the emitter bypass cap was much less than re (1/gm) at the test frequency so that the gain approximation was valid. And I wanted to be sure the input cap's impedance was much less than the input impedance of the circuit so that there wasn't any significant voltage drop at the test frequency.
Hi great video, but can you explain why the gain should increase so much simply by putting in the emitter bypass capacitor? Apologies if this is already covered in another video.
In short, it reduces the negative feedback, thus raising the closed loop gain. Page 3 of the notes compares the two cases (not-bypassed and bypassed). Also, Take a look at video #67, it has more details.
w2aew thanks. I’m going to try your examples myself. Interested to see what spice says as well. Looking for a small signal rf amp to boost the output of a ad9851 dds.
wonderful video and thank you for using a camera tripod. Video #67 had me running for the Dramamine having watched it so many times, getting up and walking around like a sailor new to port. I tried recreating the circuit in #67 but kept getting VC and VE values 13-15% off in my calculations vs. measured (VC calc = 2.29V, measured = 1.946V). I'm learning so this might be common knowledge but it appears while an emitter-bias is somewhat independent of beta variation, the formulas are significantly sensitive to VBE. I was using the 0.7V approximation for silicon transistors and getting incorrect values for a 2sc945 transistor. The 2sc945 datasheet has a VBE min = 0.55V, typ = 0.62V, and max = 0.65V. Using the typical 0.62V VBE in the equations resulted in the calculated values matching the measured. Thank you for showing the trick for AC signal to the oscilloscope. Not sure if you used the same in video #67 but when I tried there was so much noise in the low freq I couldn't keep the same attn. that was used on the HF and then I was no longer comparing apples to apples.
As always very nice&highQ video-lectures, thank so very much. (..friday evening here in scandinavia/norway, and coffee + videoes like this one is top-notch. Thanks again for sharing your quality knowledge to all of us Alan.)
We can also bypass the emitter resistor with a capacitor AND a resistor in series. This boosts the gain but can also be chosen to limit/eliminate distortion. For this circuit 75-150 Ohm in series with the cap should work nicely.
Excellent tutorial, thanks for sharing. I would like to recreate your test setup but I don't have 10x attenuator. Can you share some information about it? Maybe I can try to build my own one.
Great video! I have a circuit with a switched emitter bypass cap and a 500 ohm resistor to ground after the cap. What does that do to the signal and would the main emitter resistor still be bypassed and not factor into anything? Thanks in advance.
At DC and very low frequencies (where the capacitive reactance is high), the main emitter resistor is used to compute the gain (basically RC/RE). At higher frequencies where the capacitive reactance is low, then the 500 ohm resistor appears in parallel to RE, and the gain basically becomes RC/(RE||500).
w2aew thanks for that information. It makes some sense to me. I’m new to electronics and I am just looking for a way to adjust the output of my transistor on the fly. Can I get away with putting a trimmer pot on RC to adjust the output (lower rc/re value)? Its a 2 stage guitar boost pedal and I just want to have ability to control the volume out of stage one, the transistor.
@@Strumbum01 You can use a potentiometer to adjust the volume. It can be done at the input or at the output. But, do NOT use a trimmer pot as a volume control. Trimmers are not rated for frequent use, they are only designed for infrequent "set and forget" applications. They wear out very quickly, often rated only for a few hundred swipes. See this video for detail: ua-cam.com/video/5d_TTQ2OJtM/v-deo.html
At one time you had a video where you show why sometimes it is better to use a 2n4401 instead of a 2N3904. DO you remember the title of this video? Thank you!
You must be thinking of someone else - I don't have a video that discusses that. The 2N4401 and 2N3904 are very similar transistors. The performance of the 2N3904 is better at low collector currents than the 2N4401, and the inter-node capacitance is lower on the 3904. There's a decent discussion here: electronics.stackexchange.com/questions/231844/why-would-i-use-2n3904-instead-of-2n4401
I am pretty sure it was on one of your videos. I think it was about the current rating for switching applications. It was not necessarily a video dedicated to the '4401 or '3904 per se.
Can you show how to calculate the input capacitor value and output capacitor value because you have to add in the input impedance as Rin and output impedance formula for Rout to apply to get the capacitor value.
When the collector is directly connected to the power supply, the circuit is not a Common Emitter amplifier. This configuration is called a Common Collector amplifier, or Emitter Follower. The output is taken from the emitter. Voltage gain is basically unity, non-inverting. See my video the common emitter, common collector and common base amplifier configurations: ua-cam.com/video/zXh5gMc6kyU/v-deo.html
I don't have a video on this, but here's a short explanation. These refer to "small signal" behavior, which is typically when the BJT is in the active/saturation region (flat part of the typical IC vs VCE curves). gm is the small signal transconductance. It is the ratio of how much the collector current changes in response to a small change in base-emitter voltage. The re term is simply 1/gm. It also represents the small-signal output impedance of the emitter terminal. The ro term represents the small signal output impedance of the collector terminal.
I went to school with a guy who could explain a weeks worth of classroom lecture in math in 10 minutes over a beer. Clear, concise, and simple. You're like that guy. Great video!
The best explainer of electronics on UA-cam. Bar none.
I'd like to thank you W2EAW for demonstrating that those who truly know their stuff can be so comfortable with sharing their knowledge and professional insight with those who like to watch and learn. I am a retired technician who got his initial training in electronics in the US Navy and worked in the field of avionics for several years before getting civilian jobs in the field of test and electrical service and test/calibration for a muni. in electric substations. I am impressed because usually EE's wherever I've worked at are usually very tight lipped about sharing anything professional and you differ with your easy to understand tutorials. I'd like to give a huge thank you for that and keep them coming. Thank you for sharing with us. Oh btw, I have several pieces of t.e. including scopes (dig. and analog) sig. gens. , imp. meters and other various peices but your test bench makes me want to buy a whole lot more!
I've been 3 days trying to understand how the different values for the resistors are choosen and how can I calculate them to have a defined gain. You explained it very clearly in this video, and with the other videos that you pointed I think I finally fully understand it. So thank you very much
Just about every other tutorial gets lost in the math. I appreciate your approach from the angle of design philosophy : especially in how you clarify the decision tree of a typical design. Chef’s kiss.
I regularly recommend your videos as high quality electronics tutorials. Those videos you mentioned really helped me through my post-bac work in microelectronics. Thanks for all your hard work and attention to detail. Much appreciated.
Bravo sir, I have been driving myself crazy with math, Ive been attempting to learn the hybrid and R(pi) models. But all these videos leave out simpler insights like the bias string to base current ratio. You are doing a great service to humanity with these videos, and I hope you keep making them
A lot of times I read similar notes like this in a book and find myself having to go back and read again and again. Your tutorials and demonstration process makes this so much better to understand. Very well thought out video approach. Thanks for sharing. Your knowledge is amazing.
This one took me about two weeks of off-and-on thinking, postulating, scribbling, experimenting, planning, etc. in order to just come up with a plan for presenting in a logical, easy to understand way.
Folks often don't appreciate how much effort goes into what we used to call "platform time" that when I was an instructor at Ft Leavenworth (no, not on the prison side!) I found that you put in at least 3 hours of prep time for every hour teaching, sometimes even more; I imagine it can be even more than that when you're shooting a video...at least your questions here don't come in real time! Thanks for all the hard work Alan, it's really appreciated. 73 - Dino KL0S
I usually figure that each minute of video translates to 10-30 minutes or more of total invested time.
It shows you have both the knowledge, care and ability to present. Thanks for doing videos like this, they are very useful!
@@w2aew A lasting legacy of invaluable knowledge shared to all, saved for posterity. A simple 'Thank you' just doesn't cut it, but... Thanks (very much) anyway!
Very thorough presentation on CE amplifiers. Definitely the best on utube, and probably better than most university lectures on the subject.
That what we call teaching!!! 4 or 5 classes with just 20 minutes.thank you sir
There are good teachers and bad teachers. You are one of the very best. I've been watching several of your videos. The knowledge that you hold and then make relatively easy to understand (certainly easier than other tutors) is first rate. I actually find myself understanding what you are saying because you teach it in such a great way. Theory and practical to show your workings is especially great instead of pure theory which can be mind boggling. I'm a visual learner predominantly and with you showing the electrons wobbling around on a scope is brilliant.
With excellent short cut methods that only a real engineer can pass onto a student is invaluable as a way of referencing quickly and easily to verify that the build or design is going in the right way without over complicating things too much. Its bite sized snippets of information like that, that make it more manageable to remember. As others have said and especially at my age (50) I find myself going back to reference books several time to read the theoretical text, which is very important, but very time consuming. Your time and huge efforts are very much appreciated. Your other videos pick up on much more theoretical detail which is also superb.
Please keep up the excellent work and thank you.
I appreciate your kind words. I do put a lot of effort into these videos to convey good, concise, practical information. Even with all this effort, some people are still not satisfied (there are 12 thumbs down on this video), and I'm not sure why...
Hi Alan,
I discovered your channel recently, 3 months or so. I watched each and every one of your old videos one by one, I am up to date now.
I have never commented before (I do give a thumb up to every one of them, though, obviously), but I thought I would this time, for a change ! ;-) I mean, as you said it took you quite some time to come up with this video, but the result is excellent and I do, like many others it seems, appreciate it immensely. So I hope that the recognition you get and deserve, will keep you motivated and that you will keep doing great stuff like this whenever you find the time.
Every second of your videos is pleasing to look at and listen to. I love every aspect of your videos. The technical content, the way you present it, your lovely hand drawn notes and schematics, your experiments, quick calculations to demonstrate the point... you act and talk like a proper engineer that you are, as well as a man of passion, a pleasing and efficient blend. I think that's why many electronics teachers here in France just aren't good... most of the time they actually don' t have ANY experience in professional electronics design (and not much passion in them either). They just study EE then go straight to teaching, zero "real world" professional experience ! :-/
I also studied EE in the UK as well, at Uni for 3 years (did a B.Eng there, 20 years ago), and the teachers also looked clueless and uninspiring, couldn't sense any trace of passion in them either. Was pretty depressing...
Anyway, enough rambling. Just wanted to comment at least once, to express my true appreciation for your contribution to EE education. Keep up the excellent work ! :-) The number of subscribers, 75K to date, is a good metric I think. This alone should convince you that your are doing something good and valuable here. Sure, EEVBlog is much bigger, nearly 500K subscribers, but I think this is largely due to, as I remember him confessing once, the fact that he is more (overall I mean) of an entertainer and show man, than a teacher. Your videos however target more those interested in the educational value that an experienced design engineer can bring. This obviously is a narrower audience. In this respect, I think 75K is a really strong number which I hope you appreciate as well.
Thanks again for the time and effort you put in all your videos :-)
Vincent Trouilliez, from across the pond.
Wow, you've watched every video?? That's a lot of time invested, and I certainly appreciate that! I hope you've seen that the production quality of the videos has improved since the early days of my channel. Thank you for your very kind comments. I received my engineering degree in 1985, and I remember that many of the professors were as you described. I did have a few that had a real passion, but many did not.
Most of my videos take a lot of thought and planning - typically 10x or (much) longer than the video duration. Others are a bit more impromptu (like my video on the Z-Match tuner that I did while on vacation). Even these often require many "takes" until I'm happy with the content and flow.
I'm certainly not the "entertainer" that Dave Jones is, so I definitely understand the differences in the size of the following. Of course, he also has a blog and a very popular forum - I have none of those, just no time to do that type of thing.
Thanks again for your very nice comments - knowing that the content I put together is truly appreciated and *used* by my viewers is very rewarding and inspirational.
Thanks again for being such a loyal viewer!
Alan
Yep, every one of them, watch I did ! LOL
I don't have a TV anymore (gave up on this thing 20 years ago). These days I replace it with YT videos. So instead of watching silly and brain damaging stuff on TV, I instead spend it on watching selected/hand picked quality content on YT. I find it much more interesting and useful than TV...
I also like TheSignalPath and watched all his videos, then once I had finished TSP (and subscribed of course) I looked at your channel because YT suggested it in the "Related Channels" list on TheSignalPath page. I am glad I clicked ! :-) Then I listened to your interview with Dave on TheAmpHours radio show to know more about the man.
Yes the quality of the videos did improve ! I just re-watched your video #2 for a side by side comparison ("using the delayed time base on your Tek 485"), to refresh my memory, and the improvements are obvious... The camera is on a stand now, makes a world of a difference. Picture is neater/sharper too, and the lighting is much better/brighter. It's indeed very well sorted out in your newer videos :-)
The technical quality of your videos is now great and I don't see/feel any particular area that would need improvement. Now we just concentrate 100% on what you say and what you do on the bench, which is great. We can focus on learning rather than bitching about such or such technical problem in the filming.
Anyway, back to the lab, my old Tek 317 is waiting for my assistance.... yeah like you I have this "disease" of "collecting" various Tek scopes (mainly) as I go. They have this little something that keeps me coming back for more no matter how reasonable and rational I try to be...
Regards,
Vince
Hi Allan I just wanted to say thank you for all the thought that goes into these videos. They are by far the most simple and informative videos on this subject. Im 15 and I’m learning electronics purely for the fun of it but even at such a young age I am still able to clearly understand these videos because of your simple and straight forward way of teaching. Thanks again.
I'm getting back to basics for an ongoing project, destined for modularity and miniaturization, the potentially tiny bipolar transistor circuitry is really important for these applications. W2AEW is by far one of the most useful and enjoyable sources for this really important subject matter, thanks dude!!
I'm a long time fan , and I am really thankful for your sense of detail and nice way of explaining things. Thanks to you I am a proud owner of 2 Tek 4 channel scopes, an old crt from ebay :) and a TBS1064. For what I'm doing they are more than sufficient, the latter being my basis for accurate measurements, and quick and easy to look at comparisons, thanks to the trace colors. Especially coupled with your expert advice and great quality video productions, I have lots of 'fill in the gaps' for my general knowledge in relevant areas. Cheers!!
It is nice to finally find someone who explains electronics in a way I understand. Thanks for your hard work. Please keep it up.
Another great video! I've been researching information on BJT common-emitter amplifiers for over 2 weeks using several books. This is, by far, the most comprehensive series of videos on the subject. Thanks for taking the time to put this together
I must really thank you. You are one of the few who bothers with the math in a demonstration. I have re-watched almost every one of your videos, most more than 3 times. However, I want you to understand, the math portion of your tutorials is what makes them great for me.
Thanks - although I do try to minimize the complex math, and always intersperse with practical demonstrations and measurements.
Math is our friend. Many mistakes could be avoided by using a little math first.
awesome video dude, need i say your explanations are clearer then those given by some of my lecturers at my university.
Thank you - please pass along my videos to your fellow students, *and* your university lecturers!
I notice you did not treat the "swamped emitter" where the emitter resistance is partially bypassed to give better gain and low distortion. For example: implement the 1.2K resistor as a 400 ohm from the emitter to an 800 ohm to ground then bypass the 800 ohm. Then gain with Rc=20K will be 50, but the distortion will be very low.
Its been early 80's since I worked with these formulas, Great brush up!
VERY good video. A simple, detailed explanation that didn't skip over important points and just assume I knew what you were talking about. I have watched a bunch of these videos and you are the best instructor I have found. You got a sub.
This explains so much! So many light bulbs went off in my head.
Thank you. You are a great teacher.
You are such a good teacher Alan. I just love the videos like this, they make the subject so understandable and enjoyable. If I had the time I could immerse myself in transistors. Many thanks for all your hard work putting these video together.
I'm working through some textbooks as a hobbyist and while I understand all the equations and rules etc, I find myself not following it as well when I actually go build something. You really made it a lot easier to find a starting point for me and I'm going to go enjoy building some amps for a bit now. Thank you for the awesome videos!
Great to see you back doing the theory to practical. Always reminds me of college, and one teacher I had was Chinese. When he was doing transistor theory his accent was so bad we made him write it down. Image Vbe in a Chinese accent (no disrespect intended) and your acronyms just brought back old memories. Cheers and glad to see you back in the class.
It's important to emphasise how much extra distortion is introduced for larger signals if you bypass the emitter resistor. With a bypass capacitor in place, the gain is directly proportional to the collector current, so if the output swings close to the positive rail, the gain drops to almost nothing. If the output swings low and doubles the voltage across the collector resistor, then it doubles the instantaneous gain. That's a recipe for really nasty distortion.
The formula for gain is actually Av = - Rc / (Re+re) where re is the incremental emitter resistance = 25mV/Ic at 17°C. To reduce the effect of transistor variations and to reduce the distortion caused by the non-linear re, it makes sense to set Re at least ten times re. But the voltage across Re is Ie.Re = 10.Ie.re = 10 x Ie x 25mV/Ic. Since Ic=Ie for all practical purposes, that shows that the voltage across the emitter resistor should be at least 250mV. Making it higher reduces the gain, so a practical upper limit on the gain is achieved by designing for 250mV across Re.
Another tip is that because you want to bias the collector around half-way between Vcc and Vb, the voltage across the collector resistor will not be too far different from Vcc/2 (assuming Ve=0,25V and Vbe=0.6V). That means that the practical upper limit for the gain without bypassing the emitter is approximately -Rc/Re = - Ic.Rc / Ic.Re = - Vcc/2 / 250mV = Vcc / 500mV. So for a 12 volt supply, you won't get more than x24 gain unless you bypass the emitter resistor and then you have to keep signals below about 10mV to avoid the non-linear distortion.
A final tip: with an emitter bypass capacitor, the gain becomes Av = - Rc / (Re||Xc + re) where Re||Xc is the impedance of the parallel combination of Re and the reactance of the bypass capacitor. If we want the gain to be flat with frequency down to low frequencies, then we need the reactance Xc to be smaller than re (note: *not* just smaller than Re). For the circuit shown, with a collector current of 0.42mA, the resistance re is 25mV/0.42mA = 60R. A 47μF capacitor has a reactance of 60R at 57Hz, so that is the -3dB frequency. If you want to have the roll-off occur below 20Hz, you need around 150μF for the bypass capacitor.
Bravo. Reminds me of my electronics class in engineering but much better explained. Thank you for being considerate enough to share your practical knowledge.
Thanks once again for a well presented video. I think your videos are the best electronics videos on YT when you calculate the ratio of useful content over length. If you did a one hour video it would be like a full semester at a University.
Another excellent video. I save all of your circuit design videos and notes to the "Circuit Design" folder.
This is the best video on real deal transistor setup I can imagine! 👍
A good blend of theory and testing. Excellent. Well done.
I really appreciate your videos. I have not fully watched all of them on bjt biasing but #113 answered a lot of questions I had previously. I been trying to understand these topics for a few years and biasing outside of a simple single resistor base bias is confusing. Hopefully this makes more sense to me. Thank you.
Boom. Nice to see little re my favourite transistor parameter. Thanks for sharing this helped blow the dust off.
I am only afraid YT is not really the best way to show your amazing knowledge. I often see the subscription to your channel going down in the list, based on the fact that you don't release videos often enough. Quality content takes long to be produced! The education you give us must to be protected for future generations, and I am not joking here. Ideas anybody?
I wish I had the time to produce videos more often, but my *real job* and family life take first priority. I hope that the videos I produce will be preserved for generations - that would be a nice legacy to leave behind.
This is one of the very best videos I have seen on this subject. Thanks so much.
Great video... I always go back and re-watch those linked videos. This video answers some of the questions I've had. Thanks. Passive/active components always fun to learn about.
It's been along time since I did some calculations of this so I so when I did this a couple of weeks ago I had totally forgotten these shortcuts.
Thanks for reminding me :)
Another great video as always from an exceptional teacher.
Can you please do a video on common base amplifier and its main features and also a video on tuned RF amplifiers. There are not many tutorials out there on these curcuits.Thank you.
Fantastic video Alan! I would love for you to explain how you set up your scope. Is the attenuator really necessary for low voltage and low frequency work? Just curious!
I used the attenuator (as shown at 2:18) for two main reasons:
1) To provide a 50 ohm termination for the generator, so that the applied voltage wouldn't vary with the frequency dependent input impedance of the amplifier, and the main reason is:
2) To make a larger signal available at the scope for input signal monitoring. If we just probed the signal at the amplifier input, it would be quite small, and the signal-to-noise ratio would be poor, resulting in a noisy calculation of gain in the Math waveform. By measuring a larger signal, and then simply scaling it's value with the attenuation value, the scope sees a larger signal with better SNR.
Well demonstrated, well explained. Nice video!
What a wonderful explanation!
Any video in this series where you show the design process given a desired voltage gain Av for a low gain amplifier?
The Signal Path has an excellent one: ua-cam.com/video/Y2ELwLrZrEM/v-deo.html
WOW I've been trying to figure this circuit out for years thanks!
Your tutorials are ridiculously awesome
Excellent handwriting
Excellent tutorial Alan, precise, concise and delivered superbly, thank you.....
Love your videos, thanks for the refresher courses! At 23:29 you show and state the led current being 700 uA. How is it possible to light an led with that little current?
huh? This video is only 18 minutes long....
I keep revisiting this lesson, have a curious amplifier mind now. Any other important lessons on amplifier design, matching components, testing... would be much appreciated. If possible would love to see a lesson on DC servo for an amplifier, theory and operation...
Sir, your videos are amazing! I learn more from you than I do from my own teachers in the university!
Couldn't thank you enough. please keep us posted and thank you.
Great! I really like your videos about this basics. Its simple and straightforward. Excellent!
Excellent tutorial. Should you go with two low gain stages e.g 10 by 10 or one with 100?
It depends. It's sometimes easier to setup biasing for low gain stages, and you'll be able to get more BW out of cascaded low-gain stages.
NICE!!! MORE AMPLIFIER TIPS and TUTORIALS PLEASE!!!
Thank you w2aew! This is very clear and concise. Very helpful.
You are good, really good. I do hope you teach professionally as you are a natural.
Not really. I am a Field Applications Engineer for Tektronix. I do some teaching/tutoring in this role, but I am not a teacher per se.
Thank you very much!! This video helped me a lot in designing one of my circuits. Thanks a lot
Most [Class A Common Emitter] amps have a transformer on the output for impedance matching and removing DC bias.
A follow up on transformer design & build would be great. Building transformers is rarely documented, and is at risk of becoming a lost art.
I'll have to add that to my looooooong list of future topic considerations.
Hi! It looks like there is an oscillation in the circuit. It is more pronounced with the 20k collector resistor at 12:32. Or a picked up noise? Is it there? What it colud be?
great video! excellent teaching capabilities!
Very good explanations and shortcuts, loved your video.
Thanks a bunch. Very helpful as always. Can you please do a follow-up demo on those direct coupled multi stages? They are really confusing. Thanks again 👍🏻
I can add that to my long list...
That's great! 💗 thank you so much.
Alan, as always a magnificent effort. It goes in my library of w2aew videos on theory. (Now that I have retired, I build and test as you do and verify which makes me understand better.) My only question is who in hell gave you two dislikes?
71/72
Bill, k6whp
dit dit
Thank you, glad you liked it. I don't know who gave the thumbs-down, but I always get a few.
Another wonderful video - well done! You explain that by adding a bypass cap can cause distortion but provides higher gain. You described the higher gain, but you did not address the distortion issue. At what point (cap value or res value) might one expect distortion to become an issue?
The distortion is due to the fact that the transconductance (gm) is a function of the collector current. In the bypass case, the gain is -gm*RC, so if the transconductance changes from the highest to lowest level of the signal, the signal will be distorted. So, the more that re (1/gm) dominates the emitter resistance, the more distortion you can have.
I love this topic. Biasing is a hard thing to wrap the brain around. This year I finally pulled off putting several amps together some worked well and other needed tweaking. How would you set up a transistor as a digital switch for high current like a 3055 on pwm?
When doing switching, you generally want to switch the transistor between OFF and Saturation. For OFF condition, make sure that Vbe is near 0V. For the ON (saturated condition), make sure that Vbe is fully forward biased, with a base current ~10% of the expected collector load current.
Another fantastic video. Thank you. Can you tell me how to calculate the input and output impedance? If you covered it in another video please direct me. I know how to measure it, but how do you design a circuit with a specific impedance in mind?
Output impedance is simply the collector resistor, RC (or R3 as shown in this video). The input impedance is slightly more involved. It is the parallel combination of R1, R2 and the input impedance looking into the base. The input looking into the base in the "emitter bypassed" case is something called r_pi, which is simply r_e * Beta. From the video, r_e is 1/gm, or v_t/Ic. In the case with emitter degeneration (no bypass), the input impedance is r_pi + (Beta+1)*RE.
I would like to clarify that r_pi + (Beta+1)*Re is an input impedance (!) looking into the base, not an input impedance of the amplifier. The overall input impedance is R1 || R2 || [ r_pi + (Beta+1)*Re ] which can be approximated as R1 || R2 || Beta*(r_e + Re), since Beta is unknown and >> 1.
Thanks for sharing. If you have a moment, can you please comment on the criteria used for selection of the bypass capacitor size? Is the goal just to have a cutoff frequency well below the signal frequency? Thanks.
The goal is to have the capacitive reactance be much smaller than 1/gm at the signal frequency. 1/gm is also known as re, so the gain can alternatively be written as -RC/re. If there is any emitter resistance, then the gain is -RC/(re+RE). If the bypass cap is not much less than re, then it will reduce the gain the same way that an addition emitter resistor (degeneration) would.
Love these bjt videos!
honestly, thank you so much. superbly high quality.
In my pile of books the CE biasing examples start with a "given" collector current. Some choose quite small values...half a milliamp say. Here you talk about several hundred. I'm pretty hazy on how to select this current value and if I am connecting stages -say a CE to CC buffer that is not driving something like a speaker ) do I keep them about the same?
There are several factors that contribute to the choice of collector current. Things like power dissipation / current consumption requirements, output impedance requirements, transistor characteristics for best performance (noise, distortion, saturation, headroom, etc.), and more. There is no single universal answer regarding how to choose the desired collector current. The most common consideration would likely be the load impedance / output impedance needed in the application.
@@w2aew That makes sense, thanks so much.
Very nice video Alan, never thought about these shortcuts really - feels like one is back in school :-):-) well done 73´s / Andy
Excellent tutorial and video. Tthanks so much and keep them coming.
Very clever usage of math, the scopes I am using cannot do that. Do you know if MDO3000 also have this capability?
The MDO3000 can do this same math trick.
Great. Now I want one.
The big difference between the MDO3000 and MDO4000 is that the MDO3000 can *not* acquire RF vs time and show the RF signal characteristics along with the analog and digital signals. The MDO4000 can do this (spectrum vs. time, RF amplitude, frequency and phase variation vs. time vs. analog and digital signals).
I needed u about 60yr ago. THANK YOU! (NOT TOO OLD)
Excellent. Thanks again, Alan!
Fantstic video as always, thanks.
Idea for a future video:
Calculating input and output impedance of 2, 1 transistor amplifiers, after each other, and calculation of the size of the dc blocking cap between the 2 stages, especially the last of the two, i have searched youtube and i have found none that have made a, for me, usable video on the subject, maby you could make that video.
Greatings from Denmark
Morten
Thank you. I did answer the question about calculating the input and output impedances of a common emitter amplifier in one of my comment replies below. I agree that a video on how to select the interstage capacitors would be useful. I can add that to my looooooong list of topics...
Great and neat explanation. Thank You. I really like Your explanation-videos of analog circuits.
Great video, very clear explanation.
great explanation Alan, thank you. How did you calculate the values needed for the decoupling cap and bypass cap? Those are pretty large components... what would be the effect of using much smaller caps?
Nothing too critical. I just wanted to be sure that the impedance of the emitter bypass cap was much less than re (1/gm) at the test frequency so that the gain approximation was valid. And I wanted to be sure the input cap's impedance was much less than the input impedance of the circuit so that there wasn't any significant voltage drop at the test frequency.
Hi great video, but can you explain why the gain should increase so much simply by putting in the emitter bypass capacitor? Apologies if this is already covered in another video.
In short, it reduces the negative feedback, thus raising the closed loop gain. Page 3 of the notes compares the two cases (not-bypassed and bypassed). Also, Take a look at video #67, it has more details.
w2aew thanks. I’m going to try your examples myself. Interested to see what spice says as well. Looking for a small signal rf amp to boost the output of a ad9851 dds.
Up to your usual awesome work. Great video.
wonderful video and thank you for using a camera tripod. Video #67 had me running for the Dramamine having watched it so many times, getting up and walking around like a sailor new to port. I tried recreating the circuit in #67 but kept getting VC and VE values 13-15% off in my calculations vs. measured (VC calc = 2.29V, measured = 1.946V). I'm learning so this might be common knowledge but it appears while an emitter-bias is somewhat independent of beta variation, the formulas are significantly sensitive to VBE. I was using the 0.7V approximation for silicon transistors and getting incorrect values for a 2sc945 transistor. The 2sc945 datasheet has a VBE min = 0.55V, typ = 0.62V, and max = 0.65V. Using the typical 0.62V VBE in the equations resulted in the calculated values matching the measured. Thank you for showing the trick for AC signal to the oscilloscope. Not sure if you used the same in video #67 but when I tried there was so much noise in the low freq I couldn't keep the same attn. that was used on the HF and then I was no longer comparing apples to apples.
Great video, thanks! 😃
is it compulsory to use non-polar capacitor or we can use polar capacitor.what will be the effect on output with both types of capacitor.
As always very nice&highQ video-lectures, thank so very much.
(..friday evening here in scandinavia/norway, and coffee + videoes like this one is top-notch. Thanks again for sharing your quality knowledge to all of us Alan.)
We can also bypass the emitter resistor with a capacitor AND a resistor in series. This boosts the gain but can also be chosen to limit/eliminate distortion. For this circuit 75-150 Ohm in series with the cap should work nicely.
Can both the bias line and collector input be driven from a single power source?
Excellent tutorial, thanks for sharing. I would like to recreate your test setup but I don't have 10x attenuator. Can you share some information about it? Maybe I can try to build my own one.
I did a video on attenuator design:
ua-cam.com/video/A5gGeV7CiQ0/v-deo.html
Great video! I have a circuit with a switched emitter bypass cap and a 500 ohm resistor to ground after the cap. What does that do to the signal and would the main emitter resistor still be bypassed and not factor into anything? Thanks in advance.
At DC and very low frequencies (where the capacitive reactance is high), the main emitter resistor is used to compute the gain (basically RC/RE). At higher frequencies where the capacitive reactance is low, then the 500 ohm resistor appears in parallel to RE, and the gain basically becomes RC/(RE||500).
w2aew thanks for that information. It makes some sense to me.
I’m new to electronics and I am just looking for a way to adjust the output of my transistor on the fly. Can I get away with putting a trimmer pot on RC to adjust the output (lower rc/re value)? Its a 2 stage guitar boost pedal and I just want to have ability to control the volume out of stage one, the transistor.
@@Strumbum01 You can use a potentiometer to adjust the volume. It can be done at the input or at the output. But, do NOT use a trimmer pot as a volume control. Trimmers are not rated for frequent use, they are only designed for infrequent "set and forget" applications. They wear out very quickly, often rated only for a few hundred swipes. See this video for detail: ua-cam.com/video/5d_TTQ2OJtM/v-deo.html
Great video Neilson Shetland islands
At one time you had a video where you show why sometimes it is better to use a 2n4401 instead of a 2N3904. DO you remember the title of this video?
Thank you!
You must be thinking of someone else - I don't have a video that discusses that. The 2N4401 and 2N3904 are very similar transistors. The performance of the 2N3904 is better at low collector currents than the 2N4401, and the inter-node capacitance is lower on the 3904. There's a decent discussion here:
electronics.stackexchange.com/questions/231844/why-would-i-use-2n3904-instead-of-2n4401
I am pretty sure it was on one of your videos. I think it was about the current rating for switching applications. It was not necessarily a video dedicated to the '4401 or '3904 per se.
Thank u please make 4 us amplifier design techniques for beginners
Nice lesson. Thanks, Alan.
Awesome video, thank you.
thank you
Just subbed... Your a great tutor!
Can you show how to calculate the input capacitor value and output capacitor value because you have to add in the input impedance as Rin and output impedance formula for Rout to apply to get the capacitor value.
How do you calculate the gain when the collector is directly connected to 12v supply without the load resistor?
When the collector is directly connected to the power supply, the circuit is not a Common Emitter amplifier. This configuration is called a Common Collector amplifier, or Emitter Follower. The output is taken from the emitter. Voltage gain is basically unity, non-inverting. See my video the common emitter, common collector and common base amplifier configurations:
ua-cam.com/video/zXh5gMc6kyU/v-deo.html
very good and usefull vidéo
thank you
Great stuff alan but I cant seem to get the PDF of the notes, is the link broken?
The link should work. In either case, here is the expanded link:
www.qsl.net/w2aew//youtube/common_emitter_tips.pdf
thank you for that. my error I now have six copies
Very helpful. Thanks
Hi, do you have any videos that explain re, ro, gm? im unfamiliar with these terms when used for BJT.
Thanks a lot for your videos they help a lot!
I don't have a video on this, but here's a short explanation. These refer to "small signal" behavior, which is typically when the BJT is in the active/saturation region (flat part of the typical IC vs VCE curves).
gm is the small signal transconductance. It is the ratio of how much the collector current changes in response to a small change in base-emitter voltage. The re term is simply 1/gm. It also represents the small-signal output impedance of the emitter terminal. The ro term represents the small signal output impedance of the collector terminal.
@@w2aew Okay thank you!
Hi! Could you give me some more indication to be able to buy a "10x attenuator" and "50 ohm terminator"?