The Class A amplifier - build and test (2/2)

[@carmelpule8493]

Brilliant presentation. I have experience with all the circuits presented as I started this work in 1952, but I must say I am really enjoying how this gentleman is covering all the detail. Well done, for not only including the theoretical part , but also the simulation, the implementation practical part, and testing and other detail only an expertised person can depict, .

[@nelgau]

Each and every one of your videos is a masterpiece of exposition. Thank you for being so generous with your time and for teaching us electronics! :)

[@yoavrosenbach]

AMAZING !!!! This is how it should be thought !!!! I don't understand where are your other 1M subscribers...

[@tlmoller]

“How hard can it be?”. Love these videos. So great in all ways.

[@RicardoPenders]

You are a great teacher in electronics, I like that you are showing every detail you need to take into account when designing a circuit and you also show what the circuit does with the change of temperature, what the current consumption is when there's a signal going through and without a signal, I didn't know that the temperature would go up without the signal. So you can see that you excellent way of explaining things and showing the signals on the different meters and scopes that even someone like me who knows almost all you need to know can still learn a thing or two from watching your videos. Thank you very much for sharing this online, you make it so easy to follow along and you keep it interesting so I don't lose focus.

[@alexlo7708]

Input signal made transistor changes its own resistant value which it goes in a unidirectional way , rises up from DC quiescent operating point. The more resistant ,the less current can flow in and the less power loss.

[@librasulus]

I am too ignorant in the field to understand even the half of your content but I salute you, great content!

[@sureshlala6462]

Thanks, very educational for me to understand as I build Class A amplifiers, always nice to see if I am doing anything wrong, very well explained, cheers.

[@andromedusmoat9608]

Fast becoming my most watched channel... Keep it up!

[@rhp9797]

I loved the tease at the end! Absolutely brilliant!

[@curtstacy779]

Excellent video again. I love the way you explain things.

[@sheepbaba]

Nice one and thanks. I recently built a Class A audio amplifier kit. I just followed instructions and don't really understand how it works. This video helps. It sounds amazing. Running about 15wpc it is not too hot but has huge heat sinks and uses a current source transistor. The inductor design looks cool but am intrigued by the transformer coupling. Previously I have been using a SET valve(tube) amplifier. I can't wait to see if you find a way to make it more efficient.

[@FesZElectronics]

I'm happy you liked the video! I guess that with the valve amplifier you had the transformer on the output - so that should work more efficiently than the transistor amplifier with current sinks. However, with valves, the minimum anode voltage that you can achieve is limited - you cannot go as low as with transistors. I guess the best of both worlds would be a transistor amplifier with a transformer output - this is not that common since the price of the transformer is way more than the extra current sink transistor + heat sink.

[@sheepbaba]

@@FesZElectronics that's really interesting. The guy who made the valve amp I believe also made some transformer coupled transistor amps. Now I know why... 😊 Sadly he passed away last year. He used to make stuff for studios and even Pink Floyd.

[@urlkrueger]

Well, let me help you out. B comes next but is then followed by C and then somewhere down the list is PP. What I like about your channel is that I am learning how to change my thinking from a technician's point of view ( how does this work ) to an engineering point of view ( how do I make something that will work).

[@FesZElectronics]

PP (push-pull) is not an operating class, its just a specific implementation having active elements both "pull" and "push" the output - you can even implement class A operation with a PP stage - low side amplifier transistor and high side constant current source. Unless of course you meant something else by "PP". I'm happy you are enjoying my videos :D

[@pu5epx]

Audiophiles will love this!

[@dannyperry8070]

In calculating the static current, you are using RL 50 ohm load which is blocked from Vcc via capacitor. So I don't understand how this can be used to provide the static current. The way I see it is the static current is provided through the inductor which under DC conditions would have very little resistance and with a signal its resistance changes till RL become dominant. I really like your videos and using them to design and experiment with similar circuits.

[@rogeronslow1498]

Try doing a two-tone test. That's the acid test of linearity.

[@alexloktionoff6833]

i.e. intermodulation, two hi-frequency tones with 1KHz difference

[@FesZElectronics]

I will try this out for the next amplifier - stay tuned for Class B :D

[@acestudioscouk-Ace-G0ACE]

A lot of useful information, thanks.

[@geoelectronica]

Super tare Maestre, congratulation! Ai putea sa continui seria cu si despre amplificatoare, sunt multi pasionati, e un subiect care prinde. Exp de topicuri: the most common amplifier classes, Boucherot cell, Totem Pole, Bootstrap Circuit, LONG TAILED PAIR, constant current stage, current mirror circuit, Voltage Amplification Stage, Complementary-Feedback-Pair, single ended amplifier, etc. Cheers

[@marctamtonthat]

Thank you for your great videos. Very interesting and useful. Some DC circuits are designed to reverse the polarity every minutes in order to mitigate the wear of the filament. It would be interesting to have this feature.

[@BIGRIP87]

next letter after A is B

[@dannyperry8070]

I have tried a similar circuit to yours. What I find that without the 50 ohm load the gain varies with frequency because the impedance of L increases. With a 50 ohm load there is also some variation in gain. The larger the load resistor is the greater the variation.

[@JacquesConradie]

Very informative and well explained - thanks!

[@rubenhidalgocarrillo]

Very good video, as always. Thanks!!!

[@dannyperry8070]

Great video. Why did you not place a bypass capacitor across RE? Also why is the supply voltage 1/2 of Vload p_p? is that because of the inductor?

[@FesZElectronics]

By placing a capacitor over RE, you get a very high amount of gain which is highly temperature and transistor dependent. I kept it this way to have a more predictable value. When amplifying small signals, you want as much gain as possible, so you will use the capacitor, but for large signals, too much gain will cause distortion. Regarding the second point, yes, the inductor is allowing a higher collector voltage than the supply, so by using inductors you can get higher output voltages.

[@alexloktionoff6833]

But you can loose less even for low voltage class A amplifiers with MOSFTETs. Do you plan a video about it?

[@smak201]

Excellent video as usual! Have you considered also analyzing the noise of the amplifiers and how they work with very weak input? It would be interesting to see how different topologies and transistors (BJT, JFET) compare when there is no need to produce much power, but the input signal has very low amplitude.

[@FesZElectronics]

I guess this a different topic - typical noise figure of different component types; its an interesting topic though, I will try to do something about it at some point!

[@stefanb.933]

hello, how can an 8hz sine wave be played on a 4 ohm load?...it doesn't have to be amplified...

[@alexloktionoff6833]

How to calculate and find the best inductance for class A amplifier? Especially if use toroid /* to avoid interference !*/, and a transformer on toroid ! Do you have. video for it?

[@objection_your_honor]

Can a power FET be used in linear mode, in place of the NPN? since it's a voltage driven gate, can bigger resistors be used in biasing the gate, to decrease power loss?

[@FesZElectronics]

Yes, FET's can be used, and since they don't need current for the static operating point, it will allow the use of larger values. The only thing to keep in mind is that the exact threshold voltage for the FET is contained in quite a wide range (its not as precise as the 0.6V for the BJT); so you might need to adjust the bias resistors with a potentiometer.

[@BIGRIP87]

can i use iron core inductor for audio application? because at lower frequencies the ferrite core inductor, won't act more like an inductor. right?

[@FesZElectronics]

In general iron core is most common for low frequency (

[@BIGRIP87]

@@FesZElectronics right.

[@Flightsimer96]

4:05 : Why is the max current through the emitter resistor equal to the peak current through the load resistor?

[@sahebdarkhor]

Hi what is difference between video amplifier and audio amplifier in equal circuit?

[@dannyperry8070]

Trying to understand why the DC resistance of the inductor was not taken into consideration?

[@FesZElectronics]

I guess I skipped that just to simplify the analysis. For more accuracy that should also be considered.

[@piclife1178]

Great video. Did you try bypassing the emitter resistor with a capacitor to maintain DC operating bias but increase AC gain. BD135 give great RF performance up to 10Mhz in class C but usually end up going pop because of the high collector voltages produced.

[@SheikhN-bible-syndrome]

Can you use a poler capacitor for this?

[@tahanprahara]

Hello... how to choose the right inductor size? thankyou Sir

[@quantumdirac]

May create electronics course and sell on Udemy. I believe it will be quite popular. I will be the first one to enrol.

[@persiangulf2282]

Hi bro I have a question How we should delete dc ofset from output of class a amplifier who push speaker diaphragm out? Please help me Tnx 🙏

[@FesZElectronics]

The easy way is to add a series capacitor of large enough value so that the useful signal is not attenuated.

[@bsuryasaradhi6816]

gold!

[@marekwafel8651]

👍

[@R2AUK]

❤️👍

[@shams350z]

Hey man, hope you're doing well. You look stressed out.

[@SheikhN-bible-syndrome]

Your low in iron and it wouldn't hurt to add some more magnesium and potassium into your diet via supplements ... Just fyi

[@ladronsiman1471]

Are this calculations also similar for a fet transistor ?