This could have been a build it, test it, call it crap and leave it at that.... But thankfully this amplifier does have issues which could be rectified and has thus opened the door to a most wonderful series of amplifier design! I'm loving this! Can't wait for the next video! Thank you Tony...

Love the theory videos can wait for the next parts in the series.

Great explanation on amp design. Before KZfaq none of this info has been readily or easily available outside the industry. It's so good that guys like you take the time to talk about this in detail. I personally haven't discussed transistor circuits with anybody properly since the 1980's - nobody around (whose interested enough to to share the knowledge with). I've forgotten half of this stuff. I do remember college lecturers and technical training officers talking about amp theory when I was an apprentice TV engineer back in 1983-6. Thank you for going into this detail and bringing it all back for me. Outside of old tech* books I have it's all we have (* which I do read from time to time - and they can't really put the theory across in such a way that it is enjoyable to read all the time).

I really liked this video Tony! Very appropriate for my current level of knowledge about the topic. It helps me to understand terms I’ve heard you and others use, like ‘Voltage (amplification) Stage’, ‘current mirror’, and where and why you can adjust the ‘DC Offset’ on some amps, but not others. I was thinking I needed to buy an amp kit like this to learn myself what makes them tick, and I likely still will, but I can learn vicariously from watching you. Thanks for taking the time to share your knowledge, it is significant and much appreciated.

Great explanation! I've had bits and pieces, this time the whole circuit comes together. Can't wait to see it on a scope with the improvements.

Fun to see a test of those two amplifier circuits. you should design a quality circuit board of the winner and put it online and make a amp builder series. That would be awsome. With components and transistors that are widely available today.

@ 10:30 It was also good enough for Nelson Pass when he designed the Threshold NS10 preamp's final output circuit, using 2 - MPS6571 transistors in a quasi-comp configuration as well as Harmon Kardon Citation 12 and 16 amps, which are fairly well regarded amps for the time..Phase Linear also used that design in it's 400/700 and its newer series II line. Back when those amps were designed, it was harder to get fairly well matched PNP/NPN power transistors, so they made it work with what was available, and even when PNP/NPN's are used an emitter resistor is still almost always thrown in for better balancing. between the output components.

Thanks Tony, the fog is lifting...

Very interesting! Please continue with these excellent explanation

Fond memories of EE400 circa 1986, only you explained it better. Keep up the excellent content.

Love the walk through the schematics

Very good explanation, Tony! Quad amplifiers also use the quasi complementary design. Looking forward to the next video!

Fascinating and instructive - more please ! 🙂

Just like the sound of quasi complimentary stages ( with Sziklai pair inverters ) Have done a few mA6100 McIntosh and they always sound better to my ear than full complimentary. Keep up the good work ! Greetings from Canada.

I really like the way you explained the circuits particularly using the schematics back and forth.interesting the feedback on output cap coupled pioneer seems to be taken before and after the cap.came across an interesting article a while back about optimizing quasi comp circuit.just came across some cheap n MOSFETs so I may finish a project I started years ago based on nelson pass mod of hk citation 12.also have some old rca to-3 so maybe a bipolar version too.

Is the stopper resistor used for blocking RF frequencies? I only know the term stopper as in grid stopper with vacuum tubes where it is used for that purpose.

All I know is I miss my all Alpine and Rockford Fosgate system I had set up in my Truck. I have no idea what my Yamaha Studio Monitors have in them. They all have separate amps. I opened one once but was not able to see much. They have quite large amplifiers in them. The low range and the high range both have separate amps inside. But then again you are talking about studio equipment.

24:29 R235 should be on the on the collector side or emitter side of Q213, which is better to have ? putting on collector side, it does the adjustment through Q209, whereas if put on emitter side it will directly adjust Q213 i guess.

I bought a chinese kit.... a nice single ended tube oscillator.... swapping the output transformer leads didn't fix it.... Some day i'll get back to that project....

Re Pioneer SX-535(?) schematic, wouldn't DC reach the speaker terminal via R80 and R82?

These videos are so cool, hope there will be many more, thanks Tony. Do you or any other kind reader have suggestions of books about audio amplifiers at this "level"? I'm a hobbyist stuck at this point where I have a solid understanding of basic electronics and how components work but can't move forward since all books I've found either start from scratch or are aimed at circuit designers so they go way above my head. These videos are just right, cheers from Italy

At 23:54 I see the circuit for Q231 emitter and Q213 collector are connected together through R231 (5.6 Ohms). That is different from the positive side circuit (Q207/Q211). What is going on there?

I'm wondering if somebody has some video series exploring the differences in design with actual testing or simulation. I know JohnAudioTech does something similar with his designs, but was looking for something that's right on point. I know it takes a lot of time to do that and have a nice presentation, but I'm sure somebody must have done it.

Q2 and Q4 are together not a differential amp??

How can I learn to follow the signal path if the signal can be coming out of either the collector or the emitter side of the transistors? Makes following the signal through the circuit very confusing.

Greetings: There are two resistors markedR18 that are different va,ues: 220 ohms vs 22ohms. I suspect thevalues are different and should be diffently identif I ed or shouldbe the samevakue; which is it?

I suspect that totally leaving out the emitter degeneration resistors will lead to problems...

Good refresher for what's to come. Enjoyed watching these two videos today.