I love your videos!! I have a video suggestion. Why not test different "types" of capacitors. I look at Nichicon capacitors and they make a ton of different types of caps for different use cases. If restoring a amp, should I be paying attention to this or is it just marketing bullshit? Or is any cap that matches the original good enough?
2:50 you still shorted the bases and ommitted the diodes - for the circuit to work, you'd have to have AC (capacitive) coupling for the bases. 3:46 it's a matter of convention, in modern times American schematics I see Q, but in European circuits I see T, or even V. In Soviet circuits I often saw VT for transistors and VD for diodes. I had some doubt with the class B totem pole push-pull, and with the intermodulation distortion. Turned out to be right.
Yes, thanks. The drawing is a vast simplification not intended for build purposes. I left many things out for the purpose of simplicity explaining the basic concept.
The letter Q for transistors was chosen because the transistor is engineered to operate at a "quiscent" point, or a position along it's S curve, known as ot's "Q Point". Transformers are less often represented by the letter T and more often either represented by letters "TR" or the letter "L" which id notation for "inductance".
Hello, Flux Condenser! I was wondering if you could help me. I have an audio book that comes with a cassette tape that is broken. The audiobook is from 1999 and I'm not having luck finding a replacement or fixing it. If I sent it to you, do you think you could fix it? Thanks for all your help, and I hope to hear from you soon!
Got 'em all, but I've been building and repairing preamps, amps, mixer boards, speakers, and so on since the mid-1970s. I refer everyone to the Nelson Pass designed A40 amp that appeared in the Audio Amateur magazine issue 4/78. It is a push-pull amp using a constant current source to bias the output transistors (NPN/PNP) into Class A. It sounds wonderful! And it's a great space heater during cold winter months!
I know these fairly well on the components, but the A, B and AB was something I did not know as well as I should. I knew that the dual output was also called a push-pull amp as well. Class D is one I hear about often in car audio amps, these days. The transistor "Q" is kind-of how they look on a diagram, as well as the early can transistors had a little part sticking out of the one side so you could get the legs positioned right. Looks like a Q from the top...
An amplifier with one transistor is called "single ended". If it has two transistors (top and bottom) it is called "push-pull". A push-pull amplifier can be class A, class AB, or class B. The single ended amplifier must be class A if it is linear. The class of an amplifier and whether it is single-ended or push-pull are two different things. And the class B isn't more efficient because it has only one transistor on at a time. It is more efficient because it has less current going through the transistors with small signals. Also, it is incorrect to say ".6 volts of current". Volts measure voltage, amperes measure current. And your schematics should have dots where the wires cross if they are connected. But I'll give you one point for the IM distortion question.
www.electricaltechnology.org/2020/05/push-pull-amplifier-circuit.html/amp Quote: “Although all the configurations of the push-pull amplifier can technically be called push-pull amplifier, only the Class B amplifier is the actual push-pull amplifier. In contrast to Class A amplifier, Class B amplifier has two transistors for the push-pull electrical action of which one is NPN and the other is PNP. Each transistor will work for one half of the cycle of the input producing the necessary output. This improves the efficiency of the Class B amplifier many times higher than the Class A amplifier. The conduction angle for this amplifier is 180 degrees, because each transistor works for one half only. Class B amplifier is one of the most used amplifiers, but it comes with its own shortcoming. It generally suffers from an effect known as Crossover Distortion. Due to this effect, the signal gets distorted at 0V. A transistor requires 0.7V at its base-emitter junction to turn it ON. What that means is that the transistor will not switch ON until the voltage across its base-emitter junction does not reach 0.7V. The same phenomenon is repeated for the negative half cycle for PNP transistor. This gap in the output when there is no output from the amplifier is called Dead zone. This problem can be solved by using diodes to conduct instead of the transistors when the circuit is in the dead zone. This modified amplifier is now given a different name, it is called Class AB amplifier.”
@@FluxCondenser "Each transistor will work for one half of the cycle of the input producing the necessary output. This improves the efficiency of the Class B amplifier many times higher than the Class A amplifier. The conduction angle for this amplifier is 180 degrees, because each transistor works for one half only." I have a doubt about the quality of the source you reference although for practical purposes sufficient. But the details of can be important. As Dave explains but I delve a bit more into it: A fully driven Class A has the same efficiency as a fully driven Class B. It is for small signals that Class B obtains efficiency, which in the case of music, is going to be most of the time. The extreme case is no signal at all. The Class A will be biased to achieve half-voltage on the collector and consequently a continuous power waste of 1/4 maximum power. Class B will be cut off with zero current, voltage and waste at the output. It is interesting to study the schematic of the ICOM IC-705 transceiver. It is single-ended, Class A final amplifier BUT achieves nearly the efficiency of a push-pull Class B by adjusting the bias drive dynamically. At any given moment there's only enough bias to turn on the transistor enough to amplify the positive and negative halves of the input. Small input, small bias. Since the signal is generated in a DSP, it knows in advance that a strong drive is coming and adjusts bias accordingly.
@@thomasmaughan4798 "A fully driven Class A has the same efficiency as a fully driven Class B. It is for small signals that Class B obtains efficiency, which in the case of music, is going to be most of the time. " No. Class A cannot exceed 50% efficiency when theoretical limit of class B is 78%. Efficiency is calculated for max power on sine wave.
@@FluxCondenser You can build class A amp in PP configuration. It won't help with efficiency but will reduce some even harmonics. As well, you can make class B as single ended but only for high frequency selective power stage, where the load is a resonant tank circuit, which will filter out harmonics. You can also polarise a small signal transistor in class B and put LC as a load, but tuned into one of higher harmonics. That way you can have frequency multiplier. But yeah, for audio anything that isn't class A must be push-pull.
Nice video! As a physicist and audio guy i once knew the answers but, approaching 70, it's been a while now. Thanks for the refresher! All the best, Rob in Switzerland
FC, Hi. Just recovered from three weeks of covi*. During which, I found your channel and love all the videos! Truly liked the MC-2105 videos and am hoping that you will post the McIntosh C-22 series of videos! Bought my first Radio Shack Breadboard in 1975 and haven't died from tinkering yet... Looking forward to your next video. Take care.
"So You Think You Know Amps?" Yes. One amp is one coulomb per second. en.wikipedia.org/wiki/Coulomb Oh you mean amplifier! A. NPN on left, PNP on right. B. Class A on the left. Class B (push-pull) on the right. C. Class B, push-pull. biasing diodes shown; could be AB but a true AB should have current limiting resistors perhaps in the emitter to prevent thermal runaway. D? Intermod is non-harmonically related; one sine wave modulates another producing products.
That is probably because at low power levels your amp is working in class A but switches automatically to class AB at higher power. A lot of modern amps are built that way very few pure A class amps are still on the market. One giveaway is the power rating of the amp compared to its heft. If it claims up to say 20-25 W per channel is not going to be that heavy (but you're going to feel it), above that, an A class will be seriously heavy simply because of the power requirements, which means a huge transformer hence heft. If it claims more than that but feels light, it is definitely going in class AB at higher power levels.
