Class AB Audio Amplifier
ฝัง
- เผยแพร่เมื่อ 10 ส.ค. 2011
- Another minimal transistor audio amp project. This one is a push pull design with only three transistors. For a great class AB amp tutorial, visit this web page:
www.electronics-tutorials.ws/a... - วิทยาศาสตร์และเทคโนโลยี
Cheers for the video mate, you've literally explained in 7 minutes what 5 months of browsing a forum couldn't teach me.
I'm self taught. I finished high school and no more. :) I learn by studying, reading, doing. :)
Truly amazing!! I made this for my college project and its working perfectly fine... Thank you so much Sir!!
@anceop
The negative output is derived from two sources. The NPN for the positive wave cycles, and the PNP for the negative wave cycles. Since the sum of these two is an ac voltage, a decoupling cap is needed AND it's on the negative side of the circuit therefore it's negative lead goes to ground, and the positive to the load.
I want to thank you for your tutorials; they have saved my career! Thank you so much!
i just built one with 2SC5200 NPN and 2SA5200 PNP transistors, the amplifier it's powerful I almost cracked my ear diaphragm as I was too close to the speaker, thank you ! I also noticed an overheating of the transistors
This is our school project and what a co incidence that i were supposed to design with the same values as you did..thanks sir it's so helpfull for me
You might consider 1Ω resistors between the emitters and the output on each of the output transistors. That way, if the output transistors get hotter than the 1N4148 diodes, the bias current doesn't increase, which could lead to thermal runaway. I like the way you used the speaker and the output capacitors to serve as the bootstrap, rather than adding another resistor and capacitor to serve that purpose. Fewer components, and, more importantly, LESS DISTORTION! I never though about that. I don't see a problem with the 9 milliamp DC bias on the speaker coil, since the I^2R loss is negligible. The only possible caveat is that the output stage MUST be loaded with a low impedance load. This output stage cannot be plugged directly into an auxiliary input of another amplifier, without a low impedance shunt, because it won't pull up the high side transistor on the output stage, through the 1KΩ resistor. On the input, it might be worth while to include an emitter follower and voltage divider, to help the input transistor hold the output more accurately between the supply rails. That way, it would be less susceptible to supply voltage variations, and possibly increase your input impedance. Less distortion yet, but at the expense of some gain.
Those PPI amps are great! I used to install them. I have repaired them and what usualy goes bad are the power transistors.
I remember playing around with a circuit like that in my father's basement, the only difference here is that R1 seems to provide both bias and maybe some AC negative feedback. So far, so good, but I found that if I left it running at more than a trivial power level, both transistors would heat up, run away and burn out. I think a resistor between the emitters, with a bypass cap at each end to avoid lowering the AC gain, put a stop to that.
Great tutorial!
Here are my questions if you have the time for it:
How powerful would this amplifier be in RMS?
And what components would have to be changed to make it more or less powerful.
And lastly, I'm wondering how you figure out how much power you need on the input(5,9,12v?)
@casvanmarcel The opening track is by "Obits" and it's called "Talking To The Dog".
I want to build an audio amp in 2021 and the best videos are at least 9 years old 😂 thank you for that Tutorial!
thats because of the dirt cheap low power amp ic like the 8002 also some are class D like the tc8871 and works with very little extra passive components, for high power there are the irs2092 and you really whant class D because of the efficiency also class D sounds with virtualy no differece and it has more accuracy than analogic class a ab amplifiers.
Witty, educational and it has good music, as usual. Great stuff!
It is a nice and simple design. I did some minor modifications to get it more under control. So I suggest to separate the boot strapping from the output to allow operation of the speaker against ground. I used a bootstrap network of 2 resistors of 270 Ohm and an electrolytic of 220 µF Then I put a 10 kOhm resistor between C2 and the base of Q3 to limit the voltage gain by some feedback. I increased R2 to 150 kOhm to meet the midpoint between ground and operating voltage.
Very nice...people needs that...i will put your link in the diy audio forum ....people do not say..but they need this kind os stuff you're doing...teaching the very basic things for them..... great that..... congratulations!
aaaand you've got a new subscriber, loved the presentation
I made a Class B amplifier that's distortion free, I used an op-amp to drive the output transistors, and connected the feedback resistors to where the transistors emitters are connected so it gives a "corrected" waveform to the transistors to compensate for the cross-over distortion. It works quite well, is very efficient, does not go into thermal runaway and I use to power the speakers at my computer
do you have video aboat that ? I realy want to see it or if you can give me a shematic ?
JOSIP Žlk
I will make a video of that and show the schematics.
JOSIP Žlk
ok, here's the video of the class b amplifier I made th-cam.com/video/5OjTz3SjAXA/w-d-xo.html
you sir deserver at least Thumb Up, if not Subscribe, great job explaining, thank you very much
Great vids! Where you insert at pot into this circuit for volume control?
glad to hear the quintessential chip music on the tech vid.
Could you please tell us how you selected the biasing for these transistors? what sort of DC bias you wanted and why? Also, what is the reason for choosing a "47u"F coupling cap at the input ? (and 10 times that at the op)
Thanks.
What's the use of the third transistor Q3?
Thanks, simple circuit and works great as a guitar headphone amp!
hey Dean, would you make more electronics videos please, something with an amp or just transistors. thanks mike
Helped a lot, thank you!!
Sir, can you teach us how did you compute for the value of r1 and r2. I would like to build this project on a different voltage. Specifically i want to build it with a 5 volt source. I couldnt figure out for the value of R1 and T2. Please help. Tnx i love your video
Love this circuit. I made a few changes though. I changed the 1K resistor to a 470 ohm resistor, changed the 100K resistor to a 180K resistor, and added a 4.7K resistor before the input capacitor
And what changes you get?
Awesome project, thanks! Just finished building one. Two questions: if I wanted to use this to amplify a guitar signal (very low power), is there an easy way to up the gain a bit?
Second, would you mind if I posted a video of my assembly? Giving credit to you for design of course.
I'm interested
great job i made on a year ago works great even at 3volts
newbie question here: what component is he using to connect the audio cable to the circuit?
it works fine with 5 volt. I used 5 volt regulator. and added volume control and low pass filter. my amplifier do amazing bass.
how sir ? can you sent me the schematic diagram ?
Gabriel Bayan
TBM can you send me a schematic?? I want to make this as a school project
i'm sure you forgot the schematic by now so i wont ask
@blueblast88 The next time I do a project with those jacks I'll explain a bit more about them.
How about for stereo of this kind, it would have different power supply? As in diagram, +9v is connected to speaker. So if two channels, is like the other channel coupled to other channel. Or it doesn't produce stereo sounds.
You look like Dr.House, and as cool as Dr. House ! Thanks for the tutorial. How is it possible to improve the amplifier by adding common emitter stage or other stages? I am trying to understand how these different stages work? input, middle and output stage. thanks again.
Do you have any calculations of this circuit, like the gain, bandwith,...?
Thank you!
very nice tutorial. what is the reason of using 47uF capacitor in reverse polarity?
@nyuszifuben23 It's by "Garmisch" and it's called "U Fine". You can find it on free music archive dot org.
Ok. I'm confused. Do your transistors have an odd pinout. It appears your transitors are CBE (left to right) pinout? At 4:45 I can see you have what should be the E of the pre-amp NPN tied to the B of the 3906 (via red jumper) but that's not in your schematic?
Sure, I might be able to help. What are the emitter, base, and collector voltages around all three transistors with respect to the negative terminal of the battery?
Hi, thanks for the video! What if I increase the voltage up to 24 volts, or even 30 volts? Do resistors wattage matter much in case of voltage increase? I build the circuit and hooked my guitar pedalboard (from preamp output) into it driving a 1x12 guitar cab. It sounded amazing, I wonder if I could build a tiny portable poweramp for my rig with little more juice and headroom. As far as I can see in the datasheet these transistors can handle up to 40 volts.
Probably could increase the voltage but you might need heat dissipation.
hey, im reletivley new to schematics but i understood most of this exept for one thing. so at the top of your diagram you have a "+9 V" does that show the positive side of the power source? if so where do you connect the negative side of the power source? thanks.
My grandma doesn't want to pay $3000 for a new pair of hearing aids so I'm using this a pair of those jelly ear buds this project and a clip on microphone, thank you so much!
is there any particular reason you used a 2N3053 / 2N2905A combo instead of the more ubiquitous and much cheaper 2N2222 / 2N2907 duo?
I LOVE THIS
Another good hack! Where can I get the cool radioactive tshirt?
@HackaweekTV Thank you Dino
hey man, can you teach how to make a portable amplifier. I like your tutorials! regards!
I need a hifi audio amplifier circuit with TDA 2030A. And please explain benefit about 12-0-12 and only 12 v supply. Which is the best choice
hi. i have a DENON AVR-391 3D audio reciever for my 5.1 audio system and my centre channel is very very very low and i want to amplify just my centre channel.
what amplifier setup do i use?
WHAT IS WITH THE K1 25 OHM AT THE TOP RIGHT OF THE SCHEMATIC. THAT IS AN ODD VALUE FOR A SPEAKER. I WOULD HOPE THAT THIS AMP WOULD WORK JUST FINE WITH AN 8 OHM SPEAKER. I LOVE YOUR VIDEOS YOU ARE A GREAT TEACHER. AFTER MAKING THE CLASS A AMPLIFIER THAT WORKED SO WELL I WAS SO DELIGHTED AT HOW WELL IT WORKED I BUILD THEM OFTEN NOW. IT WAS SO EASY.THANK YOU!.
Maybe high fidelity old speaker or can be headphone impedance. My headphones have 32 ohms impedance.
Shoudn't there be a short protection on Q1/Q2?
hello I want to make an audio amplifier / booster employing a transistor long-tail pair input stage (BJT or
MOS) and a 250 mW BJT class-AB complementary output stage to drive a 25 Ω earphone
speaker using discreet transistors. Ensure maximum output compliance using a max +6 V
supply rail and a minimum total voltage gain of 20. The amplifier is to be driven by a mobile
phone so input impedance must > 32 Ω to avoid damaging its audio output port.
can it be done with this circuit?
Hey man plz can i use bc144 and bc143 for power transistor and bc 546 for preamp? i have to build it for tomorrow, thx in advance
The baby at the back of the board made me jump
nice video man.. but could you explain.. what input source impedance.. and what output inpedance is... like is it a 8 ohm input and 8 ohm output... how how you can change the parts to achieve other impedances.. thanks man
The input and output source impedances can be calculated quite accurately using the Thevenin theorem and the small signal models of the transistors. See Hybrid-Pi Model:
en.wikipedia.org/wiki/Hybrid-pi_model
The input impedance for this schematic is really small due to the fact that the input is directly connected to the npn base. Knowing that the resistance between the base and the emitter is Vt/Ib where Vt is approximately 25 mV, the input resistance is really small.
On the other hand, the output impedance is quite big, since there is not direct path to either Vcc or the ground. The resistance between the base and collector is approximately r0 which is really big (r0 = Va/Ic where Va is the early effect voltage).
en.wikipedia.org/wiki/Early_effect
It can go from 15V to 150V. So 15V/1mA = 15000 ohms. Because of this, r0 is often neglected when doing approximations.
So yeah, this amplifier circuit is far from ideal, small input impedance and big output impedance. You often want the inverse case when designing complex circuits.
That's a "guessed" operating point. It is better to have a small emitter resistor for Q3 and use a third diode in series to enable to presetting of the bias point more precisely. The gain of the circuit is also more predictable, with a better cross-over distortion figure.
If he adds another diode, he will also have to include emitter follower resistors on Q1 and Q2, or the transistors will be fully on, and would go into thermal runaway. The 2 diodes approximately match the base-emitter junction voltages of the 2 transistors. Emitter followers should be used anyway, because when the transistors are loaded, they will heat up, which lowers their junction voltages. That alone could send the circuit into thermal runaway. Heating the diodes reduces bias current, heating the transistors increases it. There's no practical way to thermal couple the diodes and transistors, to maintain uniform temperatures between them, so emitter followers are the answer.
hi, I´m making this amplifier for a school project, the problem is that my teacher request 3 stages and this only have 2... can you suggest me how can I make this amplifier with 3 stages? thank you
When i built this my pnp transistor would get very hot. I checked my wiring and found out i put the wire going to the emitter on the wrong side of the 470uf cap. However the circuit does not work when i put them on the correct side, but gets very hot and burns out if i put it on the side that works...Any advise?
Hi I'm Andrei and I want to ask you if you can make the Tda8944j amplifier to do it please
Can I use op amp 741 with this circuit
why not move the end of the diode chain to the collector of the bottom transistor has to be the same as the top transistor which should give a better signal as it will become Class A also needs a 10R resistor between the emitter of the top transistor to the collector of the bottom NPN transistor, the feedback comes from the top emitter to the base of the drive transistor via 560K resistor. I saw this version in the service manual for the TECHNICS SUA900 MK II.
The diode chain has to be between the bases of the output transistors. Since the voltage drop of the diodes is approximately the same as the base-emitter junction voltage drop of the transistors, it greatly reduces zero crossing distortion, which you would hear at lower listening levels, or in headphones. The 1K resistor that goes from the base of the high side transistor to the speaker output provides that pull up current to forward bias the transistors. (that's why the speaker is connected to Vcc) By connecting the resistor to the speaker output, it creates a bootstrap circuit, to allow the high side transistor to turn on fully, at high listening levels. This is a highly simplified version, that allows that 1K resistor to serve as bias, negative feedback, and bootstrap all at the same time, while allowing the output capacitor to serve as the boot strap capacitor as well. The TECHNICS design is for a split supply, with no output capacitor. This circuit only works as a single supply, with the speaker referenced to the POSITIVE rail. Best with a regulated supply, or a beefy battery and large capacitor across the supply rails.
@@vincentrobinette1507 you could also goggle for 5W Class A amp similar thing.
THANKS FOR THE VIDEOS
Hello sir can I use this circuit to boost input signal. For amplifire.
It is too late for me to come across your video, is it posible to use 8050-8550 transistors on this schematic?
Sir can i use an 8ohm speaker for this circuit?
You're Amazing! Thanks very much.
Can i use your pre amp with this amp
How can we design a 10 watts audio amplifier using this method ?
Can I use bipolar caps?
what is the R2 for? is it some sort of feedback, or bootstrapping?
It provides pull up current to bias the high side transistor as well as both the functions you mention.
Nice but what if you don't already have PC speakers and you want to make them with little 8 ohms/0.5W speakers and get the signal from RCA outputs of a CD player for example ?
PC speakers you show here already amplify the signal, doesn't it ?
No. They are just speakers in a plastic enclosure.
@@HackaweekTV Oh ok...And what are their specs (ohm, watt) ? You don't talk about it or I didn't listen carefully..
Seems like you just put a potentiometer in series with them ? And again, what value ?
In fact, I only have BC547 and its complement BC557 transistors and have managed to feed a tiny 8 ohms/0.5W speaker.
I give it audio signal from a RCA connector of a DVD player.
I tried a class AB on a breadboard and It works with 2 separate 12 V power supplies (=> +12V and -12V).
I can clearly hear the music but I can't make it loud enough (I think it could be louder) and the transistors are quite hot (I burned one of my fingers but the bjt's are still okay) if I don't put a collector resistor of at least 100 ohms (for both transistors of the push-pull).
I even used 2 pairs of transistors (2 NPN and 2 PNP) simply put in parallel to allow for more current but I don't think it's a proper way of doing things...
Are you sure, that the scematic is correct? Especially the position of the two diodes?
The diodes are correct: Their purpose, is to match the base-emitter voltage of the transistors, so the transistors are lightly biased. That eliminates zero crossing distortion, without drawing enough current to get hot. If the diodes have less voltage drop, the transistors run cooler, but there is distortion at very low listening levels. Depending on the temperature of the room, that voltage drop can be anywhere from .55 volts, to .7 volts per junction. If the transistors and diodes are at the same temperature, there's a "sweet spot" where the transistors draw no current, but, there is no zero crossing distortion. Ideally, the diodes would be thermally coupled to the transistors, so as they heat up from load, so would the diodes. Because that's sometimes impractical, a better solution is to add resistors between the emitters of both output transistors and the output. that way, if the transistors do heat up, the resistors add voltage drop, keeping the output transistors thermally stable.
1N4148 this diode
Schottky tiep?
Hi this is very good what is difference between video amplifier and audio amplifier in equal circuit.thanks
A video amplifier has a wider band frequency response
very cool I really liked it!! how about making an FM TRANSMITTER for music played on an mp3 player!! just trying to get away from paying about $50 dlls for a device that I am pretty sure its easy to do!!
Put a five volt regulator on the nine volt battery and connect the 5V out to your small amp. Easy peasy. LM7805 or LM340-5 should work for you.
how many watts is the speaker
@HackaweekTV If on the circuit diagram where q1 and q2 are (the output transistors) if you put anothe pair identical to them in parrallel with each other, would this mean the amplifier could then be twice as powerful?, could i then increase the voltage to the amplifier and create a larger wattage output amplifier?
So the ampifier you have the diagram would be exactly the same BUT with the addition of the extra x 2 output transistors wired exactly in parallel ( they would NOT be in the darlington configuration) so for example Q1 which is a NPN 2N3053 transistor would have another identical transistor joined to it, so base would go to base, emitter to emitter etc,wired like that and the same for the other Q2 PNP 2N2905A transistor.
I dont know the answer but i presume,it would be able to handle more voltage and current so therefor the voltage to the amplifier could be increased, maybe doubled to create a more powerful amplifier
OR...It would give out exactly the same output in wattage but it would have more head room for overloading and heat dissapation as the 2 devices would now work in harmony and share the load.
What would be the results of doing this, say Hi to Einstein, he's a great dancer :)
ROB FROM UK
Hello could you please tell me what the wattage output of the amp design on the video is? Can't seem to figure it out :( thanks!
expect to not get a reply,im still waiting, but i can sort of answer your question. This is only a tiny amplifier not a large power amplifier,so the collector current on the 2N3904 is around 200mA, and the power supply is 9 Volts....so
Watts = Volts x amps, so 9 volts x 0.2 amps = 1.8 watts max.
The true way to get an exact wattage would be to measure the output voltage of the amplifier then divide that by the impedance of the speaker and times that by the voltage = watts.
This amplifier is more of a project small amplifier, not really a power amplifier as the voltage supply is low and the transistors are not power transistors,i hope this info helps
WATTS = VOLTS X AMPS
Great. Thanks! :)
hi can you email me link to to the tutorials on all the class of amp
Can I use diode 1n4007
Yes
Can it be supplied12v
omg i used this circuit to make a power amp and it work!!!
What is the steady voltage of this amp and resistance?
@@Bisdako2013as far as I remember I made it using Tip41c and Tip42c and 28V but it hummed and the idle current was high. A better version would be with a pnp 1st stage class A preamp emitter feedback and drivers with the outputs (5 transistor amp)
Do the diodes have to be in there, isn't that just to prevent you from switching + and -
they cause the voltage difference that turns on both transistors (hobbyist, so confirm my answer)
Hi! Are you an electrical engineer??????
What university did you go to???? Just wunderin'......
How many watts is that amp?
thanks !
Thanks for watching. More electronics coming up soon.
I've made this exactly according to the drawing, but i only get a buzzing sound from the amp :( i have 2SC3858 as the NPN's, and a 2SA1494 as the PNP, and 18 Volt DC
+Crytek1337 i figured it out, im an idiot!!! the collector and emitter on a pnp transistor is switched compared to a npn transistor, hahahahaha!!! but i have alot of distortion, and im using 36 volts peak to peak
thanks! xx
if i buiold two for stereo can i power them from the same supply?
Yes, that will work
Has anyone told you that you look like Dr. House? With much more hair obviously heheh... GREAT TUTORIAL!!!!! GREAT GREAT GREAT
What is the music at the very start?
How many Giga-Watts ??
What's the music at 1:00? thx
could u send me a jpeg of the schmatic
Love the video can you do something on how to use 3.5mm audio jacks and 1/4" audio jacks i love to screw around with audio but difficult with out the proper knowledge and you may also know me as insaneinventor88 from ustream
Yes.
Very good but amateur enthusiasts may find 25 Ohm Loudspeakers hard to come by.Also has the Zobel Network been left out to reduce cost?
Why is the speaker connected to Vcc not GND !?!
It's connected to the GND via the transistors, thus the transistors controls the amount of power going trough the speaker by varying the resistance at the GND that the speaker sees.
Mtaalas
It's not connected Via the PNP transistor ,this is an AB amp, The lower terminal is connected to both Emitters ,they are the Output , but virtualy this circuit has no REF point , 9volt DC is a BAD Ref point ,because it's going to BIAS it and make things worse !
i asked my self the same thing but fuck it it works :)
If 9v supply is a battery (quiet), then connecting the speaker return to the supply is the same as returning it to GND, both are an AC ground.
It doesn't matter which side ot the supply an ac-coupled speaker is returned to. I'd be asking the question "why no decoupling capacitor on the supply"