It may not be efficient but how does it sound? Watch and find out. Patreon www.patreon.co... Mail: PO box 362, Vandalia, OH 45377 Email: johnaudiotech@gmail.com Thank You!
Many "hi end" audio brands sell PURE CLASS A amplifiers. Yes, they afre like stoves, pretty inneficient, but they will never suffer from crossover distortion or unmatched transistors on each half wave. Old tube amp in single ende config using a transformer as a load (as well as DC polarization) were pure class A.
I'd swap the current sourcing resistor for a choke. Should help with efficiency a lot. Also will improve the output power (it will double the available voltage swing).
The old car radios used that technique. Paired with a 6 Ohm 6X9 speaker, those radios were loud! They used PNP germanium transistors, so the coil went to ground, and the amplifier was positive ground referenced. That's why they ran hot, because the bias current had to be high enough, for the impedance of the speaker, and at 0 signal, the transistor had nearly the full 12~13 volts across it at ~2.5 amps. That gave a full 24 volt swing(+,-12v) available to the speaker. The large round base (TO36 case style)transistors were mounted on a very large heatsink, which usually got hot. The heat sink had to be big enough, for the transistor dissipating ~30 watts, to stay below 80°C, on a hot day. Germanium transistors have a much lower junction temperature rating,(85°C) than modern Silicon transistors.(usually 150°C) The germanium transistors were in bigger packages, mounted on bigger heatsinks, because they had less temperature swing, than silicon. Those early Class "A" output stages were used in the first radios, to replace tube radios, back in the late '60's. They indeed used a choke, instead of a load resistor, for just the reasons you mention. One transistor could produce the same amplitude, as 4 transistors in a push-pull H-bridge configuration, which replaced the class "A" design, to save power, and allow a much smaller heatsink. A stereo class "A" would draw more power than the headlights! The output stages would put about 12 watts RMS into a 6 Ohm speaker, with the engine running.(about 13.5 volts across the transistor)
@@vincentrobinette1507 Interesting tidbit of history :-) I was inspired by the typical tube class A, but because a transistor can have such low impedance we dont need to use a transformer (or in other words two tightly coupled inductors), we can just use an inductor and couple capacitively ;-)
@@akkudakkupl By replacing R1 in this schematic with a heavy inductor coil, the DC resistance of the inductor coil was low enough, that the speaker can be connected in parallel with the inductor, no output capacitor necessary. The
At the risk of adding complexity, I think the John Linsley Hood class A amp is worth trying where an active load is used in place of the resistor. Nelson Pass made some very favourable comments on this and added some interesting variations to that "1969" design.
This is a lab amp and is a good example of how simple a power amp is but you do need a strong output to handle that much current and not over heat it would have been good the tactics to have you schematic turn brown shaped like the heat sink
Thanku very much, actually in RU-vid there are two extremes very high level practical or very high level theory thankyou for the balance for biginers keppem coming sir
@John, Thanks for the great video. It is always fun to follow your channel. I have tried the circuit on LTSpice based on the model from On-Semi and managed to get similar result, of course, after many tries and errors to use the model correctly. And I have tried the actual circuit on breadboard too, it works!
Great tutorial. I've been driving myself nuts trying to work out how to make a small practice guitar amp with this circuit. I can plug an iPhone or some other headphone-level source into it and it works, but with a guitar (and a few different amp designs) I either get nothing, low signal, or crazy distortion. Is there a simple buffer or pre-amp circuit that can bolt onto the front of a design like this?
You should make a 2.1 version of this amplifier but with more power, more transistors a heat sink bigger and a cooler fan. I have a power supply of 15V/6A.
I'm curious, have you tried to validate your spice transistor model with the characteristics of the actual transistor in your circuit? With such a simple circuit it could be instructive to confront simulation and actual measurements.
Interesting as usual. But I could not understand how R6 works and the reason why it's there. Should be happy if you'd spend a few words on that. Thanks for the good work.
Could you do a video on Line level and if there's any standards for that. Maybe some comparisons using preamp music device as an example. Love you videos especially when you do your own amps. Also maybe you could explain how record players connect and why they need ground and how to build that into you amps or preamp
Thanks for sharing the video. Interesting and nice how it sounds. It sounds quite well, although maybe it is not very efficient, but it sounds great. Would it sound good with a guitar? I wonder how it would perform. Maybe another transistor is needed to rise the guitar signal level to line level...
Dear John , i constructed the amp . It has a very good sound and it is playing even without a pre-amp. I connected a small tube pre amplifier ,that its more a buffer , and i am very pleased with the result. Although the R1 resistor is heating up very high . I would be gratefull if you give me an advise about that. For the time being the amp is provided with power from a bench power suply. I am thinking of using a ATX (pc power suply) in 12 volts, unfortunately because i dont have a 15 volts transformer. What do you think about that? I am thanking you for your uploads and i am waiting for your reply . Greetings from Greece Athens
Well, it's sad that our 1 year journey with the other amplifier just ended in a pile of boards. I was expecting you would make a nice case, put it in and then on your desk where you would enjoy using it.
JohnAudioTech sir john you have 1 cap that is not in the schematic can you tell me what value it is? And where is conected?in the schematic are 2 caps but on bredboard 3 thank you
Hi John, can you please share the BDX33B.lib file, probably via Google drive or other means, I want to try the simulation but couldn't find the transistor model, appreciate for your help. I have tried the model from OnSemi, but the result is totally different. In addition, the BF=123.448 is much smaller than the datasheet which claims hFE=2500, I'm confused with those values.
I can confirm that with On's model Vce is at 14v. And the output is neglible. It's a long shot from what is measured on the bench. Either reality is broken or there is something really wrong in the model. And the bdx33b is not on Cordell's model page.
@@copernicofelinis Yeah, my simulation showed 14.135V at Vc and 106.6mA for Ic Another thing I found weird was that current drawn in the video showed 1.25A, if multiplied with the 5W 8 ohm, it would dissipate 10W and I'm not sure if the resistor can withstand it for minutes...
@@copernicofelinis My bad, last night I tried this again and managed to get the simulation worked. The simulation and real circuit have slightly difference in voltages at various points but good enough to come out 1 watt clean output as demonstrated by John. Great work from John, I have to say this again.
@@apang9999 did you use a different model? Because with the model supplied by On and with the values used by John, it doesn't output anything relevant. If I change BF to 2400 and almost all resistors' values I can get more than 1W with about 6Vpp, but distortion is 5.7%. The point is that I have to change everything in the circuit.
John thanks but practically this has a lot of power loss and heat generation. What’s the solution ? Which class power amplifier works more efficient? Does an op-amp helps? How?
hi John. How was the ajustment of R3 afterall? I am planning to build this amp and use it with a small tube preamp i m having .My basic problem is that i nave not an oscilloscope .I am amateur as you see. waiting for your reply
Cool, but until you showed the preamp feeding the signal to the base of transistor I was wondering how the heck you were creating so much sound from the speakers. I like playing with and experimenting with 1 transistor amps and have not done so for a while. I found in general expecting much more than 1/2 to 1 watt was pretty much wishful thinking and I was wondering if you have or could dream up a simple amp that really pushed the limit. If so I'd sure like to see the video.
I’m having so much trouble with amplifiers. My resistor values are never right, it’s always super quiet. I don’t understand what I’m doing wrong. Asking for a friend.
Hi! I want to make a small powered speaker for my C64 PC and have an old LM 384 5W IC amp available... can you do a video on a good circuit for that? Thanks!
Edited to avoid confusion. Yes, with some very minor alteration. In fact it gets even simpler with FETs and they can sound quite amazing too. If you want a very simple super hifi amplifier use a double triode for voltage gain (and stereo) and choose a simple FET output stage (either push pull or single ended like this one) and depending on the power supply voltages chosen and your output topography you can get as many watts as you want with excellent quality and very low component count, maybe ten or so parts per channel plus power supply - in fact shared components make a stereo version have less components per channel count. Edit No, not a stupid question at all.
@@martinda7446 You need feedback for a mosfet, as mosfets are voltage controlled current sources. The output would be heavily distorted as the voltage doesn't correlate linearly with the current.
Got a question here, the circuit is very much similar to a standard common emitter circuit, however, I found the R1 is in different location, isn't it that R4 should be connected to Vcc?
Jack, R4 is connected that way to stabilize the bias. It's a sort of feedback. Iirc it's called self-bias and it is not that much different from the feedback realized by emitter degeneration.
Personal experience with many years of SPICE modeling - always gets you “in the ballpark”, never gets you a “grand slam homer”. You still need to prototype, and tweak. But, SPICE gives you a good starting point. Regarding your comment about harmonic distortion, here is a good guide: 0.1% - no human can detect this level in music or speech. 1.0 % - a professional musician might hear it, if they are familiar with the piece being played. 3.0 % - people with “golden ears” will start to hear it. 5.0 % - most people will notice it. 10% - sounds like crap. Clipping, regardless of THD, hurts your ears to hear it.
Bob Pease used to say the soldering iron was his simulator, yeah. But here the simulation shows 100 mA while the measurement screams 1.2 amps. That's not in the same ballpark at all. It's in a different stadium in another state. Something is wrong with On's model. That's why it would be nice to see John's model.
@@davekazoroski6548 yes, but John is using a different model for the BJT. I believe it would be instructive to confront it with the model downloadable from the manufacturer's website. With the latter model Vce is 14 V and the current is 110 mA. Edit: did I just happen to have read your comment the second you've posted it?
DC in a speaker will cause the cone to shift away from it's mid-position, which can introduce distortion. Too much DC voltage will cause the voice coil to burn up.
Otherwise you will blow the coil or if you dont reach this point you will heat the coil for no reason putting stress into the speaker. DC is like NO-NO for a speaker
