The last circuit shown is a well known audio amplifier circuit.
The circuit with an OP at the input could work as well. However it is not the really easy way for high power: One would need a power stage with additional voltage gain. It needs some attention to make the two gain parts to work together. The simple 1 pole compensation is usually no more suitable as this would need only one slow stage. Compared to many of the normal OPs the simple transistor longtail pair is also relatively fast and allows thus for good overall speed. The use of inner loops with local feedback is kind of controversial - not everybody likes it. Well done, the concept with OP for the input and discrete power stage can work. Though the general concept may look simple, I consider the classical amplifier with discrete transistors easier.
However the TL07x are relatively high noise and might thus produce some noticeable hiss.
I also see a slight problem with an electrolytic capacitor with no DC bias and possible slight ( 10s of mV) reverse bias from an offset. In addition to possible distortion, there might be an issue with durability. The oxide layer will slowly get thinner and the distortion might only show up after longer use.
I also see a slight problem with an electrolytic capacitor with no DC bias and possible slight ( 10s of mV) reverse bias from an offset. In addition to possible distortion, there might be an issue with durability. The oxide layer will slowly get thinner and the distortion might only show up after longer use.
There are a couple of errors in the annotations:
Constant current generator #2 should be current mirror.
The voltage to current converter, is mislabeled.
A voltage to current converter would be a transconductance amplifier i.e. voltage in, current proportional to the input voltage out. It's really a unity gain buffer or current booster circuit i.e. input voltage = output voltage, with a high input impedance and low output impedance.
I'm aware that the poster knows this and has just worded it poorly.
AngraMelo
What are your plans now? I suggest at this stage that the way forward is:
[1] Correct/develop the TL071 amp and get it performing as well as possible to the latest mod standard that I posted.
[2] Build a Self Simple Blameless Amplifier (SSBA).
In regard to the actual build of the SSBA you have a few options:
[1] Knife and fork
[2] Your own PCB layout
[3] Stock PCB
[4] Stock SSBA kit
[5] Ready built SSBA
[1] By hand wiring using copper/brass strip/wire for the relevant signal paths, you can make a superb SSBA, but it would be a load of work and development
[2] Like [1] above you could produce a superb board, but once again it would involve much work and development. And then you have to have the PCB manufactured.
[3] Last time I looked there were a load of SSBA (or similar) boards on the market.
[4] As [3]
[5] As [3]
I would recommend [5] from a practical point of view, but as you have said that you are in this for the experience, rather than to just have an amplifier, so perhaps [3] or [4] would suit.
By the way you have already got eminently suitable output transistors, or would you like to buy another pair of output transistors for the SSBA?
AngraMelo
What are your plans now? I suggest at this stage that the way forward is:
[1] Correct/develop the TL071 amp and get it performing as well as possible to the latest mod standard that I posted.
[2] Build a Self Simple Blameless Amplifier (SSBA).
In regard to the actual build of the SSBA you have a few options:
[1] Knife and fork
[2] Your own PCB layout
[3] Stock PCB
[4] Stock SSBA kit
[5] Ready built SSBA
[1] By hand wiring using copper/brass strip/wire for the relevant signal paths, you can make a superb SSBA, but it would be a load of work and development
[2] Like [1] above you could produce a superb board, but once again it would involve much work and development. And then you have to have the PCB manufactured.
[3] Last time I looked there were a load of SSBA (or similar) boards on the market.
[4] As [3]
[5] As [3]
I would recommend [5] from a practical point of view, but as you have said that you are in this for the experience, rather than to just have an amplifier, so perhaps [3] or [4] would suit.
By the way you have already got eminently suitable output transistors, or would you like to buy another pair of output transistors for the SSBA?
I would like to go for option one!! As I friends says: aim on Mars to hit the Moon! hahahaha
I know it will be a pain in the butt but hey, Im here for the ride! If it proves a challenge to far away from my paygrade lets try option 3/4
Ill send an email to the Signal Transfer Company and see about the shipping fees, they appear to be a Licensed dealer of the boards, if they are not please let me know so I can look for someone who can actually sell them.
They are a bit pricy when doind the currency exchange (around double what I pay for my electrical bill per board not including shipping), so if I could etch them myself it would be awesome!
Also, lets to the TL071!!
Constant current generator #2 should be current mirror.That would be like calling the the input stage a long tailed pair- not very helpful or informative.
That arrangement of Q10 and Q11 has two functions, which if possible, will be explained. Just a clue: a current mirror is a constant current generator.A voltage to current converter would be a transconductance amplifier i.e. voltage in, current proportional to the input voltage out. It's really a unity gain buffer or current booster circuit i.e. input voltage = output voltage, with a high input impedance and low output impedance.Incorrect, the output transistor pairs convert an input voltage from the VAS to a current to drive the speaker (V/R).
It is difficult to chose titles for circuit functions, but Current Booster, gives totally the wrong message.
'unity gain current booster' that is a contradiction in terms.
There is not very much more to say to the SSBA circuit, after the corrected annotations. A simple current limitation for protection might be a good idea and could be done with little effort in the standard way.
For the OP based circuit , the simple local feedback version shown by Hero999 could be a good idea for less cross over distortion.
To reduce the problem that the current in the extra voltage amplification stage depends on the supply voltage, one could add diodes in series to R7/ R8 and make those resistors a little smaller. The transistor / diode combination would than be simplified current mirrors.
There would be still some supply dependence, but less (maybe half or a third).
The more radical way would be to have one side a fixed current source and only use the OP to drive one side. Power supply suppression would still be a problem. A transistor in base configuration could help to transfer the signal as a current from ground references (at the OP) to supply referenced for Q5 or Q6.
........QuoteThe more radical way would be to have one side a fixed current source and only use the OP to drive one side. Power supply suppression would still be a problem. A transistor in base configuration could help to transfer the signal as a current from ground references (at the OP) to supply referenced for Q5 or Q6.Similar to what speck proposed earlier on in the thread?
https://www.eevblog.com/forum/beginners/tl071-distortion-bad-amplifier-design/msg2030107/#msg2030107
[...]
Similar to what speck proposed earlier on in the thread?
https://www.eevblog.com/forum/beginners/tl071-distortion-bad-amplifier-design/msg2030107/#msg2030107
[...]
Similar to what speck proposed earlier on in the thread?
https://www.eevblog.com/forum/beginners/tl071-distortion-bad-amplifier-design/msg2030107/#msg2030107
who is speck ?
According to wikipedia you are probably hungry...
His nickname is spec, no K
........QuoteThe more radical way would be to have one side a fixed current source and only use the OP to drive one side. Power supply suppression would still be a problem. A transistor in base configuration could help to transfer the signal as a current from ground references (at the OP) to supply referenced for Q5 or Q6.Similar to what speck proposed earlier on in the thread?
https://www.eevblog.com/forum/beginners/tl071-distortion-bad-amplifier-design/msg2030107/#msg2030107Yes exactly that kind of circuit I was thinking of. Somehow forgot it was already in this thread.
AngraMelo
What are your plans now? I suggest at this stage that the way forward is:
[1] Correct/develop the TL071 amp and get it performing as well as possible to the latest mod standard that I posted.
[2] Build a Self Simple Blameless Amplifier (SSBA).
In regard to the actual build of the SSBA you have a few options:
[1] Knife and fork
[2] Your own PCB layout
[3] Stock PCB
[4] Stock SSBA kit
[5] Ready built SSBA
[1] By hand wiring using copper/brass strip/wire for the relevant signal paths, you can make a superb SSBA, but it would be a load of work and development
[2] Like [1] above you could produce a superb board, but once again it would involve much work and development. And then you have to have the PCB manufactured.
[3] Last time I looked there were a load of SSBA (or similar) boards on the market.
[4] As [3]
[5] As [3]
I would recommend [5] from a practical point of view, but as you have said that you are in this for the experience, rather than to just have an amplifier, so perhaps [3] or [4] would suit.
By the way you have already got eminently suitable output transistors, or would you like to buy another pair of output transistors for the SSBA?
I would like to go for option one!! As I friends says: aim on Mars to hit the Moon! hahahaha
I know it will be a pain in the butt but hey, Im here for the ride! If it proves a challenge to far away from my paygrade lets try option 3/4
Ill send an email to the Signal Transfer Company and see about the shipping fees, they appear to be a Licensed dealer of the boards, if they are not please let me know so I can look for someone who can actually sell them.
They are a bit pricy when doind the currency exchange (around double what I pay for my electrical bill per board not including shipping), so if I could etch them myself it would be awesome!
Also, lets to the TL071!!
........
It should work well with local feedback. I haven't simulated the original version, but my gut feeling is it will oscillate and be difficult to stabilise, as it has a huge gain, on the order of 20k. Local feedback sorts that out.
The SSBA is a good design and is ideal for the beginner as it allows one to see how it works. Performance wise, I'm not convinced it'll be any better or worse than an op-amp+discreet power stage (I'm talking about a better design than the TL071 posted here of course) but that doesn't matter. The main advantage of a discrete op-amp, which is what the SSBA is, it's transparent i.e. the builder, who can probe and measure every single point in the circuit. An IC op-amp is just a black box, with no way to see what's going on inside.
after the corrected annotations.