thanks.. ill look it up in the lib.. or try to find it domestically..Order this book. $2.50US is a bargain (you'll pay more for shipping) There is a great treatment of feedback, as well as alot of great information on amplifiers. Many of us used this as a text in our university studies. I still use mine for reference, 15 years later...
pls. enlighten me about this.. all i know is that i have to compute for the thevenin equivalent of the biasing network then compute accordingly to get the wanted base voltage bias.. i dont know about the currents...Your transistors have a fairly high collector-emitter current but a current that is too small in the divider that biases them. Then the transistors with low current gain will not have enough base current and temperature changes will also affect them.
It is still AC-coupled. Good modern amplifiers are DC-coupled.I'm here again.. I already figured out how to employ negative feedback in my ckt. my ckt is doing well in simulation but not so good in actual testing.
The little 9V battery is old and has a fairly high internal resistance. The fairly high supply current of the amplifier causes the 9V to drop (because of the voltage loss in the internal resistance of the battery) and produces ripple. A big capacitor across the battery is a filter and smoothes out the ripple.1.) Cap C7 (9v to ground). When I tried to make this 1000uF, the voltage in the voltage source went down. I immediately turned it off. It was about ~7V. Its supposed to dampen the ripples in the source right? Not only that, when I increased C7 from 100uf to 200uf, the gain at the output got a little bigger. That's why i tried to make it even fatter(1000uF). Can anyone tell me why is this happening?
Your Q3 has a very high gain. It is amplifying temperature differences. The old battery voltage also drops after a few seconds and Q3 is also amplifying the difference. But the other transistors have very low gain. Spread out the gain at each transistor so that one does not amplify temperature and supply voltage changes as much. If the circuit is DC-coupled then temperature and supply voltage changes will have a very small effect because the negative feedback will cancel them. Since your circuit is AC-coupled then it has no DC negative feedback.2.) The output was REALLY DISTORTED. But after about 15 to 20 seconds, the output slightly smoothens out. What really bothers me is that when i adjusted bias resistors R13 and R14 (i momentarily turn them to minimum then turn them up again) the distortion before just vanishes.
Pots are a very poor way to bias the output transistors. If you used a Vbe-multiplier transistor instead of the diodes and DC-coupling like most amplifiers then there would not be a problem.3.) minor thing: the 2n2222A and 2n2907A i use are in the round metal casings. the 2n2222A looks pristine, the 2n2907 is like.... burnt... at first it was a little yellowish. now its more brown than yellow. do you think the 2n2907a is hogging most of the current? i suspect that this has something to do with the potentiometer biasing i made, sometimes the biasing just go too low, or too high.. btw, 2 burned the first 2n2907.. i tried biasing with 100k pots at that time. i dont know what happend, but the 2n2222A was still intact.
When R9 and R10 are each 200k, the current in them is only 22.5uA. The base current in Q3 is 12.5uA to 37.7uA. The divider current should be 10 times the base current so your resistor values in the divider are way too high so the hFE of the transistor and the temperature affect the biasing very much.4.) In SIMULATION: if R9 is lower than R10 (e.g. R9=33kohms R10= 100Kohms), the output at the collector of Q3 distorted at the upper part. i tried bypassing R10 (i guessed that the AC impedances has something to do with the distortion, i was wrong) but it was still distorted.
The high capacitance of the tracks and wiring on your breadboard reduce high frequency response. The failing battery voltage probably causes the gain to slowly drop. Use a brand new name-brand 9V alkaline battery, or a regulated 9V power supply.5.) in SIMULATION of the ACTUAL CKT: the frequency response tells me that f>1kHz has a pretty stable gain, in reality, it has not.
An 8 ohm speaker is 8 ohms at very low frequencies and at a few frequencies above its resonant frequency. At resonance it is about 60 ohms and since a speaker is inductive then its impedance rises at high frequencies and at 20kHz is as high as 400 ohms.Can anyone tell me where to get a more precise model of a speaker? the 8ohm resistance just can model it.
i forgot to tell that i am not using a battery,its a power supply, loadstar.The little 9V battery is old and has a fairly high internal resistance. The fairly high supply current of the amplifier causes the 9V to drop (because of the voltage loss in the internal resistance of the battery) and produces ripple. A big capacitor across the battery is a filter and smoothes out the ripple.
Of course it is distorted, it is a very simple circuit.i tried this on simulation, it is awfully distorted... how is that?
Of course it is distorted, it is a very simple circuit.
The 1k resistor that applies base current to the 2N2222 output transistor does not supply enough current when the output swings high. Increasing the current by reducing the value of the 1k resistor will reduce the voltage gain that is already very low. So, I added a resistor in series with the 1k resistor and added a bootstrapping capacitor so that the base current for the 2N2222 transistor stays constant as the output swings high. I also biased the circuit a little better by increasing the value of the 3.3k resistor. Now the distortion is reduced and the voltage gain is increased.
No.Can you make the ciruit that you have there louder without making a lot of distortion?
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