Electronics > Beginners
TL071 distortion - bad amplifier design?
AngraMelo:
I will do that. It has been an incredible journey learning electronics.
Sometimes I feel that everyday is a kick in the butt given that the content is so extent.
Slowly Im getting the hang of it!
spec:
--- Quote from: AngraMelo on December 12, 2018, 12:07:54 am ---I will do that. It has been an incredible journey learning electronics.
Sometimes I feel that everyday is a kick in the butt given that the content is so extent.
Slowly Im getting the hang of it!
--- End quote ---
I think everybody feels like that as a newbee- I certainly did. One of the most important things is getting familiar with the basics: essential math, Ohms law, and Kirchhoff's two laws are the foundation. Then you need good teachers, and good books and videos. But most of all, you need a logical mind and to be able to make mistakes and learn from them.
The trouble is, when you are young there are so many distractions: booze, music, girls, motor bikes, cars...
spec:
I mentioned the importance of the physical layout of audio amplifiers (or any amplifiers for that matter), so attached is the schematic for a simple class A/B audio amplifier I did some years ago. Notice the connections of the power line, 0V line and the decoupling. That is the sort of schematic I will do for the reply#44 audio power amplifier.
Just as important is the layout of the PSU, so I will include a PSU schematic too.
AngraMelo:
Spec, I soldered the resistor and pot correctly nothing I do brings the current between +rail and 5200 Collector above 0ma
Zero999:
The proposed modifications by spec are good: adding a VBE multiplier and a constant current source to make the bias point less dependant on supply voltage variations and only using one common emitter amplifier.
The value of the 220μF capacitor can easily be reduced without affecting the sound quality. The input capacitor is 1μF and the input impedance is 22k, which will dominate the lower cut-off frequency, long before the 1k and 220μF. See the calculations below:
FC = 1/(2πCR)
C = 1μF and R = 22k
FC = 1/(2π*1×10-6*22×103) = 7.2Hz
C = 220μF and R = 1k
FC = 1/(2π*220×10-6*1×103) = 0.72Hz
The 220μF capacitor could be reduced to 22μF. I think the value was chosen due to a calculation error, involving the decimal place, which is very easily done!
And does it have to be solid tantalum? I don't see why aluminium won't do.
To solve the biasing issue, just connect the 22μF capacitor to -15V.
I doubt the input capacitor is that critical, just don't use a ceramic capacitor: anything else should be fine. There are many myths surrounding capacitors and audio some of which are fact, others are fiction, The main issue is ceramic capacitors which can be microphonic and introduce distortion, but all film types such as: polypropylene, polyester and and Polyethylene terephthalate (PET) are good.
Another possibility is to connect two aluminium or tantalum electrolytic capacitors back-to-back, forming a non-polarised capacitor, with half the value of the two capacitors.
For the 1μF capacitor, use two 2.2μF capacitors.
I thought the board was already done? Spec's modifications are good, but will be quite tricky to perform on an existing board. If the board can be redone then great!
--- Quote from: AngraMelo on December 12, 2018, 12:54:50 am ---Spec, I soldered the resistor and pot correctly nothing I do brings the current between +rail and 5200 Collector above 0ma
--- End quote ---
What's the voltage across each of the 100R resistors, when the input is shorted to 0V?
Did you implement all of spec's changes or only some of them?
You need to add the BC546 and other 1k resistor as well as the 1k pot for this to work.
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