Electronics > Beginners
TL071 distortion - bad amplifier design?
AngraMelo:
New 47uF capacitors are a success. Much better sound and no more noise at lower volumes.
Now to try the BC337.
Oh man, Im so freaking happy.
David Hess:
--- Quote from: Kleinstein on December 10, 2018, 04:19:24 pm ---The circuit is problematic: There is quite some gain inside the loop of the TL071. This requires quite some extra capacitors for the compensation to slow it down.
--- End quote ---
It is not quite dire. The extra voltage gain inside the loop is attenuated by the feedback network before reaching the non-inverting input. Indeed, if there was no extra voltage gain, then the operational amplifier would be overcompensated.
But I agree there are better configurations which use local feedback to control the gain added by the output stage. Below is the example I was thinking off where local feedback is applied to the *output* of the operational amplifier which becomes an input. How weird is that?
spec:
--- Quote from: AngraMelo on December 10, 2018, 09:10:59 pm ---New 47uF capacitors are a success. Much better sound and no more noise at lower volumes.
Now to try the BC337.
Oh man, Im so freaking happy.
--- End quote ---
:) Great news- it is nice when theory and practice match.
AngraMelo:
I sent you a message inbox!
spec:
CROSSED POSTS
UPDATE #1 2018_12_11 (two resistor values changed on amplifier schematic)
UPDATE #2 2018_12_11 (BC556 transistor added to better controlled constant current)
Attached below is the amplifier circuit fully worked over, but some detailed components have been omitted, like decoupling capacitors and padding resistors, for example. You will notice that there are no 47uF capacitors, but an extra transistor has been added. This transistor has no voltage or current gain and mainly functions as a level shifter. It has two other functions which I can describe if you want to know.
You will also notice that the supply rails have been reduced to 23V and -23V.
The reason for this is that, while looking at the transistor datasheets I noticed the following:
2SC5200: 230VCE
2SA1043: 230VCE
TIP41 : 60VCE
TIP42 : 60VCE
A1015 : 50VCE
C1815 : 50VCE
The two output transistors are Toshiba beauties and, obviously have no problem with +-40V supply lines, but I haven't checked the other parameters. I presume you are using 8 Ohm speakers.
The other transistors are only average in terms audio amplifiers and they limit the supply line voltage.
But, as you say that the amp is working OK with +-40V supply lines, that means that your particular transistors probably have a high enough VCE rating, so you can continue testing at risk with +40 and -40 supply lines.
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