Electronics > Beginners
TL071 distortion - bad amplifier design?
AngraMelo:
That solid tantulan is 2.2uf or 220uf? Did you see my message?
spec:
--- Quote from: AngraMelo on December 11, 2018, 01:38:00 am ---That solid tantulan is 2.2uf or 220uf? Did you see my message?
--- End quote ---
220uF if you want a really low solid base. 100uF would be very good and 22uF would knock off some of the very low bass. You can make the choice quite freely and you may find that 2u2F suits your room/speakers/sound source/personal preference
Of course, you can go really high-end (low distortion and frequency response down to DC ) and do away with the capacitor altogether: just replace it with a short circuit.The consequence would be a worst case DC current of 42mA through your speakers, but that would not worry your speakers in the slightest.
The overall frequency response of the amplifier would be a single unit slope defined only by the input polypropylene capacitor and the opamp input bias resistor. This would give a beautiful open, rolling base with the right speakers.
And if you changed the opamp for ...
Will look at your message now.
AngraMelo:
awesome! I will try different capacitors and check out the sound!
What is the op amp you were saying??? you got me curious!
spec:
--- Quote from: AngraMelo on December 11, 2018, 05:16:27 am ---awesome! I will try different capacitors and check out the sound!
What is the op amp you were saying??? you got me curious!
--- End quote ---
Will post in about 10 hours.
Note the revised schematic in reply #44
Once this amplifier is working OK what do you want to do with it?
[1] Keep as is which will be a good quality audio amplifier with a sweet smooth sound
[2] More definition, lower distortion, more articulation, more impact (opamp change mainly)
[3] Maximum fidelity for this architecture (opamp change, component changes, and physical layout changes)
By the way, I meant to say before, all resistors, except perhaps the two 0R22 resistors, must be metal film types. A future modification will possibly include changing the 0R22 resistors for 0R1 low inductance resistors.
Mark Hennessy:
Just as a side-note, it's worth saying that there is a lot of confusion about amplifier class. Putting aside class A and just considering B and AB, Douglas Self shows that actually, class B is the ideal mode of operation.
Class B means that each device handles exactly half (180 degrees) of the signal. When there is crossover distortion, then the devices are carrying less than 180 degrees; hence the amplifier is in class C mode, not class B.
The other case - when the bias is increased and the devices overlap to handle more of the signal - is class AB. In an otherwise blameless amplifier, a class AB amplifier will have slightly more distortion than a perfectly biased class B amplifier because of gm-doubling.
All explained in the book: https://www.amazon.co.uk/Audio-Power-Amplifier-Design-Douglas/dp/0240526139 - PDF versions of older editions are easily found on-line, but I'd always recommend buying a copy of the latest. The books are based on his series of articles published in Wireless World back in 1993.
The difficulty in a practical amplifier is holding that exact bias point for class B operation under all circumstances, which is why most manufacturers play it safe by increasing the bias to put the amp into class AB, which is better than risk leaving it on the edge and risk having it fall into class C under certain circumstances. The book talks a lot about schemes to improve the thermal tracking so that this ideal point can be better maintained - it's really quite fascinating. Obviously, all this is well below what is audible, but it's intellectually satisfying to chase and minimise real distortion mechanism where easy and cheap to do so.
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