Electronics > Beginners
TL071 distortion - bad amplifier design?
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AngraMelo:
That is great Spec!
That is exactly what Im looking for, im ordering the capacitors and preparing a board for the new transistors. It will be awesome!
Ill let you know of the performance and measurements I get here.
spec:

--- Quote from: AngraMelo on December 11, 2018, 10:28:14 pm ---That is great Spec!
That is exactly what Im looking for, im ordering the capacitors and preparing a board for the new transistors. It will be awesome!
Ill let you know of the performance and measurements I get here.

--- End quote ---
Glad that you like that approach because, I think it will give the best progress.

By the way, did you set up the quiescent current Iq OK?
spec:

--- Quote from: AngraMelo on December 11, 2018, 10:28:14 pm ---[I am] preparing a board for the new transistors. It will be awesome!
--- End quote ---
Can I just say this to you. The physical layout of practically all circuits has a geat impact on their performance, and with high end audio amplifiers more so.

If you look at the schematic of reply #44 you will notice that I have changed the supply line and 0V connections to indicate how they should be physically implemented. Also the reply #44 schematic is only an outline and needs a few more components: decoupling capacitors for example.

So may I suggest that you hold the board layout and I will produce a full schematic for you to work from. The schematic will look a bit weird, but don't let that put you off. When the schematic is posted we can then discuss the board layout.

Just to illustrate how important simple things are with audio amps, you can take the most stable and best sounding amp ever and just by changing a couple of 0V connections, turn it into a temperamental distorting monster.

Apart from the OV line, which is crucial, remember that a class A/B amp is inherently distorting and, as a consequence, the output transistors take huge gulps of current from the supply line for 180 degrees of the signal and no current for the next 180 degrees. And, due to various effects, this current is a rather distorted half sine wave.

Wires and PCB traces are not perfect conductors and have resistance, so the distorted half sine wave current gulps produce a corresponding distorted voltage waveform on the supply lines. It only takes a whiff of that voltage to get induced into the amp circuitry to cause high levels of distortion.
AngraMelo:
I just got home so I didnt have time to change de resistor and pot. I will do that tonight.
I have no education about pcb layout so any help would be greatly appreciated!!
spec:

--- Quote from: AngraMelo on December 11, 2018, 11:17:46 pm ---I just got home so I didn't have time to change de resistor and pot. I will do that tonight.
--- End quote ---
No sweat. By the way most small signal BJTs will be suitable for the Iq setting transistor, including BC337 family, BC546 family, BC182 family, BC107 family, etc The transistor only needs a VCE of 10V  minimum.


--- Quote from: AngraMelo on December 11, 2018, 11:17:46 pm ---
I have no education about pcb layout so any help would be greatly appreciated!!
--- End quote ---
This is the most important and difficult area. The best way forward is to take a look at some PC layouts that are already done for high end amplifiers and the schematic I mentioned previously should be a help.
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