Electronics > Beginners
Adding filters to class AB audio amp
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d4n13l:
Hi,

I picked up the attached amp from internet and made small modifications, I think it works nicely for audio but is still missing some filtering which I'm still not clear how it works. I tested the circuit as is, except by R4 and C7 which is how I've seen some filters implemented by I'm not sure how it works since the filters I've found on literature take the output from between R4 and C7, they don't put it in parallel with the output as you see here.  Also is C2 making a filter R1 or with the rest of the circuit?

Basically I'd appreciate notes on how to add high and low pass filtering here.
ledtester:
I am not an audio guru, but I would place any filters before the final amplification stage which is what the TL084 is doing.

Are the 3 other op amps in the TL084 being used?  If not you could use some of them to create active low/high pass filters. This page has pretty good info on the main types of filters used in electronics:

https://www.electronics-tutorials.ws/category/filter

See the page on "Active Band Pass Filter" for an example of how filter and amplifier stages are chained together.

wraper:
First of all this is not AB but B class amplifier. Secondly, it not a filter on the output but snubber to improve stability of amplifier.
Zero999:
That circuit is class B, not class AB, and will have some crossover distortion, so is not optimal for audio.
https://www.google.com/search?client=firefox-b-d&q=class+b+crossover+distortion

R4 and C7 form a Zobel network.
https://www.google.com/search?client=firefox-b-d&q=Zobel+network

C2 is an AC coupling capacitor, which enables the audio signal to pass through to the input of the amplifier, whilst blocking DC. Removing it will upset the biasing of the circuit, so its output will saturate close to the positive rail, instead of sitting between both supply rails.
https://www.google.com/search?client=firefox-b-d&q=AC+coupling+capacitor
wraper:

--- Quote ---Also is C2 making a filter R1 or with the rest of the circuit?
--- End quote ---
Filter consists from impedance of signal source, VR1, C2, R1. It's not good at all because it's parameters depend on signal source and VR1 position,
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