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Chip Amps Amplifiers based on integrated circuits

What is class AF power amplifier?
What is class AF power amplifier?
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Old 8th July 2019, 04:21 AM   #1
shovon is offline shovon
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Default What is class AF power amplifier?

Hi folks, I got a question regarding STK4191 amplifier. I made this amplifier with 24-0-24 vac power transformer (400va). The amplifier is rated power is 50x2 watts stereo. I do have another amplifier made with STK4231 MK-2 ic and this one rated power 100X2 watts stereo and I have used 400va 34-0-34 vac transformer. Both are sounds really very nice and clean and has decent amount of clear bass. I think these are cleaner than my class D tda8954th by sounds quality but tda bass really more and massive bass power than STK4191&stk4231MK-2. Questions are is these stk amplifiers are bridgeable? If so how am I supposed to do so? I have watched a video in YouTube how to bridge stk4141 but when I applied it to my stk4191 it doesn't work in bridge mode, probably I'm using different pcb than the other one that I saw in the YouTube. I googled it and saw the datasheet of stk's ICs it says these STKs are AF power. What is actually AF power meaning? Is AF meaning These are class A amplifier? These stk ICs are produce too much heat and required really big heatsink. I know this section is for class D and i'm apologize to post something else in here but I couldn't see any class A or class AF section in here. Please guys your reply and advise will be appreciated. Thanks for reading the post
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Old 8th July 2019, 05:41 AM   #2
ubergeeknz is offline ubergeeknz  New Zealand
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Not class AF but an AF Power Amplifier. Meaning, a Power Amplifier for Audio Frequencies (AF).

Based on the equivalent circuit, it's a quasi complementary class-AB design.
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Old 8th July 2019, 06:59 AM   #3
ubergeeknz is offline ubergeeknz  New Zealand
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In terms of bridging, should be easy if I'm reading this right...

Put the speaker between pins 10 and 13.

It looks like a differential input, so connect pins 18 and 2 together and pins 17 and 1. Ground one and use the other for input.Screenshot_20190708_185441.jpg
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Old 8th July 2019, 08:49 AM   #4
ubergeeknz is offline ubergeeknz  New Zealand
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Also this probably belongs in chip amps
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Old 10th July 2019, 09:39 AM   #5
Kay Pirinha is offline Kay Pirinha  Germany
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Quote:
Originally Posted by ubergeeknz View Post
It looks like a differential input, so connect pins 18 and 2 together and pins 17 and 1. Ground one and use the other for input.Attachment 767018

No, don't do it!
It isn't that simple, as each amplifier needs it's own NFB loop. Either put a dedicated phase inverter section (two opamps) in front of both amplifiers, or, much simpler, connect the non-inverting amp's output to the other amp's inverting input via a resistor. This resistor needs to be of exactly the same value as this amp's NFB resistor. An example is shown in the TDA7294 datasheet https://www.st.com/resource/en/datasheet/tda7294.pdf, page 13.
Note that there's no free lunch: With the simpler version of just one additional resistor the inverting amplifier also amplifies the 1st amp's distortions. Hence the overall THD increases.
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Last edited by Kay Pirinha; 10th July 2019 at 09:46 AM.
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Old 10th July 2019, 07:17 PM   #6
ubergeeknz is offline ubergeeknz  New Zealand
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Quote:
Originally Posted by Kay Pirinha View Post
It isn't that simple, as each amplifier needs it's own NFB loop.
Yeah thought that seemed too easy What is class AF power amplifier? big thinko on my part forgetting the NFB.

Ignore my dumb advice and go with Kay What is class AF power amplifier?
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