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amp distorting
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Old 27th April 2021, 05:16 AM   #1
goodguys is offline goodguys  United Kingdom
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Default amp distorting

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Hi and thanks for reading. I have built this amplifier, please see attached circuit diagram. It is working fine the midrange and treble are good but whenever the amplifier tries to reproduce a low bass note i get a lot of distortion.
What do you think is wrong can you please advise.
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Old 27th April 2021, 05:35 AM   #2
PRR is offline PRR  United States
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amp distorting
1) you can't drive Q3 ON that way (which might only matter on big bass)
2) bias diodes drawn upside down (which would not work at all, so just a drawing error)

There's much more which could be better but that is not what you are asking.
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Old 27th April 2021, 05:36 AM   #3
OldDIY is offline OldDIY
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The circuit is wrong: the lower output transistor has no bias. The top transistor is not receiving enough voltage (needs a bootstrap), so distortion occurs. There is no correct NFB from the amplifier output.

Last edited by OldDIY; 27th April 2021 at 05:42 AM.
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Old 27th April 2021, 05:46 AM   #4
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Amplifier power 2.5-4 W (max).
Усилитель на трех транзисторах - YouTube

Last edited by OldDIY; 27th April 2021 at 06:03 AM.
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Old 27th April 2021, 02:21 PM   #5
goodguys is offline goodguys  United Kingdom
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Thanks for the replies, much appreciated.
I have checked the diodes and they are as the circuit diagram states. The amp does work with the diodes.
Is there anyway to salvage this project. Can you please make changes or addition of components on the circuit diagram i included.
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Old 27th April 2021, 04:30 PM   #6
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https://bestengineeringprojects.com/...ir-transistor/
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Old 27th April 2021, 04:37 PM   #7
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Class AB Power Amplifiers
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Old 28th April 2021, 06:12 AM   #8
goodguys is offline goodguys  United Kingdom
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Thanks!


What i mean is there anything that can be done to my amp to get it working. Please, not alternative designs.


It is a cheap and cheerful project with a bass disortion problem, not intrested in negative feedback or trying to make it a high quality amplifier. Just want it be stable and make sound.


Many thanks.
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Old 28th April 2021, 07:21 AM   #9
OldDIY is offline OldDIY
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This is usually the hardest part. Especially if it is assembled according to the wrong scheme and is not configured
R2 forms nfb for dc and ac voltage. The value is selected when setting 1/2 VDC at the junction point of the emitters Q2 and Q3. Remove D2 (replace with a jumper). Connect D1 and D2 in series as shown # 2 or # 4 (reverse polarity). R3 can be reduced to 100-330 ohms.
Simple circuits require more attention to detail and more complex customization

Last edited by OldDIY; 28th April 2021 at 07:39 AM.
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Old 28th April 2021, 12:27 PM   #10
goodguys is offline goodguys  United Kingdom
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So move D2 into the same position as D1.
In the circuit diagram i provided the diodes directional arrow is pointed upwards, so in your version i should have the two diodes pointing downwards, is that correct.


Many thanks
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