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Old 25th June 2012, 07:02 AM   #1
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Default Amplifier Circuit !!

Hello guys i have reached this amplifier to construct :
2×2 Watts Power Amplifier Circuit Board and PCB Layout
But I don't know why they choose these resistance value and capacitor values, can someone help me hoe to find them ??
Thank you !!
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Old 25th June 2012, 08:49 AM   #2
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Old 25th June 2012, 10:19 AM   #3
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yes the first one !
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Old 25th June 2012, 10:27 AM   #4
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Hi , just type the magic words 'TBA 820 M' in an internet research engine
and find the datasheet . Once downloaded , open it !
There'll be the ' application circuit' and some useful informations .
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Old 25th June 2012, 10:28 AM   #5
AndrewT is offline AndrewT  Scotland
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Where is the link to the schematic? The one you are using !

Gain = +40dB and 2W of maximum output.
What are you using this for?
regards Andrew T.
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Old 25th June 2012, 10:33 AM   #6
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I am made a power amplifier using this picture and it works...
this is all I've found in that page .. but i need to know on what they were basing to choose these capacitors and resistor and at these values !!!
So I came here to share it maybe someone can help me !
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Old 25th June 2012, 03:27 PM   #7
johnr66 is offline johnr66  United States
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The large output cap blocks DC since this is a single ended single supply amp. It is really a hi pass filter which the low frequency cut off point is determined by the load impedance.

There is a film cap and 1 Ohm resistor across the output is called a "boucherot cell" or a zobel. Its purpose is to stabilize the amp at high frequencies. I am at a loss to explain why a lot of IC amps use such a low value of resistor.

This chip uses a boot strap circuit to aid the upper output transistor in swinging closer to the supply rail. It improves output power. See the datasheet for value selection.

The data sheet shows another capacitor of lower value (pf) from the output to pin 1 which is frequency compensation. See the datasheet for proper value.

R values on input set input impedance.

The TBA820 is an old IC and needs a lot of components. The TDA7231 produces the same output power without the need for bootstrapping and frequency compensation is taken care of inside the IC. It also has a row of pins for proper heatsinking as well.

An even newer IC, the TDA7267 (8pin DIP version) needs even less components and will produce higher power at a given supply voltage / load impedance. It does have a higher quiescent draw, however.

Last edited by johnr66; 25th June 2012 at 03:29 PM.
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Old 25th June 2012, 05:04 PM   #8
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my only problem is with the values they have chosen !
anw I will try to find a datasheet that will help me !!
Thank you !
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Old 29th June 2012, 06:22 AM   #9
MarianB is offline MarianB  Romania
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I might be wrong but as i see it, i don't think you will find any datasheet that will explain exactly what you need to know, it seems that you still have much to learn about the basics of how things work and datashhets do not post basics like that, it is supposed that you already have a fair knowllege of basics and only specifics details are needed. Try to study more about how audio circuits work.
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