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Old 13th January 2012, 06:03 PM   #1
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Default Help Building L4780 Amp With Absolute Minimal Components

I am trying to build a stereo amplifier based on TI's L4780 chip using the LEAST possible number of external components. I am using a dual rail power supply. I checked the forums and every circuit diagram I found is based on the reference datasheet from TI. Most bill of material have 6 more resistors and 4 or more capacitors.
Have you experimented with this chip?
Please see the attached image.
If I use a good quality power supply, can I eliminate the 4 capacitors (cs) that are in series with the power rails? How about getting rid of the resistors that I circled in red?
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Old 13th January 2012, 06:47 PM   #2
Marra is offline Marra  United Kingdom
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Checkout Peter Daniels Gainclone pages; lots of info.
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Old 13th January 2012, 06:56 PM   #3
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No one of the resistors can be deleted, because they fix the negative feedback to the amplifier, ensuring gain and distortionless operation. Caps are not recommended to be eliminated, they decouple the amplifier. Moreover, you probably MUST add some components, like a zobel network at the speaker end of the coil. Also, probably must add some ceramic .1micro 50V between power rails and ground, as closely to the chip as you can.

Good luck.
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Old 13th January 2012, 07:06 PM   #4
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I performed several searches on "Peter Daniel Gainclone" and found way too many threads. I believe the actual useful information is there somewher but I can't find it. Can you give me a more specific thread/page information?
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Old 13th January 2012, 07:06 PM   #5
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That is about as basic as you can get ..for a non inverting amplifier. You could get away removing another resistor by building it as an inverting amplifier.From the questions you ask i can tell you have very little expirience. for the amplifier to be a working first build go have a look at the data sheet and use all components listed wrongly as optional.You really need a capacitor on the input to block dc too unless you can guarentee your source is dc free. Also do a search on this forum for lm3886 and read lots and lots. By the way the chip is made by national semiconductor and not ti . ti recently merged or bought out national semi but they still run as seperate companys Even when you request samples from ti it takes you to nationals site. Best of luck you will need it Watch out for your loudspeakers too.. see the man above knows what he is talking about

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Old 14th January 2012, 01:11 AM   #6
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Yes you can get rid of all the resistors and capacitors and even the LM4780... but it will sound very, very quiet soon after you wire your power supply direct to the speakers.
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Old 14th January 2012, 01:44 AM   #7
GloBug is offline GloBug  Canada
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Here is the link to Peter Daniel's LM4780 Schematic.

Note: it shows parallel and stereo wiring. I assume you are building stereo, so look at the green layout.
http://www.audiosector.com/lm4780%20amp.pdf
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Old 14th January 2012, 01:49 AM   #8
frasco is offline frasco  Finland
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Ri/Rf controls the feedback loop (gain) and are essential. Removing Rm would mute the amp. Removing CS would result in an unstable power supply (they smooth out the converted AC wave to a steady stream of DC). RB is optional but unless you know what its effects are you should probably not remove it.

You will probably get a lot more suggestions about which components you should add.

edit: oh and define "good quality power supply" please.

Last edited by frasco; 14th January 2012 at 01:51 AM.
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Old 14th January 2012, 03:03 PM   #9
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Hi buddy,
I feel you are making a same mistake which i made a long time back. I wanted to make (and also made) the smallest possible single layer PCB for LM4780. But later i felt that there is no such realistic requirement to minimize the PCB size, its was just my carried away feeling or i wanted to satisfied my niche.

So same way, first address why you want to make a minimalistic LM4780 amp, each resister and capacitor mentioned in LM4780 amplifier has a specific role. Even they mentioned 4 optional components which will further enhance the quality of amplifier. In fact now i am thinking to remake the LM3886& 4780 PCB with including all the optional components as well.
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Old 14th January 2012, 03:08 PM   #10
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try TDA1554Q, its good for a minimal component amplifier
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