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?
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?
Attachments
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.
Good luck.
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
Regards Ian
Regards Ian
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 amp.pdf
Note: it shows parallel and stereo wiring. I assume you are building stereo, so look at the green layout.
http://www.audiosector.com/lm4780 amp.pdf
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.
You will probably get a lot more suggestions about which components you should add.
edit: oh and define "good quality power supply" please.
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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.
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.
Most of you are wrong! I just tried it on the bread board.
The 4 capacitors can be eliminated as long as a good quality power supply is used. I do not need a virtual ground as I am already using a dual rail power supply. The power supply already comes with the 4 CS capacitors that are shown in the circuit. Using the gain formula provided by the manufacturer, I can have it running on unity gain and eliminate most of the resistors.
The self proclaimed "gurus" on this forum failed!
The 4 capacitors can be eliminated as long as a good quality power supply is used. I do not need a virtual ground as I am already using a dual rail power supply. The power supply already comes with the 4 CS capacitors that are shown in the circuit. Using the gain formula provided by the manufacturer, I can have it running on unity gain and eliminate most of the resistors.
The self proclaimed "gurus" on this forum failed!
The engineers who developed the ICs are not magicians. The power IC must be decoupled from the power supply. If the chip seems stable, your leads from the main PS filter caps must be fairly short otherwise it can go into oscillation. I recommend PS decoupling film caps very near the chip and the whole arrangement on a star ground layout.
You may be able to get away without the output boucherot cell depending on the load characteristics, but I would include it.
I'd also include a low pass filter on the input to prevent frequencies beyond audio from entering the amplifier.
You may be able to get away without the output boucherot cell depending on the load characteristics, but I would include it.
I'd also include a low pass filter on the input to prevent frequencies beyond audio from entering the amplifier.
I don't think you understand. The point of the gain resistors is so you can set up an amp appropriate to the gain you want, based on input level, output level, power supply limitations. Some other chipamp chips do have fixed gain.
You wrote "good quality power supply". A good quality power supply is every component from the wall outlet to the chip's power pins. There is no need for the CS capacitors at the power supply, they are to reduce ripple caused by the chipamp in operation and thus, should be as close to it as physically (reasonably) possible.
That you can get a chip to produce sound and not have it oscillating in your particular circuit is no proof it is operating at the specs and capabilities. It could end up sounding no better than less costly chips, not reach its supposed output power so you wasted money on the power supply and heatsink size & capacity.
At unity gain. Is that what the application calls for?
Actually no, the primary goal is to make what customers want to buy. Least external components is a marketing feature. When building an amp that is not meant to fit in a case the size of a matchbook nor cost only $5, the issue of spending 5 cents on a resistor or 40 cents on a capacitors isn't very significant, nor is a few square centimeters of space on the PCB.
Instead what is important is building a product flexible enough to work in multiple scenarios so you have the largest customer base possible. They could have integrated the resistors but then fewer people want to use it. They could have integrated solid capacitors but then the chip price rises more than some low cost application BOM would rise by using less costly CS caps and in some circuits there would already be the functional equivalent of CS caps to smooth power rails for other components as well as the chipamp chip.
The goal of the amp builder should be to build the best amp reasonably possible, at least without a large increase in time/cost/space/etc. If you find it unreasonable to use capacitors and resistors, electronics may not be the best hobby to have.
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Saying "it works" is almost meaningless, unless you have the test equipment and knowledge to say HOW WELL it works.
Eliminating the four decoupling capacitors will not only set it up for possible stability and high-frequency oscillation/overheating problems. It will also limit the output's rise-time speed and hurt the transient response characteristics, making them dependent on the length of the power supply and ground rails, i.e. the rails' inductances. You will have raised the power supply impedance, as seen by the power supply pins, especially at higher frequencies (not a good thing, for sound quality). Those capacitors are meant to also act as a small local power supply, to supply the fast transient currents needed, since the rails' inductances won't allow the main psu caps to supply them. Without them, you get much larger fluctuations in the rail voltages (due to the transient currents attempting to flow through the rails' inductances), which can also cause instability and even oscillation, which can destroy the chip but would certainly lower the sound quality. You will have also increased the susceptibility to RF and other interference.
Eliminating the resistors, which should be mounted close to the chip pins, will expose the pins to stray capacitance and inductance (more potential stability problems), as well as worsen RF susceptibility. And a unity-gain configuration is of limited utility. Many chipamps are not even stable with gains of less than 10 or so.
Different chip, but if you want minimum and functional, take a look at this.
Mick Feuerbacher Audio Projects
Mick Feuerbacher Audio Projects
Thanks! I really like the minimalistic approach of this project. But, soldering right on the chip is a bit risky for me. Is there a trick for soldering right on the chip's leg? I burnt many chips that way just by overheating.
Someone recommended TPA1517. I am thinking about giving that chip a shot. I have a whole bunch of those chips. But, they are all SOICs. Can you recommend a place to buy cheap SOIC to DIP converters and individual ICs?
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