Hello everybody,
I am new to this forum but I have spent a lot of time reading loads of different threads , mainly about chip-amps and power-supplies.
I research and read a lot so here are some points which I would like to point out about the various chip-amps and which basically are valid for all of them.
First of all the feedbackloop and the capacitor to ground from it to block DC. This is an electrolitic capacitor, usually around 220uf. Apart from the relatively high tolerance of these capacitors the are not the best at all at high frequencies and one does well to place a 0.22uf MKV in parallel to improve the behaviour at higher frequencies. Just try it and compare. Another point is to place two diodes in antiparallel to the capacitor to avoid the electrolitic ever being reverse-biased, a small signal diode like a 1N4148 is sufficient and does not exist at all during normal operation of the chip-amp becase it remains turned off in forward direction below about 550mV. A capacitor with 16 V will then be perfectly safe and smaller in size so one can double it to 470 uf. The larger electrolytic is good for the bass and the MKV for midrange and treble.
The second point concerns the feedback-loop resistors. The one from the output to the negative input generally is 22k or so and if it is on the pcb someplace that is NOT GOOD becase of the inductivity of the traces on the board. An easy way to make this better is to carefully solder it directly to the pins of the chip-amp to get the shortest and smallest possible feedback-loop and then solder the 680 to 1k resistor going to the capacitor in the now empty place of the 22k one. Then close the circuit to the capacitor with a wire-link to taking the empty place of the 680/1k resistor. If you have good ears and good speakers you will notice the difference, especially if your pcb is a china one, normally with less than perfect layout.
I hope to help a little and I would be grateful for any comment and / or feedback from all of you. Michael
I am new to this forum but I have spent a lot of time reading loads of different threads , mainly about chip-amps and power-supplies.
I research and read a lot so here are some points which I would like to point out about the various chip-amps and which basically are valid for all of them.
First of all the feedbackloop and the capacitor to ground from it to block DC. This is an electrolitic capacitor, usually around 220uf. Apart from the relatively high tolerance of these capacitors the are not the best at all at high frequencies and one does well to place a 0.22uf MKV in parallel to improve the behaviour at higher frequencies. Just try it and compare. Another point is to place two diodes in antiparallel to the capacitor to avoid the electrolitic ever being reverse-biased, a small signal diode like a 1N4148 is sufficient and does not exist at all during normal operation of the chip-amp becase it remains turned off in forward direction below about 550mV. A capacitor with 16 V will then be perfectly safe and smaller in size so one can double it to 470 uf. The larger electrolytic is good for the bass and the MKV for midrange and treble.
The second point concerns the feedback-loop resistors. The one from the output to the negative input generally is 22k or so and if it is on the pcb someplace that is NOT GOOD becase of the inductivity of the traces on the board. An easy way to make this better is to carefully solder it directly to the pins of the chip-amp to get the shortest and smallest possible feedback-loop and then solder the 680 to 1k resistor going to the capacitor in the now empty place of the 22k one. Then close the circuit to the capacitor with a wire-link to taking the empty place of the 680/1k resistor. If you have good ears and good speakers you will notice the difference, especially if your pcb is a china one, normally with less than perfect layout.
I hope to help a little and I would be grateful for any comment and / or feedback from all of you. Michael
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Yes, of course you are right. Anything I could say has been said before.
Here in this forum and elsewhere . But there are people like me who are newbies to the world of gainclones and people not so new whose knowledge on the subject is very limited.
I find the forum very nice and full of lots of good information. But it is spread out over many different threads so I think it would be nice to start one in which all this is summed up and concentrated in one place.
Gainclones are no secret as you said.......but truly superb ones are so why not have one thread which enables beginners to jump ahead and build themselves one of the latter to begin with when the difference is , at least money-wise , not so big when one considers the effort to build one in the first place?
This is why I started this thread : to concentrate the knowledge and to help those who , even now , are new to the subject. People like myself included....... Cheers Michael
Here in this forum and elsewhere . But there are people like me who are newbies to the world of gainclones and people not so new whose knowledge on the subject is very limited.
I find the forum very nice and full of lots of good information. But it is spread out over many different threads so I think it would be nice to start one in which all this is summed up and concentrated in one place.
Gainclones are no secret as you said.......but truly superb ones are so why not have one thread which enables beginners to jump ahead and build themselves one of the latter to begin with when the difference is , at least money-wise , not so big when one considers the effort to build one in the first place?
This is why I started this thread : to concentrate the knowledge and to help those who , even now , are new to the subject. People like myself included....... Cheers Michael
The gainclones are about 20 years old by now. What is true for the LM3886 is basically true for all chip-amps. Exact circuitry will differ of course and so will component values.
As Adason said , quote :
"Btw gainclones were introduced 1999...and all your comments were discussed
just search and you will find" , end of quote ,
the data-sheets are as old as the chips and once out the manufacturers do not add to them nor modify them.
The data-sheets and aplication-notes can be considered a recipe so why not make a thread to have a new and up to date recipe including all the experience of those in the know to contribute to help others to not only get it right but get it excellent right from the start? Not everybody can and will make their own pcb´s so lots of people buy a kit or a pcb on Ebay , Amazon , ...... because it is cheap and makes things easier. Those kits are not the cream where layouts are concerned but most if not all of them can be very much improved with a few minor , easy and cheap modifications. Personally I am a life-long TV-tech so I can research and judge the validity of what I find but lots of people are not able to distinguish if some info they find is ok or not. All those , including me myself and I , need all the help that we can get so I would like to invite all the "top guns" to post their contributions to this end here in this thread. Concentrate the knowledge. Cheers again, Michael
As Adason said , quote :
"Btw gainclones were introduced 1999...and all your comments were discussed
just search and you will find" , end of quote ,
the data-sheets are as old as the chips and once out the manufacturers do not add to them nor modify them.
The data-sheets and aplication-notes can be considered a recipe so why not make a thread to have a new and up to date recipe including all the experience of those in the know to contribute to help others to not only get it right but get it excellent right from the start? Not everybody can and will make their own pcb´s so lots of people buy a kit or a pcb on Ebay , Amazon , ...... because it is cheap and makes things easier. Those kits are not the cream where layouts are concerned but most if not all of them can be very much improved with a few minor , easy and cheap modifications. Personally I am a life-long TV-tech so I can research and judge the validity of what I find but lots of people are not able to distinguish if some info they find is ok or not. All those , including me myself and I , need all the help that we can get so I would like to invite all the "top guns" to post their contributions to this end here in this thread. Concentrate the knowledge. Cheers again, Michael
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The feedback resistor path must be very short as 1mm track gives 1nH of inductance.
Also regarding feedback some chip amps have a minimum gain and if you dont reach it they can become unstable. The TDA7294 is an example of this and needs a gain of at least 22.
Not sure I agree concerning electrolytics. They work ok to mega hertz and that is well outside audio range.
Also regarding feedback some chip amps have a minimum gain and if you dont reach it they can become unstable. The TDA7294 is an example of this and needs a gain of at least 22.
Not sure I agree concerning electrolytics. They work ok to mega hertz and that is well outside audio range.
Indeed, and the LM3886 uses a obsolete quasi complementary output stage. Quasi complementary stages became obsolete once high power complementary PNP transistors were produced, in the 1970's IIRC. This IC was designed to be used in TV sets and was never meant to be a hifi chip.
I would like to know what you meant by "very good" in objective terms. If you want something like a THD of 0.03% (LM3886) and a output stage which is more prone to oscillation then thats fine. Self et al have been through this many times and have shown that quasi complementary output stages are more prone to oscillation and have much more asymmetric crossover distortion than complementary designs. There is a excellent complementary design called the honeybadger amp here on diyaudio which manages THD of 0.0002% at 1khz while delivering 150 watts to 8 ohms. That is real HiFi and show me any quasi complementary design which comes anywhere near that.
No self respecting electronics engineer would design a quasi complementary output stage today, and the only reason it still persists (lamentably) in the audio world is that in "high end" nothing seems to die away and anything can be marketed, which is why you still have "TDA1543 DAC's", "Single ended triode amplifiers", "NOS DAC's" etc.
Some say that is a real magic. Two exactly the same transistors on positive and negative side is way better than complementary which are never fully truly complementary.
Quasi complementary designs can be aesthetically pleasing, they look nice on paper, but in the world of electronics what looks good to the eye does not always mean it works or measures well. Its very easy to design a complementary output stage amp with 0.0002% THD, but quasi complementary design's cannot match that, infact the LM3886 is rated at a unimpressive 0.03% THD.
Quasi complementary outputs are a relic of the days (1960's) when PNP power transistors were either unavailable or extremely expensive. Those limitations are not there now, and even power audio IC designers prefer to use complementary solutions (TDA 7293) for their inherently lower distortion and improved stability advantages.
The LM3886 chip sounds fine and its easy for a DIY'er to make a good, robust amplifier which sounds great. But its not, and never was designed to be a HIFI component, nor is it the holy grail of audio power amplifiers.
Hello Grendel321,
High power chipamps do definitely have their limitations and discrete designs have no upper limit in as much as the technical possibilities are concerned, our ears are the limiting factor if we do not want to end up totally deaf.
As far as quality is concerned I want to ask if maybe you have had a look at the designs from
TOMCHR? , especially his modulus series , see Modulus 686? Search for NEUROCHROME if you have not.
Apart from that I started this thread about the LM3886 and other chipamps on purpose because precisely for DIYers they are an easy and economic way to build something useful for home. Another point is that for DIYers and especially beginners like myself (as far as the subject is concerned) it is much better to start with something thats not too complicated. No one argues that there can be and there are much better possible discrete circuits but for the average DIYer who is not an engineer in electronics nor a lifelong technician which is what I am it gets too complicated not only technically but economically and even equipment in the way of tools and instruments available.
In the sixties amps were mainly valve amps and beginnings of solid state amps gererally were goog old 2N3055 and other similar devices towards the end of that decade. I myself built more than one amp with those and I began my work with valves , EL84 El34 and the likes both single ended and up to 6xEL34 in pushpull mainly for musicians.
But all that isn´t the point of this thread about chipamps for DIY. I am sorry to criticize and no offense meant but it would be nice if this thread could be kept in the direction it was meant. Which is , as far as I am concerned , as much knowledge as possible about the chipamps and those used for and by DIYers
Thanks for your understanding and greetings Michael
High power chipamps do definitely have their limitations and discrete designs have no upper limit in as much as the technical possibilities are concerned, our ears are the limiting factor if we do not want to end up totally deaf.
As far as quality is concerned I want to ask if maybe you have had a look at the designs from
TOMCHR? , especially his modulus series , see Modulus 686? Search for NEUROCHROME if you have not.
Apart from that I started this thread about the LM3886 and other chipamps on purpose because precisely for DIYers they are an easy and economic way to build something useful for home. Another point is that for DIYers and especially beginners like myself (as far as the subject is concerned) it is much better to start with something thats not too complicated. No one argues that there can be and there are much better possible discrete circuits but for the average DIYer who is not an engineer in electronics nor a lifelong technician which is what I am it gets too complicated not only technically but economically and even equipment in the way of tools and instruments available.
In the sixties amps were mainly valve amps and beginnings of solid state amps gererally were goog old 2N3055 and other similar devices towards the end of that decade. I myself built more than one amp with those and I began my work with valves , EL84 El34 and the likes both single ended and up to 6xEL34 in pushpull mainly for musicians.
But all that isn´t the point of this thread about chipamps for DIY. I am sorry to criticize and no offense meant but it would be nice if this thread could be kept in the direction it was meant. Which is , as far as I am concerned , as much knowledge as possible about the chipamps and those used for and by DIYers
Thanks for your understanding and greetings Michael
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That needs to be considered in light of what speaker the amp is paired with. An amp cannot really be judges outside of the system with speakers (and wire between them).
dave
Guys Guys Guys
Very interesting opinions from all of you. Great.
But no real info of how to get the best possible performance out of chip amps including the LM3886 of course and how to avoid the many pitfalls there are. What is needed here is do´s and dont's for all those who are not experts on the matter. It is well known that the LM3886 can be made to do wonders. It is the how to recipe that matter and please correct me if you think I am wrong.
Cheers Michael
Very interesting opinions from all of you. Great.
But no real info of how to get the best possible performance out of chip amps including the LM3886 of course and how to avoid the many pitfalls there are. What is needed here is do´s and dont's for all those who are not experts on the matter. It is well known that the LM3886 can be made to do wonders. It is the how to recipe that matter and please correct me if you think I am wrong.
Cheers Michael
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This site has a lot of useful information about how to get close to the datasheet specs from the lm3886 which also includes a section about grounding.
Taming the LM3886 Chip Amplifier
I think the biggest pitfall in chipamp/DIY audio design and the most important thing in any power audio amplifier is the grounding, especially the location of signal grounding. Incorrect signal grounding can lead to dramatically increased THD and increased error voltages across the load.
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