Trying to get my LM3886 to work. Three attempts so far no result. Fourth attempt I've simplified the circuit and have only resistors soldered onto the actual chip tags. No circuit board.
Still nothing. I am perplexed, especially since I have built two previously that work well.
So currently I have 30 volt positive and negative supply directly connected. I have input and output directly connected. Pin 8 (mute tag) has 20k to the negative rail. The feedback loop from output to non inverting has 20k connected with 1k to ground. The CD output goes directly to the inverting input with 1k in series and 20k to ground. Thats it. No capacitors.
With the CD input fully open (max volume) I get a faint whispering through the loudspeaker.
Help!!!
Still nothing. I am perplexed, especially since I have built two previously that work well.
So currently I have 30 volt positive and negative supply directly connected. I have input and output directly connected. Pin 8 (mute tag) has 20k to the negative rail. The feedback loop from output to non inverting has 20k connected with 1k to ground. The CD output goes directly to the inverting input with 1k in series and 20k to ground. Thats it. No capacitors.
With the CD input fully open (max volume) I get a faint whispering through the loudspeaker.
Help!!!
Apologies. Wrong description. Read feedback loop from output to inverting etc.
What DC voltage do you have at speaker out pin?
Also test amp with way lower voltage, say 12 to 16 - 20 , even +/-24V , always symmetrical of course.
Didn´t happen to me with LM886 (yet) but was burnt by a lot of fake TDA2050 which with datasheet proper +/- 20-22V overheat or block or best case sputter , yet work perfectly well with milder +/-16V ...... MAYBE yours do something similar.
IF possible (you have a suitable supply lying around), worth trying at least to separate the wheat from the chaff.
Also:
Semi-undocumented but they hint at having -2.6V there when unmuted.
I expected something like that since 0.5mA mute current must pass through "3 diode drops".
Also test amp with way lower voltage, say 12 to 16 - 20 , even +/-24V , always symmetrical of course.
Didn´t happen to me with LM886 (yet) but was burnt by a lot of fake TDA2050 which with datasheet proper +/- 20-22V overheat or block or best case sputter , yet work perfectly well with milder +/-16V ...... MAYBE yours do something similar.
IF possible (you have a suitable supply lying around), worth trying at least to separate the wheat from the chaff.
Also:
Cool, but what actual voltage do you measure at the Mute pin?
Semi-undocumented but they hint at having -2.6V there when unmuted.
I expected something like that since 0.5mA mute current must pass through "3 diode drops".
with no capacitors whatsoever it's quite possible that your chip is oscillating and in current limiting. supply bypass as close to the chip as possible i would think is a must!
with no details or a pic of the setup all we can do is put forth conjecture as to what could be wrong.
do you have access to an oscilloscope?
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With the mute pin connected to the negative rail via 3.0kohm resistor. (low resistance, high current)
At 29V plus and minus I get 0.7V at speaker out and -0.9V mute pin to ground
At 20V plus and minus I get 0.6V at speaker out and -0.8V mute pin to ground. Still no sound though.
Seems like something is definitely wrong.
What's a supply bypass?
I don't have an oscilloscope. I'm an engineer but not electronics. I have a simple multimeter.
Herewith a sketch of what I've connected up.
Supply decoupling capacitors. One normally puts capacitors from the supplies to ground right next to the LM3886, because the inductance of the supply wiring may otherwise cause it to oscillate, among other issues. See the datasheet for recommended types and values: 470 uF electrolytic according to page 20.
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For some mystery reason your amp is NOT getting out of Mute. 🙁
I expect "3 diodes" drop negative, so about minus 2.1V , probably a little more because there is also an internal 1k resistor dropping some voltage too.
Here and copypasting from datasheet:
Maybe your Chipamp was damaged somehow, maybe it´s a terrible fake (because many fakes still "work" somewhat), do you have another?
Just for thoroughness: lift 1 end of the muting resistor and check its actually pulling current (1 to 10 mA or so) from Pin 8 towards -V
IF passing that current yet dropping only "1 diode" ~ -0.7V, not yet saying it´s "broken" but definitely NOT working like a real LM3886.
A sensible faker who wants to stay in business maybe won´t properly clone LM3886 for various reasons, cost or unavailability of proper masks, but at least shoulf package there "some" kind of working chipamp.
Ok, try the tests suggested above, including using another "3886" 😱
Not to discourage you, but I make Guitar Amps and had to design a discrete 40/50W class amplifier based on a pair of TIP121/126 both for own production needs and occasional repairs, go figure.
EDIT: as mentioned above, just add a couple needed capacitors:
* supply decoupling: from +V and -V to ground, near chipamp itself.
* DC negative feedback decoupling, datasheet suggested or 100uF in series with the 1k NFB resistor
* add a Zobel circuit across output pins (speaker to ground), 10 ohm and a .1uFx50V ceramic is classic, maybe try 4.7 ohm and even 1 ohm.
Always shaking my head at chipamp designers who think they can not use it.
Maybe no problem in a Lab setting but the real World is wide and dangerous.
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your sketch doesn't show where you've attached the supply ground nor the length of leads used for that purpose, if you don't have bypass caps available at the very least try shortening all supply leads and twist them together so as to minimize a possible inductive loop.
First thing is to add some supply decoupling to ground.
What is the DC offset voltage present on the output?
Then try another 3886, it may be bad.
What is the DC offset voltage present on the output?
Then try another 3886, it may be bad.
My sketch doesn't show the power source. Just the amp circuit. The supply grounds and the signal grounds are all taken radially to a single point. Power leads are twisted together. Also, each power rail is regulated and each carries three capacitors to ground, pretty much as recommended. The power source is mounted on a separate stripboard to the amplifier stripboard. The two boards sit in a small box less than 15mm apart from one another. I have already built two previously in exactly this way and they work well. Could you explain what is a bypass cap?
Bearing in mind that I don't properly know what I'm doing.
I have disconnected the unmute resistor from the mute pin (pin 8) and then measured voltage from pin 8 to ground. I get +0.6V. I don't get -2.6V at all. Out of curiosity I also measured speaker out to ground and got -1.8mV. This is with everything else connected as previously described and shown on the circuit diagram.
Does this mean rubbish chip. This is the third circuit built that doesn't work. All built in exactly the same way ( with errors, probably) using chips purchased as a batch. Does this mean that all of the chips purchased are just rubbish? I do have a previous chip and that circuit did't work either, but not from the suspect batch. Is it worth unsoldering all of that and trying this "maybe OK" chip. Guidance please.
All the other circuits tried, without success, are built with Zobel. This time I'm trying to simplify in order to isolate the problem. Is this the correct approach?
Ok, that is one test. You measured the muted voltage.
Now reconnect that resistor from pin 8 to ground and remeasure voltage ... what do you get now?
Thanks for your attention. I'm now confused. If I reconnect the mute resistor to pin 8 and then measure from pin 8 to ground I repeat what you previously asked and get -0.9V. (The resistor is 3.0k). Can you be very precise and describe what voltage you want measured.