I think he was asking you to connect the resistor between pin 8 and ground (not V-) and measure the voltage across the resistor? .
Where did you get these particular LM3886? Could they be fakes? If purchased on eBay the odds are not in your favor.
Given your supply voltages with a proper LM3886 the chip will unmute when the current into that pin exceeds => 0.5mA, you can use a 20 - 30K resistor to V-.
No DC on the output of your source? (Check with your meter) The Spike protection in the LM3886 does not like DC on the inputs and may mute the chip at some point if present. Input capacitors are not a bad idea regardless. Definitely add an electrolytic capacitor between your 1K resistor and GND. (Non polar type is recommended like Nichicon Muse or similar.)
Where did you get these particular LM3886? Could they be fakes? If purchased on eBay the odds are not in your favor.
Given your supply voltages with a proper LM3886 the chip will unmute when the current into that pin exceeds => 0.5mA, you can use a 20 - 30K resistor to V-.
No DC on the output of your source? (Check with your meter) The Spike protection in the LM3886 does not like DC on the inputs and may mute the chip at some point if present. Input capacitors are not a bad idea regardless. Definitely add an electrolytic capacitor between your 1K resistor and GND. (Non polar type is recommended like Nichicon Muse or similar.)
i'll try...they are meant to prevent high frequency noise from modulating the supply line of an associated transistor or chip and are generally implemented as close as possible physically to the device. it's not uncommon to see multiple values in parallel across +/- supply lines to ground in order to achieve stability and increase GBP.
do tell, if by your own account you've previously built two other amps using the same device and that you've not encountered the need for supply bypassing when it's seen in the application notes basic schematic?
the components marked Cs are the supply line bypasses.
I was asking about voltage present at pin 8, with >0.5mA current passing through it, so with a resistor from it to -V
Since -V is -30V, you should have 30V/3k=10mA through it, coming from inside the chipamp through pin 8 and you should measure -2.6V (maybe +/-20% would be acceptable) at pin 8 , yet you measure -0.9V
That confirms it is not an LM3886 by any means (or it´s a quite sick one).
I always suspected and not only here, that some Fakes are somewhat working devices, and in uncritical application may work, sort of.
I suspect some generic power amp chip, with some low cost "chip foundry" available chip available in bulk for peanuts, encapsulated and labelled by some "entrepreneur" like the real thing, which can be sold for a good price, doubly so since the real one has all but disappeared.
You say you bought 10 of them?
I suggest you pick another one, build the basic datasheet circuit, with all caps, datasheet value resistors, the full Monty, simply to minimize unknown variables, BUT feed it lower voltage, anything between +/-12V to, say,+/-20V , perhaps +/-24V but not more,definitely not +/-30V or higher.
My point being that they might work under reduced stress so your investment is not fully lost.
FWIW I am using my fake TDA2050 as if they were TDA 2030 and so far they work.
Not what I wanted, but hey .... worse is nothing!!!.
maaybe you can do something similar.
Now if none works under such mild conditions ..... 😱 😱 😱
But test them, testing RULES over guessing.
Ok, keep us up to date.
PS: check that your 3k unmute resistor is actually that value.
Since -V is -30V, you should have 30V/3k=10mA through it, coming from inside the chipamp through pin 8 and you should measure -2.6V (maybe +/-20% would be acceptable) at pin 8 , yet you measure -0.9V
That confirms it is not an LM3886 by any means (or it´s a quite sick one).
I always suspected and not only here, that some Fakes are somewhat working devices, and in uncritical application may work, sort of.
I suspect some generic power amp chip, with some low cost "chip foundry" available chip available in bulk for peanuts, encapsulated and labelled by some "entrepreneur" like the real thing, which can be sold for a good price, doubly so since the real one has all but disappeared.
You say you bought 10 of them?
I suggest you pick another one, build the basic datasheet circuit, with all caps, datasheet value resistors, the full Monty, simply to minimize unknown variables, BUT feed it lower voltage, anything between +/-12V to, say,+/-20V , perhaps +/-24V but not more,definitely not +/-30V or higher.
My point being that they might work under reduced stress so your investment is not fully lost.
FWIW I am using my fake TDA2050 as if they were TDA 2030 and so far they work.
Not what I wanted, but hey .... worse is nothing!!!.
maaybe you can do something similar.
Now if none works under such mild conditions ..... 😱 😱 😱
But test them, testing RULES over guessing.
Ok, keep us up to date.
PS: check that your 3k unmute resistor is actually that value.
According to the simplified internal schematic, there are three diode drops and a 1 kohm resistor internally, so you should end up somewhere around -8.8 V at pin 8 with 3 kohm from pin 8 to V- when V- = -29 V. Doesn't change the conclusion, that -0.9 V from post #10 is all wrong.
The typical performance plots go up to a -10 mA mute current, so the current is not high enough to blow up pin 8 or to bring the chip into some unintended state. I looked in the datasheet because I wondered about that.
The typical performance plots go up to a -10 mA mute current, so the current is not high enough to blow up pin 8 or to bring the chip into some unintended state. I looked in the datasheet because I wondered about that.
Thanks for that. What you've proposed is exactly what I've installed on the power lines. That is, three capacitors to ground on the regulator outputs.
Besides the pictures and the reduced stress testing, also post the seller link.
If anything, to avoid him in the future 😱
If anything, to avoid him in the future 😱
Thankyou for your attention and everybody else as well. I think I'm going to run with the rubbish chip idea. I have already constructed three previous strip boards from this batch of chips. and nothing worked,
I was left thinking that I had made some errors somewhere, each time. But perhaps the chips themselves are down. I do have a previous chip, not from this suspect batch, so I'll wire that up and try again. If I just link up the power lines and input output lines to it I could measure the pin 8 situation like I've just done. Is that feasible, or would you urge rebuilding a new stripboard with all components before investigating?
The bypasses are right next to the chip. Two separate boards, but the connecting wire and track is only 20mm in length and as already stated I have two other amps built in identical fashion that work well.
Cricklewood Electronics. I do sometimes have issue with their product quality but generally they're OK.
Ok, if you have a direct clickable link that takes us straight to what you bought, it´s better.
I want to see what they offer, what they promise, pictures they show, etc.
Telling me "Cricklewood electronics" is like saying "they are in the phone book" 😉
Maybe it´s best to build a test amp, no boards, just dead bug style, we are not aiming at usable amp but just testing some specs.
The general idea in these mystery cases is to build things the simplest way, and when/if it successfully works, we get fancy.
EDIT: can´t believe we are talking the same product and supplier, this Cricklewood sells them for GBP 26.40 and 36 😱
https://www.cricklewoodelectronics.com/search.php?mode=search&page=1&keep_https=yes
That´s why I ask for a direct link to what you actually bought.
I want to see what they offer, what they promise, pictures they show, etc.
Telling me "Cricklewood electronics" is like saying "they are in the phone book" 😉
Maybe it´s best to build a test amp, no boards, just dead bug style, we are not aiming at usable amp but just testing some specs.
The general idea in these mystery cases is to build things the simplest way, and when/if it successfully works, we get fancy.
EDIT: can´t believe we are talking the same product and supplier, this Cricklewood sells them for GBP 26.40 and 36 😱
https://www.cricklewoodelectronics.com/search.php?mode=search&page=1&keep_https=yes
That´s why I ask for a direct link to what you actually bought.
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I agree with everything you say. I forgot that you may not be UK based. The cricklewood that you have found is the correct company. I order by phone. The unit price has shot up unbelievably. My purchase was several months back and they were affordable, but not now.
I don't know what dead bug style actually means but what I've done in this case is to simply mount the chip onto a chunk of heat sink and directly connect onto the pins. No boards. I'll do this with the other ICs I've bought and test. Fingers crossed.
Assuming that you have only used one LM3886 for your measurements: integrated circuit production tests never cover everything, ICs can get damaged by electrostatic discharge and early failures are also possible. That is, even parts from a perfectly reliable supplier can occassionally turn out to be non-functional.
From what I understand, 3 or 4 were built, none from this batch worked.
That said, there might be some problem with the perfboard/veroboard layout used, or some link is missing, etc.
"Dead bug" is a colloquial/informal term which means (imagine a dead cockroach with her legs up) the chipamp bolted to a heatsink, "all its legs up in the air" and parts with longish leads soldered straight to chipamp legs.
Helps to check wiring errors, of course not practical for a complex project.
There are some examples in the chipamp section.
That said, there might be some problem with the perfboard/veroboard layout used, or some link is missing, etc.
"Dead bug" is a colloquial/informal term which means (imagine a dead cockroach with her legs up) the chipamp bolted to a heatsink, "all its legs up in the air" and parts with longish leads soldered straight to chipamp legs.
Helps to check wiring errors, of course not practical for a complex project.
There are some examples in the chipamp section.
Just an update. In the process of wiring in what might be an OK IC. Managed to blow up a voltage regulator on the the positive rail so I've gone backwards.
I'll be in touch when all that's sorted out. Sad face.
Sorry to hear about your misfortune, it happens to everyone. We'll be here when you are ready. 🙂
Ugh 🙁
Not sure about what does a voltage regulator do here,
care to expand on that?
What supply voltage do you have?
Voltage regulators? I'm building a high roll off audio filtration system that requires, a priori, five separate power amps. This needs a separate power supply unit handling large current. The ripple capacitors are gargantuan, so large in fact that for safety reasons I've had to put in a bleed circuit to take the charge out once switched off. Also, I've had to build a soft start. All other components downstream would have been so large that I postponed any further refinement, such as voltage regulation ( really for voltage adjustment rather than a resistance splitter) and all the frequency band buffer capacitors mentioned elsewhere on this thread, to each amplifier where the current handling is much lower. Altogether this system will put out 160W or so.
I've now repaired the supply board on this amplifier and wired up an old LM3886 that I found (legs up, bolted to a lump of heat sink).
It works. Yahoo!!
So, its now the story of a batch of non functioning ICs. I'll take that up with Cricklewood Electronics.
I've got two more amplifiers to build then a series of quad opamp driven brick wall, high roll off quadratic band pass filters.
Obviously, I'll make dogs breakfast of all of that so I'll be in touch.
Meanwhile, thankyou everybody for your diligence and group think, I'm extremely grateful.
Glad it does.
Well, that about sums it up, doesn´t it?
Pity your complex system requires many LM3886 though.
Maybe (didn´t check), TDA7294 is still available?
About same power class, price, in any case you are not committed to a stack of 3886 boards (I think).
EDIT: just checked, Mouser (which CAN be trusted), shows none today but some 1600 total (2 variants) expected around May 20th for U$10/11 each.
Not bad and might be an option.
As I mentioned earlier, this waiting on edge is not good for my nerves so for my 40/50W Guitar amps I designed and amp using a discrete miniboard to replace chipamps, go figure.
Actually an update of one I designed 10/15 years ago to replace TDA1514 which was very popular (specially on Marshall amplifiers) but disappeared.
I belong to a group of Argentine MI amp makers association, and an idea which is running around its to "downgrade" Technology 😱 and I mean chipamps, microprocessors, etc. , to somewhat "older" but still easily available, abbundant and cheap(ish) components , obviously not currently made but which are still stocked in warehouses.
Lack of interest in them is paradoxically a bonus, since existing supplies "should" last longer, there´s also no motivation to fake them.
As of now, just "thinking aloud", but showing desperation growing around.
WHO can realistically plan for any production run when parts "might" be available 1-3-6-12 Months into the Future?
No 100% guarantee they will be available, even if waiting 🙁
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