Just picked up a pair of (broken/for parts) amplifier boards with a total of 8 x LM3886.
Does anyone know of a simple way to test the chips?
I was thinking to put them in a simple board, but wondering if anyone knows of an easier way? Trying to avoid de-soldering them too much, as they are not the easiest things to remove.
Thanks,
geoff.
Does anyone know of a simple way to test the chips?
I was thinking to put them in a simple board, but wondering if anyone knows of an easier way? Trying to avoid de-soldering them too much, as they are not the easiest things to remove.
Thanks,
geoff.
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Hi Geoff,
You cannot avoid giving the LM3886 power. Some 2x24V or so. If you use no load, you may not need local power rail decoupling or Zobel-network. You definitely need a feedback resistor - use 10K. Connect "+" input to signal ground and connect a sine-wave to the "-" input through 1K. De-solder the LM3886 only if it seems to work.
Not a more complete test but a good indication if worth de-soldering.
You cannot avoid giving the LM3886 power. Some 2x24V or so. If you use no load, you may not need local power rail decoupling or Zobel-network. You definitely need a feedback resistor - use 10K. Connect "+" input to signal ground and connect a sine-wave to the "-" input through 1K. De-solder the LM3886 only if it seems to work.
Not a more complete test but a good indication if worth de-soldering.
1) in what way are they "broken"? They were never assembled, hence never used, hence no way to break them.
Those LM3886 are virgin, literally, and presumed good .
2) test them by using them.
Either transfer them to your own boards or finish assembling the ones you show.
3) they already are in a simple board.
4) no need to remove them if you aim at a regular chipamp, if you plan using them in a ginormous 8 chipamp parallel bridged 400W monstrosity or similar, just don´t.
In my book the beauty of chipamps lies in excellent sound and more power than needed for home use.
If you want DJ or PA duty, build discrete.
Marshall shot their own feet by using complex multichipamp amps , lots of problems, very unreliable, so don´t.
To be more specific, these looks like they came out of active / PA speakers.
According to the listing:
I've already removed them as I'm planning to use them in a hi-fi setup, and get rid of the 300w 4xLM3886 monstrosity!
I was thinking to re-use the toroidal transformers, but I think that might have been the cause of issues in these amps, as they give out 27-0-27 on the secondaries, which I think will be very close to the maximum lm3886 voltage after rectification...
geoff.
According to the listing:
I've already removed them as I'm planning to use them in a hi-fi setup, and get rid of the 300w 4xLM3886 monstrosity!
I was thinking to re-use the toroidal transformers, but I think that might have been the cause of issues in these amps, as they give out 27-0-27 on the secondaries, which I think will be very close to the maximum lm3886 voltage after rectification...
geoff.
I would start with a simple test between power inputs and the output - a dead short or open reading should tell you something is wrong. Then you can do further testing after that to make sure they are good chips.
I have not used a lot of LM3886, but my experience with 5-6 is that the "blow" in fairly significant ways, burned/charred leads close to the plastic body, or actual pieces blown of the plastic body. YMMV - good luck!
I have not used a lot of LM3886, but my experience with 5-6 is that the "blow" in fairly significant ways, burned/charred leads close to the plastic body, or actual pieces blown of the plastic body. YMMV - good luck!
27-0-27 (AC) measured by you should give 37.5-0-37.5 (DC) when rectified. Then a drop of a couple of volt when in use. OK for LM3886.
I've not measured the transformers yet, but it looks like they are rated for 220v primary. UK mains often goes over 240, so I assume that would give ~29V AC, so ~41V DC when rectified?
Which I guess is within limits, although very close!
Make a test pcb, (oversize the plated-through holes for the LM3886 footprint a little if poss).
To test a chip place deep into the holes and apply sideways pressure to force all the pins to contact their plated-through holes solidly, perhaps holding in place with a stout rubber band.
Then you can test without soldering. The holes in the pcb will eventually chew up a little of course. Oversizing them allows used chips with solder still on the pins to easily fit without having to clean them up too much.
Alternatively you have to find a ZIF socket for that footprint, which I think is a very long shot.
To test a chip place deep into the holes and apply sideways pressure to force all the pins to contact their plated-through holes solidly, perhaps holding in place with a stout rubber band.
Then you can test without soldering. The holes in the pcb will eventually chew up a little of course. Oversizing them allows used chips with solder still on the pins to easily fit without having to clean them up too much.
Alternatively you have to find a ZIF socket for that footprint, which I think is a very long shot.
That transformer is still ok,
Use The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB or Juma's Easy-Peasy Capacitance Multiplier or even 2 lm338 and get to what you need.
Use The SLB (Smooth Like Butter) Active Rect/CRC/Cap Mx Class A Power Supply GB or Juma's Easy-Peasy Capacitance Multiplier or even 2 lm338 and get to what you need.
Thanks for the info, looks interesting. Seems they are set up for dual secondaries though, will have to do some more reading to see if they would work with a centre tapped transformer.
I also started looking at AMB Sigma22, which I think would achieve the same result.
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