LM3886 amp.

[Silver1omo]

So I finally "assembled" my point to pint LM3886 amp.


It is based on ESP's project 19.
Right now is running with only 26vdc and sounds quite good, a little hum that is barely noticeable with nothing playing and with a lot more bass than the sure amp it will be replacing.

The idea is to make a MDF or ply box and match the finish of my Piccolatas.

[PWR RYD]

Re: LM3886 amp.

Looks like a fun project. Are you planning on increasing the supply voltage?

[Silver1omo]

Re: LM3886 amp.

Yes, fun indeed. I totally forgot to add the power switch...
Yes, I will increase the voltage, now I do not remember what I have available in that trafo (re-purposed from a sharp sub amp), 30-32vdc me thinks...

I still need to secure the trafo to the aluminum plate, figure out where to put the power switch (now that I run out of space in the back...) and consider a speaker protection circuit.

[Tin_Ears]

Re: LM3886 amp.

PM Neil Davis.

[tc]

Re: LM3886 amp.

Very cool! I have one that is "half-way" done. Really need to get working on that again....

Have you noticed any heat at all? (really dig the case/heat sinks). Also, have you considered putting a ground lift in it? Could then run to a star ground farther away from your chips?

Look forward to seeing the finished product. Wish more folks did amps on here....

[Silver1omo]

Re: LM3886 amp.

The top of the sinks got a bit warm after 2 hours of high volume (higher than I usually listen to in the bedroom). The star ground is currently attached to the trafo skirt.
To avoid having a bunch of cables and troubleshooting noise the ground from the input is connected to pin7 and from there to the star ground. The output ground also goes to the star ground and the IEC earth.

The speaker negative comes directly from the PS ground and in there I connect the ground of the power entry. Then 1 wire runs from there to the star ground.

So the green ones go to SG and the red to PS ground.

Last time I really played with the grounding I found this to work better. Little noise and fixed an oscillation problem.

[dcibel]

Re: LM3886 amp.

LM3886 is a great little amp, excellent value, I hope it never becomes end-of-life. LM3886 was my first DIY amp, still use it today in my garage.

Not to bash your work, I see lots of people do this but I never understood point to point wiring "free-air". You can stuff your parts in a perfboard and do the point to point underneath. The end result is much cleaner and you won't be sticking pieces of electrical tape on your heatsink to be sure there's no shorts.

[Silver1omo]

Re: LM3886 amp.

That is one of the things I love of this forum. The perfboard makes total sense...
That will be used in another iteration. I want to compare a minimalistic chipamp to this more "complex" one.

[foxfire3]

Re: LM3886 amp.

The top of the sinks got a bit warm after 2 hours of high volume (higher than I usually listen to in the bedroom). The star ground is currently attached to the trafo skirt.
To avoid having a bunch of cables and troubleshooting noise the ground from the input is connected to pin7 and from there to the star ground. The output ground also goes to the star ground and the IEC earth.

The speaker negative comes directly from the PS ground and in there I connect the ground of the power entry. Then 1 wire runs from there to the star ground.
[ATTACH=CONFIG]44081[/ATTACH]
So the green ones go to SG and the red to PS ground.

Last time I really played with the grounding I found this to work better. Little noise and fixed an oscillation problem.

So despite your grounding scheme you're not sure the source of the hum at low volume?

[Silver1omo]

Re: LM3886 amp.

So despite your grounding scheme you're not sure the source of the hum at low volume?

Yes... That shows how n00b and impatient I am. I was supposed to test a couple of other arrangements. But once I started to connect I did not stop to test...

[Silver1omo]

Re: LM3886 amp.

Increased the voltage to 30vdc (with no load). It still sings, no magic smoke was liberated.

I did notice that the space heater we have in the bedroom causes noise in the amp...

foxfire3, do you an advice to find the 'hum' source?

[audioengr]

Re: LM3886 amp.

The top of the sinks got a bit warm after 2 hours of high volume (higher than I usually listen to in the bedroom). The star ground is currently attached to the trafo skirt.
To avoid having a bunch of cables and troubleshooting noise the ground from the input is connected to pin7 and from there to the star ground. The output ground also goes to the star ground and the IEC earth.

The speaker negative comes directly from the PS ground and in there I connect the ground of the power entry. Then 1 wire runs from there to the star ground.
[ATTACH=CONFIG]44081[/ATTACH]
So the green ones go to SG and the red to PS ground.

Last time I really played with the grounding I found this to work better. Little noise and fixed an oscillation problem.

To reduce that last bit of hum, the bottom of R5 should be connected to the SG node and not shared with the PS capacitor. It is the inverting input's ground reference and is a high impedance node.

[AJ]

Re: LM3886 amp.

That is one of the things I love of this forum. The perfboard makes total sense...

To go another step forward towards a professional looking project, the LM3886 PCB's from chipamp.com are only $6ea.

[Silver1omo]

Re: LM3886 amp.

To go another step forward towards a professional looking project, the LM3886 PCB's from chipamp.com are only $6ea.

Yes, but international shipping usually is a deal breaker, for the PCBs it is about $24USD and when I was "investigating" the LM3886 I remember reading that the zobel and other addons where a good idea, so I settled for the ESP's design and again the shipping cost dictated that I could try it with no PCBs. At the time I was trying to make it a cheap project to see if I was able to do it...

So it is a repurposed trafo, free LM3886s (eval units from TI), most of the cables were from the house stock and only purchased the resistors and caps.

The next try will likely be the chipamp.com PCBs then I can compare.

To reduce that last bit of hum, the bottom of R5 should be connected to the SG node and not shared with the PS capacitor. It is the inverting input's ground reference and is a high impedance node.

I can try that...

[SirNickity]

Re: LM3886 amp.

You're braver than I am. PtP wiring a chip amp seems like a really easy way to short something out. ;)

The few 3886s I've built have been pretty much silent, so it can be done! Remember that the chip's ground pin has nothing to do with audio -- it's just a reference for the mute circuit.