LM3886 component selection

[ClaveFremen]

Originally Posted by SirPlanALot

Has the rail to rail bypassing any advantages over bypassing each rail to ground?

It depends on the sort of noise you want to filter, common mode noise should be better filtered by rail to rail caps.

Originally Posted by SirPlanALot

But sadly they don't have a 47pF or 56pF type, as is needed for Cf...
And SMD types like Panasonic EHCU are also not available, but Reichelt has them only in 330pF and 470pF, and also 100nF.

Silver mica then, for such values.

You can buy them from RS Components (you'll find also ECHU).

(CDE MC series)

Originally Posted by SirPlanALot

Will the 100nF EHCU be ok for power bypassing and Csn?

Sure, choose the correct voltage rating, obviously.

Originally Posted by SirPlanALot

Are Wima MKS-2 ok for NF input?

They're better than elcos, unbeatble for the 5mm lead spacing but using bigger caps you can have a much better quality sound.

Originally Posted by SirPlanALot

And are the Elna RJH also ok for Ci?
Because Distrelec doesn't have any Nichion caps.

You can order audiograde caps (including nichicons) from HifiCollective (GB).

I would not use RJHs for Ci

[AndrewT]

Originally Posted by ClaveFremen

...............I would not use RJHs for Ci

Why?
What capacitor parameters make that selection unsuitable?

[ClaveFremen]

None, Andrew,

They're perfectly suitable.

I would not use them for their timbre.

Inviato dal mio LT22i con Tapatalk 2

[SirPlanALot]

@ClaveFremen: Thanks for the advice, I will go through the stocks of that shops to see if they have the parts I need.

For the NF input caps: If they are the best in that size range, I think I will use them.
I have seen the sizes some others use, they are bigger than my whole PCB.

I have mentioned it earlier already: The source for this amp will be my PC.
Would using any "high-end" capacitors even make sense?
Because I cannot imagine my onboard audio was designed by audiophiles...

I don't mind trying out something like the Elna caps instead of Panasonic for PS decoupling, because thy are reasonably priced.
And if I can achieve good results with them, why not.

But I definately won't use any brick-sized capacitor-thingies which were made by virgins at full moon and sanctified by a voodoo priest, sold for the price of a mansion.
I don't say that to offend anybody here (just to be clear), I just don't like paying way too much (in my eyes) for any product.

Here's my new approach for the power supply routing.
Better? Worse?
Somehow I'm not quite sure if I like it or not...

[SirPlanALot]

I have redesigned the power supply bypassing again.
It now looks a bit more like the screenshot from ClaveFremen, thanks again for the pic!

I have also added a ground plane for Signal Ground, which only connects at the signal ground star point (located at the NF input).

What do you think about it?

Regards, Stefan

[AndrewT]

is there an output Zobel fitted?
The HF decoupling route looks as though it is a bit longer.

[jmillerdoc]

Way is your plans for the power supply? Consideration of how you will power your LM3886 chip modules you are building here is probably as important as anything else you are working on here. CarlosFM's snubberized PSU design is as popular as they get around here...I personally prefer the regulated supply he designed, either one is an excellent choice.

[SirPlanALot]

Originally Posted by AndrewT

is there an output Zobel fitted?

Yes, the output Zobel is located under C1.
A MELF resistor connecting at the output trace and crossing the V+ trace, and a 0805 capacitor.
I have marked it (blue rectangle) in the attached picture.
Is the placement ok?

Originally Posted by AndrewT

The HF decoupling route looks as though it is a bit longer.

I moved down the row of SMD parts for about 1.4mm, to make room for an alternative footprint for C9 (Cf).
Stupidly, I didn't find any SMD capacitors in the 50pF range other than ceramics (C0G or NPO).
So, if I want to use a foil type for Cf, I will have to pick a THT part.

But I could move the other parts back upwards, where they were before.
Would that be better?

Originally Posted by jmillerdoc

Way is your plans for the power supply? Consideration of how you will power your LM3886 chip modules you are building here is probably as important as anything else you are working on here. CarlosFM's snubberized PSU design is as popular as they get around here...I personally prefer the regulated supply he designed, either one is an excellent choice.

I initially planned to use the unregulated CarlosFM design and read the whole thread about it.
But then I came across the explanations of Rainwulf here on page 65: The (high-cap.) unregulated PSU for chipamps
This sounds very reasonable for me, so I think I will follow these guidelines.

[ClaveFremen]

Originally Posted by SirPlanALot

It now looks a bit more like the screenshot from ClaveFremen, thanks again for the pic!

You're welcome, Stefan

Originally Posted by SirPlanALot

I have also added a ground plane for Signal Ground, which only connects at the signal ground star point (located at the NF input).

Maybe you could separate signal ground from powerground with a low value resistor (1-10 Ohm).

Andrew, what do you think about it?

Originally Posted by SirPlanALot

Yes, the output Zobel is located under C1.
(...)
Is the placement ok?

Sincerely I don't like it much... you can possibly pollute PS lines with amp's output...

The zobel, IMHO, should go away from the groundplane.

Also try to isolate LM3886's OUT from groundplane (same reason).

I woudl suggest you to enlarge a bit the board.

Originally Posted by SirPlanALot

So, if I want to use a foil type for Cf, I will have to pick a THT part.

It wouldn't be tragedy, IMHO

[SirPlanALot]

Originally Posted by ClaveFremen

Maybe you could separate signal ground from powerground with a low value resistor (1-10 Ohm).

The two grounds are already separated by a resistor (R8) and two anti-parallel diodes (D1, D2). The connection point is located in the lower right corner, right from the output terminal, and under the input connector.

Originally Posted by ClaveFremen

Sincerely I don't like it much... you can possibly pollute PS lines with amp's output...

Interesting, as I think about it, I'm more concerned about the Zobel resistor picking up noise from the V+ trace and leading it back to the feedback input.

Originally Posted by ClaveFremen

The zobel, IMHO, should go away from the groundplane.

What about if I rotate the Zobel by 90°, so that it would go downwards instead of left?

Originally Posted by ClaveFremen

Also try to isolate LM3886's OUT from groundplane (same reason).

Ok, I will cut the plane over the output trace.

Originally Posted by ClaveFremen

It wouldn't be tragedy, IMHO

Sure, but I wonder why such low-value capacitors are not available as SMD.
I think, especially these are predestinated for SMD, to get rid of the influences of the terminal legs.
But for example the ECHU series is available from 100pf on.