Chip amp decoupling/snubberizing caps

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I am rounding up the parts for an LM3886 chip amp build. The BOM calls for a number of 0.1uF 63V capacitors decoupling/snubberizing/Zobel. The original BOM calls for polypropylene film box caps. The fit on the board is very tight not allowing for much dimensional deviations and so finding proper parts that are available in the US has been difficult. How important are the use of PP film caps in these functions vs another material like polyester? In the attached schematics they are in the PS as labeled and on Cs/Cs/Cz on the amp board.

Thanks,

George
 

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Polyester is fine for these applications, which in reality are pretty non demanding in the big scheme of things :)

If the design was RF rather than audio, or if there were extremely fast repetitive rise times involved then you might be looking to make specific choices... but decoupling and Zobel network duty is all cooking grade design. Use what fits and what is cost effective.
 
Make Cs 4.7uF/100V X7R. Such caps were not easily available when the datasheet was written but since they are now we might as well use them.

Cz can be mkt without any worries. Don't waste money on a mkp there.

Btw, your schematic is incomplete. You are missing the network in // with the feedback resistor (Cf-Rf2 in the datasheet) and one cap in between the + and - inputs (Cc). The single supply schematic is strangely more complete than the dual supply one in the datasheet.

You might also want to add an input cap (safer if you don't have an offset protection) and increase the feedback capacitor to 100uF.
 
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The 1r0 snubbers are in the wrong place on the output of the PSU.
They should be across the transformer secondaries.
DF said
If you omit the 0.1uF bypass caps in the PSU then you might not need the PSU snubber.
remove the 0.1uF, it can only increase the risk of ringing.
DC block on the input missing. (22k suits either 4u7F BiPolar, or two 10uF back to back)
RF attenuation on the input missing. (1k0 suits 330pF to 1nF across the 22k)
DC block on the NFB lower leg far too small. (680r suits 220uF, or 330uF)
00940 said
You are missing the network in // with the feedback resistor (Cf-Rf2 in the datasheet) and one cap in between the + and - inputs (Cc). The single supply schematic is strangely more complete than the dual supply one in the datasheet.
read the datasheets again and ask if you don't understand.
 
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Snubbers are placed across switching elements, often across rectifiers
Yes, across the ~~ terminals since this is effectively across the secondary.
, I presume they were adopted by the gainclone community due to the minimal smoothing used in the design and their small size?
because he did not know what the effect of adding the low esr cap to the inductance in the nearby circuit when a step change in current was imposed.
 
I may need to rethink my approach. I chose the Chip Amp.com boards as my starting/learning point for my first gain clone build. The schematics I provided are those boards and BOM. After reAding these comments it appeRs that this design is not held in high regard, although I am learning a lot. I have a few other boards, maybe I'll post the schematics and see if any of those get better reviews.

George
 
it is often possible to add components or change components to a pre-made PCB.
Have a good look at your PCB and see what mods/additions are feasible. This is a really good learning experience in becoming familiar with the PCB, it's layout, what each component does and what is possible to change in someone else's design.

Only where all your desired and some of the NEEDED mods are impractical do you throw the PCB away.
 
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