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Topic: General question(s) about 'dirty' lines & isolation (Read 1 time) previous topic - next topic


Is Zeus = dhenry?


well last thing I want to do is piss anyone off with my 'free help'....  Im just looking for some 'discussion' is all.

People who are open to explain/teach... not demanding or a requirement by any means.

Audio (and much of electronics) is a new step for me..  (graphics/web developer by trade).

Its not that I dont 'try'.. it that I need to understand and re-iterate.. and have that 'reassurance' (by someone) that I understand and have it correct.. then I feel I can read/do other things and learn because the article, abbreviations, approaches make more sense is all..


here is a more updated portion of the schematic.. to reflect the real values used on the board I am testing with..

I'll go back and read some of the articles again.. see if the more I read them.. the more things will 'click'?



That's far worse in the "wrong" direction. Approx low-pass frequency is

F3db = 1/(2*pi*100*100nF) = 15.9 KHz.

You have essentially NO low-pass filtering at all there. Small wonder it's noisy - for ALL the reasons I've
given in the past 3 dozen posts. I'm gonna let you figure it out now, given past suggestions - I'm tired now.

Also, your 47K/4.7K is giving you a 10:1 attenuation of your signal, last time it was 2:1, but that may be
what you need. You have to realize that, every time you change those values, you're affecting both
gain and frequency response. You should go learn about band-pass filters too.



When I had the original values in there.. you couldnt barely hear ANYTHING..

not only volume, but it was 'muffled'.. and clearly -not- being filtered correctly (although I guess its not being filtered correctly now either...lol)

but at least this 'direction' way.. i can HEAR things.. and they are mostly clear...etc..

but when I was using the PWM pins.. I could here a BUZZ.. -or-.. the led itself wasnt fading correctly..

Higher/lower C18/R8?  higher/lower R5/R6?...

anyways.. guess its a bit over my head for now on how to fix it...

I'll try and go back and see if anything posted make sense the second/third time around  :)


Lowpass filtering needs to selected to sound good for the material selected.
Resistors were selected for attenuation of the up to 5V signal from the DAC into the LM386 that is set up for gain of 20 so the output wasn't clipping or going past peak to peak.
Not sure I'd run PWM on the same board - it was pretty packed with components. Running 0-5V PWM at 490 Hz with a low-pass filter selected to let most of the audio band thru will also let any PWM picked be amplified and sent out, 0-5V & 5V-0 transitions occuring at 1KHz.
Could try additional power supply decoupling, add parts in parallel to the existing caps.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


RC lowpass filter calculator
maybe go to 200 ohm for R8, will work its down to sounding muffled again tho.
Designing & building electrical circuits for over 25 years.  Screw Shield for Mega/Due/Uno,  Bobuino with ATMega1284P, & other '328P & '1284P creations & offerings at  my website.


The design around the opamp is all wrong.

dhenry appears to have mistaken the LM386 audio amplifier in your schematic for an op amp, so I suggest you ignore his comment.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.



to a noob like myself.. those kind of off the wall comments really shake things up.  :(  :smiley-zipper:

random, negative comment, no desc... no follow up..


hi guys-

ok.. finally getting a free moment of spare time to fire up the iron.. :)

I have essentially removed:


and replaced those with two 'female' ended leads each...  (so I can stick a resistor or cap between each one and test out different values)

the only difference is that I have put a pot for R5/R6.. instead of two female leads each... since they share a ground...(basically there is only 3 female leads..with a trim pot used same way I am doing the resistors and caps, but I can easily replace with two separate static resistor values as well..)

this allows me to try and understand all this.. as well as play and get feedback in real time to understand how all this is 'related'..

I want to the highs to be 'crisp'...but not allow any static, hiss or pops through.....
and get as much clean, clear bass as well..

I know these are just hobby speakers so Im trying to be realistic as well.. :)

So from the comments/reading.. the 100 ohm resistor in R8 is basically doing 'nothing'.. (barely having a low pass filter)..  but if I jack that up.. its get 'muffled' not to be confused with 'muted'..

does trying:

R8 = 5-10K
R18 =  10nF
R21 = 1uF

sound a bit better?

and now.. because that R21 cap is >= 1uF.. I should be using a polarized cap?  (and this will also help on cutting out noise?)



Dec 07, 2012, 06:45 am Last Edit: Dec 07, 2012, 06:56 am by xl97 Reason: 1

ok.. so I 'did' in fact change these components to this:

R8 = 10K
R18 =  10nF/.01uF (103)
R21 = 1.0uF (105)

I also swapped out the 100k (104) trim pot .. for a 10k (103) trim pot for dialing in the 'volume' resistors..

(I havent popped it off meter the values yet though)..

better? :)

it sounds good//comparable.. but I havent tried anything 'else' along with it.. like blinking leds.. pwm.. using a MAX72xx chip...etc..et
to see if this helps in reducing any of the noise I get while using a max7219 chip to make a matrix blink or change intensity as well.

this along with going back over my board and changing all 1uF and greater caps to be polarized...etc..

(I searched.. only thing that would be a DIRECT swap for the 0603 ceramic caps currently being used are some 'pricey' 0603 tant caps...and one 0805 but I think I can squeeze it on the pads!) ..  that help for overall noise/dirty lines too....yes? :)

*this was the first time I had seen polarized/tant caps in an 0603/0805 package myself.. (digikey)..
I usually just see the yellow bigger ones in A, B, C type packages I believe they go by..

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