Signal separation

Hey guys can you please suggest something in my case i want to adjust input volume for one of my amps with out affecting others and because i already somehow ****** up my phone and my pc audio outputs acidently grounding those wires to the supply ground anyhow i dont want to loose signal strenght by separating it. Also should i just adjust input volume by grounding it with a pot? This is the picture of what i want
e0923188d8d2e92f02dc33019b7f072d617.jpg
 

rayma

Member
2011-04-29 8:37 pm
Hey guys can you please suggest something in my case i want to adjust input volume for one of my amps with out affecting others and because i already somehow ****** up my phone and my pc audio outputs acidently grounding those wires to the supply ground anyhow i dont want to loose signal strenght by separating it. Also should i just adjust input volume by grounding it with a pot? This is the picture of what i want

WTF?
 
What i want is. In case something goes wrong with my amp i want complete separation between audio output of my pc and audio input on my diy amp to be electrically separated because im not sure exactly how but i think i have backfeeded high voltage to that line and now my pc doesnt output audio.
Look idk how in the world this happened but basicly i was using my amp and suddenly i disconnected audio jack from my mp3 luckly its ok but look what happened. One of my ic lm3886t just blew of
66243f48533988c3e8df4505ea497f23766.jpg

This is my vumeter again complete mistery how did that hapen what it had connected is only audio output from pc paralel connected into my amp witch was working ok at the moment the i just blew oh and to somewhat filter the input there was like 1uf somethibg like 100v cap connected in Between low voltage input positive and negative was not mixed up plus that input is like 200mV rms look no pover was connedted and i didnt touch it when it hapened.
8cb330d3f61ff3637dc0b8b3931138f0973.jpg

d7c56b4423ef8f65a0e6f01c22018ced224.jpg
 
Oh the problem is backfeeding voltage from a failing amp to the output card of the PC/cellphone whatever expensive music source.
You could separate the input from the amp with a capacitor. usually 10 uf is sufficient, although 2.2 uf can work many times. The plus goes to the amp since digital outputs are usually under 2 vac.
Then across the input device side you can put back to back zener diodes, say 3.3 v ones, or 2.4 v ones, to clamp any AC pulses at the 4 v or 3 v level.
Then if your amp blows up, this could protect your expensive input source. These shouldn't draw much current for signals under 2 vac, just a microamp due to the 50 pf capacitance or something. That is line to line, other ends to the center and outside of the RCA jack.
I'm using a cheap transistor radio i found in the trash to check out my current amp. Not fun to listen to long term but during the "there are going to be problems" stage after construction, a cheap device that I don't mind being blown up.
Next time put a bigger heat sink on the LM3886. They are pretty easily blown naked. If you're cash strapped, cut one out of an aluminum window or door frame you find in the trash. A #4 screw and nut, a 1/8" hole drilled with a hand crank drill, there you are. That is what I did for my driver transistors, although I usually use a purchased heat sink for the output transistors. Don't forget to buy the insulator and the heat sink compound if the insulator is mica. For my LM3886 I had to buy a $3 insulator NTE425. I bought 3 LM3886 and only one insulator so far. Your supplier may have some insulator cheaper and more appropriate than newark did. Note regular purchased TO220 heat sinks aren't wide enough for the LM3886 if they have any ribs on the device side.
Have fun.
 
Last edited:

9justinas9

Member
2015-07-27 2:34 pm
Oh the problem is backfeeding voltage from a failing amp to the output card of the PC/cellphone whatever expensive music source.
You could separate the input from the amp with a capacitor. usually 10 uf is sufficient, although 2.2 uf can work many times. The plus goes to the amp since digital outputs are usually under 2 vac.
Then across the input device side you can put back to back zener diodes, say 3.3 v ones, or 2.4 v ones, to clamp any AC pulses at the 4 v or 3 v level.
Then if your amp blows up, this could protect your expensive input source. These shouldn't draw much current for signals under 2 vac, just a microamp due to the 50 pf capacitance or something. That is line to line, other ends to the center and outside of the RCA jack.
I'm using a cheap transistor radio i found in the trash to check out my current amp. Not fun to listen to long term but during the "there are going to be problems" stage after construction, a cheap device that I don't mind being blown up.
Next time put a bigger heat sink on the LM3886. They are pretty easily blown naked. If you're cash strapped, cut one out of an aluminum window or door frame you find in the trash. A #4 screw and nut, a 1/8" hole drilled with a hand crank drill, there you are. That is what I did for my driver transistors, although I usually use a purchased heat sink for the output transistors. Don't forget to buy the insulator and the heat sink compound if the insulator is mica. For my LM3886 I had to buy a $3 insulator NTE425. I bought 3 LM3886 and only one insulator so far. Your supplier may have some insulator cheaper and more appropriate than newark did. Note regular purchased TO220 heat sinks aren't wide enough for the LM3886 if they have any ribs on the device side.
Have fun.

Thanks so much thats a brilliant idea! Im gonna try it right now!
 

9justinas9

Member
2015-07-27 2:34 pm
Throw that hardwired board in the bin before you blow up any more chipamps.

Buy a reputable kit from a well recommended source and build it exactly as the build instructions tell you to.

And I'm like Rayma, I haven't a clue what that diagram is supposed to tell me.

Ok basicly i need a speparation between audio source and audio input and person above gave me a brilliant idea zener diodes back to back this way there is no way that static or other back feeding voltage go back to an audio source and destroy it
 
I have something which radio shack (rip) used to sell as 'ground breaker'. basically its an audio transformer (or two, for stereo). it helped to eliminate hum caused by pc's and such crap with improper power supply.

that's what you need...

Is the 7ah lead acid battery is bad psu fjther more neading audio transformer? And is it possible to make one myself?