hi ive built a amplifier lm3886 and a separate power supply from a atx conputer,, jumped up the voltage with a stepup converter and a filter capacitor unit ,,,,, as per attachments it plays lovely using mp3 player or phone but cuts out if i plug in a pre amp also ive disconected the earth in the power supply for the same reason ime guessing it a ground /earth issue,,,, any ideas ??? thanks

 

I don't see anything that looks like an isolation transformer in the first picture, or in the others. So you may not have any, or adequate, isolation from the mains. Such isolation is not only important, it is VITAL. My guess is that connecting a preamplifier that is not isolated causes an overload and thus the shutdown. To verify that you can try running the preamplifier on a battery and see if the problem remains. OR, try it with the preamp connected but not powered (no power connection at all) . That is my best thought not having much information at all about your hookup.

 

It sounded to me the OP used a PC ATX P.S. which is normally isolated SMPS and common is referenced to earth GND, of which the OP has disconnected, as far as I can tell.
Max.

 

wire up definettly wen in contact with an earth

I don't see anything that looks like an isolation transformer in the first picture, or in the others. So you may not have any, or adequate, isolation from the mains. Such isolation is not only important, it is VITAL. My guess is that connecting a preamplifier that is not isolated causes an overload and thus the shutdown. To verify that you can try running the preamplifier on a battery and see if the problem remains. OR, try it with the preamp connected but not powered (no power connection at all) . That is my best thought not having much information at all about your hookup.

It sounded to me the OP used a PC ATX P.S. which is normally isolated SMPS and common is referenced to earth GND, of which the OP has disconnected, as far as I can tell.
Max.

sorry ime quite new to this ,, can explain you explan in laymans terms as ime not familiar with the termilogy thanks

 

wire up definettly wen in contact with an earthView attachment 159716



sorry ime quite new to this ,, can explain you explan in laymans terms as ime not familliar with the termilogy thanks

ATX power supplies are switching supplies which need need to supply a minimum current. Without this, they will not run. Here is some very well explained information on using them as lab supplies:
https://mysite.du.edu/~etuttle/electron/elect62.htm

 

thanks for your interest ! yes its fully converted ,10 ohm resister in place between red wire and ground

 

thanks for your interest ! yes its fully converted ,10 ohm resister in place between red wire and ground

Do you have a schematic of the amplifier? On most circuits using the LM 3886, the positive and negative supplies are symmetrical about ground potential. The common or negative terminal of the +12V supply in the ATX is connected to ground. By connecting the amplifier ground to the ATX ground, you are shorting out the amplifier's negative supply which will cause the ATX supply to shut down.

 

hi just tested on the atx power supp negative

Do you have a schematic of the amplifier? On most circuits using the LM 3886, the positive and negative supplies are symmetrical about ground potential. The common or negative terminal of the +12V supply in the ATX is connected to ground. By connecting the amplifier ground to the ATX ground, you are shorting out the amplifier's negative supply which will cause the ATX supply to shut down.

 

hi ive just replaced the atx power supply with another standard smps (not from a pc ) and i have no ground issues !!! all works fine !!!!!!! although i would realy like to use the atx power supply so any idea why the atx shorts the amp (does not short the atx power suppy ) when it is earthed ????????

 

hi carp,
Do you have a sketch of what's inside the Filter rectifier.?
E

EDIT:
Checking your photo images, it looks something like this.

 

hi agian,
If that is correct, at the ATX the -V and Gnd are already connected together, so when you ground the Rect you are grounding out the booster etc.
E

EDIT:
Power off and measure the resistance from Booster neg In to Booster neg Out, I suspect there is a direct path on these two points. ???

 

hi thanks for your input but the issue is the atx power supply ie amp does not like being eathed when using atx ps .......its fine using another smps

 

hi,
If the other SMPS is ground free on the Neg out pin, it will work OK.
E

 

hi agian,
If that is correct, at the ATX the -V and Gnd are already connected together, so when you ground the Rect you are grounding out the booster etc.
E

EDIT:
Power off and measure the resistance from Booster neg In to Booster neg Out, I suspect there is a direct path on these two points. ???
View attachment 159759

ile have to strip it ! i think your right , what wouldyou sugest to do

 

hi,
If the other SMPS is ground free on the Neg out pin, it will work OK.
E

so the atx is a no go on this prodject ??

 

hi,
The problem is the Filter rectifier circuit [ that's why I chose on your other thread to use a full bridge on each winding, it gives you more flexibility on how you can use it.]
If you could find a Booster that is electrically insulated between the input and output terminals, that could be used to drive the Filter/Rect.

E

EDIT:
Re-looking over what you want to do
ie: get a dual Voltage 'higher' supply from single voltage source, which has its neg terminal grounded [ATX supply] is not feasible.

 

to round up ive disconected the earth from atx power supply (yes could be dangerous) but possible to encase whole power supply to isolate it !!!!!!!!! amplifier works with no issues apart from a bit of noise coming through the speakers at low volume ! i dont think you can get rid of dc emi ????amp sepatately earthed