hi all, i'm new here & i must say, this sight looks very helpfull so here goes:

for projects II i decided to build an amp with the tda1553q & LM1036 control IC.

The problem is that all works perfectly well EXCEPT the cooling fan, no matter how i connect it (running two transformers & two indepentand PSU's) it generates a humming noise based on the fan speed audible through the speakers. Now, when connecting it to a totally SEPERATE PSU, it's quiet... :roll:

i'm not too clued up on fan's & ac, back emf whatever it may be, so ANY help would be much appreciated

 

You didn't say if it was AC or DC. There can be two causes, one is Field coupling, where the fan puts out interference that is picked up by the preamp circuit by a trace or component located close to the fan. The other is if it is a brush motor the arcing between the brushes and the commutator can feed in to the V+- supplies. Ideally you want an metal body 110VAC or a 12VDC brushless fan. Just a guess.

 

oh yea, its a cd brushless, used in pc psu's.

i sorted it tho by putting it on its own reulator, couldnt find anything thorough on the net...

thanks anyway

 

If it is on the same power and ground system as the rest of your circuits, you have to be very careful about layout of your design (otherwise, what you are experiencing can happen)

Putting it on its own regulator wont help.. noise is something that regulators do not reject well. Your could try some heavy filtering on the supplies right at the fan connection. A better way would be to get the fan on its own supply and opto-couple the control. I do this often so I don't even have to worry about it and never had a noise issue.