Capacitors to remove noise from PSU

Nordic · 14th October 2005, 11:19 AM

Hi

I have a transformer with a 3rd secondary winding of 6V at 1A.
I used 4 FR104 diodes to make a rectifier, then connected a PC fan to the rectifier... all working and I'm very impressed with myself.

BUT, when I do connect the rectifier to the transformer, I can hear a slight noise on the amps connected to the other windings of the transformer... sounds a bit like the fan maybe makeing noise...

Is there anyway I can suppress/filter some of the noise using small capacitors or something... I got tonnes lieing around, but I don't just want to go and add random capacitors to my circuit... also not sure where they would have to go...

AndrewT · 14th October 2005, 12:33 PM

Hi,
the fan is running on pulsed DC since there is no smoothing on the supply. That may be aggravating the noise problem.
If you add caps after the rectifier the fan will see more voltage and run faster. Is that OK?
To suppress noise on the fan line you can add small caps to the AC side of the rectifier and to the DC side. Any sizes below 100nF should be OK.
You can also add caps to the other PSU supplies but these are after the horse has bolted, better to solve at source if possible.

Eva · 14th October 2005, 12:57 PM

Add a storage capacitor after the diodes, and a resistor in series with the fan. Suitable values would be over 100uF and under 100 ohms (use a 2W unit).

Nordic · 14th October 2005, 03:46 PM

Like this?

Nordic · 15th October 2005, 09:57 AM

Tried circuit like diagrame I posted above... but it has no effect...

pinkmouse · 15th October 2005, 10:18 AM

Make sure the wires to the fan are twisted together, and run as far away as possible from other, especially signal, wiring in the amp.

Dick West · 15th October 2005, 02:21 PM

Nordic,

Eva said to put the resistor in series with the fan. A capacitor in parallel and a resistor in series with the load makes a low pass filter which will help filter out the noise from the fan that creeps onto the AC. Your diagram shows the resistor in parallel, not in series, with the load.

Dick

Eva · 15th October 2005, 03:37 PM

I meant a resistor in *series* with the fan, not in paralell.

Nordic · 16th October 2005, 05:59 AM

HAHA ok, excuse me... I plead ignorance...

Will do what you said!

absolute amateur here, only completed my 3rd gainclone yesterday, and it took like an hour or so...

Nordic · 17th October 2005, 08:10 AM

Connected like this, but now fan doesn't turn... is the resistor supposed to be in seriesor parallel with the capacitor maybe?

14th October 2005, 11:19 AM	#1
Nordic diyAudio Member Join Date: Sep 2005	Capacitors to remove noise from PSU Hi I have a transformer with a 3rd secondary winding of 6V at 1A. I used 4 FR104 diodes to make a rectifier, then connected a PC fan to the rectifier... all working and I'm very impressed with myself. BUT, when I do connect the rectifier to the transformer, I can hear a slight noise on the amps connected to the other windings of the transformer... sounds a bit like the fan maybe makeing noise... Is there anyway I can suppress/filter some of the noise using small capacitors or something... I got tonnes lieing around, but I don't just want to go and add random capacitors to my circuit... also not sure where they would have to go...

15th October 2005, 10:18 AM	#6
pinkmouse diyAudio Moderator Join Date: Apr 2002 Location: Chatham, England	Make sure the wires to the fan are twisted together, and run as far away as possible from other, especially signal, wiring in the amp. __________________ Al I conceive of nothing, in religion, science or philosophy, that is more than the proper thing to wear, for a while. Charles Fort

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14th October 2005, 12:33 PM	#2
AndrewT diyAudio Member Join Date: Jul 2004 Location: Scottish Borders	Hi, the fan is running on pulsed DC since there is no smoothing on the supply. That may be aggravating the noise problem. If you add caps after the rectifier the fan will see more voltage and run faster. Is that OK? To suppress noise on the fan line you can add small caps to the AC side of the rectifier and to the DC side. Any sizes below 100nF should be OK. You can also add caps to the other PSU supplies but these are after the horse has bolted, better to solve at source if possible.

14th October 2005, 12:57 PM	#3
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	Add a storage capacitor after the diodes, and a resistor in series with the fan. Suitable values would be over 100uF and under 100 ohms (use a 2W unit).

14th October 2005, 03:46 PM	#4
Nordic diyAudio Member Join Date: Sep 2005	Like this?

15th October 2005, 09:57 AM	#5
Nordic diyAudio Member Join Date: Sep 2005	Tried circuit like diagrame I posted above... but it has no effect...

15th October 2005, 02:21 PM	#7
Dick West diyAudio Member Join Date: Aug 2004 Location: Illinois	Nordic, Eva said to put the resistor in series with the fan. A capacitor in parallel and a resistor in series with the load makes a low pass filter which will help filter out the noise from the fan that creeps onto the AC. Your diagram shows the resistor in parallel, not in series, with the load. Dick

15th October 2005, 03:37 PM	#8
Eva diyAudio Member Join Date: Oct 2003 Location: Near the sea	I meant a resistor in series with the fan, not in paralell.

16th October 2005, 05:59 AM	#9
Nordic diyAudio Member Join Date: Sep 2005	HAHA ok, excuse me... I plead ignorance... Will do what you said! absolute amateur here, only completed my 3rd gainclone yesterday, and it took like an hour or so...

17th October 2005, 08:10 AM	#10
Nordic diyAudio Member Join Date: Sep 2005	Connected like this, but now fan doesn't turn... is the resistor supposed to be in seriesor parallel with the capacitor maybe?