Hi all,
I'm from Turkey and sorry for my poor English.
Last year (!) I made an active subwoofer+satellite system with two LM1876 plus an TL084 based LPF. There are two seperated power supply for PA and LPF. The PA's power supply is made of 250VA 2 x 18v E type transformer, a 8A rectifier bridge and two 10,000uF 35v capacitor and output voltage is 22v x 2 symmetrical. On the power amplifier circuit (PCB), I have 2,200uF 35v and 100nF near each LM1876 per rail and the power lines are enoughly bold. For LPF, I have 2 x 12v 2VA E type transformer, 1 A rectifier and 1,000uF + 100nF per rail on PSU and 100uF + 100nF on the LPF PCB.. All the gnds are connected to main power supplys gnd terminal so they are star (or not?).
System has a good performance, good sound, good bass etc... But on every channel (two 25w satellite and one 50w bridged sub out) I have 50Hz noise (should I say HUM) It is not very noisy and I cannot hear it when listening music. I tried everything that I know but I cannot solve that until now!
The PA circuit is standard reference design on National's manual and also have 50Hz noise without LPF. But when I connect the LPF circuit, noise accelerate to twice...
What can I do? Pls help me..
Thanx.
I'm from Turkey and sorry for my poor English.
Last year (!) I made an active subwoofer+satellite system with two LM1876 plus an TL084 based LPF. There are two seperated power supply for PA and LPF. The PA's power supply is made of 250VA 2 x 18v E type transformer, a 8A rectifier bridge and two 10,000uF 35v capacitor and output voltage is 22v x 2 symmetrical. On the power amplifier circuit (PCB), I have 2,200uF 35v and 100nF near each LM1876 per rail and the power lines are enoughly bold. For LPF, I have 2 x 12v 2VA E type transformer, 1 A rectifier and 1,000uF + 100nF per rail on PSU and 100uF + 100nF on the LPF PCB.. All the gnds are connected to main power supplys gnd terminal so they are star (or not?).
System has a good performance, good sound, good bass etc... But on every channel (two 25w satellite and one 50w bridged sub out) I have 50Hz noise (should I say HUM) It is not very noisy and I cannot hear it when listening music. I tried everything that I know but I cannot solve that until now!
The PA circuit is standard reference design on National's manual and also have 50Hz noise without LPF. But when I connect the LPF circuit, noise accelerate to twice...
What can I do? Pls help me..
Thanx.
Hi,
Are you sure that hum is 50Hz? If u havent measure it with scope, i think that hum is 100Hz and comes from grounding problems. If u arent sure which frequency it is, measure it with scope.
But if it is 50Hz, hmm....then i cannot say anything. Maybe keeping mains voltage away from electronics will help, or try to twist primary/secondary AC cables together, make metallic case for transformer,.....
ps. Also my mother tonque isnt english
- Mika
Are you sure that hum is 50Hz? If u havent measure it with scope, i think that hum is 100Hz and comes from grounding problems. If u arent sure which frequency it is, measure it with scope.
But if it is 50Hz, hmm....then i cannot say anything. Maybe keeping mains voltage away from electronics will help, or try to twist primary/secondary AC cables together, make metallic case for transformer,.....
ps. Also my mother tonque isnt english
- Mika
Hi!
In your case I would suggets that u measure hum with scope if its 100 hz then try adding 7815 and 7915 to the PSU of operatioanl amplifiers and put 0.1 uf ceramic type capacitors as near as possible to the operational amplifier, if u still get hum try checking grounds/dry solds els try changing shield wire inputs and outputs and try reducing the distance between pre and crossover.
In your case I would suggets that u measure hum with scope if its 100 hz then try adding 7815 and 7915 to the PSU of operatioanl amplifiers and put 0.1 uf ceramic type capacitors as near as possible to the operational amplifier, if u still get hum try checking grounds/dry solds els try changing shield wire inputs and outputs and try reducing the distance between pre and crossover.
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