Problem of subwoofer amplifier

[Tony Stewart]

Lack of isolation or grounding or RF filtering is known to be a major cause RF noise. Either add a ground wire or RF cap to chassis from nearest earth ground.

Sub-woofer persistent hum is commonly caused power supply ripple at 2x line frequency from large capacitor aging.

 

[Nikolai Petrenko]

Here are shematics:
https://www.dropbox.com/s/tbh07sdmzzybemd/Power supply.bmp?dl=0
https://www.dropbox.com/s/sznw9384rb09nf8/la4440.bmp?dl=0
https://www.dropbox.com/s/mee4wv9ojkdl9bt/Tda2003 bridge.bmp?dl=0

 

[Nikolai Petrenko]

noise in satellite speaker like hiss and in subwoofer is hum

 

[audioguru]

Hiss is caused by a poor quality active device (maybe an opamp). There are noisy general purpose opamps and there are low noise audio opamps available for almost the same price.
Hum might be caused by poor shielding (all audio cables should be shielded) and a solderless breadboard has every long messy wire as an antenna for it to pickup mains hum from the air. The filter capacitors in the power supply for the audio amplifiers might be bad or too small. If your audio devices are powered from the mains and are far apart then the connection between them might have a ground loop.

 

[Nikolai Petrenko]

have you see the schematics???

 

[Nikolai Petrenko]

i use pcb not breadboard but wire seem be pretty long

 

[audioguru]

i use pcb not breadboard but wire seem be pretty long

Inside an audio amplifier, the wire from the input jack to the pcb input should be very short or it should use shielded audio cable.
The external input connecting cables should be shielded audio cables.
Then they do not pickup mains hum from the air because mains hum is all around.
If you short the input jack (its live wire to its ground wire) and the hum goes away then the unshielded wires are picking up mains hum.

 

[Nikolai Petrenko]

I dont have shield cable. I want to wrap aluminium foil around cable. It work well?

 

[audioguru]

All audio products come with shielded audio cables. Many department stores sell shielded audio cables. All electronic parts stores sell shielded audio cables. Do you live on the moon where there is no stores?
Wrapping aluminum foil around cables does not work well and how will you attach it to the ground of the circuit?

My VERY sensitive Sound Level Indicator project does not pickup mains hum because I made a compact stripboard layout and used a 1" (2.5cm) piece of shielded audio cable from its electret microphone to the preamp input:

 

[Nikolai Petrenko]

Yes, no store around. If i want to buy sth like resistor i need go at least 25km. If they sell shielded cable, this cable has diameter 25mm. Lol. I ask some experienced man, they said if will work well if roll several times. I found that can solder aluminium with motorbike oil as flux and lead free solder

 

[audioguru]

I am sorry to hear that you live on the moon. No store? Motorbikes?

 

[Nikolai Petrenko]

I'm not 18 years old yet, so can't use a motorbike. Use bus to go spent almost 1 day. I too busy, can go out and buy exclude after 7pm, summer holiday i have many time but it so far ( over 7 month )

 

[canadaelk]

PM me your address and I will mail you some shielded wire. E

 

[Nikolai Petrenko]

Canada too far from Vietnam. I only have a chance to pay you when you travel to Hanoi.

 

[canadaelk]

It's a gift.....E

 

[Nikolai Petrenko]

thanks. can you post your email address

 

[canadaelk]

You can send me a pm through ETO. Never advertise your private email address on a forum (unless you love spam!). E

 

[Willen]

I am sorry to hear that you live on the moon. No store? Motorbikes?

Hi AG,
Do not feel amazing. I am an Alien too.

 

[Nikolai Petrenko]

I drew this circuit, 2nd order sallen key filter use bjt instead of opamp because I hate to make supply circuit for it from DC. But I NOT SURE THAT IT WILL WORK WELL, please correct my mistakes . Here is the schematic link:
https://www.dropbox.com/s/hfbughbjde837hs/sallen key filter.bmp?dl=0

 

[audioguru]

An opamp has MUCH less distortion than a transistor. Your first transistor is not biased so it will not work. An opamp would also need to be biased then it would not need a dual polarity supply. I made remarks about your errors: