A excellent Pre-amp

[badboy6120]

And Mooly
The X'over frequency (120Hz) is ok for sub or should be lower?
and this circuit doesn't need a high pass filter to filter the frequency below 10 or 20HZ?

 

[Mooly]

I'm no expert on subs and the actual acoustics of them.

120hz sounds about right but I imagine depends on the design of the sub enclosure and its response. And the main speakers too of course.

I wouldn't think you need filter anything below 10 or 20 hz unless you play vinyl which would cause massive rumble.

 

[Frank Berry]

You can attenuate the low frequency response a bit if you reduce the value of C2 on the input of your power amplifier.
Other than that, you could add a couple of Opamp stages to your Low Pass Filter and attenuate the audio below the low frequency limit of your sub.

 

[badboy6120]

thanks a lot Mooly & Frank for your all advices. really helped me
Frank what did you mean by this??? :

This circuit shouldn't produce any additional hum. It will amplify any hum that is present on the input.
It may be a problem with the layout or a grounding issue. You may also need better filtering of the power supply outputs.

 

[Frank Berry]

Make sure that the electrolytic capacitors on the + and - outputs of your power supply are large enough. Your schematic shows 2.2uf. They should be much larger.

 

[badboy6120]

No Frank, they are 2200uf (2.2milifarad)

 

[badboy6120]

I'll post the PCB of the new sub's filter in a few minutes.

 

[badboy6120]

And here's the PCB of this Sub's filter
Size of PCB = 13*6 Cm
Size of download = 26 KB

http://up6.iranblog.com/files2/35Sub-filter.rar

 

[badboy6120]

I'll post the pictures of the PCB that I'm going to make tomorrow

 

[badboy6120]

Any idea about this PCB???