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PostPosted: 20 Jun 2016, 07:04 

Joined: 20 Jun 2016, 06:11
Posts: 1
Location: India
First of all, hello to all.. I'm new here.
I hope I've posted in the correct section.

I wanted to make a music system of my own, so I opened and old stereo cassette player / radio. I have all the stuff removed inside it and placed my design in that place.

I couldn't have the complete design attached. It's exceeding the limit everytime.
I have attached the amplifier rig schematic and datasheet.
But I'll try to explain the overall schematic.

I am using two TDA2030A amplifier chips. One for each speaker. It's not stereo, in fact mono, but two speakers because one for bass /woofer and another of midrange.
So to split the spectrum I have used two opamp Butterworth filters(high pass and low pass) . The cutoff is 150hz. Above it goes to amplifier IC and then to 10w 8 ohm speaker while below 150hz goes to 25w 4 ohm speaker via the other amplifier.

Now the amplifiers are rigged up as per the dual supply configuration as in the datasheet (except for R4, C7 and R5. See attach). All the four circuits, LPF, HPF, Amp1, Amp2 are Parallely connected to the bipolar supply made from two 12v lead acid batteries.

I rigged it up, and placed it in the box and connected the supply.. There's a 3hz noise coming from both the speakers. Irrespective of input and volume. It doesn't play anything, but the 3hz is continuously pounding the speakers. The amps donot seem to heat up.. And I checked the circuits again. But in vain.

I don't know if this is happening due to the absence of the capacitor 220nF across the speakers, but is it important? What does it do?
One more doubt is why are there two pairs of supply bypass capacitors? Isn't only one pair enough.. If yes which pair?

What else might be the cause of this problem? Any help would be great.

Thank you.

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PostPosted: 18 Jul 2016, 08:20 

Joined: 26 Oct 2012, 21:00
Posts: 201
Location: ontario canada
the cause of the problem is the omission of R4 and C7 without these components the amp is oscillating so severely that it's motorboating (the 3 hz your hearing)

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